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0003 =========================================================
0004 Geant4 - an Object-Oriented Toolkit for Simulation in HEP
0005 =========================================================
0006
0007 Xray_SiliconPoreOptics
0008 ------------------
0009 P.Dondero (1), R.Stanzani (1)
0010 Apr 2023
0011
0012 1. Swhard S.r.l, Genoa (GE), Italy.
0013
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0015
0016 Contacts: paolo.dondero@cern.ch, ronny.stanzani@cern.ch
0017
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0019 Acknowledgements: example developed within the ESA AREMBES Project, Contract n.
0020 4000116655/16/NL/BW. Valentina Fioretti provided the simplified mass model, as
0021 described in [1].
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0023
0024 Xray_SiliconPoreOptics is an example of the application of Geant4 in a space
0025 environment.
0026 The geometry used in this example represents a single reflective pore used to
0027 simulate on a smaller scale the effect of the millions of pores forming the
0028 mirror of the ATHENA Silicon Pore Optics (SPO), as described in [1].
0029 The main purpose of the simulation is the estimation of the induced residual
0030 background at the pore exit caused by proton scattering at grazing angles
0031 (<1deg).
0032 Reflection steps inside the pore and relevant information are saved on a .root
0033 file for subsequent analysis [2]. For execution time optimization purposes, only
0034 particle steps respecting specific conditions (e.g. reflection length and volume
0035 name) are stored.
0036 An example of ROOT-based analysis of the output file is included
0037 ("./analysis/analysis.C") and can be used to obtain basic data representations.
0038 Xray_SiliconPoreOptics implements a physics list dedicated to space radiation
0039 interactions, developed within the ESA AREMBES Project for the ATHENA mission,
0040 called Space Physics List (SPL).
0041 The example shows a way to optimize the simulation's execution time
0042 and output size by selectively saving data based on specific combined conditions
0043 (e.g. position, eventID and process name).
0044 NOTE: in a multiple-run session, the last run always overrides the root file.
0045
0046 1 - GEOMETRY
0047
0048 The geometry is given in the GDML format, and consists of a single Silicon pore
0049 aligned to the ideal optics symmetry axis of the SPO [1], i.e., the Z-axis of
0050 the Geant4 reference system. The pore has the following parameters:
0051 - length: ~203.0 mm
0052 - pore entrance size: ~0.83x0.61 mm
0053 - pore thickness: 0.17 mm
0054 Three volumes (DummyEntrance, DummyExit and DummySphere) are used to save the
0055 state of the particles as they pass.
0056
0057 2 - INPUT FLUX
0058
0059 100keV protons are emitted with a Cosine-law distribution from a planar surface
0060 (same dimensions of the pore) at 1mm above the entrance, within a cone of +-1 deg
0061 aperture, as described in [1].
0062
0063 3 - PHYSICS LIST
0064
0065 This example implements a dedicated physics list called "Space Physics List",
0066 developed within the ESA AREMBES Project. This physics list has been designed
0067 focusing on the ATHENA physics processes, but contains high precision
0068 models that can be used in a more general space application.
0069 In details, this physics list provides a custom electromagnetic part combined
0070 with the QBBC hadronic physics list.
0071 In addition, the G4EmStandardSS Physics List is used to simulate the single
0072 scattering inside the pore, as it is associated to a specific region
0073 from the macro file.
0074 In general, the use of SS only in selected regions allows the simulation to
0075 reduce CPU consumption in the majority of the volumes and be very accurate in
0076 the desired ones.
0077 The default production cuts are selected for all volumes, i.e. 1mm.
0078
0079 4 - HOW TO RUN THE EXAMPLE
0080
0081 Compile code and execute Xray_SiliconPoreOptics in 'batch' mode from the macro
0082 file:
0083 ./XraySiliconPoreOptics run01.mac
0084 For this example, the multi-thread (MT) capability of Geant4 is enabled by
0085 default.
0086 To specify the desired number of threads, the user can use the command
0087 "/run/numberOfThreads" in "run01.mac". To show the output from a single thread
0088 in the terminal, the user can use the "/control/cout/ignoreThreadsExcept
0089 {THREADNUM}" command.
0090
0091 5 - STEPPING
0092
0093 Within the "SteppingAction" class relevant information about the particle's
0094 state are stored in Tuples [2], defined in the "HistoManager" class.
0095 The tuples contain the following information:
0096 1. event ID
0097 2. volume name
0098 3. track ID
0099 4. coordinates (x,y,z)
0100 5. angles (theta, phi)
0101 6. process name
0102 7. parent ID
0103 8. the number of internal reflections whenever the particle reaches one of the
0104 dummy volumes defined above.
0105
0106 6 - ANALYSIS
0107
0108 Xray_SiliconPoreOptics provides an analysis macro example (analysis.C) to
0109 visualize data in the following representations:
0110 - a histogram for the normalized efficiency for Theta and Phi;
0111 - a pie chart for the number of reflections inside the pore.
0112 The normalized efficiency serves to observe the angular distribution of the
0113 exiting protons, normalized over the total entering particles. A proton is
0114 selected if it enters the first volume (pore entrance), exits from the second
0115 empty volume (pore exit) and enters the sphere at the detector side (the
0116 hemisphere below the pore). No pore interaction is required.
0117 The pie chart reports the number of reflections with the highest probability.
0118
0119 7 - VISUALISATION
0120
0121 The visualisation manager is set via the G4VisExecutive class in the main()
0122 function in xray_SiliconPoreOptics.cc.
0123 The initialisation of the drawing is done via a set of /vis/ commands in the
0124 macro vis.mac. This macro is automatically read from the main function when
0125 the example is used in interactive running mode.
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0128
0129 References
0130
0131 [1] Fioretti V et al. "The Geant4 mass model of the ATHENA Silicon Pore Optics
0132 and its effect on soft proton scattering", Space Telescopes and Instrumentation
0133 2018: Ultraviolet to Gamma Ray. Vol. 10699. SPIE, 2018.
0134 [2] BRUN, René, et al. "The ROOT Users Guide". CERN, http://root.cern.ch, 2003.
0135
