Experiments of full non-inductive current drive on HT-7

Full text: Some experimental results of steady-state operation and full non-inductive current drive have been obtained on HT-7. Three types of experiment are used to study long pulse discharge, quasi-steady-state operation and full non-inductive current drive. The first one is OH plasma current together with current droved by LHW for long pulse discharge. The second is to keep the plasma current constant and the loop voltage come close to zero by means of adjusting of the LHW power for quasi-steady-state operation or quasi non-inductive current drive, the OH heating field still has a little feedback control effect when the current droved by LHW is instable. The third is the current droved by LHW larger than the plasma current kept by feedback control system of OH heating field for full non-inductive current drive. In the third type experiment there are two phases. Phase I: constant plasma current and negative loop voltage, the OH heating coil current is reducing; Phase II: the loop voltage and the current of OH heating coil are zero, so the plasma current is not controlled by OH heating field and which is larger than the plasma current in phase I set in the feedback control system of OH heating field. The phase II is known as full non-inductive current drive plasma and can be sustained tens of seconds. The experiments show that the plasma current in the full non-inductive drive case is instable due to no adjusting effect of OH heating field, when the waveguide tube discharge lead to the LHW power injecting tokamak plasma decrease. This instability of plasma current will increase the interaction of plasma with limiter and first surface and bring impurity. All discharges of full non-inductive current drive are terminated because of impurity spurting. The off-axis deposition of LHW power will drive fast electrons and generate a halo plasma current profile. In full non-inductive current drive plasma, the impurity profile is different from that in the plasma of type I and type II. The new experiments of the interaction of LHCD and IBW (unbalance momentum injecting) or ICRH (balance momentum injecting) in the full non-inductive current drive plasma phase will show in the meeting. (author)