Cold blanket studies in Jutphaas

An impermeable cold plasma-gas blanket surrounding a hot plasma core reduces the plasma-wall/limiter interaction. Moreover, accumulation of impurities in this blanket can be expected. Fueling from a blanket may be possible as shown by experimental results, though not fully explained by classical transport of neutrals. An anomalous inward flux of protons may be caused by drift-type instabilities. Experimental studies of a cold impermeable plasma have been done on the tokamak-like RINGBOOG device. Particle diffusion is in agreement with Pfirsch-Schluter theory and an extension thereof to a higher collisionality. A scaling law for the neutral pressure at the wall as a function of the plasma parameters in the cold blanket has been verified experimentally. The high neutral density, necessary to maintain n/sub e/ approximately equal to 1021 m-3, causes hydrogen line radiation to dominate the energy balance. Numerical studies on the transport of neutrals in a cold blanket, including detailed balancing of the various excited states and reabsorption of radiation, are in agreement with the profiles in our resistive arc-discharges. Extrapolations to a blanket around a thermonuclear core are possible