Gabriele Cosmo
105 lines
5.4 KiB
Markdown
105 lines
5.4 KiB
Markdown
\page Examplech5 Example ch5
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\author G. Paternò, A. Sytov - INFN Ferrara Division (Italy) \n
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paterno@fe.infn.it, sytov@fe.infn.it
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### INTRODUCTION
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Example ch5 is an application for simulating a positron source.
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Although the conventional approach based on an **amorphous target** is possible,
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the application is primarily designed to simulate positron sources based on oriented crystals.
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In the latter case, both the **single-crystal** and the **hybrid scheme**
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can be investigated [[1]](#1).
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### DESCRIPTION
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One or two main volumes can be present in the setup, depending if the user wants to consider
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a conventional/single-oriented-crystal scheme [[2]](#2) or the hybrid scheme [[3]](#3).
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In the hybrid scheme, the first volume is an oriented crystal (typically along a crystalline axis)
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that serves as a radiator, whereas the second volume is a randomly oriented crystal
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(equivalent to an amorphous volume) where the photons emitted by the radiator are converted
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into positrons.
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The converter can be composed of small spheres (the so called _granular target_ - GT)
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so as to reduce the energy deposition and the thermomechanical stress.
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In addition, from _one to three scoring screens_ are present to score the particles
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leaving or enetering the aformentioned volumes. In particular the scoring screen identified
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with number 2 is positioned just downstram of the radiator, while scoring screens 0 and 1
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are positioned just upstream and downstream of the converter, respectively.
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In a conventional or a single crystal scheme, only the scoring screen 0 is present
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and it is automatically positioned just downstream of the single volume positioned.
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An **advanced hybrid scheme that includes an ideal bending magnet or a collimator**
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to remove the charged particle or limit the number of particles impinging on the converter,
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respectively, **can also be considered** [[1]](#1).
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Through a set of custom macro commands, the user can define the geometry ad the scoring strategy.
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A description of all the available options is provided in _run.mac_ (inside the macros folder).
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As an example, the Orientetional Coherent (OC) effects (including radiation) in crystals
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(enabled by G4ChannelingFastSimModel), which by deafult are activated, can be deactivated
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through the command: `/crystal/setOCeffects false`.
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The back surface of the radiator crystal is placed at z=0 (with z as the beam direction),
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while the front position of the possible converter can be set up via macro.
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Various macros are available to simulate different configurations: run_conventional.mac,
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run_single_crystal.mac, run_hybrid.mac, and run_hybrid_granular_target.mac
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for a conventional, single oriented crystal and hybrid with solid or granular target,
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respectively. The parameters set in these macros come from the study carried out for
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the positron source of FCC-ee [[2]](#2).
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However, they can be changed to investigate different cases.
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The output is recorded into a root file whose name can be set by macro
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(default is output/output.root), as a set of ntuples.
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The ntuple "scoring_ntuple" is used to score the features of the particles impinging
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on the scoring screens. It contains the following variables (columns):
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"screenID", "particle", "x", "y", "px", "py", "pz", "t", "eventID"
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which represents:
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- the screen ID (column 0),
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- the particle name (column 1),
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- the impinging x,y coordinates in mm (columns 2,3),
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- the momentum components (MeV) of the particle (columns 4-6),
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- the time of arrival of the particle in ns (column 7),
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- the event ID (column 9).
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The ntuple "edep_rad" and "edep_conv" are used to store the energy deposited (MeV)
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in radiator and converter, respectively, thus they contain simply the variables:
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"edep", "eventID"
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The ntuple "edep_spheres" is instead used to store the energy deposited (MeV) inside the spheres
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of a granular target/converter. It contains the variables:
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"volumeID", "edep", "eventID"
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where volumeID identify the single sphere inside the target. This ntuple is filled only if the
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target is indeed granular (it can be activated through the command /det/setGranularConverter true).
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Finally, the ntuple "scoring_ntuple2" is used to score the features of the particles leaving
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the radiator or the target/converter. It contains the following variables (columns):
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"particle", "x", "y", "z", "px", "py", "pz", "t", "eventID", "trackID"
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which represents:
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- the particle name (column 0),
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- the impinging x,y,z coordinates in mm (columns 1-3),
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- the momentum components (MeV) of the particle (columns 4-6),
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- the time of arrival of the particle in ns (column 7),
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- the event ID (column 8),
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- the track ID (column 9).
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The three-dimensional distributions of energy deposition in the converter
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(radiator if the converter is not present) can be scored through the standard
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box mesh scorer defined in the attached macros.
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To visualize these data one should use the python notebook analysis_ch5.ipynb.
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Once the example is build, an interactive session with the graphic user intergace (GUI)
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showing a defualt geometry set through macro geom.mac can be run by simply typing
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`./ch5` in a terminal after moving inside the build directory.
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### REFERENCES
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<a id="1">[1]</a> M. Soldani, et al. NIM A 1058 (2024): 168828 (https://doi.org/10.1016/j.nima.2023.168828).
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<a id="2">[2]</a> F. Alharthi et al. NIM A 1075 (2025): 170412 (https://doi.org/10.1016/j.nima.2025.170412).
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<a id="3">[3]</a> N. Canale et al. NIM A 1075 (2025): 170342 (https://doi.org/10.1016/j.nima.2025.170342).
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