Heating experiments in the ion cyclotron range of frequencies on EBT-S

Abstract

Heating experiments in EBT-S have been conducted in steady-state plasmas at continuous wave power levels up to 20 kW in the ion cyclotron range of frequencies (15–30 MHz). Power coupling efficiencies and wave propagation measurements have been obtained at reduced power levels over the frequency range 15–50 MHz. Wave dispersion properties are in qualitative agreement with simplified theory. Substantial ion heating is obtained in deuterium plasmas above 25 MHz, the point at which wave propagation begins. At this frequency, only the 3rd-10th ion cyclotron harmonics of deuterium are present in the core plasma. Ion heating under these circumstances is considerably greater than theoretically predicted for EBT-S parameters. A residual proton component is also heated. However, collisional energy transfer from the protons to the deuterons is too small to account for the deuteron heating. The stored energy of the relativistic electron annuli increases substantially with the application of wave power. Near the antenna, the stored energy more than doubles at a power level of 15 kW. The mechanism producing this dramatic effect is not well understood at present. A small reduction in the ambipolar electric field is also observed during wave heating.