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An overview of the shielding problems around high energy laser-accelerated beams

An overview of the shielding problems around high energy laser-accelerated beams. Anna Ferrari Institute of Safety Research and Institute of Radiation Physics Helmholtz-Zentrum Dresden-Rossendorf , Germany. Outline. Key aspects in the shielding strategy

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An overview of the shielding problems around high energy laser-accelerated beams

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  1. An overview of the shielding problems around high energy laser-accelerated beams Anna Ferrari Institute of Safety Research and Institute of Radiation Physics Helmholtz-Zentrum Dresden-Rossendorf, Germany

  2. Outline • Key aspects in the shielding strategy • The example of the ELI facility in Czech Republic: • A look at the facility • Characterization of the source terms for the electron and the proton case • FLUKA Monte Carlo simulation to optimize the longitudinal shielding

  3. Key aspects in the shielding strategy We have to deal with a rapidly evolving field, where many parameters that are important for the radiation protection cannot be completely frozen at this stage: • evaluated spectra of the secondary particles can evolve ( source terms characterization can evolve !) • the workload (shots/day) can increase with the • increased experience and technological improvements - Conservative and rigorous approach (realistic, not pessimistic) - Flexible solutions where possible

  4. A look at the design of the ELI facility in Czech Republic

  5. Proton acceleration area e- acceleration area Target areas

  6. Definition of the source terms: the most critical cases in energy • 0.1 Hz electron beamlines • Laser parameters: 300 J, 280 fs, 1 PW, =0.8 m, f=130 mm, f/# >100, a0=2 • Acceleration Regime: Blowout regime, external injection, Lacc=530 cm • Electron beam parameters: 41 GeV, 1.3 nC • Assumptions for simulations: 50 GeV(Gaussian distribution), 1.5 nC, • DE/E=10%, Div.=1° • 0.1 Hz proton beamlines • Laser parameters: 1.5 kJ, 30 fs, 50 PW, =0.8 m, 5x1023 W/cm2 • Target parameters: 1 m, solid H • Proton beam parameters: • Ecut-off = 4 GeV, h = 20% (Davis et al., 40 fs, 5x1023 W/cm2,1 mm - H) • Ecut-off = 3.7 GeV (OSIRIS sim., 15 fs, 5x1023 W/cm2) • Assumptions for simulations:3 GeV(rectangular distribution), 6x1011 p/pulse, • DE = 300 MeV, Div.=40°

  7. Definition of the source terms: the most critical cases in intensity • 10 Hz electron beamlines • Laser parameters: 50 J, 80 fs, 0.6 PW, =0.8 m, f=130 mm, f/#  40, a0=5 • Acceleration Regime: Blowout regime, self injection • Electron beam parameters: 3.7 GeV, 1 nC • Assumptions for simulations: 5 GeV(Gaussian distribution), 1 nC, • DE/E=10%, Div.=1° • 10 Hz proton beamlines • Laser parameters: 50 J, 20 fs, 2.5 PW, =0.8 m, 1022 W/cm2 • Target parameters: 1 m, solid H • Proton beam parameters: • Ecut-off = 500 MeV, h = 35% (Davis et al., 40 fs,1022 W/cm2,1 m - H) • Assumptions for simulations:200 MeV(rectangular distribution), 1012 p/pulse, • DE = 10 MeV, Div.=4°

  8. Operational time and dose limits Reasonable actual assumptions for the beamline working time: • 0.1 Hz: 100 shots/day (15 min/day) • 10 Hz: 6000 shots/day (10 min/day) A factor 10 has been “implicitly” taken into account, in view of future development • Project goals: • Public: 0.1 mSv/year (1/10 of the legal limit) • Workers: 1 mSv/year

  9. Steps of the radiation protection Monte Carlo calculations • Characterization of the source terms • for the Monte Carlo, • realistic description of the chamber around • (Astra GEMINI model has been assumed) • Characterization of a beam dump model, to be optimized for the material • choice and dimensions (it must guarantee the appropriate longitudinal • and lateral radiation containment) • Evaluation of the fluences of the secondary fields and of the total doses • (in terms of Ambient Dose Equivalent)

  10. Fluence - H*(10) conversion coefficients in FLUKA Conversion coefficients from fluence to ambient dose equivalent are based on ICRP74 values and values calculated by M.Pelliccioni. They are implemented for protons, neutrons, charged pions, muons, photons, electrons (conversion coefficients for other particles are approximated by these). In the card: AMB74 is the default choice for dose equivalent calculation

  11. Muons Monomaterial dump in AISI-316L, 4 m long Muon fluence rate (muon cm-2 s-1) Muons exiting from the dump dN/dlogE d (part GeV-1 sr-1 per primary E(GeV) Main contributors and problems of a monomaterial dump 50 GeV case Processes included: - muon production from pion decay - direct photomuon production

  12. Neutron fluence rate (neutrons cm-2 s-1) Main contributors and problems of a monomaterial dump 50 GeV case Neutrons Huge amount of backscattered radiation

  13. 10 nSv/day  if 1 y = 300 days (10 months), we have only 3Sv/y ! Even if this solution is satisfactory under the point of view of the dose rate beyond the shielding wall, it is not good under the point of view of the backscattered radiation and of the induced radioactivity

  14. 5 GeV case Any solution good for the 50 GeV, 0.1 Hz case is automatically fully satisfactory for the 5 GeV, 10 Hz case

  15. use not only one material at high Z but a suitable soft material (high density graphite) as dump core (surrounded by a high-Z shielding). Advantages: -smaller neutron yield - much less activation problems - energy deposition over a wider range the build-up region of the secondary radiation produced in the interaction with beam dump moves toward the central part of the dump, with a more effective shielding (the hardest part of the secondary radiation is confined inside the dump  autoshielding effect) The idea of a multimaterial dump use borated polyethylene in the external part to absorb the moderated neutrons coming from the center of the dump

  16. 60 cm borated polyetilene E(GeV) E(GeV) Results I : 50 GeV electrons, 0.1 Hz

  17. 3-mat dump: - borated polyethylene - core in carbon fiber surrounded by AISI-316L 10 nSv/day in the 100 shots/day hypothesis in the 1000 shots/day hypothesis, only 100 nSv/day Dump Pipe end Wall Source Poly-Bor + C St. steel 0.01 Sv/d H*(10) longitudinal profile

  18. Proton fluence Neutron fluence Results II : 3 GeV protons, 0.1 Hz 3-mat dump: - borated polyethylene - carbon fiber - AISI-316L

  19. H*(10) rate in the 1000 shots/day hyp. Ambient dose equivalent rate

  20. Conclusions Main aspects of the shielding assessment in target areas of the ELI-Czech Republic facility have been fixed: • the source terms for electron and proton beams have been set • the shielding study in the electron and in the proton hall is almost • complete in the worst cases (in energy and in beam intensity): • the choice of of a 3-mat structure (borated polyethylene + a core in carbon • fiber surrounded by a cylinder in stainless steel/iron ) is optimal for the • dump design both in the electron and in the proton case we hope that this experience can be useful for the shielding assessment of the ELI-NP laser areas

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