This simulation is inspired by the geant4's advanced example named purging_magnet.
ICESPICE (Internal Conversion Electron SPectrometer In Coincidence Experiments) is a mini-orange spectrometer in devolpment at the John D. Fox Lab at Florida State University. ICESPICE uses permanent magnets to separate electrons from other types of particles, reducing background noise and enhancing the study of internal conversion electrons. The concept was first introduced by van Klinken (1972), with modern examples including fIREBALL and the Mini-Orange Spectrometer at CIAE.
The goal of this simulation is to import an external magnetic field from COMSOL and simulate electron trajectories and detector responses using Geant4.
Prerequisites:
- Geant4 version: 11.2.0
- ROOT version: 6.30/06
- CMake version: 3.29.2
Installing Geant4 I have included a script to install Geant4 on MacOS. A similar script exists at geant4_setup_tools for Ubuntu 22.04.
Building and running the simulation:
mkdir build
cd build
cmake ..
make
./ICESPICEIn COMSOL, the magnetic field is simulated for an arrangement involving five 1"x1"x1/8" N42 Neodymium magnets. These magnets are arranged around a tantalum attenuator, which is a rod with a diameter of 1/8" and a height of approximately 30mm, placed within a vacuum volume. The setup is designed to create a toroidal magnetic field, optimizing the path of electrons from a positive z position (source) towards a focused negative z position (detector).
The magnetic field data from COMSOL is exported to a .csv file, which includes spatial and vector field data at half-millimeter intervals within a 10cm x 10cm x 14cm region centered at the origin. Given the extensive data coverage and fine resolution, the file size is typically large (>1 GB) and could not be put on github. The COMSOL output must be converted to the correct format (same as the "purging_magnet" example) for the code to read it. This script can be found in ./scripts/comsol_to_geant_table.py.
The geometry of ICESPICE is easily imported into Geant4 using CADMESH. From SolidWorks, the assembly geometry is exported to a .step file. This is then imported into FreeCad and then exported as a .obj file. This is annoying but SolidWorks doesn't allow you to export an assembly as an .obj file. The .obj file can be easily read into geant4 using CADMESH. I had to change the groups ('g ') in the .obj file to objects ('o '). The name of the objects must not have spaces too.
Multiple scripts exist in different folders for the simulations of different purposes.