Plasma diagnostics using synchrotron radiation in tokamaks

Emission of synchrotron radiation for electron temperature diagnostics in dense and hot tokamak plasmas is discussed. This novel diagnostic scheme is motivated by the need to overcome several limitations of the familiar first and second harmonic method, caused by cutoff, refraction, and harmonic overlap. Emission at high harmonics is not restricted by density and temperature upper limits, and the method is then particularly appropriate for reactor relevant regimes. This method yields global information on the electron temperature profile, since the source of high harmonic emission is poorly localized in space. Synchrotron radiation is emitted by electrons over a wide spectrum of energies, ranging from thermal to superthermal values, and is therefore also useful to investigate deviations of the electron velocity distribution from the Maxwellian. In contrast, the source of the optically thick low harmonic radiation is highly localized in the ordinary space near the resonance points, which implies that the energy of the emitting electrons lies in the subthermal range. The basic theory of the method is presented and illustrated by numerical applications, for plasma parameters of relevance for International Thermonuclear Experimental Reactor (ITER) [ITER-JCT and Home Teams, Plasma Phys. Controlled Fusion 37, A19 (1995)]. (C) 1996 American Institute of Physics.