Modulational excitation of drift waves by a beam of lower-hybrid waves

The results of theoretical and experimental studies on excitation of drift waves in a tokamak plasma under the conditions of experiments on lower-hybrid (LH) plasma heating and current drive are presented. It is shown that for sufficiently strong LH pump levels the main effect resulting in the drift wave excitation is the LH wave modulational instability. It is found that the modulational excitation of long-wavelength drift oscillations (with the wavelengths exceeding the length of the LH pump wave) is described by a dispersion equation similar to the equation for the usual hydrodynamical beam instability. This allows us to treat the excitation of the long-wavelength drift waves as modulational excitation by a beam of the LH waves. The theoretical results obtained are compared with the data of the tokamak Tore Supra [Proceedings of the 12th International Conference on Plasma Physics and Controlled Nuclear Fusion, Nice, 1988 (International Atomic Energy Agency, Vienna, 1989), p. 9] experiment. Qualitative accordance of the theoretical and experimental results is demonstrated. copyright 1996 American Institute of Physics