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GAIA radiation transport simulation using Geant4 - PowerPoint

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					The ESA GAIA mission

G.Santin*, P.Nieminen
Space environments and effects analysis section
ESTEC

* RHEA System SA

Geant4 Collaboration Workshop 2003
TRIUMF, 5 September 2003
The GAIA mission
Multi-epoch survey of the
central regions of galaxies with
high spatial resolution and
multicolor photometry

Successor to ESA’s Hipparcos
satellite (1989-’93)
    a factor of more than 100
     improvement in accuracy
    a factor 1000 improvement in
     limiting magnitude, and
    a factor of 10000 in the
     number of stars observed

Target for the launch: 2010
    L2 orbit




                         G.Santin - The ESA GAIA mission - Geant4 Workshop, Vancouver 5 Sept 2003   2
The GAIA spacecraft


   Service Module (SVM)
       Electronics, propellant,
        antenna,…
   Payload Module (PLM)
       Optical bench
           Mirrors
           Focal Plane
   Sun shield



                                                     Detectors: Silicon CCDs
                                                          Surface: 60x75 cm2
                                                          250 x 6Mpixels




                   G.Santin - The ESA GAIA mission - Geant4 Workshop, Vancouver 5 Sept 2003   3
Measurement technique




           G.Santin - The ESA GAIA mission - Geant4 Workshop, Vancouver 5 Sept 2003   4
Radiation environment
and effects
  Solar radiation
      Protons, heavy ions, electrons,
       neutrons, gamma rays, X-rays…
      Event driven – occasional high fluxes
       over short periods.
  Cosmic rays
      Continuous low intensity (~4/(cm2 s))
      Heavy ions
  Trapped radiation (not relevant here)
      Continuous with variable intensity                   Environment particles cause radiation
       source of radiation                                  damage to electronic components, solar
      Electrons ~< 10 MeV                                  cells and materials
      Protons ~ <102 MeV                                   Effects include:
                                                                 Surface and Deep dielectric charging
                                                                 Single Event Upset / Latch Up
                                                                 Increased background
                                                                 Degradation, dose, NIEL
                                                                 DNA (biological) damage
                                                            Other environment components
                                                            (energetic and low-energy plasma,
                                                            Oxygen atoms, debris) here neglected

                       G.Santin - The ESA GAIA mission - Geant4 Workshop, Vancouver 5 Sept 2003          5
GAIA in a L2 orbit
  Orbit choice: L2 orbit
      1.5 million km in the anti-Sun
       direction
      uninterrupted observations
         Earth, Moon and Sun remain behind
          the spacecraft viewing direction
         chosen for other astronomy
          missions, like Eddington, Herschel-
          Planck and JWST

                                                  L2



 sun              Earth           1.5e6 km



                          Moon
                          orbit

                                    x-y Period ~ 178 days
                                     z period ~ 184 days


                      G.Santin - The ESA GAIA mission - Geant4 Workshop, Vancouver 5 Sept 2003   6
L2 orbit and radiation environment

  Very stable thermal and radiation environment, compared to other
  considered orbit hypotheses
  Not affected by the trapped particle belts    Dose from statistical models
  Cosmic rays and solar event particles         (JPL’91, 90%CL, 6y)

      outside the geomagnetic shielding
                                                       Dose and rates from CRÈME’96
  Effects from the magnetotail                         + solar event databases
      dynamics caused by variations of the solar wind density and velocity




                                                 [Steve Evans-
                                                    MSFC]

                    G.Santin - The ESA GAIA mission - Geant4 Workshop, Vancouver 5 Sept 2003   7
    GAIA Geant4 simulation: geometry model


             Selection from CAD engineering model
             volumes
                   STEP interface not complete for GAIA                                 Overview, open PLM

                   Even simple CATIA elements cannot
                    be imported
             Accurate description of the materials



PLM with detector                   SVM detail         Optical bench and
radiator                                                        detectors




                              G.Santin - The ESA GAIA mission - Geant4 Workshop, Vancouver 5 Sept 2003        8
Source description
   Protons spectra relevant for the L2
   radiation environment

       “Flare” model environment
          CRÈME’96 (worst week/day, peak 5
            min)
       Quiet time environment
          CRÈME’96 model (2010-2016)
       6 year mission total proton fluence
          JPL’91, 90% confidence level
       Individual solar events
          Examples of real data spectra
          NOAA database
          Bastille day event




                    G.Santin - The ESA GAIA mission - Geant4 Workshop, Vancouver 5 Sept 2003   9
Physics description
  LHEP_PRECO_HP standard G4 physics list:
      Geant4 standard electromagnetic processes
      LHEP_PRECO_HP for the hadronic physics
            pre-equilibrium decay model for modeling the inelastic interaction nucleons
            LEP and HEP parameterized models for the other inelastic interactions
            Point-wise evaluated cross section data to model neutron interactions from thermal neutron energies
             up to ~20 MeV (capture, elastic scattering, fission and inelastic scattering)
            Fission fragments not available
            Data base used: G4NDL version 3.7.


  Secondary e+/- and gamma production cut: global 10 micron
      Thin multi-layer insulating foils (< 100 micron)
      Analysis of damage on the CCD, thin protecting and active layers
      Difference wrt standard cut 0.7 mm ~ 10-50 %
      Moved recently to cuts per region (to avoid low cuts in SVM)

  Moving to Binary Cascade (PRECOBIC) model
      For low energy hadronic interactions, better secondary description
      + HP models for low energy neutrons
            UR: standard list BIC_HP ?
      Problems with g4.5.1 (seg faults) seem to be solved with g4.5.2

                         G.Santin - The ESA GAIA mission - Geant4 Workshop, Vancouver 5 Sept 2003                  10
                                             Flux on the CCD surface




Counts of different particle species on the
CCD surface (from front or back)
    Mono-energetic proton source
          Energies from 1 MeV to 50 GeV
          Each energy point normalized to # incident
           protons
    Spherical source
          Cosine-law emission
          Limited solid angle


    Convolved with environment spectra
    Integrated over the energy
          Total results on rates

    Flux results are interesting for background
     estimates and NIEL analysis


                       G.Santin - The ESA GAIA mission - Geant4 Workshop, Vancouver 5 Sept 2003   11
Extract from MULASSIS code:


                                                                                           NIEL analysis
•     JPL data which are used in SPENVIS. They are for protons only


2) ROSE data from CREN RD48
For actual use of this tabulation, please refer to:
A. Vasilescu and G. Lindstroem
                                                                                     NIEL based on flux information
Displacement damage in Silicon
                                                                                     and CERN coefficients
on-line compilation: http://sesam.desy.de/~gunnar/Si-dfuncs
                                                                                          MULASSIS macroscopic approach
proton induced displacement damage in silicon
-most reliable data, listed for kinetic energies between 1 keV and 9 GeV-
G.P. Summers et al., IEEE NS 40 (1993) 1372
M. Huhtinen and P.A. Aarnio; NIM A 335 (1993) 580 and priv. comm.*)
*) tabulation see also: A. Ferrari (ATLAS TDR '97), priv. comm. 1997


neutron induced displacement damage in silicon
-most reliable data, listed for kinetic energies between 0.1meV and 10 GeV-
P.J. Griffin et al., SAND92-0094 (Sandia Natl. Lab. 93), priv. comm. 1996
A. Konobeyev, J.Nucl.Mater. 186 (1992) 117
M. Huhtinen and P.A. Aarnio, NIM A 335 (1993) 580 and private comm.*)
*) tabulation see also A. Ferrari (ATLAS TDR '97), priv. comm. 1997
                                                                                     GAIA NIEL simulation data
pion induced displacement damage in silicon                                          convoluted with input spectra
most reliable data (checked with exp. values around resonance at 200 MeV),
listed for kinetic energies between 15 MeV and 9 GeV
M. Huhtinen and P.A. Aarnio, NIM A335 (1993) 580 and priv. comm.*)
*) tabulation see also: A. Ferrari (ATLAS TDR '97), priv. comm. 1997

electron induced displacement damage in silicon
listed for kinetic energies between 300 keV and 200 MeV:
The only reliable data are from:
G.P.Summers et al., IEEE NS 40, No 6 (1993), 1372



                                   G.Santin - The ESA GAIA mission - Geant4 Workshop, Vancouver 5 Sept 2003          12
Total Ionising Dose TID analysis
 Total Ionising Dose
     Same approach as flux and NIEL analysis
        Mono-energetic simulations
                                                                                 Quiet time, 2010
        Results convoluted with input spectra


 Contribution to the TID VS primary proton
 energy



 2D distribution of doses                                                          JPL’91, 6 years
     No significant effect observed




                                                                         CRÈME’96, Worst Week


                     G.Santin - The ESA GAIA mission - Geant4 Workshop, Vancouver 5 Sept 2003        13
Estimates for various geometry configurations

                                                                                      2 mm glass cover
    TID and NIEL as a function of
        Tent thickness
        CCD shielding side panels
        Front/Back – ill. CCD
        CCD surface shield (glass)

    Results: ESTEC Technical Note, v1r1

    Effect: modify the spectrum of the
    particles impinging on the CCD
                                             Side CCD panels

  Standard geom

                                                                Thicker tent
                                                                    Back-ill. CCD +
                                                                    side panels



                                   Back-ill. CCD


                      G.Santin - The ESA GAIA mission - Geant4 Workshop, Vancouver 5 Sept 2003           14
Comparisons with other tools:
CCD Glass shield option, thermal tent thickness

    Tent: 0.12 mm eq. Al
                                                          MLI tent thickness: 0.3 and 0.5 mm
    Front-ill. CCD
                                                          Back-ill. CCD (16um)
    Quartz cover
                                                          No CCD glass cover
        Thickness between 0.1 and 5 mm
         (overlapping the Alenia study)
                                                          Back Shield: 11 mm Al




                                                               Substantial agreement
                                                                (discrepancies <~ 20 %, to be
                                                                investigated)


                    G.Santin - The ESA GAIA mission - Geant4 Workshop, Vancouver 5 Sept 2003    15
SSAT – Sector Shielding Analysis Tool
Shielding sectorial analysis
 Ray tracing: from a user-defined point
 within a Geant4 geometry 
     shielding levels (fraction of solid angle for
      which the shielding is within a defined
      interval) and
     shielding distribution (the mean shielding
      level as a function of look direction).
 It utilizes geantinos
 Provides both global shielding and shielding
 from single materials




 GAIA: view from the CCD surface               thermal tent

                                                   mirrors and
                                                   supports
                                                                 CCD front
                                                                 cover and                        antenna
                                                                 electronics    optical bench

                       G.Santin - The ESA GAIA mission - Geant4 Workshop, Vancouver 5 Sept 2003        16
Conclusions
  Complete model of the GAIA mission developed
      All relevant volumes
      Fair level of geometry complexity


  Ionising and NIEL dose estimates have been obtained
      Results in agreement with other estimates
      Help in the spacecraft design phase


  Geant4 capabilities appreciated by the GAIA mission team
      Analysis detail, geometry model flexibility, dose prediction power




                     G.Santin - The ESA GAIA mission - Geant4 Workshop, Vancouver 5 Sept 2003   17

				
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