At the first stage of the electron cyclotron emission imaging(ECEI)diagnosticproject on HT-7,a 16-channel vertical-resolved ECEI diagnostic has been developed and installedon HT-7 tokamak to measure electron cyclotron emission with a temporal resolution of 0.5 μsec.The system works at a fixed frequency of 97.5 GHz.The sample volumes of the system arealigned vertically with a vertical channel spacing of 11 mm,and can be shifted across the plasmacross-section by varying the toroidal magnetic field.The high spatial resolution of the system isachieved by utilizing a low-cost linear mixer/receiver array and an optical imaging system.Thefocus 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 togetherwith 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 betweenthe distribution of light intensity from the images and the plasma pressure indicates a nearly linearrelationship.The discharge images taken by the camera and the plasma parameters measured bythe probes also indicate the existence of low frequency turbulent events with a time scale less thana few mini-seconds.
Based on the single biasing electrode experiments to optimize the confinement ofplasma in the device of KT-5C tokamak,dual-biasing electrodes were inserted into the KT5Cplasma for the first time to explore the enhancing effects of biasing and the mechanisms of thebiasing.By means of applying different combinations of biasing voltages onto the dual electrodes,the changes of E_r,which are the key factor for boosting up the E_r×B flow shear,were observed.The time evolution showed that the inner electrode played a major role in dual-biasing,whichdrew larger current than the outer one.The outer electrode produced little influence.It turnedout that the dual-biasing electrodes were as effective as a single one in improving the plasmaconfinement,for the mechanism of biasing was essentially an edge effect.
A detailed study of photon temperatures(T_(ph))of hard X-ray emission in lowerhybrid current drive(LHCD)plasmas is presented.The photon temperature increases with theincrease in plasma current and decreases with the increase in plasma density.In lower hybridpower 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 reasonableexplanation for the experimental observation.Both experimental and numerical results reveal thatthe photon temperature depends mainly on global effects of the fast electron population,synergybetween the fast electron and the loop voltage and the Coulomb slowing down.
