Executive Summary. Overview. Section 1

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1 Executive Summary Overview This Conceptual Design Report (CDR) presents the plans for a major new international research facility at the GSI Laboratory (Gesellschaft für Schwerionenforschung) at Darmstadt, Germany. The specific facility concept presented here was developed over the last year. It is based on a broad spectrum of workshops, working group reports and general discussions, organized by GSI and by the user communities involved over a period of several years. It builds partly on recent reports from various international committees that have reviewed the different science areas involved. The principal goal of the new facility is to provide the European science community with a worldwide unique and technically innovative accelerator system to perform future forefront research in the sciences concerned with the basic structure of matter, and in intersections with other fields. The facility will provide an extensive range of particle beams from protons and their antimatter partners, antiprotons, to ion beams of all chemical elements up to the heaviest one, uranium, with in many respects world record intensities. The new facility builds, and substantially expands, on the present accelerator system at GSI, both in its research goals and its technical possibilities. The proposed facility consists of a 100/200 Tm double-ring synchrotron SIS100/200 and a system of associated storage rings for beam collection, cooling, phase space optimization and experimentation (Figure 1). It uses the present accelerators, a universal linear accelerator (UNILAC) and a synchrotron ring accelerator (SIS18), as injector. The heart of the new facility, the double-ring synchrotron, provides for fast acceleration utilizing novel, rapidly cycling super-conducting magnets, which are presently being developed in collaboration with laboratories in the USA and in Russia. A key feature of the new facility will be the generation of intense, high-quality secondary beams. These include beams of short-lived (radioactive) nuclei often referred to as rare isotope beams and beams of antiprotons. Secondary beams are produced in nuclear reactions induced by beams of stable particles. To achieve the desired intense secondary beams, the primary beam intensities must be correspondingly high. Compared to the present GSI facility, a factor of 100 in primary beam intensities, and up to a factor of 10,000 in secondary radioactive beam intensities, are key technical goals of the proposal. Other characteristics are excellent beam qualities of both primary and secondary beams. This will be achieved through innovative beam handling techniques, many aspects of which have been developed at GSI over recent years with the present system. This includes in particular electron-beam cooling of high-energy, high-charge state ion beams in storage rings and bunch compression techniques. Finally the new facility will provide beam energies a factor of 15 higher than presently available at GSI for all ions, from protons to uranium. 5

2 Figure 1: The existing GSI facility (blue) with the linear accelerator UNILAC, the heavy-ion synchrotron SIS18, the fragment separator FRS and the experiment storage ring ESR; and the new project (red) with the double-ring synchrotron SIS100/200, the high-energy storage ring HESR, the collector ring CR, the new experiment storage ring NESR, the super-conducting fragment separator Super-FRS and several experimental stations. The present UNILAC/SIS18 complex serves as injector for the new double-ring synchrotron. 6

3 The science that can be uniquely explored with the planned facility spans a wide range of research areas. In most general terms, the scientific thrusts of the facility can be summarized by the following broad research goals. The first goal is to achieve a comprehensive and quantitative understanding of all aspects of matter that are governed by the strong (nuclear) and the weak force, the two important short-range forces out of altogether four known ones, that critically determine the structure of matter at the microscopic level. Matter at the level of nuclei, nucleons, quarks and gluons is governed by the strong interaction and is often referred to as hadronic matter. The research goal of the present facility thus encompasses all aspects of hadronic matter, including the investigation of fundamental symmetries and interactions that are relevant for this regime. The second goal addresses many-body aspects of matter. While we have been extremely successful during the past century in exploring matter at ever deeper levels, finding smaller and smaller building blocks, we have also found that the structure of matter has an intrinsic complexity which is more than just the linear superposition of its components. These many-body aspects play an important and often decisive role at all levels of the hierarchical structure of matter. They govern the behavior of matter as it appears in our physical world as well as on the hadronic level. These two broad science aspects, the structure and dynamics of hadronic matter and the complexity of the physical many-body system, transcend and determine the more specific research programs that will be pursued at the future facility (Figure 2). These include: i) investigations with beams of short-lived radioactive nuclei, addressing important questions concerning nuclei far from stability, areas of astrophysics and nucleosynthesis in supernovae and other stellar processes, and tests of fundamental symmetries, ii) the study of hadronic matter at the sub-nuclear level with beams of antiprotons, in particular of the following two key aspects: confinement of quarks and the generation of the hadron masses, the latter being intimately connected to the spontaneous breaking of chiral symmetry, a fundamental property of strong interactions, iii) the study of compressed, dense hadronic matter through nucleus-nucleus collisions at high energies, iv) the study of bulk matter in the high-density plasma state, a state of matter of interest for inertial confinement fusion and various astrophysical settings, v) studies of Quantum Electrodynamics (QED), of extremely strong (electromagnetic) field effects, and of ion-matter interactions. 7

4 Figure 2: An illustration of the hierarchical structure of matter and of the science areas to be addressed at the planned new GSI facility. These areas include (from bottom to top): research into the quark-gluon structure of hadrons, and into the properties of compressed nuclear matter with the potential transformation into quark matter; studies into the structure and properties of atomic nuclei, in particular nuclei far from stability that are important for astrophysical processes; investigations of the properties of bulk matter under extreme conditions through dense plasma research; and studies of Quantum Electrodynamics and ultra-strong fields in atoms, as well as other interdisciplinary activities in the areas of materials research and radiation biology. All research programs that will be performed at the future facility have a strong scientific and instrumental interconnection. This allows the technical features of the facility to be used in a synergetic and thus cost-effective way. It is one of the outstanding strengths of the proposal that experiments of up to four program areas can be run to a large extent simultaneously in a parallel operation. This provides the equivalent of a full, state-of-the-art dedicated facility to each research area, at a substantial cost saving overall. The facility is expected to serve about 2000 international users, predominantly from university groups, about twice the number of users presently involved in research at GSI. There has been considerable involvement by the user community, both in formulating the various science cases presented in this Report, and in voicing strong interest and support for involvement in the development, construction and future research programs of the proposed facility. 8

5 This Executive Summary provides an overview of the key aspects of the new facility: the science case, the technical facility description, and how it is matched to the research requirements, the necessary research and technical developments, interconnections and synergy between programs, cost, schedule and organization, comparison to other facilities, as well as safety and environmental issues. The main body of the Conceptual Design Report presents detailed descriptions and discussions of each of these topics. 9

6 1 The Science Case 1.1 Research with Rare-Isotope Beams Nuclei Far From Stability Physics Motivation The atomic nucleus, core of the atom and carrier of essentially all visible mass in the universe, has been the subject of intense investigations for many decades. Yet the last decade has seen a major re-orientation and the emergence of new frontiers in nuclear physics research. Two reasons, scientific and technical, are mainly responsible for this change. First, the realization that the quark-gluon sub-structure of the building blocks of nuclei, the protons and neutrons, must have important consequences for our fundamental understanding of the atomic nucleus itself and for the origin of the nuclear force that binds nuclei. Second, the availability of energetic beams of shortlived (radioactive) nuclei, in the following referred to as rare isotope or exotic nuclear beams, has allowed us to begin the exploration of the structure and dynamics of complex nuclei in regions far away from stability. As any other physical system under extreme conditions, nuclei, pushed to their limits in neutron or proton numbers, reveal new features which lead to new insights and understanding. GSI has played an important, and in certain respects seminal and pioneering role in the development of and in the research with beams of short-lived nuclei. The highenergy primary beams of stable nuclei from the present accelerator system have allowed one to develop important features of secondary, radioactive beams, generated through in-flight fragmentation, and of their use in experiments. The work in this field, at GSI and other laboratories around the world, has triggered considerable excitement in the nuclear structure communities and a thrust for more powerful nextgeneration facilities. While the present secondary, radioactive beam intensities have allowed first explorations of the new regions of unstable nuclei, a significant increase in beam intensities is mandatory to fully pursue the envisioned research opportunities. The present Conceptual Design Report has this as one of the central goals. The new facility will provide primary beams of stable isotopes at intensities that are a factor of 100 higher than presently available at GSI. Secondary radioactive beam intensities will even increase by a factor of up to 10,000 through advanced concepts for beam separation and secondary beam phase-space handling. The maximum beam energies of the radioactive species will be unparalleled by any other existing or planned facility. Altogether, this will allow sensitive experiments with secondary beam species far away from stability. This is also the region of the shortest-lived exotic nuclei, which can be best studied with the method of in-flight fragmentation. 10

7 The Research Program The main scientific thrusts in the study of nuclei far from stability are aimed at three areas of research: i) the structure of nuclei, the quantal many-body systems built by protons and neutrons and governed by the strong force, towards the limits of stability, where nuclei become unbound, ii) nuclear astrophysics delineating the detailed paths of element formation in stars and explosive nucleosynthesis that involve short-lived nuclei, iii) and the study of fundamental interactions and symmetries exploiting the properties of specific radioactive nuclei. Nuclear Structure Studies: In an atomic nucleus, three of the four fundamental forces (strong, electromagnetic, weak, gravitational) are important. The strong force plays the most decisive role. It fundamentally acts between the quarks, the constituents of the nucleons (protons and neutrons). Some of this action leaks out of the nucleon and generates the attractive, short-ranged nuclear force between the nucleons. This nuclear force is counteracted by the repulsive electromagnetic force between the protons. The weak force transmutes unstable atomic nuclei into others and ultimately into stable nuclei. Studies on atomic nuclei are thus intimately intertwined with those on fundamental interactions and on sub-nucleonic degrees of freedom. Strong interactions are described within the framework of Quantum Chromodynamics (QCD) which, however, does not deliver a precise analytical form of the interaction at a length scale relevant to nucleon-nucleon interactions. Moreover, the nucleonnucleon force within the nucleus is different from that between two free nucleons and depends in particular on the proton and neutron densities of the surrounding nuclear medium. To determine the emerging effective interaction represents a fundamental goal of nuclear physics. Probing nuclei under extreme conditions in various respects paves the way towards a more comprehensive understanding of nuclear matter. Stability of nucleonic matter is governed by neutrality in isospin, i.e. the strong force prefers the number of protons and neutrons to be equal. (This is similar to atoms, where charge-neutral systems with equal number of protons and electrons are energetically favored.) Counteracting this isospin-symmetry is the repulsive Coulomb force between the positively charged protons, which leads to a surplus of neutrons in stable heavy atomic nuclei. Altogether, slightly fewer than 300 stable isotopes exist in nature. They make up the stable 81 elements found on Earth. In the nuclear chart (Figure 1.1), the stable nuclei are found in a very narrow band of proton-to-neutron ratios. Proton and neutron numbers that are unbalanced with respect to isospin symmetry with Coulomb corrections, lead to decreasing nuclear stability. If, for example, more and more neutrons are added to a nucleus of given 11

8 proton number, the binding energy of the last neutron drops steadily and eventually the nucleus decays by spontaneous neutron emission. At this neutron dripline the nucleus becomes unbound. Except for the very light nuclei, the neutron dripline is still unknown. Similarly, if one adds more and more protons to a nucleus, the nuclei will also become unbound, when the proton dripline is reached. The proton dripline has been accessed for the light and medium-heavy nuclei, but is still unknown for the heavy nuclides. The number of elements is limited by the Coulomb force acting between the protons, which for very heavy nuclei leads to spontaneous disintegration (fission). In total, more than 6,000 different bound nuclei (though unstable against weak decays) are expected to exist. However, where exactly are the very limits of nuclear existence? How many protons and neutrons can be bound in a nucleus? Much of what we know about nuclei results from the study of reactions between nuclei. In the past, a major limitation in such experiments was that in any reaction both beam and target species needed to be stable. This imposed severe constraints on both the type of information that could be gained, and the region of the nuclear chart that could be accessed. Having beams of unstable nuclei available allows one to interchange the roles of beam and target particles and to perform reaction studies in inverse kinematics. In this way, many nuclei away from stability become accessible for reaction studies, a prerequisite for detailed nuclear structure investigations of these weakly bound nuclei. The structure and dynamics of such loosely bound nuclei is very different from that of stable nuclei. Rather diffuse surface zones, so-called halos and skins, were observed in neutron-rich unstable isotopes. Among other features unique to such exotic nuclei, one expects to encounter novel types of shell structures, new collective modes, new isospin pairing phases, possibly new decay modes (double proton emission) or regions of nuclei with special deformations and symmetries (Figure 1.1). Effects of nucleonic clustering should become more prominent, giving rise to unusual nuclear geometries. Theoretical models have to be further developed in order to achieve a profound understanding of the expected new data on exotic nuclei. Outstanding problems are the appropriate effective interactions in new regions of density and isospin, manybody methods that account for the weakness of the (often used) mean field, and structure and reaction models that can cope with the expected strong coupling of bound states with the close-lying continuum states. In addition to density and isospin, another degree of freedom for exploring the nuclear many-body problem is strangeness. Replacing nucleons by hyperons, which contain a strange quark, a third almost unexplored dimension is added to the nuclear chart. These new perspectives for nuclear structure research, which are complementary to studies with unstable beams, are part of the antiproton physics program outlined in Chapter

9 Exploring nuclear structure and nuclear stability under extreme conditions is important for a full comprehension of the nuclear many-body system. It is also the basis for understanding the various and complex pathways of nucleosynthesis and nuclear astrophysics. Figure 1.1: The chart of atomic nuclei. Stable nuclei, as found on earth, are marked by black squares. The yellow area covers unstable (radioactive) nuclei already produced in the laboratory. Many more unstable nuclei are predicted to exist (green area). The limits for binding of protons or neutrons are the so-called proton or neutron driplines. The different neutron driplines shown illustrate the uncertainty of theoretical predictions. For very large proton numbers, the existence of bound nuclei is limited by spontaneous fission. Also shown are: the magic proton and neutron numbers (2,8,20 ), the observed unstable doubly magic nuclei (full white dots), the N=Z line, where proton and neutron numbers of a nucleus are equal, and the superheavy elements (SHE) synthesized so far. A major goal of future rare isotope beam facilities is the exploration of the limits of nuclear stability when approaching either of the borderlines. Some examples of specific questions are illustrated in the figure: two-proton decay; isospin T=1 and T=0 pairing, production of superheavy elements, formation of neutron skins and halos, disappearance of shell gaps (50, 82, 126) or modification of shell structure with increasing neutron number, and the expected coupling of bound and continuum states. Nuclear Astrophysics: All atomic nuclei in the universe beyond lithium have been and still are being created in stars. In various stellar environments this nucleosynthesis proceeds via the formation of transient nuclei that decay into stable ones, either directly or after several intermediate steps. The remnants of these processes, dispersed from dying stars into the interstellar space, eventually contract and serve as the seeds for a new generation of stars and their companions, such as our sun and the earth. Hence the saying, we all are made of stardust. Unveiling the 13

10 birthplaces and pathways of stellar matter creation means nothing less than unraveling the ultimate roots of our own existence. In order to understand the formation, evolution, and final fate of stars, and to reveal stellar sites, pathways, and time scales of the synthesis of the elements, astrophysicists and nuclear physicists work closely together. Astrophysics defines possible stellar scenarios in terms of temperature, density, pressure and chemical composition, and nuclear physics supplies fundamental characteristics, such as masses and lifetimes, of key nuclei that are transiently created and destroyed during the complex steps of nucleosynthesis. However, as stellar scenarios might depend on nuclear structure, vice versa, nuclear properties might be altered in different stellar environments. The actual pathways of nucleosynthesis can be redrawn only by a careful analysis of the data from both disciplines, including many iterations of experiments as well as of theoretical modeling. Light and medium-heavy elements are produced by nuclear fusion in the hot and dense core of the stars. After a long-lasting burning of hydrogen into helium, heavier and heavier nuclei are formed by subsequent nuclear fusion processes. Each of them releases about a million times more energy than any chemical process, which is the reason why our sun can provide the earth with heat and light for many billions of years (Figure 1.2). Fusion ceases with the element iron. The reason is that fusion into still heavier nuclei would require input of energy. As a result medium-sized stars burn out after this stage has been reached. Only in very massive stars the creation of heavy atomic nuclei proceeds further on the neutron-rich side, by the interplay of neutron capture (preserving the proton number, but enlarging the neutron number by one unit) and of beta decay (transmuting a neutron into a proton). The stable, heavy and neutron-rich atomic nuclei found in our solar system have been produced in at least two processes, as it was concluded from their abundances. One of them, the slow neutron capture process (s-process), creating nuclei close to the valley of beta-stability, is believed to be generally understood. Most of the heavy atomic nuclei, however, originate from an explosive process of nucleosynthesis, the so-called rapid neutron capture (r-process). The true stellar site of the r-process is still uncertain; alternative suggestions are: supernovae of type II or the merging of neutron stars. Just as little is the detailed path of the r-process known, due to a lack of precise nuclear data in this region. Only a few beta-lifetimes have been measured at the closed neutron shell N = 82. Recent data have even suggested, that in very old (metal-poor) stars medium-heavy elements (Z< 50) were made by an additional r-process, different from the one, which led to the element formation observed in our solar system. A major goal of the new facility at GSI is to provide unstable atomic nuclei near and beyond the N = 126 closed neutron shell, and to measure their masses, which govern the r-process path, and their beta-decay half-lives, which determine the accumulated abundance pattern along this path. Thereby a long-standing puzzle can be for the first 14

11 time experimentally addressed, namely in what way the heaviest elements like thorium, uranium, and their precursors have been created. Figure 1.2: Based on key properties of unstable nuclei, nuclear astrophysics is seeking for a reliable description of the various kinds of stellar nucleosynthesis by which all elements beyond lithium have been and still are being created. One of its major aims is to understand the abundance of the elements in the universe. Some of the presumed scenarios of matter creation in stars are: nuclear fusion, e.g. in the sun; explosive rapid neutron capture (r-process) possibly occurring during the outbreak of supernovae of type II like the supernova 1987A; rapid proton capture (rp-process) occurring in novae explosions of accreting white dwarfs like Nova Cygni 1992, or in X-ray bursts emerging from accreting neutron stars. The remnants of a supernova might become a fast-rotating neutron star with degenerate, ultra-dense nuclear matter. At present, in particular the explosive nucleosynthesis is to a large extent not yet understood, due to the lack of appropriate nuclear data. Neutron-deficient nuclei close to the proton dripline are produced in other explosive scenarios, as signaled by Novae explosions of accreting white dwarfs, or by X-ray bursts, thought to emerge from the surface of accreting neutron stars. In these processes, hydrogen is explosively burnt via a sequence of rapid proton captures (rpprocess) and beta-plus decays (i.e. the transformation of a proton into a neutron by emission of a positron and a neutrino) near the proton dripline. Many of the questions concerning the rp-process have not yet been answered. At the new GSI facility, all relevant rp-nuclei will become accessible. To date, we have at best a qualitative understanding of the many aspects of stellar nucleosynthesis. In particular, the explosive stellar processes are only qualitatively understood, including the formation as well as the specific properties of their 15

12 remnants, such as neutron stars (Figure 1.2). Experiments based on the new generation of exotic nuclear beams will allow for a major step forward in this field, by providing the relevant properties such as masses, lifetimes, and reaction rates of appropriate key nuclei very far from the valley of stability. Those data are the basic ingredients for understanding the intricate details of nucleosynthesis, the evolution and fate of the stars and, finally, the abundance of the elements in our solar system, our galaxy, and in the universe. Fundamental Interactions and Symmetries: The Standard Model of Elementary Particle Physics summarizes our present knowledge on the fundamental building blocks of matter the quarks and the leptons and their interactions via exchange particles (so-called gauge bosons). It describes the electromagnetic, the weak and the strong force, and the fundamental symmetries (or symmetry violations) underlying these forces. The Standard Model has withstood three decades of extensive experimental scrutiny. Despite its great success, most physicists are convinced that the Standard Model eventually needs to be replaced or at least extended. The reason is that it contains disturbingly many parameters whose numerical values cannot be derived from the theory itself, and also other aspects that seem quite unnatural. Therefore, many high-energy physics experiments are aimed to search for possible extensions of the Standard Model. Besides these investigations in particle physics, low-energy precision experiments in nuclear and atomic physics also show a unique discovery potential for this field. The major thrust of the nuclear physics studies focuses on the weak interaction, in particular on precision experiments of the beta decay of specific exotic nuclei, emphasizing symmetry violation and the different interaction types of the weak force. Such studies comprise accurate tests of parity and time-reversal symmetry, sensitive tests of the conserved vector current (CVC) hypothesis, and sensitive searches for other than vector-axial vector (V-A) contributions to the weak interaction, such as scalar or tensor or (V+A) terms, that would hint at the existence of additional exchange bosons of the weak interaction. In particular, the new GSI facility would be uniquely suited to extend high-precision measurements of super-allowed transitions significantly beyond the present limit of Z=27 (Figure 1.3), probing the Vud matrix element at the hadronic vertex of the weak interaction and, thus, the intensely discussed unitarity of the CKM (Cabibbo-Kobayashi-Maskawa) matrix. Low-energy experiments addressing fundamental symmetries and their possible violations have been performed for a long time. The new facility will open a qualitatively and quantitatively new era, since the considerably increased production yields for exotic nuclei together with novel beam manipulation techniques, such as beam cooling, deceleration to rest and storage in ion or atom traps, will increase the precision achievable in these studies by one order of magnitude and more. As an example, selected unstable ions, which are presently far out of reach, can be produced, decelerated to rest, stored and cooled in Penning or Paul traps, and then serve as unique probes for substantially improved investigations of beta-neutrino correlations 16

13 (Figure 1.3). Compared to data presently available, these measurements will provide much more stringent constraints on scalar or tensor contributions, and on possible time-reversal (T)- or charge-and-parity-reversal (CP)-violations in the weak interaction. Figure 1.3: Symmetries and symmetry violations of the weak interaction can be investigated with high sensitivity at the new facility proposed at GSI. The figure illustrates some examples: measurements of electron-neutrino correlations of appropriate unstable atomic nuclei (bottom); extending high-precision measurements of super-allowed Fermi transitions (Ft-values) significantly beyond the present limit of Z=27, thus addressing the Vud matrix element at the hadronic vertex of the weak interaction. The matter-antimatter symmetry is symbolized by the materialization of a high-energy photon (coming from above) on a proton (recoil track) into an electron (left-handed spiral) and a positron (right-handed spiral). The search for violations of the underlying charge parity (CP) symmetry is a further research topic at the planned facility, which is part of the antiproton physics program outlined in the following chapter. Instrumentation For the production of beams of unstable nuclei, two different approaches are followed: the in-flight method, where high-energy heavy-ion fragmentation of stable nuclei is used as the production method, and the Isotope Separation On-Line (ISOL) technique, where stopped target fragments are post-accelerated. The former technique provides fast, clean separation independent of the chemical element; the latter is superior in terms of beam intensity for a number of elements, and in terms of beam quality (although the beams from in-flight fragmentation cooled to highest phase-space density via electron beam cooling in ion storage ring, also can provide excellent beam 17

14 quality). There is a general consensus that both approaches should be pursued, since they are highly complementary. A first generation of in-flight nuclear-beam facilities is in operation at various laboratories in Europe, the USA, and in Japan. Among these, GSI is playing an important role, since it is the only facility worldwide, where beams of all elements are available with energies up to about 1 GeV/u. This has opened the possibility to utilize fragmentation from even the heaviest ion beams and also in-flight fission of uranium for the production of isotopically separated, secondary unstable beams. In addition, the time structure of the beams from the synchrotron accelerator SIS18 allows the injection of short bunches of projectile fragments into the storage-cooler ring ESR, where they can be electron cooled to extremely small emittances. This storage-coolerring facility at GSI is worldwide the only one that operates with unstable nuclei. Figure 1.4: Predicted productions rates (for nuclei with half-lives larger than 100 ns) at the proposed facility. Stable nuclei (black symbols), closed shells, and the limits of known nuclei are indicated. At the new facility, hitherto unexplored parts of the presumed r-process path (hatched area) will become accessible, in particular around the closed neutron shells N=82, N=126 and even beyond. At present, efforts are under way worldwide to improve the potential of rare isotope beam facilities in terms of beam intensity, separation efficiency, beam quality, and instrumentation. In view of the successful operation at GSI of a synchrotron driver accelerator coupled to a projectile-fragment in-flight separator and a storage-cooler 18

15 ring, it seems natural to propose the installation of an international next-generation in-flight facility for Europe at GSI. Production rates, expected at the new facility for unstable nuclei with half-lives larger than 100 ns are shown in Figure 1.4. The maximum beam energies of the radioactive species will be unparalleled by any existing or planned facility. This will allow novel and unique nuclear physics studies, including sensitive experiments addressing even secondary beam species very far away from stability. This is also the region of the shortest-lived secondary nuclei, which can be best studied by means of in-flight fragmentation. The major components of the proposed facility are shown in Figure 1.5. Their design builds on the experience gained with the existing facility, but implements new features that significantly expand the scientific and technological potential. The most important components of the new facility are: A synchrotron accelerator complex that provides primary ion beams of all elements from hydrogen to uranium with intensities that are up to two orders of magnitude larger than the ones from the present GSI facility, i.e ions/s. In this high-intensity mode, the beam energy is variable up to 1.5 GeV/u. A large-acceptance Super-conducting FRagment Separator (Super-FRS) that will accept a much larger phase space compared to the present FRS. Its pertinent feature will be to collect projectile-fission fragments with the same efficiency presently achieved for projectile-fragmentation products. Fission of uranium is a very efficient source for very neutron-rich medium-mass nuclei. The Super-FRS serves an experimental area with equipment dedicated to ion reaction studies at high energies, injection into storage rings, and an energybunching stage. The latter one provides the possibility to stop beams in solid or gaseous material with strongly reduced range straggling. It also provides energy-focused low-energy secondary beams. A storage-ring system, the Collector Ring CR and the New Experimental Storage Ring NESR, for storage, accumulation and cooling of the largeemittance fragment beams. Their design aims at maximum collection efficiency and thus will remove a major limitation at the present storage ring. Both, fast stochastic pre-cooling in the CR and subsequent electron cooling in the NESR will be applied. In connection with internal targets, scattering experiments of radioactive nuclei on light probes such as on hydrogen or helium become feasible. A further option is to intercept the NESR with a small electron storage ring for electron-nucleus collisions (the ea-collider) to probe charge distributions and form factors of exotic nuclei by means of elastic and inelastic electron scattering. Clearly, many of these features represent major technological challenges. This holds e.g. for the Super-FRS, the efficient and fast stochastic cooling in the CR, the equipment needed for in-ring experiments with stored beams in the NESR including the electron-nucleus collision experiment and its spectrometers. 19

16 The proposed facility at GSI will provide novel scientific opportunities in the fields of nuclear structure physics with unstable ion beams, in nuclear astrophysics, and in studies of fundamental symmetries and interactions. The scientific potential of physics research with exotic nuclear beams has been assessed by international and European expert groups. A Working Group of NuPECC, the Nuclear Physics European Collaboration Committee, has formulated detailed recommendations for new major facilities in this field. The present proposal meets the criteria imposed therein on a next-generation European in-flight exotic-nuclear-beam facility. The physics program as proposed is competitive with that at the most advanced facilities of this kind, in particular the planned facility RIA, currently under consideration in the USA, and at RIKEN, Japan, the exotic-nuclear-beam factory RIBF for phase I, already under construction. In many respects, e.g. those of highest beam energies and efficiently coupled storage rings, the planned facility at GSI will provide unique, unsurpassed experimental opportunities. Figure 1.5: Schematic view of the proposed exotic-nuclear-beam facility. The super-conducting two-stage fragment separator (Super-FRS) provides beams of unstable nuclei for the double storage ring system (Collector Ring CR and New Experimental Storage Ring NESR), including an intersecting electron ring (ea collider), as well as for high- and low-energy experimental areas. 20

17 1.2 Research with Antiprotons Hadron Spectroscopy and Hadronic Matter Physics Motivation The strong force governs the microscopic structure of matter. It dominates the interaction between the nucleons, i.e. the protons and neutrons within the atomic nucleus, and it is the key force that determines the interaction between the quarks within the nucleon and within other hadrons (strongly interacting particles). Achieving a full quantitative understanding of matter at this level in all its forms strongly interacting or hadronic matter as it is called is one of the most challenging and fascinating areas of modern physics. During the last two decades hadronic physics has moved from phenomenological to fundamental understanding. The theory of Quantum Chromodynamics (QCD) is now regarded as the basic theory of the strong interaction. It is elegant and deceptively simple, but generates an enormous richness and complexity of phenomena. Possible forms of matter range from the spectrum of strongly interacting hadrons and nuclear species to compact stars of extreme density and to the quark-gluon plasma, a state of matter in the early universe and possibly in the interior of very heavy stars. The fundamental building blocks in QCD are the quarks, which interact with each other by exchanging particles, the gluons. QCD is simple and well understood at short-distance scales, much shorter than the size of a nucleon (<< m). In this regime, the basic quark-gluon interaction is sufficiently weak and one can apply perturbation theory, a calculational technique of high predictive power, which yields very accurate results when the coupling strength is small. In fact, many processes at high energies can quantitatively be described by perturbative QCD, using this approximation. The perturbative approach fails completely when the distance among quarks becomes comparable to the size of the nucleon, the characteristic dimension of our microscopic world. Under these conditions, the force among the quarks becomes so strong that they cannot be further separated, in contrast to the electromagnetic and gravitational forces, which fall off with increasing distance. This unusual behavior is related to the self-interaction of gluons: gluons do not only interact with quarks but also among themselves, leading to the formation of so-called gluonic flux tubes connecting the quarks. As a consequence, quarks have never been observed as free particles, they are confined within hadrons, complex particles made of 3 quarks (baryons) or a quarkantiquark pair (mesons). Baryons and mesons are the relevant degrees of freedom in our environment. An important consequence of the gluon self-interaction and if found a strong proof of our understanding of hadronic matter is the predicted existence of hadronic systems consisting only of gluons (glueballs) or bound systems of quark-antiquark pairs and gluons (hybrids). In the evolution of the universe, some microseconds after the big bang, a coalescence of quarks to hadrons occurred, which was associated with the generation of mass. The elementary light quarks, the up and down quarks, that make up the nucleon have 21

18 very small masses which amount to only a few percent of the total mass of the nucleon. Most of the nucleon mass, and therefore of the visible universe comes from the QCD interaction. This generation of mass is associated with the confinement of quarks and the spontaneous breaking of chiral symmetry, one of the fundamental symmetries of QCD in the limit of massless quarks. These phenomena, the confinement of quarks, the existence of glueballs and hybrids, and the origin of the mass of strongly interacting, composite systems related to confinement and the breaking of chiral symmetry are long-standing puzzles and represent the intellectual challenge in our attempt to understand the nature of the strong interaction and of hadronic matter. GSI has a distinguished history of having made important contributions to the physics of strong interactions. The present proposal will enable GSI to play an equally significant role in the future. The Research Program The proposal demonstrates that antiproton beams of unprecedented intensity and quality in the energy range of 1GeV to 15 GeV, as provided by the new GSI facility, will be an excellent tool to address these fundamental questions. Antiproton beams in this energy regime, stored in the High-Energy Storage Ring (HESR) for in-ring experiments, will provide access to the heavier strange and charm quarks and to copious production of gluons. As illustrated in Figure 1.6, this physics program offers a broad range of investigations that extend from the studies of Quantum Chromodynamics to the test of fundamental symmetries. The key components of the antiproton program are summarized as follows: Determining the interaction potential through precision spectroscopy has been a successful tool at all levels of the structural hierarchy of matter, as for example in atoms and molecules. Because the charm quark is heavy enough so that it lends itself to non-relativistic perturbative treatments far more reliably than the light up, down, and strange quarks, an optimal testing ground for a quantitative understanding of confinement is provided by charmonium spectroscopy, i.e. the spectroscopy of mesons built of charmed quark-antiquark pairs (c c ). The proposed program, using resonant antiproton-proton annihilation, is a quantitative and qualitative extension of successful experiments performed recently at the antiproton accumulator at Fermilab, USA. However, these studies (which ended in 2000) were limited in scope by lower antiproton energies (< 9 GeV), lower luminosities ( cm -2 s -1 ), and a detector capable of detecting only electromagnetic reaction products. At GSI, advanced antiproton cooling techniques leading to high energy resolution and a more versatile detector set-up will be employed which will allow for the first time the measurement of both electromagnetic and hadronic decays with high precision. The goal is to achieve a comprehensive precision spectroscopy of the charmonium system for a detailed study especially of the confinement part of the QCD potential. This in turn will help understand the key aspects of gluon dynamics, which are being investigated and quantitatively predicted in the framework of Lattice QCD. 22

19 Recent experiments at LEAR/CERN have demonstrated that particles with gluonic degrees of freedom are produced copiously in proton-antiproton annihilation in the light quark sector. A central part of the antiproton program presented in this proposal is the first search for gluonic excitations, glueball and hybrids, in the charmonium mass range where they are expected to be less mixed with the multitude of normal mesons. The unambiguous discovery of the gluonic modes would establish an important missing link in the confinement problem of hadrons. Figure 1.6: Mass range of hadrons accessible at the HESR with antiproton beams. The figure indicates the antiproton momenta required for charmonium spectroscopy, the search for charmed hybrids and glueballs, the production of D meson pairs and the production ofξ baryon pairs for hypernuclear studies. The energy range covered by the former Low Energy Antiproton Ring (LEAR) at CERN is indicated by the arrow. GSI has an active ongoing program of studying how the nuclear medium modifies the properties (masses, widths, etc.) of light mesons (pions and kaons), and how these phenomena are related to the partial restoration of chiral symmetry. The proposed experimental program at the HESR will address the open problem of interactions and of in-medium modifications of hadrons with charm quarks in nuclei. This is, on the one hand, an extension of the present GSI research program. On the other hand, this program will provide the first insight into the gluonic charmonium-nucleon and charmonium-nucleus interaction. A quantitative knowledge of charmonium-nucleon 23

20 cross-sections is considered to be of crucial importance in the identification of the formation of the quark-gluon plasma in ultra-relativistic heavy-ion collisions. A new and largely unexplored dimension in the chart of nuclides is introduced by replacing an up or down quark by a strange quark in a nucleon bound in a nucleus, leading to the formation of a hypernucleus. A new quantum number, strangeness, is introduced into the nucleus. Antiproton beams at the proposed facility will allow efficient production of hypernuclei with more than one strange hadron. This program opens new perspectives for nuclear structure studies and is thus a novel complement to the proposal to study the structure of nuclei with radioactive beams. The nucleon with the strange quark (hyperon) is not restricted in the population of nuclear states as neutrons and protons are. These exotic nuclei offer a variety of new and exciting perspectives in nuclear spectroscopy and for studying the forces among hyperons and nucleons. One of the most important symmetries of physics is CP (charge conjugation C spatial parity P). This symmetry implies that the laws of physics also apply to a system after the combined action of exchanging particles by their antiparticles and by reflection of the system in a spatial mirror. However, if CP symmetry were to hold perfectly, none of the matter in the universe, neither stars nor human beings, would exist since matter and antimatter would have completely annihilated each other. The observed dominance of matter in the universe may be attributed to CP violation, an effect directly observed in the decay of neutral kaons and very recently in B mesons. With the HESR storage ring running at full luminosity, CP violation can be studied in the charm meson sector and in hyperon decays. Should significant CP violation be observed in either case, one would have to invoke physics beyond the Standard Model. Two of the research areas with antiprotons, the in-medium properties of charmed hadrons and the structure of atomic nuclei with one or more strange hadrons, are examples of the close intellectual connection between the physics with antiprotons and two other major thrusts of the current proposal, relativistic nucleus-nucleus collisions and nuclear structure physics with radioactive beams. They contribute in a synergetic way to the broader goal of achieving a deeper understanding of the structure of hadronic matter in all its forms. The close connection between the various components of the present proposal is also evident in the pursuit of symmetry tests and symmetry breaking effects, which are the key for our understanding of how the world is built from the fundamental building blocks. Instrumentation and Detectors In the realization of the above research objectives, the technical capabilities and the uniqueness of the proposed facility are of great importance. Figure 1.7 shows the High-Energy Storage Ring (HESR) for antiprotons with its key components: a highenergy electron cooling section that will provide beams of unprecedented quality and precision, and the internal target facility with an advanced detector system. The highenergy electron cooling is a particular technological challenge. To this end a detailed research and development project and a collaborative effort has been initiated with 24

21 experts from Fermilab and Novosibirsk. The detector design incorporates most recent technologies to reach the required performance criteria with regard to mass, momentum, and energy resolution, hit resolution, particle identification and solid angle coverage. As discussed in the main section of the report, the combination of the high-quality antiproton beam and this detector system provides a powerful and unique facility, unparalleled worldwide, to carry out this research. Figure 1.7: Layout of the High-Energy Storage Ring (HESR) with the electron cooler and the almost hermetic detector system at the internal target position. 25

22 1.3 Nucleus-Nucleus Collisions at High Energy Compressed Nuclear Matter Physics Motivation Violent collisions between heavy nuclei promise insight into an unusual state in nature, that of highly compressed nuclear matter. In addition to its relevance for understanding fundamental aspects of the strong interaction, this form of matter may exist in various so far unexplored phases in the interior of neutron stars and in the core of supernova explosions. Novel phases of strongly interacting matter are expected to occur in the core of neutron stars where the density exceeds that of nuclei by up to a factor of 10. In this case, a variety of competing structures is predicted, such as condensates of mesons (quark-antiquark pairs), a large population of hyperons (particles containing up, down and strange quarks) or a plasma of quarks and gluons (the elementary particles of the strong interaction). In particular, particles carrying strange quarks are likely to play a vital role in neutron stars. Moreover, strangeness may exist in the form of unconfined quarks in chemical equilibrium with up and down quarks and/or with particles composed of quarks (hadrons), populating extended regions inside the neutron star. So far none of these scenarios can be excluded by astronomical observations or theoretical considerations. Further progress in the understanding of the behavior of strongly interacting matter at high densities requires new information on (i) the properties of hadrons in dense nuclear matter, (ii) the deconfinement phase transition from hadronic to quark-gluon matter at high baryon densities, and (iii) the nuclear equation-of-state at high baryon densities. These particular aspects can be explored in heavy-ion collisions which provide the unique possibility to create and investigate compressed nuclear matter in the laboratory. This experimental approach permits the study of the strong interaction and its underlying theory, Quantum Chromodynamics (QCD). The planned experiments address some of the most fascinating and challenging problems of strong interaction physics: the phenomenon of confinement (why are quarks not observed as individual particles?) and the origin of the mass of hadrons (why is a hadron that is composed of light quarks much heavier than the sum of the masses of its constituents?). The question of hadron masses is closely related to chiral symmetry, a fundamental property of QCD in the limit of vanishing quark masses. There are robust theoretical predictions that chiral symmetry is at least partially restored in hot and compressed hadronic matter. This has intriguing consequences. Among other effects the masses of hadrons in compressed hadronic matter can differ from the corresponding free masses. Changes in the in-medium properties of the rho-meson are suggested by the data on electron-positron pair emission in nucleus-nucleus collisions at the CERN SPS. Moreover, first signs for a mass modification of K-mesons in compressed 26

23 hadronic matter have been seen in detailed studies of nucleus-nucleus collisions at the GSI synchrotron SIS18. This observation is regarded as an experimental support for the idea of kaon condensation in neutron stars. Exploring the QCD phase diagram with heavy-ion collisions In the laboratory hot and dense nuclear matter can be generated in a wide range of temperatures and densities by colliding atomic nuclei at high energies. For a very short time highly compressed nuclear matter is formed in the collision zone. Simultaneously, a major fraction of the kinetic energy of the two nuclei is converted into heat. If the energy pumped into the collision zone is sufficiently large the quark-gluon substructure of nucleons comes into play. At first, nucleons are excited to short-lived states (baryonic resonances consisting of three quarks) which decay by the emission of mesons (quark-antiquark pairs). At somewhat higher temperatures, also baryonantibaryon pairs are created. This mixture of baryons, antibaryons and mesons, all strongly interacting particles, is generally called hadronic matter, or baryonic matter if baryons prevail. At even higher temperatures the hadrons melt, and the constituents, the quarks and gluons, can move freely forming a new phase, the quark-gluonplasma. The phases of strongly interacting matter are illustrated in Figure 1.8. The temperature at which hadrons are expected to dissolve forming a quark-gluon plasma is about 170 MeV. During the first few microseconds after the big bang the universe went through a phase transition where the quarks and gluons were confined into hadrons. Simultaneously, the chiral symmetry was spontaneously broken. This critical temperature is probably reached in lead-on-lead collisions at the CERN-SPS. These experiments have reported evidence for the formation of such a new state, presumably the quark-gluon plasma. The new experiments at RHIC are expected to substantiate these findings and provide further information on this unexplored state of matter. Future experiments at the Large Hadron Collider (LHC) at CERN aim at studying the phase transition as well as the properties of the quark-gluon plasma at even higher temperatures. In all these experiments the phases of hadronic matter are studied at extremely high temperatures and low net baryon densities, where the number of particles and anti-particles are approximately equal. This region of the phase diagram, which corresponds to the conditions in the early universe, is characterized by small values of the baryon chemical potential (Figure 1.9) The area at large baryon densities, however, is much less explored, both experimentally and theoretically. Pioneering experiments have been performed at the AGS in Brookhaven. Nuclear reaction experiments at the future facility at GSI aim at a detailed and comprehensive investigation of super-dense baryonic matter. The research program includes the measurement of penetrating probes, which escape essentially undistorted from the compressed nuclear collision zone. The energies of the heavy-ion beams delivered by the proposed accelerator are optimized for studies of hadronic matter at moderate temperatures but very large baryon densities. The 27

24 planned heavy-ion collision program will enter a new era with new diagnostic probes and thus has a unique and unparalleled research potential. Figure 1.8: A schematic phase diagram of strongly interacting matter. The net baryon density is the density of baryons minus the density of antibaryons. Similar to water, nuclear matter exists in different phases as function of temperature and density. The liquid phase is realized in atomic nuclei at zero temperature and at saturation density (300 million tons/cm 3 ). At low densities, the nucleons (i.e. protons and neutrons) behave like a gas. As the temperature is raised, the nucleons are excited into baryon resonances. Furthermore, quark-antiquark pairs ( mesons ) are produced. This hadronic phase is represented by the white area. At higher temperatures, a phase transition from hadronic matter to quark-gluon matter takes place ( deconfinement ). The transition temperature is about 170 MeV (at net baryon density zero) which is 130 thousand times hotter than the interior of the sun. Such conditions did exist in the early universe a few microseconds after the big bang and can be created in heavy-ion collisions at ultra-relativistic energies as provided by the accelerators SPS (CERN), RHIC (Brookhaven) and the future LHC (CERN). In highly compressed cold nuclear matter as it may exist in the interior of neutron stars the baryons lose their identity and dissolve into quarks and gluons. The critical density, at which this transition occurs, however, is not known. Similarly, the entire high-density area of the phase diagram is virtually unexplored. At very high densities and low temperatures, beyond the deconfinement transition, a further new phase is expected, where the quarks are correlated and form a color superconductor. At the critical point the deconfinement/chiral phase transition is predicted to change its character. The research program at the new facility at GSI aims for the exploration of the high-density area of the phase diagram. This approach is complementary to the investigations performed at the CERN-SPS, the RHIC facility at Brookhaven, USA, at the future LHC facility (ALICE project) at CERN. 28

25 The Research Program The proposed heavy-ion reaction program at the future facility will open up the possibility to extend the present studies at SIS18 to much higher baryon densities. Moreover, the hadronic matter generated at the future facility, is not only characterized by the highest achievable baryon densities but also by the highest relative abundance of strange baryons, i.e. baryons with strange quarks. These expectations are based on theoretical interpretations of experiments at the AGS (Brookhaven) and the SPS (CERN) where for beam energies around 30 GeV/u a maximum was found in the ratio of strange to non-strange particles. This maximum is unique to nucleus-nucleus collisions. It is thus a many-particle phenomenon, which characterizes the properties of compressed baryonic matter formed in such nuclear collisions. The present knowledge about the phase diagram of strongly interacting matter is shown in Figure 1.9 in terms of the temperature and the baryochemical potential. The data obtained at CERN-SPS and RHIC indicate that for very high beam energies the transition from the quark-gluon plasma to hadronic matter and the chemical freeze-out occur almost simultaneously. In Figure 1.9 it is illustrated that the fireball produced at SPS hadronizes at low baryon density. Consequently, hadronic fireballs with large baryon density are only accessible at beam energies below SPS energies. The hatched area indicates the region of dense baryonic matter to be studied at the future facility at GSI. Our experimental approach is to measure simultaneously observables which are sensitive to effects of high baryon densities and to phase transitions. In particular, we focus on the investigation of: short-lived vector mesons. Their spectral properties, the mass and the width, can be studied in the dense nuclear medium by their decay into lepton pairs. Since the leptons are almost unaffected by the passage through the highdensity matter, they provide, as a penetrating probe, almost undistorted information on the conditions in the interior of the collision zone. These studies will substantially benefit from the experience presently gained in experiments with the electron spectrometer HADES at GSI. strange particles, in particular baryons (anti-baryons) which contain more than one strange (anti-strange) quark. Hyperons serve as a probe for high baryon densities. mesons containing a charm or an anti-charm quark (open charm, e.g. D- mesons). The effective masses of D-mesons a bound state of a heavy charm quark and a light quark are expected to be modified in dense matter similarly to those of kaons. Such a change would be reflected in the relative abundance of charmonium (c c ) and D-mesons. 29

26 charmonium production and propagation as a probe for quark-gluon matter at high baryon densities. An experimental investigation of charm production requires heavy-ion beams at energies near to and well above the charm production threshold. macro-dynamical effects, like collective flow of nuclear matter during the expansion of the initially compressed system. Such probes provide constraints on the underlying equation of state which is of great significance e.g. for astrophysical problems. Moreover, the measurement of the flow of charmonium and multistrange hyperons will provide new information on the behavior of these rare probes in dense baryonic matter. event-by-event fluctuations are expected near the critical point. The identification of a critical point would provide direct evidence for the existence and the character of a deconfinement phase transition in strongly interacting matter. Figure 1.9: The phase diagram of hadronic matter plotted as a function of temperature and baryochemical potential. The baryon density rises steeply with increasing chemical potential, corresponding to 0.3 and 6 times normal nuclear matter density for the marked circles, respectively. The blue curve shows a prediction from a lattice QCD calculation for the phase boundary between the quark-gluon plasma and the hadronic phase. The experimental points and the pink curve characterize the properties of matter at chemical freeze out, i.e. the time when in the explosion of the collision zone the separation between particles is so large that reactions cease. Here nb denotes the sum of baryons and antibaryons densities. The part of the phase diagram to be investigated at the future facility at GSI is marked by the hatched area. 30

27 In the experiment particle multiplicities and phase-space distributions, the collision centrality and the reaction plane will be determined. The simultaneous measurement of various particles permits the study of cross correlations. This synergy effect opens a new perspective for the experimental investigation of nuclear matter under extreme conditions. Such systematic and detailed measurements include the variation of experimental conditions like beam energy and atomic number of the colliding nuclei and require a dedicated accelerator with high beam intensities, large duty cycle, excellent beam quality and high availability. The confinement problem and the quest for the origin of hadron masses are also central issues of the proposed research program with antiproton beams. In collisions between antiprotons and nuclei one probes cold nuclear matter at normal density ρ = ρ0, while in heavy-ion collisions one can explore the properties of matter at densities much higher than ρ0 and at finite temperature. Combining the results from both research programs will provide data on hadronic matter over the wide range of baryon densities. This illustrates the close links between the different research directions of the proposed project. The joint effort to unravel fundamental features of the strong interaction and the properties of hadronic matter in all its forms makes the new project at GSI a unique facility worldwide. Instrumentation and Detectors The proposed experiments will be performed with two detector systems. One of them is an adapted version of the currently used di-electron spectrometer HADES that can cover experiments in the lower energy regime of the new facility. A superconducting dipole magnet combined with particle tracking and time-of-flight measurement is proposed for the study of nucleus-nucleus collisions up to the highest beam energies available at the new facility. The full detector arrangement is shown schematically in Figure The high segmentation of the detector and the read-out electronics are adapted to rates of about a million nucleus-nucleus collisions per second with up to 1000 particles per collision. The handling of the corresponding data rates is a particular challenge for future developments in information technology. 31

28 Figure 1.10: Schematic detector setup for the study of nucleus-nucleus collisions at the future facility at GSI. The first detector is an extended version of the currently used electron spectrometer HADES. The second detector comprises a big dipole magnet with particle tracking and time-of-flight capabilities. Both detectors will be used alternatively for the lower and higher beam energy range available. 32

29 1.4 Ion Beam and Laser Beam Induced Plasmas High Energy Density in Bulk Matter Physics motivation In the familiar environment we live in, matter exists predominantly in the solid, liquid or gaseous phase. This, however, does not hold for the universe at large, where most of the visible matter exists as plasma. Very often plasma is called the fourth state of matter. When one heats a solid, it first turns into a liquid and subsequently into a gas. The addition of still more energy leads to a regime, where the thermal energy of the atoms or molecules forming the gas is so large, that the electrostatic forces which ordinarily bind the electrons to the atomic nucleus are overcome. The system then consists of a mixture of electrically charged ions and electrons and neutral particles as well. In this situation, the long-range Coulomb force determines the statistical properties of the sample. In the universe, plasmas exist in a wide range of densities and temperatures (Figure 1.11). There are several methods to produce a plasma in the laboratory such as electrical discharges in a gas or laser irradiation of a sample. Intense heavy-ion beams have added another method since they became available from powerful ion accelerators. They are unique for producing uniform large-volume plasmas by irradiation of a solidstate target. At the same time, they also provide excellent diagnostic methods to analyze the plasma properties. A particularly interesting plasma region, the dense, strongly coupled plasma, is located at relatively low temperature and high density. The interior of the giant planets Saturn or Jupiter are interesting examples for this dense plasma region. The investigation of the properties of dense plasmas is at the focus of plasma physics research with the new facility. Here, the determination of the equation of state (EOS) of materials under extreme conditions of pressure and temperature will be a key topic at the new facility. Of particular interest is the occurrence of phase transitions in cold compressed material, e.g. the insulator-to-metal transition of diamond expected at 10 Mbar, the insulator-to-metal transition of solid hydrogen predicted above 5 Mbar, or the plasma phase transitions at temperatures of about 1 ev. With the presently available beam pulses from the SIS18, a specific power deposition up to 50 GW/g is achieved resulting in a pressure inside the investigated solid-state target of only some 10 kbar. The Research Program The new facility with the 100 Tm heavy-ion synchrotron and a bunch compression system for the generation of very intense short ion bunches below 50 ns pulse length will extend the available beam deposition power from the current level of 50 GW/g by more than two orders of magnitude up to 12,000 GW/g. This will open up unprecedented opportunities for the production of ion beam heated and/or compressed plasmas. The plasma regions that can be studied with such ion beam heating and beam-plasma interaction experiments at GSI are indicated in Figure

30 Figure 1.11: Densities and temperatures of plasma states existing in the universe, e.g. at the sun surface, the sun core or the center of Jupiter. The temperature is given in units of electronvolts (ev); 1 ev roughly corresponds to 10,000 K. For comparison the parameter regions of magnetic and inertial confinement fusion are also shown. The plasma parameter Γ = 1 separates the region of ideal and strongly coupled plasmas. The normal solid-state density is marked by the arrow. At the new facility, strongly coupled plasmas with densities close to those prevailing in the center of Jupiter can be investigated. In comparison, the PHELIX laser, which is presently being installed at GSI, allows plasmas at higher temperatures, but lower densities to be explored. Through multiple shockwave techniques, the high-intensity fine focused SIS100 beam will allow pressures in the Mbar regime to be reached. Under these extreme conditions hydrogen, iodine, xenon and other cryogenic gas crystals are expected to perform a phase transition into a metallic state. Unexplored regions of the equation of state of matter at high densities and temperatures will thus be reached, providing new insights into the properties inside large planets and stars. In addition to the plans for the new ion beam facility, GSI is presently carrying out another unique project for plasma and atomic physics research. The high-energy / high-power laser system, PHELIX (Petawatt High-Energy Laser for Ion Experiments), is currently being installed at the facility. PHELIX is a laser in the kj regime with the option to produce ultra-short, high-intensity light pulses with a total power above 1 PW (10 15 W). This laser will be able to produce a light pressure exceeding the pressure in the interior of the sun. Thus GSI will offer the unique opportunity to exploit, in a synergetic way, both intense ion and laser bunches for dense plasma 34

31 research. The plasma regions that can be accessed with PHELIX are indicated in Figure In particular the combination of ion and laser beams will facilitate novel beam-plasma interaction studies on the structure and properties of matter under extreme conditions of high energy density, similar to those existing deep inside stellar objects with kev temperatures and more than 100 times solid-state density. To produce and investigate very dense and comparatively cold plasmas, novel beam shaping techniques and target configurations are being developed. The usual beam shape favors a cylindrical target geometry. The common experimental scenario is therefore a quasi-cylindrical plasma volume created by focusing an ion beam onto the target. Higher compression at lower temperatures can be achieved with a hollow cylindrical beam focus at the target position as sketched in Figure 1.12 (left). Such a ring focus was recently demonstrated at GSI with a plasma lens operated under specific conditions. With this technique, cylindrical implosion experiments will become possible. Simulations show that in such implosions pressures a factor of 10 higher than those achieved in usual beam heating experiments can be reached. Moreover, the hollow cylindrical beam technique offers the opportunity of applying strong magnetic fields along the target region (Figure 1.12, right). If such strong external fields (of the order of 30 T) are introduced, the effect of magneto-thermal insulation may allow temperatures in the kev region to be reached. Figure 1.12: The principle of magnetized targets for heavy-ion beam experiments. The focus of the ion beam is of annular shape. An example of such a ring-focus, which was already achieved with the GSI plasma lens, is shown in the left part of the figure. Highest plasma parameters are obtained, where the annular beam heats the outer line material in the annular focus region only and the inner cold portion of target is accelerated inward by the beam heated material. At magnetic field strengths of about 30 T, one expects, due to the effect of magneto-thermal insulation, plasma temperatures in the kev region to be reached. The diagnosis of dense plasmas is a challenging task, because most of the standard diagnostic tools, which are well known from atomic and plasma physics, fail due to the high density and exotic electronic behavior of the sample to be probed. Spectroscopy in the visible and near UV-range is usually not applicable due to the large absorption 35

32 inside the sample. Similar restrictions apply to interferometric measurements and optical imaging. Furthermore, the extremely dense states of matter are available in the laboratory only in a highly transient state. The planned experiments therefore require a high temporal resolution of the diagnostic devices, comparable with the hydrodynamic time scale for the expansion of the beam heated target material, which is of the order of nanoseconds or even shorter. To investigate the rapidly changing properties of dense plasmas at or well above the solid-state density, short X-ray bursts of high brightness are required. The PHELIX system is designed to serve as a versatile driver for X-ray backlighting of heavy-ion driven targets. The laser is equipped with a front-end, which is able to generate multiple laser pulses of sub-ns pulse duration, with each pulse to be timed independently. Therefore transient phenomena, like the dense, strongly coupled plasmas, generated by the SIS100 beam can be investigated with high time resolution. The measurement using X-rays can be extended and complemented by the use of short, intense pulses of energetic protons. These intense, low-emittance ion beams can also be produced with the PHELIX system, and then be used for radiographic measurements of dense plasma phenomena. Instrumentation and Detectors The experimental area planned for high energy density-plasma physics is shown in Figure It has two beamlines with beams from SIS100 and two interaction chambers. In order to keep the highest phase space density, the ion beam transport to the target chambers will make use of super-conducting transport elements. One beamline will be equipped with a plasma lens for generating a very small beam focus or, alternatively, an annular beam focus. This beamline will be used for the production and study of extremely dense and hot plasmas, utilizing e.g. the implosion scenarios described above. The other beamline serves a target chamber equipped with multiple instrumentation for investigating transport properties in dense plasmas, such as electrical conductivity, pressure gauge measurements or optical measurements. After traversing the target, the SIS100 beam is characterized by time-of-flight measurements and with an ion spectrometer. Further diagnostic tools are the laser beam pulses from PHELIX and ion beam pulses from the SIS18 that can also be delivered to both target regions. All plasma physics experiments will be performed as single shot measurements with several tens of shots per day. The impact of the plasma research program on the overall beamtime offered at the new facility will thus be rather moderate. Yet, the ion beam intensities, bunched into short pulses due to a very powerful beam compression system, together with the Peta-Watt laser system, will facilitate a worldwide unique and forefront research program. 36

33 Figure 1.13: Principal set-up of the experimental area to investigate strongly coupled plasmas. The beam from the SIS100 will be directed and focused onto two separate target stations A and B by super-conducting quadrupoles and by a plasma lens. A second ion beam from the SIS18 or laser pulses from PHELIX serve to diagnose the properties of the dense plasmas produced. Additional tools for diagnosis provide for pressure gauge, electrical conductivity, optical and other measurements. 37

34 1.5 From Fundamentals to Applications Quantum Electrodynamics, Strong Fields, and Ion-Matter Interactions Physics Motivation The new facility at GSI has key features that offer a range of new opportunities in atomic physics and related fields. First, high charge-state ions, moving at velocities close to the speed of light, generate electric and magnetic fields of exceptional strength. Second, at those relativistic velocities, the energies of optical transitions, such as those of lasers, are boosted to the X-ray region. The strong fields carried by heavy, highly-charged ions are their outstanding attributes for atomic and applied physics research. Together with anticipated high beam intensities a range of important experiments is envisioned. Figure 1.14: In relativistic, high-z ion-atom collisions, extremely intense photon fields arise due to both, the high nuclear charges and the extremely high velocities. This will even lead to the creation of real particle-antiparticle pairs (e.g. e + e ). For the heaviest ions, Quantum Electrodynamics (QED), the Standard Model of electromagnetism and a basis of modern physics, will be probed near the critical field limit associated with the extreme conditions of high charge states and high velocities. The fields present in highly relativistic collisions are strong enough to produce real e + e pairs directly out of the vacuum (Figure 1.14). Precision studies of QED in bound states will become possible through the large Doppler shifts of highly relativistic ions, which generate extreme energy shifts for photons in the ion rest frame. As a consequence, even the heaviest few-electron ions can now be studied in precision QED experiments by using state of the art laser systems. The Doppler effect will also be used for the first time for laser cooling of heavy, highly-charged ions, promising beams 38

35 at relativistic energies and brilliances that are suited for unique precision studies in atomic and nuclear physics. Moreover, the interaction of relativistic, highly-charged heavy ions with matter provides new possibilities in applications, in particular for material modifications and testing as well as in biophysics and in space research. Atomic Physics Research At SIS200, and the associated fixed target area, the elementary atomic interaction processes with matter can be studied at high values of the relativistic Lorentz factor γ. In this case the electric and magnetic fields increase dramatically and are strongly deformed. In contrast to lower energies where magnetic forces are generally of minor importance, they start here to equal the electric ones. This high-relativistic region could not be addressed in any detail up to now. For example, at high γ the magnetic terms will completely change the elementary photon-electron interaction reflected by photo-ionization and radiative recombination. Moreover, new and fundamental recombination, excitation and ionization processes involving pair creation will come into play. The high Lorentz boost for photons will allow precision laser spectroscopy of highly-charged especially Lithium-like heavy ions using standard laser techniques at normal photon energies. Laser cooling of relativistic heavy ions can be investigated. At the New Experimental Storage Ring (NESR) both, atomic structure and ion-atom collisions of highly-charged ions can be studied free of background. The excellent qualities of the heavy ion beams allow, in the strong field limit, the study of subtle higher order effects for elementary interaction processes as well as tests of fundamental symmetries. The electron-electron interaction, manifested in autoionization and dielectronic recombination, will be studied at the new electron target by means of cooled heavy-ion beams, decelerated in special cases for improved sensitivity. There, even the innermost electrons of high-z ions will be probed with drastic increases of interaction strengths due to magnetic effects. The collision of counter-propagating laser pulses with the electron bunches from the attached electron collider will create intense X-ray pulses. Additionally, behind the NESR, a dedicated experimental area for extracted highlycharged, heavy ions at low energies opens the area of adiabatic collisions far off charge-state equilibrium, of exotic multi-excited states formed by multi-electron capture and their stabilization, as well as the field of precision spectroscopy and QED tests in bare and few-electron heavy atomic nuclei. In this context, the deceleration of these heavy ionic species with subsequent capture in an ion-trap and ion cooling will provide for a new regime of sensitivity. The unique features of the new facility together with powerful experimental tools also pave the way to highly sensitive tests of fundamental symmetry principles, such as parity conservation or time-reversal invariance. Moreover, stored, cooled and polarized nuclei would allow one to search for a nuclear electric dipole moment, caused by a simultaneous violation of both, parity and time-reversal symmetry. By measuring beta-neutrino correlations of trapped and cooled radioactive nuclei the Standard Model of weak interaction can be tested with high sensitivity. 39

36 The advanced studies at the new facility will strongly benefit from the experience gained at the existing SIS/ESR. In particular, the heavy-ion storage ring ESR has played a pioneering role in opening unexplored fields of research with energetic heavy ions. Both, atomic structure and atomic collision dynamics under the extreme conditions of the strongest fields available were investigated at SIS/ESR in a regime where relativistic effects only begin to become important. QED studies for the strongfield case have successfully been started. For elementary processes, like photonelectron or electron-electron interactions, unexpected effects of the magnetic part in the strong-field cases have been already seen at low γ values. In parallel, atomic structure investigations have also reached an impressive level of precision. By means of collinear laser spectroscopy the ground state hyperfine-splitting of very heavy, hydrogen-like atoms has been probed with high accuracy. Based on this experience, nuclear properties like radii, spins, magnetic dipole moments and higher electromagnetic moments of nuclei very far off stability will be addressed at the new facility by experimental techniques of atomic physics. Many of the research topics mentioned from collision studies to spectroscopy that were started successfully at the ESR, will be expanded into new regimes under much better and advanced experimental conditions at the NESR. Applications In the field of applied research beyond materials research, plasma physics and biophysics the cancer therapy with heavy ions is certainly the most prominent success of GSI. A major focus of future research in the realm of applied physics will be the continued exploration of fundamental interaction processes of relativistic heavy ions with matter. Because of their high energy, heavy charged particle beams have an important potential in ground-based research for space missions. A major hazard for flight into deep space is cosmic and solar radiation. While solar particles are mostly protons and helium ions at moderate energies, the spectrum of cosmic radiation extends with significant intensity up to iron ions and to energies in the TeV/u region (Figure 1.15). In the interaction with biological systems like the cells of human tissue or with electronic devices like computer memories, heavy charged particles can cause severe damage. In the case of biological systems, the DNA inside the cell nucleus seems to be the most prominent target. The complex interplay of the repair capacity of a cell with the extension and severity of the particle-induced lesions determines the fate of hit cells. Alterations in the genetic code may cause cancer or long-term mutations. A similar process as for the biological lesions is responsible for the failure of electronic devices. The production of locally high ionization densities and free charges causes single event upsets or a local damage in semiconductors. Therefore, it is very important to test electronic modules for their radiation hardness with heavy ions before they are launched into space. Even for large devices such as complete satellites, spacecraft components, or entire detector set-ups the radiation sensitivity and damage due to relativistic projectiles at different locations and depths can be tested. 40

37 Figure 1.15: Energy spectrum of the particles in cosmic radiation. The ion beams have very large penetration depths and can also be used to create regions of local structural changes deeply buried in a target. Using radioactive beams available at the new facility, radioactive probe ions can be deposited in a target depth far from the surface and unreachable by other techniques. The large ion range also offers new possibilities of carrying out experiments under extreme conditions as, for example, track formation in a sample under very high pressure, where the projectiles must first traverse the thick walls of the pressure-producing device. Instrumentation The experimental areas at the new facility provide a range of novel instrumentation for atomic and applied research. From SIS200 the unprecedented combination of high intensities and of acceleration up to γ = 23 will be available. The new multi-purpose experimental atomic physics area will be supplied by ion beams both from SIS18 and SIS200. A target station for high-energy ions will also serve for the irradiation of samples for biological and materials research and will be equipped with a raster scan system. In addition, laser installations are planned for various experimental areas of the new GSI facility. In particular, the high-power PHELIX facility will allow the study of interactions of the most intense laser fields with heavy ions. The NESR will be the workhorse for atomic physics experiments (Figure 1.16). Compared to all other heavy-ion storage rings currently in operation or under construction, the NESR will be the most flexible one, providing the most intense beams up to bare uranium. Moreover, a broad spectrum of instrumentation will be available, such as an internal gas jet, an electron target, and electron bunches provided by the electron collider for interactions with collinear, high-intensity laser pulses. 41

38 For a wide range of ion velocities, the interaction of highly-charged ions with matter will be investigated in fixed target experiments. This experimental area will be located next to the NESR and is devoted to experiments with fast or slow ions. An important feature of the NESR is its capability to decelerate heavy ions. The highlycharged ions can, after extraction, be actively slowed down further, even to rest, for ultra-precision studies in the heavy ion trap facility HITRAP. Compared to EBIT facilities (electron-beam ion traps), the HITRAP facility will allow the capture of highly-charged ions of any element up to uranium with substantially higher yields. The intense secondary beams, produced at the Super-FRS and decelerated in the NESR, will also allow the trapping of exotic nuclei, as also described in Chapter 1.1 Figure 1.16: The New Experimental Storage Ring NESR with its instrumentation for atomic physics experiments. The NESR can be supplied with highly-charged heavy ions from SIS18 and with exotic nuclei from Super-FRS. At the gas jet target, ion-atom reaction mechanisms as well as the ionic structure will be studied; beyond X-ray spectroscopy, zero-degree electron spectroscopy and recoil-ion momentum spectroscopy, laser spectroscopy will be applied here. At the electron target, the atomic assisted electron-electron interaction will be studied; here also laser techniques and X-ray spectroscopy will support the experiments. At the electron collider, electron pulses will interact head-on with laser pulses producing forward emitted X-ray pulses. Moreover, the highly-charged heavy ions can be decelerated in the NESR down to the MeV/u region and extracted toward a fixed target area. There, atomic reactions with highly-charged ions at low velocities will be performed; also here X-ray spectroscopic and laser techniques will be applied. Attached to the fixed-target area, the ions can be decelerated down to almost rest in the HITRAP facility and captured into a trap system for precision measurements. 42

39 2 The Facility To achieve the science goals described in the previous sections, GSI, in close collaboration with universities and the international science and accelerator communities, has worked out technical plans for the new facility. Beam concepts for the different research areas, technical descriptions of the accelerator facility and its various subsystems, and the necessary research and development for the new facility are described in detail in Section 3 of this Conceptual Design Report (CDR). Layout and Technical Specifications Briefly, the concept and layout of the new facility (Figure 2.1) has evolved from the science requirements as follows: substantially higher intensities are achieved, compared to the present system, through faster cycling and, for heavy ions, lower charge state which enters quadratically into the space charge limit. The reduced charge-state, at the desired energy of up to 1.5 AGeV for radioactive beam production, requires a larger bending power. All these aspects are fulfilled by the SIS100 synchrotron. It also generates intense beams of energetic protons, up to 60 GeV, and from these antiprotons. Heavy ion beams of high energy, i.e AGeV, are generated using ions in a high charge state plus the additional, somewhat slower but still rapidly cycling SIS200 synchrotron ring. The intensity required for these beams allows for long spills. Similarly, the SIS200 can be used as a stretcher for radioactive beams. Both, primary and secondary beams can be injected, cooled and stored in a system of rings with internal targets and in-ring experimentation. Rings may be shared for uses with different beams. Based on the developments and excellent experiences with cooled beams at the present GSI facility, the future program will broadly take advantage of this aspect of beam handling. The total system then provides beams with the following characteristics: Full range of ion beam species: The proposed facility will accelerate all ions from protons (and also antiprotons) up to the heaviest element, uranium. This will provide the necessary broad basis for the multi-disciplinary research program proposed for the new facility. Highest beam intensities: Intensities of primary heavy-ion beams will increase by a factor 100, secondary radioactive beams by a factor of up to 10,000 over the present GSI facility. This will allows one to push the sensitivity of experiments involving primary beams, but more importantly, to produce high-intensity secondary beams, i.e. beams of short-lived nuclei and antiproton beams, which are the basis of much of the new research frontiers presented in this CDR. Substantial increase in beam energy: an increase by about a factor of 15 in energy is foreseen for beams as heavy as uranium. In this energy regime nucleus-nucleus collisions are believed to generate hadronic matter at the highest densities, a further key research program in this CDR. Moreover, this enables the study of charm production in highly compressed matter. 43

40 Precision beams: these will be achieved through sophisticated beam handling methods, such as stochastic and electron cooling of ion beams, in particular also of the secondary radioactive and antiproton beams. Together with the statistical precision and high sensitivity that results from high beam intensities and interaction rates, the precision-quality beams will allow to enter totally new areas of research in all of the science fields discussed in this CDR. Figure 2.1: Present layout of the existing UNILAC/SIS18/ESR facility (blue) and the planned new facilities (red): the Super-conducting Synchrotrons SIS100/200, the Collector Ring CR, the New Experimental Storage Ring NESR, the Super Fragment Separator Super-FRS, the proton linac, and the High-Energy Storage Ring HESR. Also shown are the planned buildings for plasma physics, nuclear collisions, radioactive ion beams, and atomic physics experiments. 44

41 Rings as accelerator structures of choice: for ion beams, from protons to uranium synchrotrons provide the most economical solution for very high beam energies. But more importantly, for the research program described in this CDR, accelerator rings are unique in their capability to store, cool, bunch, and stretch beams and thus to fulfill the stringent beam phase-space requirements from experiments. The choice of a ring system for the new facility also matches perfectly to the existing accelerator, which thus can be used as the injector. Technical innovations and challenges: the technical requirements set by the scientific goals in this CDR can only be met with new technological solutions. The most important ones include: the development of rapidly cycling, super-conducting magnets for the synchrotrons; electron beam cooling for ions over a broad energy range, in particular also for the high-energy antiproton beam; bunch compression and fast extraction of intense heavy-ion beams down to 50 nanosecond bunch width, and thus into the Gigawatt beam power regime; techniques for ultra-high vacuum and development of a super-conducting large acceptance beam-fragment separator for efficient collection and beam shaping of secondary radioactive beams. If one were to summarize the facility goals in one sentence, one might state these as pushing the intensity and the precision frontiers, although this would not capture the full scope of what is proposed. In particular, the higher energies of the beams of heavy nuclei such as uranium are an important part of the program. Nevertheless, the energy gains are modest, since pushing the energy frontier, as in elementary particle physics, is not central to the facility here. The major technical innovations and challenges are in the fields of high-intensity and precision beams of unstable nuclei and antiprotons. The existing accelerator facility of GSI consists of the universal linear accelerator UNILAC, the heavy-ion synchrotron SIS18, and the experimental cooler/storage ring ESR. The UNILAC, commissioned in 1975 and upgraded several times, is today with its three injectors probably the most versatile and powerful heavy-ion linac around the world. The SIS18 and the ESR were constructed between 1985 and With SIS18, stable nuclei of all elements in the periodic system, from hydrogen to uranium, can be accelerated to more than 90% of the speed of light. At the ESR, innovative techniques such as electron cooling and stochastic cooling have been developed and used in experiments with high-energy heavy-ion beams for the first time. In particular the application of these beam cooling techniques to secondary beams of unstable nuclei, produced by fragmentation or fission reactions and collected and stored, has produced seminal results. Through these techniques unprecedented beam qualities could be achieved, opening new areas of research. SIS18 will act as the injector for the new facility. The central part of the planned new accelerator facility is a synchrotron complex consisting of two separate synchrotron accelerator rings with 100 and 200 Tm maximum magnetic rigidity. Both synchrotron rings have the same circumference of about 1100 m and will be installed in the same tunnel. They will be equipped with 45

42 new, rapidly cycling super-conducting magnets in order to minimize construction and operating costs. For the highest intensities, it is planned to operate the 100 Tm synchrotron at high repetition rate (2-4 Hz), i.e. with ramp rates of up to 4 Tesla per second for the dipole magnets. The goal of the first synchrotron ring (B = 100 Tm) is to achieve intense pulsed (10 12 ions/pulse) uranium (q = 28 + ) beams at 1 GeV/u and intense pulsed ( ) proton beams at 29 GeV. (For the high-intensity proton beams, needed for antiproton production, an additional dedicated linac injecting into SIS18 is planned.) Both, heavy-ion and proton beams at the mentioned particle intensities can be compressed into 50 ns bunches required for the production and subsequent storage and efficient cooling of exotic nuclei and antiprotons. The short intense ion bunches are also required for plasma physics experiments. With the double ring facility, continuous beams with high average intensities of up to ions per second can be provided for 1 GeV/u heavy ions, either directly from the SIS100 or by transfer to, and slow extraction from the 200 Tm ring. The 200 Tm ring can provide high-energy ion beams with maximum energies around 30 GeV/u for Ne 10+ beams and close to 23 GeV/u for fully stripped U 92+ beams, respectively. The maximum intensities that are possible in this mode are 5 x ions per second. Since for nucleus-nucleus collisions, intensities between 10 8 and 10 9 per second provide the maximum luminosity that the complex, large detectors can take, the high-charge state, high-energy beams can be extracted over extended periods (order of seconds) as an essentially continuous beam. Slow extraction from the SIS100 is an additional option for extending the flexibility of parallel operation for experiments. The accelerator facility will be complemented by three additional cooler-storage rings: A collector ring (CR) for stochastic cooling of radioactive ion or antiproton beams from the production targets. In addition, this ring offers the possibility for mass measurements of short-lived ions, by operating it in the isochronous mode. A new experimental storage ring (NESR) serving as an accumulator and storage ring both for radioactive ions and antiprotons. The NESR will be equipped with stochastic and electron cooling devices. In addition, it has to provide for sections for electron-ion scattering and internal target experiments with ions. Layout and design of the NESR is a particular challenge, since it attempts to incorporate a range of functions unprecedented for any existing storage ring. A high-energy storage ring (HESR) for antiprotons up to 14 GeV. This ring will operate with an internal target and associated detector set-up. It will be equipped with a high-energy electron cooler (up to 5 MeV electron energy) and a stochastic cooling system to compensate for beam degradation due to target interaction and intra-beam scattering. This new combination of accelerator and storage rings aims for 100 times higher primary ion beam intensities than the present system and, in conjunction with the new Super-conducting Fragment Separator (Super-FRS), for an increase of radio- 46

43 active beam intensities by a factor of up to 10,000. It will provide high-luminosity antiproton beams, high-energy proton and ion beams (about 15 times higher than presently available at GSI), and short ion pulses with energies up to 100 kj. The key parameters and specifications of the proposed synchrotrons and cooler/storage rings are shown in Table 2.1. The beams that can be provided for the different research fields are displayed in Table 2.2. Table 2.1: Key parameters and features of the proposed synchrotrons and cooler/storage rings Ring Synchrotron SIS100 Synchrotron SIS200 Collector Ring CR New Experimental Storage Ring NESR High-Energy Storage Ring HESR Circumference [m] Bending Power [Tm] Beam Energy GeV/u U GeV protons Specific Features fast pulsed superferric magnets up to 2 T, 4 T/s, bunch compression to 50 ns, fast and slow extraction, 5x10-12 mbar operating vacuum GeV/u U 92+ pulsed super-conducting cosθmagnets up to 4 T, 1 T/s, slow extraction with high duty cycle, 5x10-12 mbar operating vacuum MeV/u, A/q=2.7 3 GeV antiprotons MeV/u, A/q=2.7 3 GeV antiprotons GeV antiprotons acceptance for antiprotons: 240 x 240 mm mrad, p/p=±3x10-2, fast stochastic cooling of radioactive ions and antiprotons, mass spectrometer for shortlived nuclei electron cooling of radioactive ions with up to 450 kev electron-beam, precision mass spectrometer, accumulation and stochastic cooling of antiprotons, internal target experiments with atoms and electrons, electron-nucleus scattering facility stochastic cooling of antiprotons up to 14 GeV, electron cooling of antiprotons up to 9 GeV 47

44 Table 2.2: Primary beam parameters from the SIS100/200 facility for the different research fields Research Field Radioactive Ion Beams Energy Peak Intensity Average Intensity 1.0 to 1.5 GeV/u for all elements up to uranium Antiprotons 29 GeV p Dense Nuclear Matter up to 22.3 GeV/u U up to 30 GeV/u Ne per cycle for storage ring experiments per second high duty cycle for fixed target experiments Pulse Structure 50 ns for transfer into the storage ring 2.5x10 13 per -- < 50 ns cycle per second high duty cycle -- Plasma Physics Atomic Physics.4 to 1 GeV/u ions 2x10 12 per cycle ns (fixed target) 1 to 22.3 GeV/u ions per second high duty cycle -- Parallel Operation and Synergy An important consideration in the design of the facility was a high degree of truly parallel operation of the different research programs. Simple beam splitting and switching to different target locations is of course generally possible at an accelerator with relatively little effort. But this would in general not change the integrated luminosity. Truly parallel operation, with the constraints of accelerator cycles, is considerably more difficult. It would, however, provide maximum integrated beamtime, or integrated luminosity for each of the different programs operated in parallel. This implies that the facility operates for the different programs more or less like a dedicated facility. The proposed facility concept is therefore very cost-effective. A modest addition in facility structure, say an additional storage ring, can provide an essentially full scale new program without the need of a central facility, since that already exists for the other programs, or vice versa. The proposed scheme of accelerator and storage rings has the characteristics to optimize such a parallel and highly synergetic scheme. We are confident that the proposed scheme will work very well due to the considerable development and experience at the present facility: At the existing system, parallel operation of different beams from the three UNILAC injectors, acceleration of these beams to different energies and with different intensities, and serving different experiments at the UNILAC, at SIS (including ion beam tumor therapy), and at the ESR, has been routinely demonstrated. Figure 2.2 illustrates how parallel operation would be performed with a cooled and post-accelerated antiproton beam, in parallel to 48

45 a fixed target experiment with radioactive beams and/or relativistic heavy-ion beams slowly extracted from the second synchrotron ring SIS200, and an additional beam for plasma physics. Figure 2.2: Schematic illustration of the highly efficient parallel operation at the new facility. In the example shown, all four different scientific programs are served in parallel: A proton beam (orange), accelerated in SIS100, produces antiprotons (orange dashed) in the antiproton target-station, which are then collected, accumulated and cooled in the CR/NESR storage-ring combination, injected and accelerated in SIS100, and then transferred to the HESR for in-ring experiments. In parallel, i.e. during the fraction of the SIS100 super-cycle not needed for the protons, a primary ion beam (blue) is accelerated in SIS100 and slowly extracted to the Super- FRS to produce radioactive secondary beams (blue dashed) for fixed target experiments. (Alternatively the radioactive beams could be sent to the CR and NESR instead of the antiprotons). In addition, every seconds a high-energy heavy-ion beam (gray) is accelerated in SIS100/200 and slowly extracted for nuclear collision experiments; these experiments require a lower beam intensity than the maximum possible from the accelerator. Moreover, intense beam pulses (green) are provided every few minutes for plasma physics experiments that require very low repetition rates. Accelerator Research and Development for the New Facility The concept for the proposed new facility is based on experience and developments at accelerators in nuclear and high-energy physics worldwide, and it also builds on the unique specifications and novel techniques developed at the existing GSI facility. Beyond this, new concepts and schemes to be introduced at the new facility, such as rapidly cycling super-conducting magnets, will require extensive and thorough simulation, design, engineering and prototype work. This holds for various aspects of 49

46 the synchrotrons as well as the storage rings. One of the major milestones to be reached within the next two to three years is the construction of model and prototype magnets as a reliable basis for the production of magnets for the synchrotrons SIS100 and SIS200. With regard to these technological developments for the planned accelerator complex, national and international cooperations have been or are being established in the following areas: (i) (ii) (iii) (iv) (v) (vi) fast cycling super-conducting magnets: with the Joint Institute for Nuclear Research (JINR), Dubna, Russia, which has special expertise in iron dominated window-frame super-conducting magnets (of the NUCLOTRON type with fast ramp rates but limited maximum fields), and with the Brookhaven National Laboratory (BNL), Brookhaven, USA, which has special expertise in cosθ-type super-conducting magnets (of the RHIC-type with so far low ramp rates but higher maximum fields). high-energy electron cooling of ions and antiprotons, beam compression systems for the generation of short intense ion pulses, design of an electron ion collider for electron scattering experiments off unstable nuclei: in collaboration with the Budker Institute for Nuclear Physics (BINP), Novosibirsk, Russia, which has broad expertise in accelerator technology, in particular in electron cooling devices. fast stochastic cooling systems: RIKEN, Japan; Technical University Darmstadt. Design of the proton linac: University of Frankfurt; special expertise in efficient accelerator structures. (vii) Cryogenics: Technical University Dresden, CERN and DESY; special expertise in design and operation of large scale cryogenic systems (viii) Field calculations for magnets and accelerator structures: Technical University Darmstadt In addition, cooperation agreements are under discussion with further laboratories from France, Italy, Japan, Russia, and the USA for specific topics associated with the new facility. 50

47 3 Civil Construction The new accelerator complex will be constructed east of the existing GSI facility. This is determined by the fact that the existing accelerator will serve as injector for the new facility. The civil construction scheme furthermore takes in to account the need to conform to radiation protection requirements, ecological aspects, and to minimize costs for the buildings and technical facilities. Several schemes have been investigated by a professional company, consulting in civil construction: the first concept placed all accelerators and facilities deep underground; the second placed all facilities above ground; the third and final concept is a combination of the former ones placing certain components below and other parts of the facility above ground. Taking into account the above mentioned aspects radiation protection, ecology and cost-effectiveness led to the architectural concept shown in (Figure 3.1): The large double ring with a circumference of about 1,100 meters will be laid out underground in a ring tunnel at a depth of 24 meters. The drilling of the tunnel can be carried out very cost-effectively using the shield driving technology. The underground arrangement also results in considerable cost savings when it comes to the measures for radiation shielding. Another important advantage of the concept is that it preserves the forest currently covering the region above the double ring. Figure 3.1: Location of the projected new international facility All of the other buildings and facilities will be arranged south of the large ring tunnel. For these buildings, an above-ground solution is more economical here. The construction of the above-ground buildings will require the clearance of approximately 14 hectares of forest that will be replanted in another area. 51

48 4 Environmental and Safety Aspects for Design and Operation of the New Facility Just like with the present facility, safety is a top priority also with the new facility for all phases of the project: R&D, construction, and operation. First analyses of safety aspects, calculations, simulations and estimates of safety risks are described in Section 5 of this CDR. The operation of any high-energy accelerator with its target and experimental facilities is a potential source of risks for humans and the environment. There are several sources of radiation which will be discussed in the following: During the acceleration cycle in the synchrotron, a small fraction of the partially stripped ions will loose electrons due to interaction with the rest gas. These ions leave the orbit and hit the beam tubes, inducing radiation. The vacuum specifications for SIS100/200 are such that these beam losses are tolerable. The radiation has also to be kept to a low level in order to avoid the quenching of the super-conducting magnets. Nevertheless, the required shielding is quite substantial and the choice of an underground installation for the SIS100/200, also motivated by ecological considerations, was obvious. The extracted beams are sometimes shaped in geometrical size with the help of collimators and scrapers. These are strong sources of radiation, which need to be shielded locally by large-thickness iron and concrete walls. The target inside the experiment is another source of radiation, since it is there where the interaction of the beam with the target material sample is intended. Often the detectors are not capturing all the produced particles and a full shielding of the experimental cave is required. Finally, the beam, which has not undergone an interaction, is dumped into the beam dump where all the energy is lost through nuclear reactions and through electromagnetic stopping. In addition, worst case scenarios of, e.g. lost beams due to malfunction of beam optics elements, have been studied and considered in the detailed shielding project. As a consequence of these considerations, it was opted for a policy to dimension the shielding such that it would provide for absorption of all muons produced. A survey of the induced radioactivity in the accelerator structure and the production of radionuclides in the cooling loops and in the air of the accelerator tunnel was made, and dose rates have been estimated for these areas. The impact of high-energy neutron radiation, which penetrates into the environment, is described by an estimate on the production and on the migration of long-lived radioactivity into the earth, and on the associated exposure through consumption of drinking water enriched by these radionuclides 52

49 In addition to the risks originating from ionizing and non-ionizing radiation, an analysis was performed of the impact of the facility on the environment, of the danger of fire and of toxic substances, and other sources of danger. Recommendations for protection and safety measures are made which will influence the final design of the facility. Other important aspects for industrial safety near accelerator facilities have also been considered. Examples are health effects caused by electromagnetic fields, production of toxic compounds such as ozone or nitrogen oxides, the safe use of robots for the handling of highly activated components, and the release of helium from quenches of the super-conducting magnets, leading to possible asphyxiation. A further serious subject for the safety of the facility, especially for the underground accelerator, is fire protection. Protection measures are proposed, such as the definition of fire sectors (special sectors with rooms for storing radioactive materials), escape routes and manholes, usage of non-flammable materials and fire alarm devices. In this context, it has also been considered that the contact of air with cryogenic devices can lead to a selective condensation of oxygen which will increase the risk of fire. 53

50 5 Costs, Schedule and Organization Cost Estimate The present estimate of the total cost of the facility is 675 MEuro. Of these are 225 MEuro for civil construction and infrastructure, 265 MEuro for accelerator components and 185 MEuro for instrumentation and major detectors. These costs include all manpower costs for commercial activities, in particular civil construction and fabrication by industry of various components and sub-systems, including installation, some testing and quality assurance. The cost does not include redirected manpower from GSI (120 full-time-equivalent positions (FTE) on average for the duration of facility construction) and new (permanent and temporary) staff (140 FTE) for engineering design, procurement, assembly, on-line testing and commissioning and for project management. Schedule The proposed schedule for realizing the facility extends over 9 years. Certain research and development projects already started this or in the recent year. The overall schedule consists of the following partially overlapping phases (Table 5.1). Table 5.1: Schedule for realizing the new facility. Organization The project will be of international scope with substantial contributions from outside of Germany. An adequate institutional structure must allow the various partners to 54