Improvement of Ion Confinement in Core Electron-Root Confinement (CERC) Plasmas in Large Helical Device

Abstract

An increase in ion temperature has been observed with superposition of centrally focused electron cyclotron resonance heating (ECRH) to plasmas heated by high-energy neutral beam injection (NBI) in Large Helical Device. The ion-temperature (T_i) rise is accompanied by the formation of electron internal transport barrier (ITB). A transport analysis shows that ion transport as well as electron transport is improved with the reduction of anomalous transport. A neoclassical ambipolar flux calculation shows a positive radial-electric field (E_r) in the region of the T_i rise, and E_r should suppress the enhancement of ripple transport due to the T_i-rise. These analyses indicate the ion transport improvement in the core electron-root confinement plasmas. Toroidal rotation is driven in the co-direction by applying ECRH, and the toroidal rotation velocity is increased with the T_i rise. A correlation between the T_i rise and toroidal rotation is suggested.