Choice of constants of motion coordinates in numerical solving of the three-dimensional Fokker-Planck equation for tokamaks

Abstract A set of constants of motions is chosen which is found suitable for numerical solving of the three-dimensional neoclassical kinetic equation for low collisionality plasmas in tokamaks. With the chosen set, the constants of motion space is well filled with a unique correspondence to the orbits allowed in the configuration. The numerical treatment of the boundary between the trapped and counter-passing particles becomes more straightforward, because the boundary becomes a function of only one constants of motion coordinate.