The CQL3D Fokker-Planck code

CQL3D is a general purpose computer code for modeling auxiliary heating in tokamaks. It calculates the radial distribution of 2D in momentum-space bounce-averaged, ion and electron distribution functions in toroidal geometry, consistent with deposition of rf and/or neutral beam injected power and a diffusive radial transport model. This calculation is carried out with an array of bounce-averaged Fokker-Planck (FP) solvers running on noncircular magnetic flux surfaces, giving the steady-state, toroidally-averaged distribution resulting from a balance between collisions, dc electric field, rf quasilinear diffusion, synchrotron radiation, neutral beam injection, and radial diffusion. CQL3D is coupled to ray-tracing codes for electron cyclotron, lower hybrid, and fast waves, to a neutral beam deposition code, and to a noncircular equilibrium code. We describe the code, providing expressions and methodology for calculation of the FP coefficients from each of the constituent processes, and give benchmark applications in order to validate the major components of the code.