MHD instability and limiting currents in ohmic plasma heating in the ''Uragan-2'' stellarator

The results of the experimental investigation of helical instability of current-carrying plasma in the three-way ''Uragan-2'' stellarator are presented. Instability has been investigated by measurements of magnetic field disturbances outside the plasma filament. The diagram of limiting currents depending on the angle of torsion of force lines in the initial structure of the magnetic field and the direction of the ohmic heating current is constructed. In the field of a ''direct'' current direction the magnetic field of which increases the resulting angle, of torsion the complex spatial instability structure is preserved over the total range of the discharge current. Regimes with ''reverse'' current direction are more unstable. Plasma losses velocities turn to be higher as compared with ''direct'' current regimes already at relatively small value of the discharge current. The region of the angle of torsion 0.7-1 of current ''direct'' orientation turns to be optimum for ohmic plasma heating. For discharge currents being not near to the limiting one the pseudoclassical law of electron energy containment is realized