GRAS ValidationGRAS Validation and and

GEANT4 Electromagnetic Physics GEANT4 Electromagnetic Physics ParametersParameters

R. Lindberg, G. Santin; ronnie.lindberg@esa.int

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?

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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)

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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)

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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

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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

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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%

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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

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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