Influence of the shape and magnitude of the discharge current pulse on plasma containment and heating in Tokamak-3

The author systematizes the results of measurements of plasma energy and energy replacement time as a function of the shape and magnitude of the discharge current pulse. It has already been established that the maximum transverse energies E ⊥ and energy replacement times τ E in Tokamak-3 are reached 2-3 ms after the peak of the discharge current I. I n this paper, the author shows how E ⊥ (t) and τ E (t) depend on the shape of the discharge current pulse and the duration of the discharge. An attempt is made to connect the observed relationships with the current density distribution. The internal (ℓ i ) and external (L ext = 2 ln(b/a)) self-inductance coefficients of the plasma column are measured and, on the basis of the results, an estimate is obtained of the shear averaged over the radius a. Hypotheses are advanced regarding the nature of the processes which determine the observed patterns of behaviour. One possible explanation is the presence of either dissipative helical instability (tearing mode) or overheat instability in the initial stage of the discharge and during the current rise.