Plasma processes accompanying fast current decrease in the Tuman-3 tokamak

The authors report an investigation of the influence of radial current distribution on the Tuman-3 tokamak plasma parameters under the conditions of ohmic heating with a twofold current decrease for a period 4-6 times shorter than the magnetic field diffusion time-scale. A slight change in the parameters was observed in the current ramp-down phase. The characteristic relaxation time of the plasma parameters after the current drop was considerably larger than the energy confinement time and comparable with the field diffusion time-scale. The influence of the current ramp-down on the boundary plasma is also studied. Narrowing of the current density profile is accompanied by a 1.5-2-fold rise of the energy confinement time compared with its steady-state value.