Gabriele Cosmo
136 lines
6.2 KiB
Plaintext
136 lines
6.2 KiB
Plaintext
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=========================================================
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Geant4 - an Object-Oriented Toolkit for Simulation in HEP
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=========================================================
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Xray_SiliconPoreOptics
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------------------
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P.Dondero (1), R.Stanzani (1)
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Apr 2023
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1. Swhard S.r.l, Genoa (GE), Italy.
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Contacts: paolo.dondero@cern.ch, ronny.stanzani@cern.ch
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Acknowledgements: example developed within the ESA AREMBES Project, Contract n.
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4000116655/16/NL/BW. Valentina Fioretti provided the simplified mass model, as
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described in [1].
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Xray_SiliconPoreOptics is an example of the application of Geant4 in a space
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environment.
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The geometry used in this example represents a single reflective pore used to
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simulate on a smaller scale the effect of the millions of pores forming the
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mirror of the ATHENA Silicon Pore Optics (SPO), as described in [1].
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The main purpose of the simulation is the estimation of the induced residual
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background at the pore exit caused by proton scattering at grazing angles
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(<1deg).
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Reflection steps inside the pore and relevant information are saved on a .root
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file for subsequent analysis [2]. For execution time optimization purposes, only
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particle steps respecting specific conditions (e.g. reflection length and volume
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name) are stored.
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An example of ROOT-based analysis of the output file is included
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("./analysis/analysis.C") and can be used to obtain basic data representations.
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Xray_SiliconPoreOptics implements a physics list dedicated to space radiation
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interactions, developed within the ESA AREMBES Project for the ATHENA mission,
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called Space Physics List (SPL).
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The example shows a way to optimize the simulation's execution time
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and output size by selectively saving data based on specific combined conditions
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(e.g. position, eventID and process name).
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NOTE: in a multiple-run session, the last run always overrides the root file.
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1 - GEOMETRY
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The geometry is given in the GDML format, and consists of a single Silicon pore
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aligned to the ideal optics symmetry axis of the SPO [1], i.e., the Z-axis of
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the Geant4 reference system. The pore has the following parameters:
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- length: ~203.0 mm
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- pore entrance size: ~0.83x0.61 mm
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- pore thickness: 0.17 mm
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Three volumes (DummyEntrance, DummyExit and DummySphere) are used to save the
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state of the particles as they pass.
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2 - INPUT FLUX
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100keV protons are emitted with a Cosine-law distribution from a planar surface
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(same dimensions of the pore) at 1mm above the entrance, within a cone of +-1 deg
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aperture, as described in [1].
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3 - PHYSICS LIST
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This example implements a dedicated physics list called "Space Physics List",
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developed within the ESA AREMBES Project. This physics list has been designed
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focusing on the ATHENA physics processes, but contains high precision
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models that can be used in a more general space application.
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In details, this physics list provides a custom electromagnetic part combined
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with the QBBC hadronic physics list.
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In addition, the G4EmStandardSS Physics List is used to simulate the single
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scattering inside the pore, as it is associated to a specific region
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from the macro file.
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In general, the use of SS only in selected regions allows the simulation to
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reduce CPU consumption in the majority of the volumes and be very accurate in
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the desired ones.
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The default production cuts are selected for all volumes, i.e. 1mm.
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4 - HOW TO RUN THE EXAMPLE
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Compile code and execute Xray_SiliconPoreOptics in 'batch' mode from the macro
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file:
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./XraySiliconPoreOptics run01.mac
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For this example, the multi-thread (MT) capability of Geant4 is enabled by
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default.
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To specify the desired number of threads, the user can use the command
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"/run/numberOfThreads" in "run01.mac". To show the output from a single thread
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in the terminal, the user can use the "/control/cout/ignoreThreadsExcept
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{THREADNUM}" command.
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5 - STEPPING
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Within the "SteppingAction" class relevant information about the particle's
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state are stored in Tuples [2], defined in the "HistoManager" class.
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The tuples contain the following information:
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1. event ID
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2. volume name
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3. track ID
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4. coordinates (x,y,z)
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5. angles (theta, phi)
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6. process name
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7. parent ID
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8. the number of internal reflections whenever the particle reaches one of the
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dummy volumes defined above.
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6 - ANALYSIS
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Xray_SiliconPoreOptics provides an analysis macro example (analysis.C) to
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visualize data in the following representations:
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- a histogram for the normalized efficiency for Theta and Phi;
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- a pie chart for the number of reflections inside the pore.
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The normalized efficiency serves to observe the angular distribution of the
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exiting protons, normalized over the total entering particles. A proton is
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selected if it enters the first volume (pore entrance), exits from the second
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empty volume (pore exit) and enters the sphere at the detector side (the
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hemisphere below the pore). No pore interaction is required.
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The pie chart reports the number of reflections with the highest probability.
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7 - VISUALISATION
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The visualisation manager is set via the G4VisExecutive class in the main()
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function in xray_SiliconPoreOptics.cc.
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The initialisation of the drawing is done via a set of /vis/ commands in the
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macro vis.mac. This macro is automatically read from the main function when
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the example is used in interactive running mode.
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References
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[1] Fioretti V et al. "The Geant4 mass model of the ATHENA Silicon Pore Optics
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and its effect on soft proton scattering", Space Telescopes and Instrumentation
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2018: Ultraviolet to Gamma Ray. Vol. 10699. SPIE, 2018.
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[2] BRUN, René, et al. "The ROOT Users Guide". CERN, http://root.cern, 2003.
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