channeling/ch5/README.md

0001 \page Examplech5 Example ch5
0002
0003 \author  G. Paternò, A. Sytov - INFN Ferrara Division (Italy) \n
0004 paterno@fe.infn.it, sytov@fe.infn.it
0005
0006 ### INTRODUCTION
0007 Example ch5 is an application for simulating a positron source.
0008 Although the conventional approach based on an **amorphous target** is possible,
0009 the application is primarily designed to simulate positron sources based on oriented crystals.
0010 In the latter case, both the **single-crystal** and the **hybrid scheme**
0011 can be investigated [[1]](#1).
0012
0013 ### DESCRIPTION
0014 One or two main volumes can be present in the setup, depending if the user wants to consider
0015 a conventional/single-oriented-crystal scheme [[2]](#2) or the hybrid scheme [[3]](#3).
0016 In the hybrid scheme, the first volume is an oriented crystal (typically along a crystalline axis)
0017 that serves as a radiator, whereas the second volume is a randomly oriented crystal
0018 (equivalent to an amorphous volume) where the photons emitted by the radiator are converted
0019 into positrons.
0020 The converter can be composed of small spheres (the so called _granular target_ - GT)
0021 so as to reduce the energy deposition and the thermomechanical stress.
0022 In addition, from _one to three scoring screens_ are present to score the particles
0023 leaving or enetering the aformentioned volumes. In particular the scoring screen identified
0024 with number 2 is positioned just downstram of the radiator, while scoring screens 0 and 1
0025 are positioned just upstream and downstream of the converter, respectively.
0026 In a conventional or a single crystal scheme, only the scoring screen 0 is present
0027 and it is automatically positioned just downstream of the single volume positioned.
0028
0029 An **advanced hybrid scheme that includes an ideal bending magnet or a collimator**
0030 to remove the charged particle or limit the number of particles impinging on the converter,
0031 respectively, **can also be considered** [[1]](#1).
0032
0033 Through a set of custom macro commands, the user can define the geometry ad the scoring strategy.
0034 A description of all the available options is provided in _run.mac_ (inside the macros folder).
0035 As an example, the Orientetional Coherent (OC) effects (including radiation) in crystals
0036 (enabled by G4ChannelingFastSimModel), which by deafult are activated, can be deactivated
0037 through the command: `/crystal/setOCeffects false`.
0038
0039 The back surface of the radiator crystal is placed at z=0 (with z as the beam direction),
0040 while the front position of the possible converter can be set up via macro.
0041
0042 Various macros are available to simulate different configurations: run_conventional.mac,
0043 run_single_crystal.mac, run_hybrid.mac, and run_hybrid_granular_target.mac
0044 for a conventional, single oriented crystal and hybrid with solid or granular target,
0045 respectively. The parameters set in these macros come from the study carried out for
0046 the positron source of FCC-ee [[2]](#2).
0047 However, they can be changed to investigate different cases.
0048
0049 The output is recorded into a root file whose name can be set by macro
0050 (default is output/output.root), as a set of ntuples.
0051
0052 The ntuple "scoring_ntuple" is used to score the features of the particles impinging
0053 on the scoring screens. It contains the following variables (columns):
0054
0055 "screenID", "particle", "x", "y", "px", "py", "pz", "t", "eventID"
0056
0057 which represents:
0058 - the screen ID (column 0),
0059 - the particle name (column 1),
0060 - the impinging x,y coordinates in mm (columns 2,3),
0061 - the momentum components (MeV) of the particle (columns 4-6),
0062 - the time of arrival of the particle in ns (column 7),
0063 - the event ID (column 9).
0064
0065 The ntuple "edep_rad" and "edep_conv" are used to store the energy deposited (MeV)
0066 in radiator and converter, respectively, thus they contain simply the variables:
0067 "edep", "eventID"
0068
0069 The ntuple "edep_spheres" is instead used to store the energy deposited (MeV) inside the spheres
0070 of a granular target/converter. It contains the variables:
0071 "volumeID", "edep", "eventID"
0072 where volumeID identify the single sphere inside the target. This ntuple is filled only if the
0073 target is indeed granular (it can be activated through the command /det/setGranularConverter true).
0074
0075 Finally, the ntuple "scoring_ntuple2" is used to score the features of the particles leaving
0076 the radiator or the target/converter. It contains the following variables (columns):
0077
0078 "particle", "x", "y", "z", "px", "py", "pz", "t", "eventID", "trackID"
0079
0080 which represents:
0081 - the particle name (column 0),
0082 - the impinging x,y,z coordinates in mm (columns 1-3),
0083 - the momentum components (MeV) of the particle (columns 4-6),
0084 - the time of arrival of the particle in ns (column 7),
0085 - the event ID (column 8),
0086 - the track ID (column 9).
0087
0088 The three-dimensional distributions of energy deposition in the converter
0089 (radiator if the converter is not present) can be scored through the standard
0090 box mesh scorer defined in the attached macros.
0091
0092 To visualize these data one should use the python notebook analysis_ch5.ipynb.
0093
0094 Once the example is build, an interactive session with the graphic user intergace (GUI)
0095 showing a defualt geometry set through macro geom.mac can be run by simply typing
0096 `./ch5` in a terminal after moving inside the build directory.
0097
0098 ### REFERENCES
0099 <a id="1">[1]</a> M. Soldani, et al. NIM A 1058 (2024): 168828 (https://doi.org/10.1016/j.nima.2023.168828).
0100
0101 <a id="2">[2]</a>  F. Alharthi et al. NIM A 1075 (2025): 170412 (https://doi.org/10.1016/j.nima.2025.170412).
0102
0103 <a id="3">[3]</a>  N. Canale et al. NIM A 1075 (2025): 170342 (https://doi.org/10.1016/j.nima.2025.170342).
0104