Overview In the report published by the Nuclear Physics European Community Committee (NuPECC) entitled Radioactive Nuclear Beam Facilities it was stated that the next generation of radioactive ion beam (RIB) facilities should aim at having an intensity of accelerated radioactive beams being a factor 1000 higher than any facility presently running or in the commissioning stage. These considerations have been reinforced by the work done by the NuPECC on a Long-Range Plan for Nuclear Physics in Europe. The emerging scenario is that european option should at least include - An In-Flight facility based on in-flight fragmentation or fission of high intensity heavy ions (approved upgrade of GSI) - EURISOL, an ISOL Post-accelerator facility, capable of providing a range of energies from the thermal ones to 100 MeV/u, and a range of isotopes covering the whole nuclear chart from the light nuclei to the superheavies and the range between the proton and the neutron drip lines; EURISOL comprises i. A driver accelerator ii. A neutron converter iii. The targe-ion-source unit iv. A charge breeder v. The post-accelerator vi. Experimental instrumentation The EURISOL programme (G. Fortuna from Legnaro is a member of the Steering Committee) started on January 1, 2000 and is supported by the EU commission under a specific Reasearch and Technical Development (RTD) contract within the 5 th Framework Programme (FP5). The present phase should be followed by: - Completion of R&D studies under a specific Design Study contract within FP6 - A full Engineering Design Study within FP7 - Construction phase - Full operational phase after 2010 Scientific Case Nuclear Structure at the Extremes Current problems in nuclear physics deal with nuclear properties (like charge, angular momentum, etc.) very far from the normal ones, measured for nuclei stable or close to the stability valley, where completely new phenomena are anticipated. a) Nuclei very far from stability The number of known nuclei is about 2500, while it is expected that about a total of 5000 should be stable againg nucleon emission and spontaneous fission. Therefore, about 2500 nuclei are still to be found and their properties measured, the so-called Terra Incognita. Completely new phenomena are expected to occur far from stability, for instance a change in the shell structure which would lead to properties different from those predicted by the Shell Model, as well as the presence of a far-extending halos with low
nuclear density. Also the position of the proton and neutron drip lines (the borders of the stability region against nucleon emission and spontaneous fission) are very uncertain. In particular, the fission drip line for very heavy and superheavy elements is completely unknown. b) Nuclei with very high spins Nuclei with very high spins can show fascinating phenomena such as the wide variety of shapes, as well as the so-called superdeformation that leads to a large ratio between different dimensions of the nucleus c) Nuclei at extreme densities and temperatures Nuclei may exist in very different states of density, being diluted or compressed, and temperature, that can be different from zero. Here the high energy per nucleon that can be reached at new facilities is very important Nuclear Astrophysics and Nucleosynthesis Nucleosynthesis occurring in events like supernova explosions involve nuclei very far from stability as a chain of production of elements. The main processes are the r-process (rapid neutron capture) that is supposed to go deeply into the terra incognita, and the rpprocess (rapid proton capture) that is better known as a sequence but whose corresponding cross sections (in particular proton capture) are not known. Experiments involving very exotic nuclei need much higher intensities than available at existing facilities. Fundamental Interactions and Symmetry Laws Several areas have been identified: - Study of super-allowed β transitions to verify the unitary of the CKM matrix - Exotic interactions in the β decay beyond vector and axial vector ( observation of recoil nuclei) - Search for deviations from maximal parity violation of from time reversal invariance in strangeness-conserving β decay of polarized nuclei ( observation of polarization of decay electrons) - Investigation of parity non-conservations in atomic transitions of heavy atoms Potential of RIBs in Other Branches of Science - Deep implantation of radioactive nuclei in solids, diffusion experiments, studies of semiconductors, etc. - Radioisotopes obtained may be used for medical applications Comparison of RIBs production techniques - In the In-Flight method, heavy ion beams in the range of 100 MeV/u to 1 GeV/u strike a thin target, undergoing fragmentation or fission. The fragments are selected in flight by a Fragment Recoil Separator, then directed to another target.
RIBs with very short half-lives can be produced, but with the same energy range as the primary beam and with poor beam quality - In the ISOL method, a thick target is bombarded with a primary (proton) beam from a driver or from a neutron beam obtained by spallation. Nuclei are then transformed to ions, then re-accelerated. The method works only for relatively long half-lives (larger than about 1 ms), but provides very good beam quality and energy from tens of kev up to 100 MeV/u, therefore with higher flexibility in energy. Main Options for the EURISOL Facility Both neutron- and proton-rich nuclei have to be produced. Neutron-rich nuclei are best produced through fission by an intense neutron beam, which in turn can be produce through spallation by an intense proton beam impinging on a heavy nuclear target. It follows that the proton driver must deliver energies around 1 GeV with ma currents, i.e. it has to have MW power. Proton-rich nuclei can be produced by the same primary proton beam on a spallation target, but in this case an intensity in the order of hundrends of µa is sufficient. The baseline option is therefore a 1 GeV, 5 ma, 5 MW, CW proton linac, upgradable to 2 GeV. The linac should be composed by three sections: low, intermediate and high-energy. The low-energy part can be based on existing devices developed mainly in Italy and France. The high-energy section could be based on elliptical superconducting cavities, in whose technology considerable progress has been made. Such technology is also of wide interest for various accelerator projects for different communities. The intermediate-energy section could be based on a relatively new technology, independently phased superconducting radio-frequency cavities (SCRF) of various types, which still need the outcome of important R&D efforts, recently launched by various laboratories in Europe. Pulsed operation, necessary if the driver is to be shared in a multipurpose facility, is acceptable for EURISOL under certain conditions. As an example a 50 Hz cycle has been envisaged, where the 20 ms period of the machine is filled with several pulses of different length that can be sent to different facilities. The 50 Hz turns out to be a lower limit to the pulsing frequency to avoid an excessive power load per pulse on the target. State-of-the-art of specific components for a high-energy proton driver 1. Injector: several laboratories are presently involved in large R&D and construction efforts. Los Alamos National Laboratory has been the first to operate such a high intensity machine (LEDA, with intensities at the level of 100 ma DC). In Europe, the main project has been the IPHI (Injecteur de Protons de Haute Intensité). A high intensity injector for 100 kev protons with currents in the 50-100 ma range has been successfully developed within the project TRASCO (TRAsmutazione SCOrie) for nuclear waste transmutation, at INFN-LNS. It is based on an ECR (Electron Cyclotron Resonance) type of source. 2. The high intensity injector is the heart of the SPES (Study for the Production of Exotic Species) project at INFN-LNL. SPES is a project partly funded within TRASCO.
3. The low energy section (about 5 MeV energy and about 30 ma current) is based on the RFQ (Radio-Frequency Quadrupole) technology, already developed in France but not tested on beam. Major work has been done at INFN-LNL, within the TRASCO project (Full design of 6 sections and construction of the first two). Brazing was done at CERN and a test was foreseen at CERN. The last 4 sections construction is in progress and is financed within the ADS (Accelerator Driven hybrid reaction System) project. 4. Intermediate energy section ( 85 MeV energy and about 30 ma current). It is the most difficult. Question is whether to make it normal-conducting or superconducting (SC). Focusing and accelerating at the same time at such high current but still low velocities is the issue. Two options are envisaged: a) a structure with many units and a few cells per unit (spoke-cavities, mainly developed at ANL, RIA-Rare Isotope Accelerator project); b) a structure with many independently phased cells (more flexible). INFN-LNL (within TRASCO) has been working on many independently-phased cells working at 352 MHz. One SC cell has been successfully constructed and tested. Still another option are SC quarter-wave cavities (INFN-LNL). 5. High energy section (1-2 GeV energy and about 5 ma current). This section is necessarily SC because of the high power. The main technical problem is how to transfer the power to the cavities and then to the beam. CERN has been working on SC cavities based on copper sputtering. This is a known technology but it works for β > 0.66. Within TRASCO (INFN Milano/LASA: Laboratorio Acceleratori e Superconduttivitá Applicata, INFN Genova) CERN technology has been used to build cavities that can work at β = 0.85. A TRASCO cavity made at CERN was tested in a machine cryostat with a modified LEP-type coupler. Therefore, both TRASCO and the CERN SPL (Superconducting Proton Linac) high energy sections are based on tested components. Additional R&D has been performed at INFN Milano & Genova sections within TRASCO to switch to 704 MHz and bulk Niobium cavities (TESLA/SNS: Spallation Neutron Source technology). This means smaller cavities that can work at β as small as 0.47. The prototype built is a 5-cell unit. This new cavity has been tested in France and at Jefferson Lab (Newport News, Virginia). For this new cavity, the cryostat has been designed, while the problem of the couplers has not been solved yet. One possibility is to copy the solutions adopted by the Spallation Neutron Source (SNS) being planned at Oak Ridge in the USA (most work done at Jefferson Lab and Los Alamos National Lab). Other original design studies for the high energy part that EURISOL as well as other high-intensity projects may benefit from are: the ASH (Accélérateur Supraconducteur pour Hybride). A common design of the high energy section is also found in the ADS (Accelerator Driven hybrid reaction System) driver (CEA-CNRS/INFN).
Research Facilities Offering Possibilities for Synergy with EURISOL - High-Energy Physics. An Integrated Project already approved and funded within FP6 is CARE, dealing with accelerator developments for high-energy physics. Relevant to the EURISOL driver is the IPPI task of CARE which concerns R&D for an intense pulsed proton injector, up to 200 MeV. - Neutrino (and muon) factories. Such a factory may be based on a pulsed linac. 4 MW is the typical power required. - b Beams. Here an intense proton driver feeding a radioactive beam facility à la EURISOL, would produce a radioactive beam which would provide, in turn, by means of its ß-decay, a single-flavored neutrino beam of well-defined energy spectrum. Following recommendations by both High-Energy and Nuclear Physics committees (ECFA/ESGARD, NuPECC), it has been decided to include a ß-beam study as part of the proposed EURISOL Design Study. - Accelerator-driven hybrid reaction systems (ADS) for nuclear waste incineration. The European Road Map quotes 10 MW for a demonstration facility, and 50 MW CW for the full industrial application. A preliminary design study for a demonstration facility, funded by the European Commission, is currently under way. Within FP6, there is an Accelerator Working Package of the Integrated Project EUROTRANS on demonstration of transmutation. - Spallation neutron sources for material science, presently under construction in the USA (SNS) and in Japan (Joint Project), or planned in Europe (ESS). These projects use multi-mw linac accelerators in pulsed mode. - Technological irradiation tools for the development of new radiation-resistant materials. A proton beam power around 10 MW is needed. Cost Estimate The Total Driver Accelerator estimated capital cost (which includes all equipment necessary for the three linac sections up to 1 GeV) is 122 MEuro. The cost of the upgrade to 2 GeV is estimated to be around 65 MEuro. The total estimated capital cost for EURISOL is estimated to be 613 Meuro. Installation cost is estimated to be 16.4 Meuro. Site Currently, three possibilities are considered for the site: - A national laboratory (Legnaro, GANIL) - CERN - An underdeveloped country (eastern?)
Appendix Table 1: RIB facilities based on the In-Flight technique, existing or under construction
Table 2: RIB facilities based on the ISOL technique, existing or under construction Table 3: Proposed new RIB facilities in Europe and USA