Distinctive Features of Lower Hybrid Current Drive in Plasma of the FT-2 Tokamak

Experiments on the lower hybrid current drive (LHCD) were performed in plasma of the FT-2 tokamak at the microwave pulse duration of ΔtRF ≤ 20 ms covering the entire quasi-stationary stage of the plasma current Ipl(t) = 35 kA. At the relatively low plasma densities 〈ne〉 ~ (0.3–0.6) × 1019 m−3, the regimes were observed and analyzed corresponding to the full replacement of the plasma ohmic current by the non-inductive current generated using LHCD. During the LHCD in the denser plasmas, the formation of the Improved Core Confinement (ICC) regime was observed near the axis of the plasma column. New data was obtained on the threshold of transition to the ICC regime and its dependence on the input microwave power. The details of the transition to the ICC regime were analyzed for deuterium and hydrogen plasmas. It was ascertained that the highest LHCD efficiency was obtained in deuterium plasma at the densities of 〈ne〉 ~ (1.3–1.4) × 1019 m–3.