Particle confinement and the anomalous Doppler instability during combined inductive and lower-hybrid current drive

Increases in average density have been observed during lower-hybrid current-drive experiments (LHCD) on the Versator II tokamak Phys. Rev. Lett. 48, 152 (1982), and on other LHCD experiments where inductive-Ohmic and lower-hybrid current drive are combined. In the present experiment it is found that this density increase is the result of an improvement in global particle confinement time τp in comparison to purely Ohmic discharges with similar plasma parameters. Furthermore, it is found that the improved confinement deteriorates when the anomalous Doppler relaxation instability of the anisotropic high-energy electron tail becomes unstable during LHCD, and the loss rate of tail electrons increases. However, energetic electron losses alone are at least an order of magnitude too small to explain this deterioration in particle confinement.