A reduced fast ion transport model for the tokamak transport code TRANSP

Fast ion transport models currently implemented in the tokamak transport code TRANSP (Hawryluk 1980 Physics of Plasmas Close to Thermonuclear Conditions (Brussels: CEC)) are not capturing important aspects of the physics associated with resonant transport caused by instabilities such as toroidal Alfvén eigenmodes (TAEs). This work describes the implementation of a fast ion transport model consistent with the basic mechanisms of resonant mode-particle interaction. The model is formulated in terms of a probability distribution function for the particle's steps in phase space, which is consistent with the Monte Carlo approach used in TRANSP. The proposed model is based on the analysis of the fast ion response to TAE modes through the ORBIT code (White and Chance 1984 Phys. Fluids 27 2455), but it can be generalized to higher frequency modes (e.g. compressional and global Alfvén eigenmodes) and to other numerical codes or theories.