Sawtooth mixing effects on ICRF power deposition in tokamaks

A series of experiments was performed on TFTR in which the toroidal field strength, and hence the location of the ICRF resonance layer, was varied. Electrons were heated primarily via collisions with the fast tail ions produced by the rf heating. The net power deposited to electrons on axis can be directly inferred from ECE measurements of the rate of rise of the central electron stored energy immediately following a sawtooth crash. Comparisons between these meaurements and calculations of the net central electron heating obtained using the SNARF tokamak simulation code as well as PPL's ray tracing/Fokker-Planck code implied that the predicted power deposition was too localized. Results obtained by incorporating a sawtooth mixing model for the fast ions into the deposition codes are in good agreement with the experimental measurements