On Monte Carlo Operators Describing Coulomb Collisions in Toroidal Plasmas Q. Mukhtar , T. Hellsten and T. Johnson School of Electrical Engineering, KTH, Association VR-Euratom, Sweden. Modelling of ICRF-heating can be carried out with Monte Carlo codes with operators describing the wave-particle interactions and Coulomb collisions. The collision operator describes the transfer of power to the background species and relaxation towards a local isotropic distribution function. The ion-ion collisions are important for isotropization of the perturbed distribution functions, because they produce a radial electric field in the neoclassical particle transport. In uniform plasma the Coulomb collisions should relax the distribution function towards a Maxwellian with constant density and temperature. Here a model collision operator, applicable to the banana regime in toroidal plasmas is presented, which has been verified in 2D (in pitch angle and radius). The neoclassical transport is caused by collisional scattering between trapped and passing particles. Since the averaged flux surface location of a trapped particle in axisymmetric plasma is approximately given by the location of its turning points, / T P Ze φ ψ ≈ , the transport of trapped particles can be calculated from the changes of their canonical angular momentum. In order to speed up the Monte Carlo simulations, large time steps are preferred. Systematic errors may then occur due to the finite time steps, due to which errors may be increased near boundaries in phase space where the Monte Carlo operators become singular. Furthermore, the Coulomb collision operator should be compatible with neoclassical transport in particular not producing any particle transport caused by the ion-ion collisions. Model A generic model, including neoclassical effects in the banana regime is tested, to assess numerical limitations. The orbits are thin, described by (, ) r ξ , where is the minor radius and r ξ is the pitch angel at the outer midplane. The energy W is constant, only the change in pitch angel is taken into account. Only the trapped particles undergo radial transport as they change their parallel velocity due to pitch angel scattering. For trapped and passing particles the scattering is assumed to take place where the orbits intersect the midplane on the low field side. In neoclassical theory the distribution function deviates slightly from a local Maxwellian such that ion-ion collisions do not give rise to a particle flux. The change in pitch angel by Coulomb collision in homogeneous plasma is given by 38 th EPS Conference on Plasma Physics (2011) P4.095