COLLISIONAL STOCHASTIC RIPPLE DIFFUSION OF ALPHA-PARTICLES AND BEAM IONS ON TFTR

Predictions for ripple loss of fast ions from TFTR are investigated wi th a guiding centre code including both collisional and ripple effects . A synergistic enhancement of fast ion diffusion is found for toroida l field ripple with collisions. The total loss is calculated to be rou ghly twice the sum of ripple and collisional losses calculated separat ely. Discrepancies between measurements and calculations of plasma bet a at low current and large major radius are resolved when both effects are included for neutral beam ions. A 20 to 30% reduction in alpha pa rticle heating is predicted for q(a) = 6-14, R = 2.6 m DT plasmas on T FTR owing to first orbit and collisional stochastic ripple diffusion.