A detailed description of the time behaviour of a hydrogen discharge in the ST-Tokamak is based on measured radial electron temperature and density profiles at 12 different times, together with measurements of the Ohmic-heating current and voltage, the temporal, spatial, and spectral distributions of hydrogen light, the ion temperatures, and impurity concentrations. Early in the discharge the electron temperature profiles show evidence of a skin effect that develops on a time-scale of several milliseconds into a peaked profile of about 2.2 keV maximum. Thereafter the peak temperature stops growing and develops into a flat plateau, the width of which appears to be determined by the Kruskal-Shafranov limit. The average particle confinement time scales with , and reaches a maximum of 13-14 ms. The power balance is dominated by electron loss and re-cycling, rather than ion loss or radiation. The recycling process at the aperture limiter appears to involve sufficiently energetic neutral atoms to provide a fairly flat radial source function for particles, and hence to influence directly the development of the radial distribution of power input and energy balance.

This work supported by the U.S. Department of Erfsrgy Contract No. DE-AC02-76-CHO-3073. Reproduction, trans-? Fatten, publfcatlon, use and disposal, ]n Mhole or In z part, by or for the United States Government Is permitted.

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Bands of radiation in the 30–70 Å wavelength range, ascribed to unresolved resonance lines of various tungsten ions, have been observed in a variety of discharges in the PLT tokamak. The amount of tungsten present in the discharge appears to depend sensitively on the peripheral plasma temperature, and it may be dropped significantly by adding small amounts of neon or oxygen, and also by appropriate programming of hydrogen influx. In high-tungsten discharges the observed bands account for a large fraction (∼ 0.5 or more) of the power input near the centre of the plasma.