Probe Measurements in Experiments with Additional Working Gas Puffing into Frontal Region of Lower Hybrid Antenna of the FT-2 Tokamak

In the experiments at the FT-2 tokamak, it was ascertained that the additional puffing of working gas into the region immediately adjacent to the launching antenna suppresses the development of parametric instability, which is considered to be the main obstacle to efficient penetration of the lower hybrid wave into the inner regions of the tokamak plasma. Using probe measurements, radial profiles of electron density and temperature in the scrape-off layer (SOL) were obtained, as well as their changes during the lower hybrid pulse were traced. It was shown that local gas puffing causes toroidal inhomogeneity of the edge plasma parameters. By means of performing direct measurements, the effect of plasma “forcing-out” from the frontal region of the radiating antenna under the action of ponderomotive force in the field of the introduced wave was detected. The effect of ponderomotive force on the edge plasma parameters and, as a consequence, on the antenna–plasma coupling efficiency should be taken into account in large-sized facilities at high powers.