Investigation of anomalous Doppler instability in ohmic and LHCD discharges in the HT-7 tokamak

We present the results of our experimental studies on a discharge in the Hefei Tokamak-7 (HT-7) device with a specific instability whose emergence coincides with a sudden jump in electron cyclotron emission (ECE) that shows the transverse energy of the plasma. It is shown that, in this slide-away discharge regime, the current is carried by a relatively small group of runaway electrons and that the period of high-frequency small-amplitude oscillations varies from 1 to 2 ms, which depends on the value of the loop voltage in ohmic discharges. In low hybrid current drive (LHCD) plasmas, the period of high-frequency small-amplitude oscillations in the ECE signal during the whole period of anomalous Doppler instability (ADI) is about 2 ms. It is also found that the ADI in ohmic and LHCD discharges can restrain the magnetic oscillations.