Application of intermediate frequency range fast wave to JIPP T-IIU and HT-2 plasmas

Fast waves well above the fundamental ion cyclotron frequency were applied to JIPP T-IIU and HT-2 tokamak plasmas to study current drive, electron heating and third harmonics ion cyclotron heating. In HT-2, up to 10 kA of plasma current was driven by a 100 MHz fast wave in the density range of (0.3-3) × 10¹⁸ m^-3, which corresponds to one to ten times above the lower hybrid current drive density limit. In JIPP T-IIU, an efficient electron temperature increase was observed on application of 130 MHz fast waves in the density range of (2-3) × 10¹⁹ m^-3, two orders of magnitude higher than the lower hybrid density limit. In a further, still higher density range of above 3 × 10¹⁹ m^-3, the third harmonics cyclotron heating of the additionally heated target plasma yields a heating efficiency that is as high as that of fundamental harmonic heating.