Anomalous Ion Heating in Lower Hybrid Wave Sustained Plasmas on the TST-2 Spherical Tokamak Device

Power flow is important to understand the lower hybrid wave (LHW) sustained plasmas in the TST-2 spherical tokamak device. During LHW power modulation experiments responses of ion temperature were found. The ion temperature increased at the edge region during ON phases of LHW power, while the ion temperature was kept constant at the central region. A 0-dimensional power balance at a steady state was investigated, and it was found that the collisional ion heating by bulk electrons is about two orders of magnitude smaller than the charge exchange loss and the neoclassical transport loss. The results indicate anomalous ion heating by additional unidentified heating mechanism. The estimated additional heating power itself is much smaller than the LHW power, but there are several ambiguities in the estimation, and a further study is necessary. (c) 2023 The Japan Society of Plasma Science and Nuclear Fusion Research