Recent results of ultra low q experiments in TORIUT-6 AND REPUTE-1

Abstract

In REPUTE-1, the radiation barrier has been overcome and ion and electron temperatures of ⪅ 0.6 keV (Ti) and ⪅0.3 keV (Te) have been achieved at an electron density of (0.2–0.7) × 1020 m−3 and toroidal beta values of 12-18%. A resistivity anomaly due to m = l kink activity has been observed which may be connected with the peaked temperature profile and the rather broad current density profile. The plasma resistance is lower than that of reversed field pinch discharges in REPUTE-1 and decreases with increasing plasma current. In TORIUT-6, the effects of current ramp-up and carbonization of the first wall have been studied. A hollow current density profile, typical of ultra low q equilibria, is preserved which may be due to the skin current effect. The difference between current ramp-up discharges and standard discharges is the extended duration of the quiescent phase and the preservation of the position of the pitch minimum away from the axis in the ramp-up discharges. After carbonization, the duration of the quiescent phase increases and the plasma resistivity is reduced by 50%.