Radiation losses in PLT during neutral-beam and ICRF heating experiments

Radiation and charge-exchange losses in the PLT tokamak are compared for discharges with Ohmic heating only (OH), and with additional heating by neutral beams (NB) or RF in the ion cyclotron frequency range (ICRF). Spectroscopic, bolometric and soft-X-ray diagnostics were used. The effects of discharge cleaning, vacuum wall gettering, and rate of gas inlet on radiation losses from OH plasmas and the correlation between radiation from plasma core and edge temperatures are discussed. – For discharges with neutral-beam injection the radiation dependence on type of injection (e.g. co-injection versus counter- and co- plus counter-injection) was investigated. Radial profiles of radiation loss were compared with profiles of power deposition. Although total radiation was in the range of 30–60% of total input power into relatively clean plasma, nevertheless only 10–20% of the total central input power to ions and electrons was radiated from the plasma core. The radiated power was increased mainly by increased influx of impurities, however, a fraction of this radiation was due to the change in charge-state distribution associated with charge-exchange recombination. – During ICRF heating radiation losses were higher than or comparable to those experienced during co- plus counter-injection at similar power levels. At these low power levels of ICRF heating the total radiated power was ∼ 80% of auxiliary-heating power. Radiation losses changed somewhat less rapidly than linearly with ICRF power input up to the maximum available at the time of these measurements (0.65 MW).