Mode conversion and absorption of fast waves at high ion cyclotron harmonics in inhomogeneous magnetic fields

Abstract

The propagation and absorption of high harmonic fast waves is of interest for non-inductive current drives in fusion experiments. The fast wave can be coupled with the ion Bernstein wave that propagates in the high magnetic field side of an ion cyclotron harmonic resonance layer. This coupling and the absorption are analyzed using the hot plasma dispersion relation and a wave equation that was converted from an approximate dispersion relation for the case where λi=k⊥2ρi2/2≳1 (where k⊥ is the perpendicular wave number and ρi is the ion Larmor radius). It is found that both reflection and conversion may occur near the harmonic resonance layer but that they decrease rapidly, giving rise to a sharp increase in the absorption as the parallel wave number increases.

Modeling of the control of the driven current profile in ICRF MCCD on EAST plasma

“…27,28 The location is determined by factors such as the RF wave frequency and species mix. 18 The locations of the IIHR layer and the fundamental resonance layer of H in the RF frequency range from 32 to 40 MHz are shown in Fig. 2, with a fixed minority ion (H) concentration of 24%.…”

“…16,17 In multi-species plasma, however, an FW may convert to an ion-cyclotron wave (ICW) and a short-wavelength ion-Bernstein wave (IBW) near the ion-ion hybrid resonance (IIHR) layer. [18][19][20] The underlying mechanisms of the mode conversion (MC) are generally described by the cold plasma dispersion relation 18…”