An Investigation of LHCD Efficiency and Transformer Recharging in the EAST Tokamak

The efficiency of lower hybrid current drive (LHCD) for limiter and divertor configurations in the EAST tokamak is investigated using hot electrical conductivity theory and experimental formulas. The results indicate that the efficiency of current drive in a divertor geometry is slightly higher than that in a limiter one. To interpret the experimental results, the GENRAY code is applied to calculate the propagation and absorption of the lower hybrid wave (LHW) in different configurations. The numerical results show that the variation in the parallel refractive index (N//) between the two configurations is quite large. Transformer recharging experiments were also successfully conducted in EAST. By means of the Karney-Fisch method, the absorption index (α) and the upshift factor of refraction (β) for the LHW are obtained. In addition, the maximum recharging efficiency in EAST is about 4% in the divertor configuration, with a line-averaged electron density of ne_av = 0.7 × 10¹⁹m^–3.