Effects of tungsten radiation on the behaviour of PLT tokamak discharges

Bands of radiation in the 30-70A 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 (approximately 0.5 or more) of the power input near the centre of the plasma. (author)