Plasma heating in stellarator/torsatrons and tokamaks by ion cyclotron waves

High power ion cyclotron heating experiments are currently planned for the Heliotron-E device in Kyoto and for the ATF torsatron at Oak Ridge. Reliable solutions for the rf fields and wave absorption are needed to optimize antenna designs and heating scenarios as well as to determine heating profiles and tail formation for interpretation of confinement experiments. The complicated field structure in torsatrons makes a number of approximations commonly used in studying ICRH in tokamaks of questionable validity. For example in tokamaks the cyclotron resonance and ion-ion hybrid resonance layers are to a good approximation vertical sections and small changes of frequency or B field result in small shifts in their locations. However, in a torsatron a saddle point in B occurs near the magnetic axis so that resonance and cutoff layers occur on two sheets oriented either horizontally or vertically. Small changes of frequency therefore can cause radical changes in the resonance cut-off topology. We have investigated this phenomenon by performing 2-D calculations of the wave fields and heating profiles in a cold plasma model. We have also begun to investigate the effects of finite temperature in this geometry by calculating cyclotron damping/mode conversion in a slab having non-monotonic B profile. Resonances and cutoffs therefore exist in pairs and by adjusting the wave frequency can be made to merge together and annihilate in pairs