THERMAL AND NONTHERMAL ELECTRON-CYCLOTRON EMISSION BY HIGH-TEMPERATURE TOKAMAK PLASMAS

An analysis of the electron cyclotron emission (ECE) spectra emitted b y a high-temperature tokamak plasma in the frequency range of the seco nd and third harmonic of the electron cyclotron frequency is made, bot h in purely Maxwellian and in non-Maxwellian cases (i.e., in the prese nce of a current-carrying superthermal tail). The work is motivated ma inly by the experimental observations made in the supershot plasmas of the Tokamak Fusion Test Reactor (TFTR), where a systematic disagreeme nt is found between the T-e measurements by second-harmonic ECE and Th omson scattering. We show that, by properly taking into account the ov erlap of superthermals-emitted third harmonic with second-harmonic bul k emission, the radiation temperature observed about the central frequ ency of the second harmonic may be enhanced up to 30%-40% compared to the corresponding thermal value. Moreover we show that, for parameters relevant to the International Thermonuclear Experimental Reactor (ITE R) with T-e(0) > 7 keV, the overlap between the second and the downshi fted third harmonic seriously affects the central plasma region, so th at the X-mode emission at the second harmonic becomes unsuitable for l ocal T-e measurements. (C) 1997 American Institute of Physics.