Conditions for efficient ion heating in the interaction of lower hybrid waves with plasma are experimentally determined. Experiments show that efficient lower hybrid heating stimulates a transition to the improved confinement mode. The formation of internal and external transport barriers is associated with strong central ion heating, which results in a change of the radial electric field E r and an increase in the shear of the poloidal plasma velocity. The improved confinement mode in the central region of the discharge is attained under the combined action of lower hybrid heating and an additional rapid increase in the plasma current. A new mechanism for the generation of an additional field E r is proposed to explain the formation of a transport barrier.

The mechanism for the switching off of the lower hybrid current drive in the FT-2 tokamak is studied. It is shown that the lower hybrid wave-driven current is switched off when a parametric instability, which causes lower hybrid waves to decay into slowed waves interacting with plasma ions, develops at the plasma periphery. The onset of a parametric instability is attributed to the fact that the electron temperature falls off in the course of discharge, thereby lowering the instability threshold.

The Thomson-scattering plasma diagnostic technique, which is based on a multipass-laser-probing and interresonator scheme, is used to study the dynamics of lower hybrid plasma heating in the FT-2 tokamak. Results of measurements of the plasma electron temperature and density are presented for two lower hybrid heating regimes with different plasma-energy condinement times.