PARAMAGNET

Long-Pulse Laser-Plasma physics simulation code

This code has been written to simulate laser-plasma interactions in the long (~1ns) pulse regime. Given the collisionality of this regime allows us to model the plasma using MagnetoHydrodynamics (MHD) coupled to a Paraxial laser solver.

Prerequisites:

• PETSc - this has been tested with version 3.8
• OpenMP

How to install/compile:

Clone the repository and cd into the main directory. Ensure the environment variables are set for the PETSc directory; this should be in the .bashrc file. Install with the command make all. This will create a binary in the bin directory.

How to define a simulation problem:

Modify the files Initial.cpp and Global.cpp to set the initial condition and simulation parameters respectively.

The Global.cpp file contains global variables that are set at compile time. The Physical State section contains definitions of:

• the reference density n0,
• the reference temperature T0,
• the ionization state Z(which at present only works up to Z=8),
• the period of the simulation (in seconds)
• the physical dimensions of the simulation box (x,y,z, in metres) The Collisional Parameters should not be changed. The Mesh Variables section contains a set of parameters that set the mesh parameters. The only ones that should be changed are the variables m,nx,ny,nz which set the number of timesteps and the number of cells in x,y,z respectively. The Laser Variables section contains the parameters for the laser solver. The parameters one can change are:
• The wavelength wl in metres,
• The intensity Intensity in watts per square metre, The Output Varibales section defines whether a field should be saved to file as output from the simulation, and tfrac defines how many steps there are between output dumps (tfrac=10 means output is dumped every 10 timesteps). The Boundary conditions section defines the boundaries in x, y and z.

In the Inital.cpp file one can set the initial profile of the various fields. To set a profile, find the discrete form of the profile on a cartesian mesh (with cell position i,j,k for the x,y and z dimensions respectively). Ensure the profile is set in normalised units. The initvalue array contains the intial state of the code, with the indicies nin representing number density, Tin temperature, Vxin the x velocity and Bxin the magnetic field in x. The laser field is defined on the z=0 boundary, as such only profiles with k=0 should be used.

Once all modifications to the Global and Initial files are complete, recompile the source using make all.

How to run:

Set the number of OpenMP threads using OPENMP_NUM_THREADS=N where the number of threads is N. Run with the command ./bin/MAGNET. The output can be found in raw ASCII format and VTK format in the output directory.