The evolution of plasma parameters as governed by edge phenomena during Ion Bernstein Wave (IBW) heating

IBW heating has been investigated in the PLT tokamak and compared to conventional fast wave ICRF heating. While central temperature rises of comparable magnitude are observed for both methods, several differences in plasma behavior, particularly in the plasma periphery, are observed. An increase in plasma density is observed in both ICRF and IBW heating. This increase, however, is larger for IBW heating at comparable power and is accompanied by a decrease in recycling as opposed to the increase observed during fast wave heating. This phenomenon is interpreted as an increased particle confinement time. A decrease in carbon VI line intensities is observed only during IBW heating. This decrease can be partially attributed to the reduction of C⁵⁺ ion concentration due to direct acceleration by the RF waves and partially to neutral density reduction. The increase in heavy metal impurities during fast wave heating is consistent with the increased sputtering expected from the enhanced recycling, however, this explanation cannot be used for the increase during IBW heating since recycling is reduced. Instead, impurity accumulation due to the enhanced particle confinement may be responsible.