At the first stage of the electron cyclotron emission imaging （ECEI） diagnostic project on HT-7, a 16-channel vertical-resolved ECEI diagnostic has been developed and installed on HT-7 tokamak to measure electron cyclotron emission with a temporal resolution of 0.5 usec. The system works at a fixed frequency of 97.5 GHz. The sample volumes of the system are aligned vertically with a vertical channel spacing of 11 mm, and can be shifted across the plasma cross-section by varying the toroidal magnetic field. The high spatial resolution of the system is achieved by utilizing a low-cost linear mixer/receiver array and an optical imaging system. The focus location may be shifted horizontally when translating one of the optical imaging elements. The details of the system design and laboratory testing of the ECEI optics are presented together with the preliminary experimental results.
Drift instability in plasma generated by electron cyclotron resonance （ECR） in KT- 5D device was investigated by using a fast camera and Langmuir probes. The similarity between the distribution of light intensity from the images and the plasma pressure indicates a nearly linear relationship. The discharge images taken by the camera and the plasma parameters measured by the probes also indicate the existence of low frequency turbulent events with a time scale less than a few mini-seconds.
Based on the single biasing electrode experiments to optimize the confinement of plasma in the device of KT-5C tokamak, dual-biasing electrodes were inserted into the KT5C plasma for the first time to explore the enhancing effects of biasing and the mechanisms of the biasing. By means of applying different combinations of biasing voltages onto the dual electrodes, the changes of Er, which are the key factor for boosting up the Er × B flow shear, were observed. The time evolution showed that the inner electrode played a major role in dual-biasing, which drew larger current than the outer one. The outer electrode produced little influence. It turned out that the dual-biasing electrodes were as effective as a single one in improving the plasma confinement, for the mechanism of biasing was essentially an edge effect.
A detailed study of photon temperatures （Tph） of hard X-ray emission in lower hybrid current drive （LHCD） plasmas is presented. The photon temperature increases with the increase in plasma current and decreases with the increase in plasma density. In lower hybrid power and phase scanning experiments; there is no appreciable change in the photon temperature. The numerical results based on ray-tracing calculation and Fokker-Planck solver gives reasonable explanation for the experimental observation. Both experimental and numerical results reveal that the photon temperature depends mainly on global effects of the fast electron population, synergy between the fast electron and the loop voltage and the Coulomb slowing down.
