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

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


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


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


A look at the design of the ELI facility in Czech RepublicA look at the design of the ELI facility in Czech Republic


Target areasTarget areas

e- acceleration area Proton acceleration area


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°


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°


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


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)


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


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


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


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


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


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)


Results I : 50 GeV electrons, 0.1 HzResults I : 50 GeV electrons, 0.1 Hz

60 cm borated polyetilene

E(GeV) E(GeV)


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


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


H*(10) rate in the 1000 shots/day hyp.

Ambient dose equivalent rate


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

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

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