GRAS Validation and GEANT4 Electromagnetic Physics Parameters R. Lindberg, G. Santin;...
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Transcript of GRAS Validation and GEANT4 Electromagnetic Physics Parameters R. Lindberg, G. Santin;...
GRAS ValidationGRAS Validation and and
GEANT4 Electromagnetic Physics GEANT4 Electromagnetic Physics ParametersParameters
R. Lindberg, G. Santin; [email protected]
Space Environment and Effects Section, ESTEC
2
Presentation OutlinePresentation Outline
Introduction A few Words About GRAS and MULASSIS GRAS Internal Validation
Comparison with MULASSIS GEANT4 Electromagnetic Physics
Tuning the parameters in GRAS GRAS applied to complex geometry: ConeXpress Conclusions
3
IntroductionIntroduction ConeXpress radiation analysis
ESABASE Ray-tracing and SHIELDOSE-2 curve
GEANT4 Ray-tracing (SSAT) and SHIELDOSE-2 curve
Used following tools for comparison
GRAS Developed by G. Santin and
V. Ivantchenko Uses GDML geometry;
modular physics Modular analysis driven via
script
SSAT Developed by Qinetiq Ray-tracing (a.k.a sector
shielding analysis)
MULASSIS Developed by Qinetiq 1D multi-layer geometry.
4
ConeXpress ResultsConeXpress Results GEANT4 SSAT ray-tracing results agree with ESABASE However, GEANT4 GRAS full Monte Carlo gives very different
results (orders of magnitude) Uses same geometry model as SSAT analysis
First validation attempt GEANT4 internal comparison
GRAS ↔ MULASSIS Shows discrepancy of ~20 % for a semi-infinite slab case
Greatest difference in lower energy range (≤ 2 MeV) for electrons
5
Understanding the Problem Understanding the Problem (1/3)(1/3)
GRAS vs. Mulassis 0.25 - 2.75 MeV
1.00E-08
1.00E-07
1.00E-06
1.00E-05
1.00E-04
1.00E-03
1.00E-02
1.00E-01
1.00E+00
0 0.5 1 1.5 2 2.5 3
Electron Energy (MeV)
Av
era
ge
Do
se
pe
r E
ve
nt
(Me
V)
GRAS
GRAS gamma
GRAS e-
The geometry setup used was the semi-infinite slab case
2 mm Silicon target 3 mm Aluminium shield
Dose in energies below 1.5 MeV comes from gamma radiation
e--contribution starts to dominate around 1.5 MeV
3
6
Understanding the Problem Understanding the Problem (2/3)(2/3)
Dose (MeV) for Electron Energies 0.25-2.5 MeV
1.00E-08
1.00E-07
1.00E-06
1.00E-05
1.00E-04
1.00E-03
1.00E-02
1.00E-01
1.00E+00
0 0.5 1 1.5 2 2.5 3
Electron Energy (MeV)
Ave
rag
e D
ose
per
Eve
nt
(MeV
)
Total dose GRAS
Total dose Mulassis
GRAS e- contr.
Mulassis e- contr.
GRAS gamma
Mulassis gamma
GRAS analysis was inserted into MULASSIS to obtain e- and gamma cont. Gamma contribution agrees well between the two. Simulations show that there were differences in the e- contributions between
GRAS and MULASSIS
7
Understanding the Problem Understanding the Problem (3/3)(3/3)
Dose Ratio GRAS/MULASSIS
0%
50%
100%
150%
200%
250%
0 0.5 1 1.5 2 2.5 3Electron Energy (MeV)
Rat
io
Total Dose
e- Contribution
Dose from gamma-contribution is the same but... …e- contribution differs and… …statistical errors are small (<1%) compared to total dose value, so
difference is not due to statistical error, furthermore… …the difference in dose between GRAS and MULASSIS is largest at
“threshold energy”, so… …what’s the catch?
8
Electron EM Processes and Fine Electron EM Processes and Fine TuningTuning
Same EM physics used in GRAS and MULASSIS
Cause of different results was due to “fine tuning” of the electromagnetic energy loss modelling
Several parameters influence the modelling of GEANT 4 EM: facRange:
Maximum fraction of kinetic energy that particle can loose in a step Integral:
If true, dE(step) is obtained with integral of dE/dx curve Cuts:
Is the production cuts for secondary electrons StepMax:
Is one of the most important. Limits the maximum step length. “Process” in GRAS. This parameter is not available in MULASSIS
9
Internal Validation Internal Validation Conclusion (1/2)Conclusion (1/2)
GRAS gives near perfect agreement with MULASSIS when using the same EM physics parameter
GRAS vs. Mulassis in Slab, e-, MaxTheta=0 deg
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 1 2 3 4 5 6 7 8
Particle Energy (MeV)
Ave
rag
e D
ose p
er E
ven
t (M
eV
)
Dose, StepFunction=1.0
Dose, StepFunction=0.2
Mulassis
GRAS / MUL.
99.0%
99.5%
100.0%
100.5%
101.0%
0 1 2 3 4 5 6 7 8
Electron Energy (MeV)
Ra
tio
GRAS / MUL.
Integral set to true facRange set to 1.0 stepMax set to 100 mm
(similar to not having stepMax at all)
10
Internal Validation Internal Validation Conclusion (2/2)Conclusion (2/2)
Several runs were conducted to verify correlation E.g.
Sphere case, maxtheta=90, protons and electrons,
Ratio GRAS / MULASSIS, sphere geometry
90.0%
95.0%
100.0%
105.0%
110.0%
0 2 4 6 8
Particle Energy (MeV)
Rat
io
2-7 MeV e-
Ratio GRAS / MULASSIS, sphere geometry
96.0%
98.0%
100.0%
102.0%
104.0%
0 100 200 300 400 500
Particle Energy (MeV)
Rat
io
30-400 MeV protons
Notice the scale.
11
EM Physics Tuning – Parametric EM Physics Tuning – Parametric StudyStudy
Parametric study to look at effects of different settings
Parameter ranges:
facRange: 0.2 - 1.
Integral: Boolean – true or false
Cuts: between 0.01 100 mm
StepMax: between 0.01 100 mm (100 mm ~ no step limiting)
12
Parameter Comparison (1/2)Parameter Comparison (1/2)Average Dose for Particle Energy of 1.25 MeV
0
0.0001
0.0002
0.0003
0.0004
0.0005
0.0006
0.01 0.1 1 10 100StepMax (mm)
Avr
. D
ose
pe
r E
ven
t (M
eV
)
Cuts= 0.01 mm
Cuts=0.10 mm
Cuts=1.00 mm
Cuts=100.00 mm
Average Dose for Particle Energy of 2.00 MeV
00.010.020.030.040.050.060.070.080.09
0.01 0.1 1 10 100StepMax (mm)
Avr
. Dos
e pe
r E
vent
(M
eV)
Cuts= 0.01 mm
Cuts=0.10 mm
Cuts=1.00 mm
Cuts=100.00 mm
Average Dose for Particle Energy of 1.75 MeV
0
0,004
0,008
0,012
0,016
0,01 0,1 1 10 100
StepMax (mm)
Avr.
Dose
per
Eve
nt
(MeV
)
Cuts= 0.01 mm
Cuts=0.10 mm
Cuts=1.00 mm
Cuts=100.00 mm
Average Dose for Particle Energy of 1.50 MeV
0
0.0002
0.0004
0.0006
0.0008
0.001
0.0012
0.01 0.1 1 10 100StepMax (mm)
Avr.
Dos
e pe
r Eve
nt
(MeV
)
Cuts= 0.01 mm
Cuts=0.10 mm
Cuts=1.00 mm
Cuts=100.00 mm
Dose differs 2.5x depending on StepMax
13
Parameter Comparison (2/2)Parameter Comparison (2/2)1.5 MeV Particle Energy, Cuts=0.01 mm
0.0005
0.0006
0.0007
0.0008
0.0009
0.001
0.01 0.1 1 10 100
StepMax (mm)
Avr
. Dos
e pe
r E
vent
(M
eV)
False, 1.0
False, 0.2
True, 1.0
True, 0.2
1.5 MeV Particle Energy, Cuts=100.00 mm
0.0005
0.0006
0.0007
0.0008
0.01 0.1 1 10 100
StepMax (mm)
Avr
. Dos
e pe
r E
vent
(M
eV)
False, 1.0
False, 0.2
True, 1.0
14
Tuning Effect with Space Env. Tuning Effect with Space Env. SpectraSpectra
Ran simulations in GRAS for different spectra and Al shielding thickness: e- GTO e- MEO (Galileo) e- GEO p+ GEO
MULASSIS simulated by using StepMax=100.00 mm and StepFunction=1.0
Trapped Electron Spectra
1,00E+07
1,00E+09
1,00E+11
1,00E+13
1,00E+15
1,00E+17
1,00E+19
0 2 4 6 8
Energy (MeV)
Flue
nce
(/cm
2/M
eV)
MEO
GTO
GEO
15
Tuning Effect with Space Env. Tuning Effect with Space Env. SpectraSpectra
Trapped e- GEO spectrum
Average dose per event (MeV)
Al. thick. mm GRAS e-
MULASSIS e- GRAS/MUL
3 0,02983 0,02410 124%
4 0,00818 0,00653 125%
5 0,00281 0,00228 123%
10 0,00038 0,00041 95%
Trapped e- MEO spectrum
Average dose per event (MeV)
Al. Thick. mm GRAS MULASSIS GRAS/MUL
3 0,04824 0,04066 119%
4 0,01458 0,01167 125%
5 0,00474 0,00363 131%
10 0,00045 0,00046 97%
Trapped e- GTO spectrum
Average dose per event (MeV)
Al. thick., mm GRAS MULASSIS GRAS/MUL
3 0,05391 0,04625 117%
4 0,01736 0,01399 124%
5 0,00591 0,00456 130%
10 0,00047 0,00049 96%
solar proton GEO spectrum
Average dose per event (MeV)
Al. thick. mm
GRAS e-
MULASSIS e- GRAS/MUL
3 1,88 1,88 99,8%
4 5,58 5,57 100,1%
5 4,12 4,13 99,9%
10 3,33 3,34 99,8%
16
Next Step – Complex Next Step – Complex GeometryGeometry
Currently conducting analysis on complex geometry – ConeXpress
Use radiation spectra from SPENVIS Run each particle spectra separate and combine to obtain total
ionised dose. Presents different problems than simple geometry
Number of simulated events has to be very high due to thick shielding generated by subsystems, especially for electrons
17
Next Step – Complex Next Step – Complex GeometryGeometry
GDML model of ConeXpress
18
ConclusionsConclusions Internal validation (GRAS ↔ MULASSIS) successful
Earlier difference due to different physics parameters
GRAS Parametric study of EM physics parameters shows difference Up to 30%, using a space environment spectra Up to 2.5 times, using mono-energetic beam particle source
Tentative set of parameters chosen as facRange to 0.2 Integral set to true Cuts around 0.01 mm StepMax around 0.1 mm – trade-off between CPU time and small step size
impacts radiation analyses results Suggested implementation of StepMax and facRange in MULASSIS