On electron Bernstein waves in spherical tori

Abstract

The high-β operating regime of spherical tori (ST), such as in the National Spherical Torus Experiment (NSTX) and the Mega Amp Spherical Tokamak (MAST), makes them attractive fusion devices, For access to such high-β regimes it is necessary to heat and to drive currents in ST plasmas. In the electron cyclotron range of frequencies, such plasmas are overdense to conventional electron cyclotron waves. However, in this frequency range. electron Bernstein waves (EBWs) offer an attractive alternative as they have no density cutoffs. EBWs can be excited in a ST plasma by mode conversion of the extraordinary or the ordinary mode at the upper hybrid resonance. The applications of EBWs in STs range from plasma start-up and heating of the plasma to modifying and controlling its current profile. The controlling of the current profile could provide better confinement as well as help suppress neoclassical tearing modes. The mode conversion to EBWs has been detailed in a, variety of papers. This paper deals with two particular topics that further quantify the role of EBWs in spherical tori. The first topic is on the relevance of relativistic effects in describing the propagation and damping of EBWs. The second topic is on plasma current generation by EBWs.