Three dimensional Fokker-Planck calculation of alpha particle distributions: a TFTR simulation

Abstract

The evolution of the alpha particle distribution function in a TFTR DT supershot is simulated using a 3-D Fokker-Planck code that allows for a time varying alpha particle source and for collisions with the evolving thermal plasma. It is important to include large orbit width effects as these lead to differing distribution functions in velocity space at the high and low field sides of the tokamak. The predicted time variations of the profiles of alpha particle density and of the heating of the background plasma agree well with Monte Carlo calculations by the TRANSP plasma simulation code, though the Fokker-Planck approach has the advantage that it gives smoother distribution functions