Implementation and verification of a new model collision operator in gyrokinetic code COGENT

Impurity transport in the tokamak plasma is a topic of great importance in fusion research. On the one hand, the radiation losses from high-Z impurities at the core plasma can fatally hinder the performance of fusion devices. On the other hand, impurities close to the edge help reduce the heat fluxes to the device's walls. Although many aspects of the impurity transport theory, such as local neoclassical theory, are now well developed, understanding global impurity transport remains a challenge and requires numerical simulation tools. The development and implementation of such collision operators is a subject of active research. While the Fokker - Plank operator derived from the first principle does, in principle, result in the highest fidelity simulation, the high computational cost makes its use impractical for many applications of interest. An alternative approach is to construct a model operator that, while simpler and faster to compute, still models the collision process reasonably well.

This poster presents the implementation and verification of a new unlike-particle collision operator in the gyrokinetic code COGENT. This collision operator consists of a test-particle component, describing collisions with a Maxwellian background, and a field-particle component, designed to conserve total momentum and energy during collisions. The poster presents a series of verification exercises that establish the model operator's validity and its range of applicability.