an overview of the shielding problems around high energy laser-accelerated beams
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ELI-NP: the way ahead, 10-12 March 2011 1Anna Ferrari
An overview of the shielding An overview of the shielding problems problems
around high energy laser-accelerated around high energy laser-accelerated beamsbeams
Anna FerrariAnna Ferrari
Institute of Safety Research and Institute of Radiation PhysicsInstitute of Safety Research and Institute of Radiation Physics
Helmholtz-Zentrum Dresden-RossendorfHelmholtz-Zentrum Dresden-Rossendorf, Germany, Germany
ELI-NP: the way ahead, 10-12 March 2011 2Anna Ferrari
Key aspects in the shielding strategy
The example of the ELI facility in Czech Republic:
OutlineOutline
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
ELI-NP: the way ahead, 10-12 March 2011 3Anna Ferrari
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:
- Conservative and rigorous approach (realistic, not pessimistic)
- Flexible solutions where possible
Key aspects in the shielding strategyKey aspects in the shielding strategy
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
ELI-NP: the way ahead, 10-12 March 2011 4Anna Ferrari
A look at the design of the ELI facility in Czech RepublicA look at the design of the ELI facility in Czech Republic
ELI-NP: the way ahead, 10-12 March 2011 5Anna Ferrari
Target areasTarget areas
e- acceleration area Proton acceleration area
ELI-NP: the way ahead, 10-12 March 2011 6Anna Ferrari
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, E = 300 MeV, Div.=40°
Definition of the source terms: the most critical cases in energyDefinition 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, E/E=10%, Div.=1°
ELI-NP: the way ahead, 10-12 March 2011 7Anna Ferrari
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, E = 10 MeV, Div.=4°
Definition of the source terms: the most critical cases in intensityDefinition 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, E/E=10%, Div.=1°
ELI-NP: the way ahead, 10-12 March 2011 8Anna Ferrari
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)
Project goals:
Public: 0.1 mSv/year (1/10 of the legal limit) Workers: 1 mSv/year
A factor 10 has been“implicitly” taken into account, in view of future development
Operational time and dose limitsOperational time and dose limits
ELI-NP: the way ahead, 10-12 March 2011 9Anna Ferrari
Steps of the radiation protection Monte Carlo calculationsSteps of the radiation protection Monte Carlo calculations
1. Characterization of the source terms for the Monte Carlo, realistic description of the chamber around (Astra GEMINI model has been assumed)
2. 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)
3. Evaluation of the fluences of the secondary fields and of the total doses (in terms of Ambient Dose Equivalent)
ELI-NP: the way ahead, 10-12 March 2011 10Anna Ferrari
Fluence - H*(10) conversion coefficients in FLUKAFluence - 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
ELI-NP: the way ahead, 10-12 March 2011 11Anna Ferrari
Main contributors and problems of a monomaterial dumpMain contributors and problems of a monomaterial dump
50 GeV case
dN/d
logE
d
(pa
rt G
eV-1
sr-1 p
er p
rim
ary
Muons exiting from the dump
E(GeV)
Processes included:
- muon production from pion decay - direct photomuon production
Muons
Muon fluence rate (muon cm-2 s-1)
Monomaterial dump in AISI-316L, 4 m long
ELI-NP: the way ahead, 10-12 March 2011 12Anna Ferrari
Main contributors and problems of a monomaterial dumpMain contributors and problems of a monomaterial dump
Neutron fluence rate (neutrons cm-2 s-1)
50 GeV case
Huge amount of backscattered radiation
Neutrons
ELI-NP: the way ahead, 10-12 March 2011 13Anna Ferrari
10 nSv/day if 1 y = 300 days (10 months), we have only 3Sv/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
ELI-NP: the way ahead, 10-12 March 2011 14Anna Ferrari
Any solution good for the 50 GeV, 0.1 Hz case is automatically fully satisfactory for the 5 GeV, 10 Hz case
5 GeV case
ELI-NP: the way ahead, 10-12 March 2011 15Anna Ferrari
The idea of a multimaterial dumpThe idea of a multimaterial dump
II. use borated polyethylene in the external part to absorb the moderated neutrons coming from the center of the dump
I. 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)
ELI-NP: the way ahead, 10-12 March 2011 16Anna Ferrari
Results I : 50 GeV electrons, 0.1 HzResults I : 50 GeV electrons, 0.1 Hz
60 cm borated polyetilene
E(GeV) E(GeV)
ELI-NP: the way ahead, 10-12 March 2011 17Anna Ferrari
10 nSv/day in the 100 shots/day hypothesis
in the 1000 shots/day hypothesis, only 100 nSv/day
3-mat dump: - borated polyethylene - core in carbon fiber surrounded by AISI-316L
Source
Pipe endDump
Poly-Bor +C
St.steel
Wall
0.01 Sv/d
H*(10) longitudinal profile
ELI-NP: the way ahead, 10-12 March 2011 18Anna Ferrari
Results II : 3 GeV protons, 0.1 HzResults II : 3 GeV protons, 0.1 Hz
Neutron fluenceProton fluence
3-mat dump: - borated polyethylene - carbon fiber - AISI-316L
ELI-NP: the way ahead, 10-12 March 2011 19Anna Ferrari
H*(10) rate in the 1000 shots/day hyp.
Ambient dose equivalent rate
ELI-NP: the way ahead, 10-12 March 2011 20Anna Ferrari
ConclusionsConclusions
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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