LOWER HYBRID ION HEATING IN THE FT-2 TOKAMAK

The paper generalizes the results of plasma heating experiments in the FT-2 tokamak. It is shown that the generation of fast ions is associated not with the region of linear transformation, n(LH), but with the parametric decay region, n(d) congruent-to (0.3-0.5)n(LH). In the narrow zone n(d), strongly slowed down waves were observed (by a method relying on enhanced scattering of microwave radiation) at a frequency of about 0.7f0 (where f0 is the frequency of the heating radiation); these waves had a narrow spectrum with a width of a few megahertz. As the plasma density increases, the decay region is shifted towards the edge, but it remains 'attached', for all practical purposes, to one local density. This process helps to explain the central heating of the main ion component, the generation of fast ions at the edge, and the switching off of the interaction between the lower hybrid wave and the electrons, which stops current drive.