Evolution of the electron temperature profile of ohmically heated plasmas in TFTR

Abstract

Blackbody electron cyclotron emission was used to ascertain and study the evolution and behaviour of the electron temperature profile in ohmically heated plasmas in the Tokamak Fusion Test Reactor (TFTR). The emission was measured with absolutely calibrated millimetre wavelength radiometers. The electron temperature profile normalized to the central temperature and the minor radius was observed to broaden substantially with decreasing limiter safety factor q_a and to be insensitive to the plasma minor radius. Sawtooth activity was seen in the core of most TFTR discharges and appeared to be associated with a flattening of the electron temperature profile within the plasma core where q 1. Two types of sawtooth behaviour were identified in large TFTR plasmas (minor radius a 0.8 m): a 'normal' sawtooth with typically 35–40 ms period and a 'compound' sawtooth with 70–80 ms period. The compound sawtooth was characterized by what appeared to be a partial reconnection, which occurs away from the plasma core, in addition to a full reconnection. A multiple linear regression analysis of the central electron temperature T_e(0), with toroidal field B_T, major radius R, minor radius a, plasma current I_p and effective ion charge Z_eff, results in a scaling of the form , for which the major radial dependence was obtained by comparison with earlier PLT data.