Transport characteristics of deuterium and hydrogen plasmas with ion internal transport barrier in lhd

A remarkable achievement of Ti0 = 10 keV with Zeff = 2 was obtained in Large Helical Device (LHD). In order to clarify transport characteristics in ion internal transport barrier (ion ITB) formation with isotope effect, a dataset of pure deuterium (nD/ne > 0.8) and pure hydrogen (nH/ne > 0.8) plasmas for high-ion-temperature (high-Ti) regime were analyzed, and two mechanisms of transport improvement were characterized. A significant reduction of ion heat transport in the core of both deuterium plasmas and hydrogen plasmas was observed, indicating ion ITB formation. The dependence of the heat transport on temperature ratio (Te/Ti) and normalized Ti-gradient (R/LTi = -(R/Ti)(dTi/dr)) was investigated in the core region, in which gyrokinetic simulations with GKV code predicts the destabilization of ITG modes. The Te/Ti dependence shows ITG-like property, while a significant deviation from the ITG-like property is found in the R/LTi dependence, indicating suppression of ITG mode in large R/LTi regime and resultant ion ITB formation. In the comparison between deuterium and hydrogen plasmas, the lower transport in the deuterium plasma are observed both ion and electron heat diffusivities, indicating significant isotope effect. It was found with the nonlinear turbulent transport simulation with GKV that the zonal flow enhancement contributes the ITG suppression in the deuterium plasma. These mechanisms contribute to production of highTi plasmas (Ti0~10 keV) with multiple-ion conditions. .