Fokker Planck collision operator

We implement the nonlinear Fokker-Planck collision operator for self collisions using the weak-form finite-element method. This is documented in the ExCALIBUR/NEPTUNE report 2070839-TN-07. A publication based on this report is in progress. Full online documentation will follow.

Input parameters

A series of 0D2V Fokker-Planck input files can be found in

examples/fokker-planck/

and examples of 1D2V pre-sheath simulations with the Fokker-Planck collision operator can be found in

examples/fokker-planck-1D2V/

noting that the timestepping or resolution parameters may require modification to find a converged simulation.

The basic input namelist is structured as follows

[fokker_planck_collisions]
use_fokker_planck = true
# nuii sets the normalised input C[F,F] Fokker-Planck collision frequency
# for frequency_option = "manual"
nuii = 1.0
frequency_option = "manual"

Set use_fokker_planck=false to turn off Fokker-Planck collisions without commenting out the namelist. The default option for frequency_option = "reference_parameters", where nuii is set by the reference parameter inputs. Further specialised input parameters can be seen in the source at setup_fkpl_collisions_input() in moment_kinetics/src/fokker_planck.jl.