Implementation status of the extreme light infrastructure - nuclear physics (ELI-NP) project

Transcription

1 Implementation status of the extreme light infrastructure - nuclear physics (ELI-NP) project S. Gales, and N. V. Zamfir Citation: AIP Conference Proceedings 1645, 201 (2015); View online: View Table of Contents: Published by the American Institute of Physics Articles you may be interested in Strong field physics and QED experiments with ELI-NP 2 10PW laser beams AIP Conference Proceedings 1645, 416 (2015); / High power femtosecond lasers at ELI-NP AIP Conference Proceedings 1645, 219 (2015); /

2 Implementation status of the Extreme Light Infrastructure Nuclear Physics (ELI-NP) Project S. Gales 1, a), N.V. Zamfir 1 for the ELI-NP team 1 ELI-NP, Horia Hulubei National Institute for Physics and Nuclear Engineering, 30 Reactorului Street, RO Bucharest-Magurele, Romania a) Corresponding author: sydney.gales@eli-np.ro Abstract. The Project Extreme Light Infrastructure (ELI) is part of the European Strategic Forum for Research Infrastructures (ESFRI) Roadmap. ELI will be built as a network of three complementary pillars at the frontier of laser technologies. The ELI-NP pillar (NP for Nuclear Physics) is under construction near Bucharest (Romania) and will develop a scientific program using two 10 PW lasers and a Compton back-scattering high-brilliance and intense gamma beam, a marriage of laser and accelerator technology at the frontier of knowledge. In the present paper, the technical description of the facility, the present status of the project as well as the science, applications and future perspectives will be discussed. Keywords: high-power lasers, Compton back-scattering, high-brilliance narrow bandwidth gamma beams, laser driven nuclear physics, Nuclear Resonance Fluorescence; photo-fission, astrophysics INTRODUCTION The European Strategic Forum for Research Infrastructures (ESFRI) has selected in 2006 a proposal based on ultraintense laser fields with intensities reaching up to W/cm 2 called ELI for Extreme Light Infrastructure. The construction of a large-scale laser-centered, distributed pan-european research infrastructure, involving beyond the state-of-the-art ultra-short and ultra-intense laser technologies, was funded for construction in September The three pillars of the ELI facility are built in Czech Republic, Hungary and Romania [1]. The Romanian pillar is ELI-Nuclear Physics (ELI-NP) [2,3]. Its mission covers scientific research involving two domains where only very few experimental results were reported until now: laser-driven experiments related to nuclear physics, strong-field quantum electrodynamics with associated vacuum effects and a Compton back-scattering high-brilliance and intense low-energy (<20 MeV) gamma beam, a combination of laser and accelerator technology at the frontier of knowledge. The ELI-NP research center will be located in Magurele near Bucharest, Romania. The facility, worth 295 million euros is financially supported by European Regional Development Fund in two phases: 180 million euros in and the rest in the next cycle of the European Funds. The project is implemented by Horia Hulubei National Institute for Physics and Nuclear Engineering (IFIN-HH). The project started in January 2013 and the new facility will be operational by the end of Civil engineering construction has started in June 2013 and should be completed by the summer of In Figure 1 is shown the construction status in the summer of Exotic Nuclei and Nuclear/Particle Astrophysics (V). From Nuclei to Stars AIP Conf. Proc. 1645, (2015); doi: / AIP Publishing LLC /$

3 FIGURE 1. View of the construction site of ELI-NP in the summer of 2014 The construction site covers a total area m2 where more than one third will be devoted to the experimental halls. This paper presents the planned high-power laser and the gamma- beam systems. It also describes the main scientific themes and associated experimental tools to be developed and implemented at the ELI-NP facility. TECHNICAL DESCRIPTION OF THE ELI-NP FACILITY ELI-NP hosts two major research instruments: a high-power laser system (HPLS), with two arms reaching up to 10 PW for each arm and a gamma-beam system (GBS) that will provide very intense and narrow-band gammarays with energies up to 19 MeV. Eight experimental areas will be available for performing experiments using the laser beams, the gamma beams or combined. High-Power Laser System (HPLS) at ELI-NP The high-power laser system of ELI-NP will be constructed by an association between Thales Optronique SA France and Thales System Romania. It consists of a chirped pulse amplification system at about 820 nm central wavelength, with a dual front-end architecture, in order to minimize down-time for the laser facility. Each of the two parallel chains includes Ti: Sapphire amplifiers to bring the final output energy to the level of a few hundreds of Joule. Subsequently, the pulses are compressed to around a 20 fs pulse duration that implies a peak power of 10 PW at a repetition rate of 1 shot per min for each of the two arms. Along the two amplification chains, additional outputs with corresponding optical compressors will be installed. Their corresponding power levels are 0.1 PW and 202

4 1 PW at repetition rates of 10 Hz and 1 Hz, respectively. The intensity in reach for the 10PW arm is W/cm 2. The pointing stability requires a very tight specification for building vibration, where static damping of the floor is provided across the entire laser area and experiment areas. Synchronization of the laser pulses delivered from the parallel amplifiers is secured by the use of the common front-end. The overall control command of the HPLS will be TANGO-based, a distributed control system, used for controlling any kind of hardware or software systems that is working based on the client-server model. The software is developed by the European Community of Synchrotrons and is also used in other major projects like Laser Megajoule and Cilex Apollon [4] from France. The Laser Beam Delivery System (LBDS) is the interface between the laser system (the six optical outputs: PW@10 Hz, 2 1 PW@1 Hz and 2 10 PW@1/minute) and experiments. It takes care of both optical outputs delivery and electronic synchronization of the lasers with the Gamma Beam System (GBS) and with the experiments. The main technologies under scrutiny in the LBDS are relay imaging, plasma mirror for temporal contrast enhancement, mirror based polarization control and adaptive optics for high-quality focus on target. From the experiments involving HPLS as a source, the lay out of the LBDS is shown in Figure 2. The main requests for the experimental areas are the following: E1 experimental area is dedicated to Laser-driven Nuclear Physics experiments using heavy ion beams such as Th. As a consequence, high temporal contrast and circular polarization are needed. As the intended intensities in the focus are of the order of W/cm 2, adaptive optics and short focal distances will be implemented. E6 Experimental area is dedicated to Strong-Field QED experiments. The tightly focused beams on solid targets will be used for electron positron pair creation studies. In this case, the requested specifications are similar to the ones for laser-driven Nuclear Physics experiments. As the intended intensities in the focus are of the order of W/cm 2, adaptive optics and short focal distances will be implemented. FIGURE 2. Basic lay out of the experimental rooms using the high intensity laser beams. 203

5 E7 experimental area is dedicated to combined laser-gamma experiments where the synchronization of the laser with the laser that drive the Compton backscattering process is a must. Moreover, coherent combination of the two laser pulses is requested on the long run, in order to provide the highest possible intensity on target. E4 and E5 experimental areas are dedicated to irradiated materials science experiments where laser pulses produce various radiation types: electrons, gamma, protons, neutrons and positrons. The delay between the pulses shall be controlled over up to 10 ns with sub 10 fs resolution. The technologies required for the 0.1 PW and for the 1 PW outputs are polarization elasticity control, plasma mirror for temporal contrast enhancement, and adaptive optics. L Gamma Beam System at ELI-NP (GBS) In designing a state-of-the-art gamma-ray beam system, several requirements have to be fulfilled, such as bandwidth as small as possible, strong increase of the peak brilliance and of the gamma beam flux, reduction of the gamma beam size. The gamma beam will be produced by the Compton backscattering of light photons on accelerated electrons. The photons are provided by an average power, high-repetition rate laser. The pulse energy is expected to be in the few hundreds of mj range and frequency doubling of such laser pulses would provide green photons to be frequency up-shifted through the Compton backscattering process to 19 MeV. The gamma beam will have a bandwidth smaller than 0.5%. The electron accelerator will be a warm linac, with two acceleration stages of 360 MeV each. The energy of the Compton backscattered beam is given by the relation: 2 1+ cosθ L (1) Eγ = 2γ e EL 2 2 4γ eel 1+ ( γ eθγ ) + a0 + 2 mc Where 4γ eel = recoil parameter ; 2 mc ee al = = normalized potential vector of the laser field; mω c E = laser electric field strength; EL =! ωl Thus, in the case of a head-on collision with (q L =0) & backscattering (q g =0), using a green laser with E L ~ 2.5 ev (green) and an electron beam with E e ~ 360 MeV the gamma beam will have an energy of E γ < 3.5 MeV. The highest electron energies reachable will be of 720 MeV, allowing the production of up to 19 MeV gamma photons. The very low cross section for Compton scattering will be compensated in obtaining high brilliance gamma beam by very intense high repetition rate photon beam, very intense low emittance electron beam and a very small and precise interaction volume. Through a public tender procedure, the development of the gamma beam system has been awarded to a European consortium led by INFN Italy and composed of European leading research institutions and private companies in accelerator and laser technologies. 204

6 The specifications for the GBS (see Table 1) were established in a series of workshops and meetings organized with the scientific community interested in ELI-NP and industry, in order to satisfy the needs of the scientists for the progress of their research, but also to have realistic expectations that are technically feasible within the time frame of project implementation. TABLE 1. Specified output parameters for the gamma beam system. Type Units Range Photon energy MeV Divergence µrad Average Bandwidth 5.0 x 10-3 Number Photon/s within FWHM bdw 1/(s ev) < Peak Brilliance (N ph /sec mm 2 mrad 2 0.1%) Minimum Frequency Hz 100 Gamma Ray Macropulses SCIENTIFIC PROGRAM, EXPERIMENTAL LAY-OUT AND INSTRUMENTS A significant fraction of the international scientific community contributed to the shaping of the ELI-NP facility is a series of workshops [5]. The latest ones, held in June 2013 and April 2014, were centered on laser-driven experiments and on nuclear science with gamma beams and defined ten development directions for the facility. For each of them, writing of Technical Design Reports (TDRs) was triggered and further developed during the workshops. In addition to fundamental themes, applications of HPLS and GBS are under study. Ionizing radiation metrology, radiation induced damage and gamma beams induced nuclear reactions are major active research area in nuclear physics and engineering. Their applications extend from the nuclear power plants to medicine and from space science to material science and to accelerators engineering. The experimental areas will accommodate three types of experiments: laser-driven experiments will be performed at E1, E4, E5 and E6 experimental areas; gamma experiments will be performed at E2, E3 and E8 experimental areas, while combined experiments are planned at E7 experimental area. A layout of the Gamma Beam system and of the experimental areas is displayed in Figure

7 FIGURE 3. General lay out of the Gamma beam system Laser-driven nuclear physics experiments As a leading facility in laser-driven nuclear physics, ELI-NP will take advantage of the specific properties of laser driven radiation production, such as ultra-short time scale and the relatively broadband spectrum of secondary radiation at the experimental areas E4 (two 100TW pulses at 10Hz) and E5 (two 1PW pulses at 1Hz). Ion driven nuclear physics research will be performed at the E1 experimental area. Here, laser-accelerated heavy ions will drive nuclear reactions and further experiments related to astrophysics. The flagship experiment involves production of neutron rich isotopes using fission of Thorium and subsequent fusion process, to shed light on one of the most important questions in today's physics: the formation of heavy elements (beyond Fe) in the universe. The needed data for the formation of heavy elements in the region of lead (Z=82) and beyond are masses and lifetimes of key isotopes, e.g. very neutron-rich isotopes (15 neutrons away from the stability line), and the fusion cross section even with secondary beams of radioisotopes is so low that in practice these key measurements are not within reach today. Using HPLS with a CD 2 production target and a very thin thorium reaction target, one may reach fusion of two very neutron-rich isotopes originating from the fission of Th (for example fusion of Z= 35) leading to this unknown mass region [6]. First circular polarized laser beam incident on production target produces through RPA a high density bunch of 232 Th, 12 C and D ions. Then fission reactions will take place. 232 Th ion bunches interacts with 12 C (or 1 H) in the 1 st layer and 12 C and D nuclei interacts with 232 Th in the 2 nd layer of reaction target. One light and another heavy fragments are produced: 232 Th + ( 12 C, 1 H) X L + X H 12 C (or D) Th Y L +Y H Following their production the two light fission fragments (X L, Y L ) fuse in the reaction target and neutron rich nuclei (close to N=126) are produced. Such experiments require significant experimental development in the field of laser-driven ion acceleration. in order to produce intense heavy-ion bunches in the 5 10 MeV/n energy range relevant for fission and fusion reactions. 206

8 The experimental area E6 will host experiments related to strong-field quantum electrodynamics. High intensity on solid targets, up to W/cm 2 is intended. The type of experiments will imply a different set of diagnostics tools, compared to the ones at E1 where ion-driven nuclear physics experiments will be performed. Here, electronpositron production in laser-irradiated solid targets and their subsequent behavior will be the main object of study [7]. The combined experiments from E7 area will host a vacuum chamber where one pulse from each 10 PW HPLS output and the gamma beam will be focused. Nuclear Science and applications with high brilliance low-energy gamma beams The ELI-NP gamma beam experimental program will have allow us to explore new territory in the field of Nuclear Resonance Fluorescence (NRF) and experiments above the particle separation threshold, such as studies of giant resonances, nuclear astrophysics reactions, and photo-fission experiments. A schematic lay-out of such experiments is displayed in Figure 4. The incoming narrow band width beam excites a single excited state, whose decay is studied in the experiment. The excited state can be below or above the particle separation energy, which lies at about 8 MeV. In the former case, the NRF method is applied and, in the latter case, induced reactions, such as (γ,n), (γ, p), FIGURE 4. Principle of NRF experiments The low-energy gamma experiment area E2 (Eγ<3.5 ΜeV) shall be mainly dedicated to Nuclear Resonance Fluorescence (NRF) experiments and applications. Due to the brilliance of the gamma-ray beam, significantly increased with respect to existing facilities, experiments on materials whose availability is very limited will become feasible. For example the photo-response below the particle separation energy is currently investigated in NRF experiments [8] at existing gamma-beam facilities, such as bremsstrahlung facilities at the S-DALINAC electron accelerator in Darmstadt (see e.g. Ref. [9]) or at the High Intensity Gamma-ray Source (HIGS) at the TUNL facility at Duke University (see e.g. Ref. [10]). The advances in gamma-ray beam brilliance at ELI will increase the sensitivity of NRF experiments and thus it offers the opportunity to perform NRF studies on small target samples. This opens up an entire new area of applicability of the NRF method to materials that may be available only in quantities of a few mg, like long-lived radioactive isotopes of heavy actinides. 207

9 The high brilliance, small bandwidth and tunable energy of the low-energy gamma beam may revolutionize the characterization of nuclear materials. The tunable-energy gamma-ray beam can be locked on the known excitation energy of the isotope to be located and identified (each isotope has a unique fingerprint) and the energy response of the detectors will clearly indicate the location and presence or absence of the isotope in the bulk material (e.g. in a nuclear waste container). This technique will be extremely useful in the management of sensitive Nuclear Materials and radioactive waste for isotope-specific identification of 238 U/ 235 U and 239 Pu. It will allow the scan of containers for nuclear material and explosives, the inspection of spent fuel elements, and the quantitative measure of the final 235 U, 238 U content in order to optimize the geometry towards the longer use (20%) of fuel elements in the reactor core. The E8 experimental area at ELI-NP is dedicated to experiments that can use the entire range of gamma ray energies, but mainly the higher energies 3 19 MeV. Photo-fission and photodisintegration experiments are foreseen for this area, three TDR workgroups being involved in the design of the equipment to be placed here. An intense and high-energy resolving γ ray beam from ELI-NP will open up new horizons for the investigation of the nuclear photo-response at and above the separation threshold. An example for such studies is the detailed investigation of the pygmy dipole resonance (PDR) above and below the particle threshold, which is very essential for nucleosynthesis in astrophysics. The PDR occurs close to the neutron-emission threshold and its decay is governed by the coupling to the large number of states around the threshold. Both, the GDR and the PDR can be covered within the energy range of the ELI-NP beams. In the experiments the excitation functions for elastic and inelastic scattering will be measured, revealing possible fine-structures/splitting of PDR and GDR. The excitation function with high resolution for (γ,n) and (γ,charged-particle) channels, allows one to determine the branching ratios for various decay channels. The polarized beam will also allow determining the E1 or M1 type of excitation for the observed structures [8]. Photo-fission is a topic where ELI-NP gamma beam will bring significant advances. So far bremsstrahlung was used to induce fission of actinide nuclei. Two classes of experiments have been identified: a) High-resolution photo-fission studies in the actinides, investigation of the second and third potential minima, angular and mass distribution, cross-sections, studies of rare photo-fission events, such as triple fission, highly asymmetric fission, etc. b) Low-energy gamma beams are fully efficient at 15 MeV for producing short-lived and refractory elements in thin U targets using a gas-cell catcher (IGISOL technique [11]) with high efficiency. After their separation, the nuclei of interest will be transported to different measurement stations. Laboratory astrophysics experiments aiming at explaining the nucleosynthesis processes will be possible, through direct or inverse reactions. Reactions relevant for the p- and r-processes will be investigated, to advance the explanation of the formation of a large part of the known elements in the Universe. All p-nuclei can be synthesized from the destruction of pre-existing nuclei of the s- and r-type by a combination of (p, γ) captures and (γ,n), (γ,p) or (γ,a) photo-reactions [12]. In particular, charged-particle detector systems, needed to measure nuclear reaction cross-sections of the proton and alpha burning processes and most importantly the 12 C(α,γ) reaction crosssection relevant for stellar helium burning, are being investigated [13]. In order to carry out the scientific program discussed above, a number of different state-of-the-art instruments are being considered. These include: a high-resolution spectrometer of (segmented) large HPGe (clover) detectors, combined with good timing e.g. LaBr3 detectors, a spectrometer with medium resolution of large LaBr3 detectors and a neutron detector array, a tape station and a close-geometry spectrometer for high-resolution decay studies, a 4π charged-particle array of segmented DSSSD detectors and a TPC gas cell for astrophysics reaction measurements. 208

10 In addition, a variety of applied research proposals have been received by ELI-NP using low-energy brilliant intense gamma, neutron and positron beams, which will open new fields in materials science and life sciences. ELI-NP will feature a brilliant positron beam, the E3 experiment area being dedicated to research based on this beam, including imaging and applications [5]. The new production schemes of medical isotopes (e.g., 99 Mo currently used in therapies, 195m Pt for nuclear imaging to determine efficiency of chemotherapy, and 117m Sn, an emitter of low-energy Auger electrons for tumor therapy) via (γ, n) processes may also reach socio-economical relevance. Computerized tomography with gamma ray beams for non-destructive inspection of objects, will benefit also from high-energy quasi monochromatic and high beam intensity to shorten the scanning time. CONCLUSIONS The ELI-NP facility combines two research facilities with parameters beyond the state of the art, namely a highpower laser system with two amplification arms to deliver 10 PW and intensities on the target in the range of W/cm 2 at least every minute, and a gamma beam system to deliver up to 19 MeV photons. Their outstanding performances will allow approaching a virgin science field, at the frontier between the strong-field QED and nuclear physics. Benefiting from the support of a large number of specialists across the globe, the ELI-NP facility is on track with Technical Design Reports and construction of the experimental areas. Commissioning is expected to take place in ACKNOWLEDGMENTS We would like to thank the members of the ELI-NP team for their tremendous work in implementing the project. This work is supported by the Project Extreme Light Infrastructure Nuclear Physics (ELI-NP) Phase I, a project co-financed by the Romanian Government and European Union through the European Regional Development Fund. REFERENCES 1. Gérard A. Mourou, Georg Korn, Wolfgang Sandner, John L. Collier (eds.) ELI Extreme Light Infrastructure: Science and Technology with Ultra-Intense Lasers Whitebook, (THOSS Media GmbH, 2011). 2 N.V. Zamfir, EPJ Special Topics, 223, 1221(2014) 3. N.V. Zamfir, EPJ Web of Conferences 66, (2014) 4. G. Cheriaux, F. Giambruno, A. Freneaux, F. Leconte,et al, Apollon-10P: status and implementation, in: AIP Conference Proceedings on Light at Extreme Intensities 1462, 78 (2012) P.G. Thirolf et al., EPJ Web of Conferences, 38, R.Hajima et al., J. Nucl. Sci. Tech. 45, 441 (2008). 8. U. Kneissl, N. Pietralla, A. Zilges, J. Phys. G, R (2006) 9. D. Savran et al., Phys. Rev. Lett. 100, (2008). 10. A. P. Tonchev et al., Phys. Rev. Lett. 104, (2010). 11. J. Aystö et al., Phys. Rev. Lett. 69, 1167 (1992). 12. K.-L. Kratz et al., Astrophys. J. 403, 216 (1993). 13. W. A. Fowler, Rev. Mod. Phys. 56,149 (1984). 209