Studying the limiting β in experiments with current ramp-down in the Tuman-3M tokamak

The possibility of obtaining high values of the β parameters, characterizing the efficiency of the tokamak magnetic fields application for plasma confinement is studied. The possibility of obtaining high values in the ohmic H-mode in the plasma with a circular cross section in the boronized chamber is demonstrated. The current ramp-down at the quasi-stationary stage of the ohmic H-mode was carried out with the purpose of further increase in the β values. Deterioration of plasma confinement after the current ramp-down due to the H-mode switch-off, caused by decrease in the heating rate below the threshold one, is noted