On lower hybrid current drive in high magnetic field fusion reactor level tokamaks

Abstract This paper mainly studies the effects of high magnetic field and quasi-linear effects on lower hybrid current drive (LHCD) in fusion reactor-level tokamak. The critical magnetic field B c value for LHCD is 9.64 T. Below this value, high magnetic field effect do not need to be considered for LHCD on fusion reactor-level tokamaks such as ITER and China Fusion Engineering Test Reactor (CFETR). On the CFETR tokamak with toroidal magnetic field up to 6.5 T, a comparative study of low-field and high-field side (HFS) launch of LHCD was conducted using coupled ray-tracing equation and the Fokker–Planck equation. The spectrum N ||0 of LHCD with three typical frequencies, which can effectively drive currents, is −1.7 to −1.6. The optimal poloidal launching angles are θ = 145 ∼ 165° on HFS, and θ = −60° to −30° or 30°–50° on low-field side (LFS). At injection power of 1 MW, the current drive efficiency is 30–60 kA MW −1 . The current profile is relatively localized, with its peak at a radial position where ρ > ∼0.50. Injection from HFS or LFS has a significant impact on LHCD. For high-power injection, the influence of quasi-linear effect needs to be considered. When injecting from HFS, the LHCD efficiency increases significantly with the increase of injection power, reaching ∼60 kA MW −1 at 30–40 MW. For injection from LFS, LHCD efficiency increases gradually with the increase of injection power, with a maximum not exceeding 50 kA MW −1 even at 100 MW. HFS injection should be prioritized for LHCD on fusion reactor level tokamaks, and the output power level of a single klystron needs to be higher for higher LHCD efficiency.