Systematic numerical analysis of ECCD exploring injection conditions with high CD efficiency and current profile controllability in JA DEMO

Systematic Electron Cyclotron Current Drive (ECCD) simulations were performed in JA DEMO plasma (T_e=34keV and n_e=1.0×10²⁰m⁻³ at the center) for various injection conditions of EC waves, including wave frequency, injection direction and injection position. Different injection positions surrounding the plasma are comprehensively scanned, including midplane and upper launch on the high/low field side (HFS/LFS) of the plasma. Numerical results indicated that higher harmonic absorptions deteriorate the ECCD efficiency regardless of injection positions. High ECCD efficiencies for each injection position were obtained when avoiding higher harmonic absorptions. The maximum ECCD efficiency of 46 kA/MW was obtained for upper LFS launch with an optimal frequency and direction. An important finding from the systematic analysis is that such an efficient ECCD exceeding 40 kA/MW is expected for a wide range of injection positions of upper and midplane LFS launch. This result is favorable for fusion reactor design, indicating flexibility in EC port arrangement for efficient ECCD. Current profile controllability in JA DEMO was also discussed in two injection cases: the upper LFS launch and the conventional midplane LFS launch. Driven current density profiles with various injection angles from each injection position successfully cover the regions from the center to mid-radius of the plasma, where external current drive is required to achieve a weak reversed shear. Furthermore, sufficient ECCD efficiencies of 35–46 kA/MW at the upper LFS launch and of 35–43 kA/MW at the midplane LFS launch are obtained.