Kinetic simulations of fast ions in stellarators

The steady-state distribution function of neutral beam injection (NBI) fast ions is calculated numerically for the LHD and TJ-II stellarators using the code ISDEP (Integrator of Stochastic Differential Equations for Plasmas). ISDEP is an orbit code that solves the guiding centre motion of fast ions using Cartesian coordinates in position space, allowing arbitrary magnetic configurations and the re-entering of particles in the plasma. It takes into account collisions of fast ions with thermal ions and electrons using the Boozer and Kuo-Petravic collision operator. The steady-state distribution function is computed with a time integral following Green's function formalism for a time-independent source. The rotation profiles of the fast ions are also estimated, thus computing their contribution to the total plasma current. In addition, energy slowing down time and escape distribution are studied in detail for both devices.