Radial transport of medium- and high-Z ions during co- and counter-neutral-beam heating in the PLT tokamak is studied, using molybdenum and scandium ions as tracer elements. The time evolution of the radial profiles of several ionization stages of both elements, injected by laser blowoff during the neutral-beam heating, is measured under three significantly different beam-plasma combinations. No noticeable differences in the radial profiles attributable to the beam direction are observed. However, a given injected amount resulted in considerably larger interior concentrations of the tracer element in the counter-beam heating cases, suggesting larger penetration of the plasma periphery. Computer simulation with the MIST code suggests a net inward drift of the order 103 cm·s−1 superposed to a diffusion coefficient of the order 104 cm2·s−1 for both scandium and molybdenum ions. Injection of larger amounts of the tracer element, sufficient to cause measurable central electron temperature changes, resulted in dramatic changes in ion-state distributions, making some appear peaked in the centre while others disappeared. This effect could be produced with both co- and counter-beam heating, but with lesser amounts in the latter case. It is interpreted as rearrangement of the ionization balance, rather than any preferential accumulation of the injected element.

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.

Strong minority proton heating is produced in PLT through ion cyclotron resonance damping of fast waves at moderate rf power levels. In addition to demon strating good proton confinement, the proton ene-.rgy distribution is consistent with Fokker-Planck theory which provides the prescription for extrapolation of this heating regime to higher rf power levels.