Direct conversion of a fast wave into ion Bernstein modes caused by density fluctuations

An analytical study is presented of the interaction between a fast Alfvén wave having a frequency larger than the ion-cyclotron frequency, and low frequency density fluctuations. When appropriate k, ω matching conditions are satisfied, the interaction results in a beat current that acts as an in-situ antenna, exciting ion Bernstein modes resonantly. Since such modes have relatively small damping for large parallel phase velocities, their excitation can significantly enhance the damping of fast waves having small k∥, particularly in those regions of the plasma where the temperature is relatively low. The interaction with coherent, as well as with broad band density fluctuations is investigated, and the role of plasma nonuniformities is examined. Specific features of relevance to ion-cyclotron range of frequency heating of tokamak plasmas are considered.