QED-Cascade

Monte Carlo package for simulating strong field QED interactions.

Standard Install

For large scale simulations (e.g modelling pair production) it is advised that you install the standard version of QED-Cascade and make use of MPI.

Dependencies:

• CMake > 3.5
• HDF5
• OpenMP (optional)
• MPI (optional)

Installing:

Use the following commands to install QED-Cascade:

git clone https://github.com/robbiewatt1/QED-Cascade.git
cd QED-Cascade
mkdir Build
cd Build
cmake ..
make install -j
export QED_TABLES_PATH=<root_dir>/Tables

Where root_dir is the path to the project root directory (e.g. root_dir=/home/robbie/Documents/QED-Cascade). QED_TABLES_PATH must be reset every new terminal session. This can be done automatically by adding export QED_TABLES_PATH=<root_dir>/Tables to the bottom of ~/.bashrc (~/.bash_profile for macOS).

To build with OpenMP or MPI replace cmake .. with either:

cmake .. -DBUILD_OPENMP=ON
cmake .. -DBUILD_MPI=ON

Once installing has finished, a directory should appear in the code root called "Install". The code executable is located in: ./Install/bin/.

Running the code:

The code will write all output to the current working directory. To manage files, it is advised that you create a new directory inside ./Simulations for each new simulation performed. An example input deck is given in: ./example/example.ini. To run this test simulation, use the following (assuming you are in the code root directory):

mkdir Simulations/example
cp ./example/example.ini Simulations/example/
cd Simulations/example
../../Install/bin/QEDCASC example.ini

or if running with MPI, replace the last line with:

mpiexec -n <np> ../../Install/bin/QEDCASC example.ini

where np is the number of processes.

After running the code, two files will be written to the current directory. input-check.txt gives a summary of the input parameters and is a useful check that file parsing has been successful. example.h5 is an hdf5 file containing all the code output.

Python Install (QEDCascPy)

For small scale simulations (i.e. MPI is not required) the python version of QED-Cascade (QEDCascPy) is recommended.

Dependencies:

• python3
• pip > 10
• Numpy
• matplotlib (for example script)

Installing:

I recommend creating a new python virtual environment for QEDCascPy (either virtualenv or conda environment). After creating a new environment QEDCascPy can be installed with the following commands:

git clone https://github.com/robbiewatt1/QED-Cascade.git
pip install ./QED-Cascade

Multithreading

If you are using Linux, multithreading will be enabled by default. However, if you are using macOS, multithreading will be disabled. This is due to the apple clang compiler not supporting OpenMP. To enable multithreading on macOS use the following steps:

First download a compliler such as llvm which supports openMP. llvm can be installed using Homebrew. If you haven't already installed Homebrew then do so with

/bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"

Then install the llvm compiler with

brew install llvm

which will probably install in /usr/local/opt/llvm.

We now need to tell QEDCascPy to enable OpenMP and specify that we want to use the llvm compiler. To do so use the following command:

CC=/usr/local/opt/llvm/bin/clang CXX=/usr/local/opt/llvm/bin/clang++ LDFLAGS="-L/usr/local/opt/llvm/lib" BUILD_OPENMP=ON pip install ./QED-Cascade

This might need changing if Homebrew installs llvm in a different place.

Running the code:

An example python script using QEDCascPy is found in example/QEDCascPy_example.py. This will simulate an electron beam colliding head-on with a laser pulse. To run this script use

python example/QEDCascPy_example.py

This should produce some plots of the electrons energy distribution before and after the collision as well as the photons emitted.

Geant4

If anyone actually reads this and wants to use the QED-Cascade primary event generator for Geant4, please notify me and I'll write some documentation.