Numerical investigation of ECCD under the CFETR concept design parameters

Abstract

RF power in the electron cyclotron (EC) frequency range is planned to be injected to the plasmas of China Fusion Engineering Test Reactor (CFETR). Numerical investigation for electron cyclotron current drive (ECCD) is performed under the parameters of the latest/final version of the CFETR concept design (R = 7.2 m, a = 2.2 m, BT = 6.5 T). The TORAY-GA ray-tracing code is used to optimize frequency and launcher ports of EC waves. It is found that both 240 GHz and 250 GHz EC waves can meet the desired current drive demand in the target radial region (ρ ≤ 0.40). The 240 GHz EC wave is the optimum candidate. It can be launched either from equatorial launcher (EL) port, upper launcher (UL) port or top launcher (TL) port. EC waves with frequency equal to or larger than 250 GHz will be suffered strong parasitic second harmonic absorption if it is launched from EL port. Except for 250 GHz wave launched from EL port, ECCD efficiency increases with the increasing of EC frequency in the range of 190 ∼ 250 GHz. The maximum CD efficiency γCDn20RIec/Pin can reach 0.3 taking account for improvement of the CD efficiency about 20% enhanced by momentum conserving correction in the central radial region (ρ ≤ ∼ 0.20), either by 240 GHz EL-ECCD or 240/250 GHz UL-ECCD launching from (Ri, Zi) = (8.2, 4.5) m. Large toroidal incident angle α is needed for higher EC frequency to obtain an efficient CD efficiency. Necessary and sufficient conditions for successful and effective TL-ECCD are given. Compared to UL-ECCD, TL-ECCD does not significantly improve the efficiency of ECCD in the mid-radius region (ρ = 0.4 ∼ 0.6). Most cases of TL-ECCD significantly improve the efficiency of ECCD in the mid-radius region compared with EL-ECCD, but some cases does not. It is different from the results of previous theoretical simulations, in which TL-ECCD shows significantly improve ECCD efficiency than EL launcher. These findings are of significance for design of an efficient ECCD system under the CFETR design parameters.