Field Simulation for LArPix

This field simulation was developed for LArPix, a pixelated readout system for the Liquid Argon Time Projection Chamber (LArTPC).

The field simulation is based on Garfield++, a toolkit for the simulation of particle detectors.
Further details about Garfield++ can be found at: Garfield++ Website

Finite Element Method (FEM)

The finite-element field maps were calculated using Elmer and Gmsh.
Learn more at: Garfield++ Elmer Examples

For detailed instructions on generating finite-element field maps using the mesher Gmsh (website) and the field solver Elmer (website), refer to this documentation:
Garfield++ Elmer Documentation

These instructions also explain how to use the field maps for electron transport simulations in Garfield++.

Interactive Example

An example implementation can be found in this interactive notebook:
Garfield FEM Notebook

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Steps to Build the Field Simulation

1. Install Softwares

   • Gmsh: https://gmsh.info
     Used for defining our detector geometry and creating a finite element mesh.

   • Elmer: http://www.elmerfem.org
     Used for solving for the electrostatic fields.

     • Installing Elmer on macOS can be tricky
     • The following method works for me (macOS Sequoia 15.4.1)

         brew install openblas
         
         # brew install freecad (run this if the freecad was not installed successfully in the last step)
         
         mkdir elmer
         
         cd elmer
         
         git clone https://github.com/ElmerCSC/elmerfem.git
         
         mkdir build
         
         cd build
         
         cmake -DWITH_MPI:BOOLEAN=FALSE -DCMAKE_INSTALL_PREFIX=$(pwd)/../install -DHOMEBREW_PREFIX=/opt/homebrew ../elmerfem
         
         # cmake -DWITH_MPI:BOOLEAN=FALSE -DCMAKE_INSTALL_PREFIX=$(pwd)/../install -DMACPORTS_PREFIX=/opt/local ../elmerfem (if you use MacPorts)
         
         make
         
         make install
     

   • ROOT: https://root.cern.ch
     A prerequisite for Garfield++ (with Python enabled).

   • Garfield++: https://garfieldpp.web.cern.ch/garfieldpp
     Used for detector simulation.

2. Construct the Geometry

   • The LArPix geometry was created using CAD software; it was imported as a .step file into the .geo file format; the detector (2x2 detector in this example) was build in the .geo directly
   • Convert .geo to .msh file
     • Run gmsh <geometry_file>.geo -3 -order 2

3. Calculate the Fields

   • Convert .msh to Elmer mesh files
     • Run ElmerGird 14 2 <mesh_file>.msh
     • This will create a directory containing mesh.boundary; mesh.elements; mesh.header; mesh.nodes
   • Calculate Electric Field and Weighting Field
     • Run ElmerSolver <solver_input_file>.sif (both <electric_field>.sif and <weighting_field.sif>) in the parent directory to the Elmer mesh files (The folder location is specified in the .sif);
     • This will create the calculated field files .result; the .result will be generated in the same folder as the Elmer mesh files.

4. View fields and calculate the induced current

   • LArPix field response simulation code can be found in the larpix_v2b/field_response_simulation.ipynb