Current drive with combined electron cyclotron wave and high harmonic fast wave in tokamak plasmas

The current driven by combined electron cyclotron wave (ECW) and high harmonic fast wave is investigated using the GENRAY/CQL3D package. It is shown that no significant synergetic current is found in a range of cases with a combined ECW and fast wave (FW). This result is consistent with a previous study [Harvey et al., in Proceedings of IAEA TCM on Fast Wave Current Drive in Reactor Scale Tokamaks (Synergy and Complimentarily with LHCD and ECRH), Arles, France, IAEA, Vienna, 1991]. However, a positive synergy effect does appear with the FW in the lower hybrid range of frequencies. This positive synergy effect can be explained using a picture of the electron distribution function induced by the ECW and a very high harmonic fast wave (helicon). The dependence of the synergy effect on the radial position of the power deposition, the wave power, the wave frequency, and the parallel refractive index is also analyzed, both numerically and physically. Published by AIP Publishing.National Natural Science Foundation of China [11375085, 11405082, 11575055, 11375053]; NMCFSPC [2014GB107004, 2013GB107001, 2013GB104004, 2013GB111000, 2015GB110002]SCI(E)ARTICLEgongxueyu@126.com122