Enhanced ICRF (ion cyclotron range of frequencies) mode conversion efficiency in plasmas with two mode conversion layers

Abstract

The ICRF (ion cyclotron range of frequencies) mode conversion regime efficiently provides local electron heating. The efficiency of mode conversion could be enhanced due to the interference between the reflected waves (Fuchs V et al 1995 Phys. Plasmas 2 1637–47). Plasmas of large-scale tokamaks can include multiple mode conversion layers which results in a complicated picture of mode conversion. The 1D theory of mode conversion in plasmas with two ion–ion hybrid resonance layers is presented. Using the phase-integral method the analytical expression for the conversion coefficient is derived within a cold plasma model. The possible enhancement of the mode conversion coefficient in such plasmas is shown. The developed theory is used to analyze the role of carbon ions in the (3He)H scenario of ICRF heating. As hot plasma effects may decrease the amount of power ultimately ending up on mode converted waves, a brief discussion of numerically obtained results but relying on a hot plasma model is included.