Impact of hot plasma effects on electron cyclotron current drive in tokamak plasmas

Focusing on the impact of hot plasma effects on electron cyclotron current drive (ECCD), this paper presents the numerical results of top launch ECCD (TL-ECCD) and outside midplane or equatorial-plane launch ECCD (EL-ECCD) in the HL-3-like tokamak plasmas. For EL-ECCD, there is little difference in the calculated results under the cold and hot plasma propagation models, and the results are not affected by the dominant current drive mechanism of EC waves. In the cases of TL-ECCD, the large initial parallel refraction makes the influence of hot plasma effects on ECCD become significant. In the range of toroidal magnetic fields B _T discussed in this paper, the difference between the calculated results under the two propagation models rapidly decreases as the value of B _T decreases, and the difference between the two is already very small in the range of 1.8 T ⩽ B _T ⩽ 2.0 T. Therefore, the influence of hot plasma effects can also be neglected for TL-ECCD, and the cold plasma propagation model can be directly adopted. For the HL-3-like tokamak equipped with a dual-frequency EC wave system at 140 GHz and 105 GHz, if the addition of a TL-ECCD is considered in the existing outside midplane and upper launch manners, through appropriate combination of 140 GHz TL-ECCD and dual-frequency outside EL-ECCD, the ECCD can be used in a larger B _T window (1.8 T ⩽ B _T ⩽ 2.25 T) and a wider radial range (0.1 ⩽ ρ ⩽ 0.8–0.9) to generate current efficiently. The normalized current drive efficiency of the TL-ECCD is nonlinear with the injected EC power, it reaches the maximum at the injected power of 6–8 MW. This is of significance for the stable operation of HL-3-like tokamak with high plasma current above 1 MA.