Ion cyclotron emission from fusion products and beam ions in the Tokamak Fusion Test Reactor

Abstract

Ion cyclotron emission (ICE) observed during deuterium and deuterium-tritium experiments in TFTR can be driven by both fusion products and injected beam ions. The emission driven by fusion products is a result of the excitation of the fast magnetoacoustic wave through toroidicity affected cyclotron resonance, the magnetoacoustic cyclotron instability. For beam driven ICE, the excitation mechanism, outlined by R.O. Dendy et al. (Phys. Plasmas 1 (1994) 3407) for the cylindrical case, is generalized by including the curvature and ∇B drift in the local resonance condition. The phase velocity of the destabilized, predominantly electrostatic, wave is typically an order of magnitude smaller than the Alfvén velocity. For both fusion and beam driven ICE, it is found that the instability growth rate is greatly increased as compared with the cylindrical case and reaches its maximum for nearly perpendicular propagation. The results of the numerical and analytical stability analysis are consistent with the experimental observations and provide an explanation for the simultaneous excitation of sequential multiple cyclotron harmonics of the fast ions, the sublinear correlation of the growth rate with the fast ion density and the stabilizing effect of the increasing fast ion velocity spread.