The article reports the results of experimental campaigns on plasma ohmic heating
performed during 1999-2000 on the spherical tokamak Globus-M. Later experimental results with
the tokamak fed by thyristor rectifiers are presented in detail. The toroidal magnetic field
and plasma pulse duration in these experiments were significantly increased. The method of stray
magnetic field compensation is described. The technology of vacuum vessel conditioning, including
boronization of the vessel performed at the end of the experiments, is briefly discussed.
Specific features of neutral gas column breakdown in
spherical tokamaks by applied inductive voltage are outlined. Also discussed is the influence
of ECR preionization on the breakdown conditions. Experimental data on plasma column formation
and current ramp-up in different regimes of operation with the magnetic flux of the central
solenoid limited to ∼100 mWb are presented. A significant reduction of the background
density after boronization (below 2 × 1018m-3) allows the density to be
completely controlled with external gas puffing and makes
the influence of the wall negligible. The magnetic flux consumption efficiency is discussed.
The results of magnetic equilibrium simulations are presented and compared with experiment.
Ramp-up of the plasma current of 0.25 MA for a time interval of about 0.03 s with about 0.02 s
flat-top at a toroidal field strength of 0.35 T allows the conclusion that the target design
parameters of Globus-M could be achieved in a double swing regime.
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