A current drive by using the fast wave in frequency range higher than two timeslower hybrid resonance frequency on tokamaks

Abstract

Abstract.An efficient current drive scheme in central or off-axis region is required for the steady state operation of tokamak fusion reactors. The current drive by using the fast wave in frequency range higher than two times lower hybrid resonance (w>2wlh) could be such a scheme in high density, high temperature reactor-grade tokamak plasmas. First, it has relatively higher parallel electric field to the magnetic field favorable to the current generation, compared to fast waves in other frequency range. Second, it can deeply penetrate into high density plasmas compared to the slow wave in the same frequency range. Third, parasitic coupling to the slow wave can contribute also to the current drive avoiding parametric instability, thermal mode conversion and ion heating occured in the frequency range w<2wlh. In this study, the propagation boundary, accessibility, and the energy flow of the fast wave are given via cold dispersion relation and group velocity. The power absorption and current drive efficiency are discussed qualitatively through the hot dispersion relation and the polarization. Finally, those characteristics are confirmed with ray tracing code GENRAY for the KSTAR plasmas.

Current drive by using lower hybrid fast wave in VEST

“…RF current drive schemes that have been explored so far using LHCD or fast waves below the lower hybrid resonance frequency have exhibited weaknesses in terms of density limit or low efficiency. However, the fast wave in the same frequency range as LHCD, the so-called lower hybrid fast wave (LHFW), might provide a high efficiency current drive with relatively good penetration in high density plasma [28]. First, it has a relatively large perpendicular group velocity compared to the lower hybrid slow wave (LHSW) which is used for LHCD.…”