1. filit.py

This is the main field line tracing Python3 program.

1.1. Configuration

Configure the run prior to execution:

• select target mode between the following: 'matrix', 'line-horizontal', 'line-vertical'

  tar_mode = 'line-horizontal'

• choose number of targets per line:

  ntargets1D = 100

• choose number of toroidal turns:

  nturns = 50

• select the step size in mm of the field line for interpolation (this modifies variable n_grid_phi_enhanced; you can do it ad hoc):

  step_phi_mm = 1

• write the name (full path) of magnetic equilibrium

  input_file = 'snapfile.80.nc'

• full limiter limiter path (optional); if none, write the following:

  lim_path = ''

1.2. Execution

To run the script do:

python3 filit.py

Depending on the number of targets, number of turns and plotting resolution (see filib.py), it can take from 1-100 minutes to compute and plot a field line tracing experiment.

2. fiload.py

This is an auxiliary Python3 script to load and plot the results of the main program.

2.1. Configuration

• full path of filit.py output file:

  filename = 'results/matrix_ntargets-10000_nturns-500'

• boolean for plotting initial target distribution:

  plot_initial = 0

2.2. Execution

To run the script do:

python3 fiload.py

Depending on the number of targets, number of turns and plotting resolution (see filib.py), it can take from 1-10 minutes to load and plot a filit.py output file.

3. filib.py

This is an auxiliary Python3 script containing all the functions to run filit.py and fiload.py:

• read_data_hint: reads magnetic equilibrium data from HINT output file (see https://github.com/yasuhiro-suzuki/HINT3D.git).
• read_limiter: reads limiter data from MKLIM output file (see https://github.com/yasuhiro-suzuki/HINT3D.git).
• limiter_boundary: computes the boundaries of the limiter just for plotting.
• create_targets: creates a target distribution in a line (horizontal or vertical) or a matrix. This function can be easily improved.
• step_phi_cylindrical_rk4: 4th order Runge-Kutta specific for the following field line cylindrical equation:
  • field_line_function: cylindrical equation of field line to be evaluated at the differents steps of a Runge-Kutta scheme.
• delete_outer_particles: deletes particles outside computational boundaries.
• delete_outer_particles_limiter: deletes particles outside dynamical limiter.
• plot_Poincare_Lc: this representation script provides Poincaré plots and connection length plots for the field line tracing done to our magnetic equilibrium. =======

FiLiT

This function traces field lines for any 3D vector field to compute Poincaré plots and connection length. Particularly, for tokamaks and stellarators, given its 3-dimensional magnetic field components.

1. Definition of Field Line

A field line for a given vector field is a 3D curve for which the vector field is tangent at every point in space.

We use a cylindrical reference frame for the vector fields (R, phi, Z) to follow field lines but, thanks to the modularity of the program, this can be easily modified to other geometries

2. Limiter Geometry

If a limiter geometry is available, the option can be selected to compute more realistic trajectories, dynamically deleting particles that go outside our limiter boundaries.

3. Inputs

To run this program, the following files are necessary:

• 3D cylindrical (magnetic) field (for magnetic fields, preferably an equilibrium) netcdf file containing radial, toroidal and vertical components of the field:

  https://mega.nz/file/kk1mmKjK#ZyX3waZSOhuUkpyO_aMJv_z_cmZKIGY9fqAY1HmpriM

• 3D limiter (optional) netcdf file containing information on the inside/outside for the simulation:

  https://mega.nz/file/cltyUTxI#qp17DSp_pkJovx3cDTcIavt6kdzk0tJzIvyeJknn9mw

4. Branches

v1.2 (default)

• All interpolation functions are Python imported.
• First loop on turns and then loop on particles.
• Step size definition not uniform for every point but good approximation.
• Plotting improvements were carried out, still work to do.
• Difficult to parallelize but fastest version.
• Possible change of magnetic field periodicity with respect to the limiter.
• 2D geometries not implemented but easy.
• Contains Fortran version

v1.1 (old)

• All interpolation functions are Python imported.
• First loop on turns and then loop on particles.
• Step size definition not uniform for every point but good approximation.
• Plotting improvements were carried out, still work to do.
• Difficult to parallelize but fastest version.
• Possibility to change magnetic field periodicity not implemented.

v1.0 (old)

• All interpolation functions are manually written.
• First loop on turns and then loop on particles.
• Step size definition not uniform for every point but good approximation.
• Plotting improvements were strongly needed.
• Possibility to change magnetic field periodicity not implemented.

v2.0 (slow)

• All interpolation functions are Python imported.
• First loop on particles and then loop on turns.
• Step size definition uniform for every point but good approximation.
• Plotting improvements were carried out, still work to do.
• Easier to parallelize particle loop but slowest version.
• Possibility to change magnetic field periodicity not implemented.

Authors

• Carlos Romero Madrid