TsElectricFieldMap: A Custom TOPAS Extension for Non-uniform Electric Fields

Created by Cameron Poe (cameronpoe@uchicago.edu) and Kepler Domurat-Sousa (domuratsousa@uchicago.edu)

Enrico Fermi Institute, University of Chicago

3 October 2023

About the extension

This custom TOPAS extension modifies TsMagneticFieldMap to create non-uniform electric fields from a modified Opera-3d .TABLE file containing electric field data.

This package also includes a Python script to turn Ansys .fld-formatted files into the modified Opera-3d .TABLE-formatted files required by the extension.

How to use the extension

To install the extension, follow the instructions on the TOPAS installation guide at https://www.topasmc.org/user-guides. The only files you need for installation are in the topas_extension/ directory.

The efield_table_creator.py script takes as inputs the path of your Ansys .fld file and then creates an Opera-3d .TABLE file in the non-uniform_efield_tables/ directory.

To use the efield_table_creator.py script, scroll to the __main__ section of the code. In the General Parameters section, set MODE to non-uniform and set output_file_name to what you want the .TABLE file to be called. Do not include .TABLE in that variable; it will be added by the code.

In the Non-uniform Mode Parameters section, set ansys_file_nonuniform to the path of the Ansys .fld file you wish to convert. This Python script uses mm and kV/mm as the intrinsic units, so set ansys_position_scale_nonuniform to the value that turns the .fld position units to mm.

This script can process Ansys simulations that have symmetry in one dimension. If this describes your .fld file, set repetition_axis to the axis of translational symmetry (e.g. 'x' if your simulation is in y and z). Set repetition_depth to the extent in mm of the object containing your field in the symmetric axis. If your simulation does not have translational symmetry in one dimension, set these values to '' and 0, respectively.

The Python script also has the ability to run some simple checks. These are included in the uniform_tests/, linear_tests/, and nonuniform_tests/ directories, but you can also re-create these files using the Python script. To do so, set the MODE in the General Parameters section appropriately, then modify any parameters in the respective Test Parameters section.

Extension next steps

This extension can still be improved, but our research group does not have incentive since our final detector design does not use non-uniform electric fields.

The biggest improvement would be to translate the Python .fld to .TABLE converter script into the C++ of the extension. This would involve a couple things. First, the extension would need to be modified to parse a .fld file instead of a .TABLE file. The header information is the biggest difference, so instead of retrieving fNX, fNY, and fNZ in the first line of the .TABLE file, the extension would need to calculate those quantities from the grid min, max, and size arrays in the .fld file. Second, the indexing behavior could be changed. This is optional. The current extension assumes that rows in the .TABLE file are sorted least-to-greatest first in X, then in Y, then in Z. While this is how .fld files are sorted, a more general solution would be to calculate ix, iy, and iz using the grid min, max, and size arrays and the position vector in a row of the .fld file. These index values would then no longer rely on the data being sorted in a specific order.