[en] The soft x-ray pulse-height-analysis technique is a conventional tool to measure electron temperature on tokamaks. The soft x-ray spectra distortion due to the energy resolution of the detector will affect the temperature and impurity concentration determination. To evaluate these effects, distorted spectra as functions of energy resolution are derived by numerical modelling. The results show that the low-energy resolution detector can fit for the large-sized tokamak soft x-ray spectra

[en] Experimental properties of monster sawtooth activities in ohmic HT-7 plasma are presented. The monster sawtooth activities belong to global fluctuations and are characterized with a series of large core collapses on SXR intensity traces with a long period, a large amplitude fluctuation and a large inversion radius, However, they emerge without apparent deterioration of plasma confinement and without major plasma disruption. During the events, long partial sawtooth collapses and abundant MHD phenomena are also observed

[en] A Stokes vector and Mueller matrix formalism are adopted to model the optical train of the motional stark effect (MSE) system. The method to find all four elements of Stokes vectors and optical parameters of MSE system is presented in this article. A new fitting model for MSE calibration is discussed. A method for the measurement of offset angle of MSE is also presented. The nonideal effects of the background unpolarized and polarized light of non-Stark effect are analyzed

[en] An avalanche photodiode (APD) has been used as soft X-ray energy pulse-height analysis system for the measurement of the electron temperature on the HT-7 tokamak. The experimental results obtained with the APD with its inferior energy resolution show a little difference compared to the conventional high energy-resolution Si (Li) detector. Both numerical analysis and experimental results prove that the APD is good enough for application of the electron temperature measurement in tokamaks

[en] A new high-resolution tangential imaging X-ray crystal spectrometer (TXCS) is described for implementation on the Experimental Advanced Superconducting Tokamak (EAST) to provide spatially and temporally resolved data on the toroidal plasma rotation velocity and on the ion and the electron temperature. These data are derived from observations of the satellite spectra of helium like argon (Ar XVII). The TXCS will provide data for all experimental conditions, which include ohmically heated discharges as well as plasmas with radio-frequency (RF) waves and neutral-beam heating. The latest experimental results show that lower hybrid waves (LHW) induce a co-current change in a toroidal rotation of up to 4/s in the L-mode plasma core region. A modification of the toroidal rotation develops on the extended plasma region and a long time scale (≥1 s). The experimental setup and the initial experimental results are presented.

[en] The behavior of fast electron were studied in several kinds LHCD experiments. In long pulse LHCD discharge, the global improved confinement and temperature transition were observed after the broadening of HX-ray emission profile, which means a significant current profile modification. In high power LHCD experiments, the local HX-ray emission shows the formation of ITB correlated with the deposition profile of LH wave. The profiles of HX-ray emission broaden in accord with the increase of plasma current in ramp-up experiments. In synergistic experiments, the HX-ray spectra show the IBW interacts with electron strongly and accelerates the fast electrons produced by LHCD. In counter-LHCD experiments, the temperature of HX-ray (THX) and the decrease of loop voltage, which are lower than those in normal LHCD experiments, show the effects of counter current drive. The SX-ray emission profile becomes more peaked in counter-LHCD, which suggests the improvement of the core electron confinement. (author)

[en] A seven-channel NaI(Tl) detector array installed on HT-7 superconducting tokamak has been used to measure the hard X-ray (20 keV < E_hv < 500 keV) emitted from plasma. The physical mechanism of LHW propagation and absorption in plasma was investigated by the measurement of hard X-ray radial distribution at different discharge parameters

[en] Plasma rotation driven by RF waves such as lower hybrid current driven (LHCD) and ion cyclotron range of frequencies (ICRF) heating is considered to be able to provide the sufficient rotation for suppressing RWM instability on ITER. Substantial rotation has been recorded on major MCF devices without external momentum input. Recent experimental rotation observations of H-mode plasmas on EAST under LHCD and ICRF were presented in this paper. It was found that co-current core rotation increase was induced for H-mode discharges. For stationary type-III H-mode, core plasma rotation was constant. Type-I ELM decreases the rotation over each burst while ion temperatures remain unchanged. Rotation increase in H-mode plasmas scales proportionally to the increase in plasma stored energy normalized by the plasma current. (author)

[en] Lower hybrid waves (LHWs) with a selected n_// spectrum have been used to control the energy deposition profiles, and then the wave driven current profiles effectively in tokamak discharges. In authors' lower hybrid current drive experiment in the HT-7 tokamak, it was found that the set-up of the wave energy deposition profile is a graduation process. In the beginning phase of the wave injection duration, the waves (with different n_// spectra) deposit almost all their energy in the central region of the plasma column, even if their n_// are very different. Up to around one hundred milliseconds, the wave energy deposition profiles can only take their corresponding shapes according to the n_// spectra of LHWs. It also shown that this evolution process is affected obviously by the LHW driven current profile, which has been formed early

[en] A diagnostic neutral beam (DNB) has been installed on the HT-7 tokamak for the measurement of charge exchange recombination spectroscopy (CXRS). The H_α-light Doppler shift spectroscopy from the drifted duct is measured to determine the components of the neutral beam. The fractions of neutral beam species are investigated under a wide range of arc voltages and extraction high voltages of the beam aimed to the optimized species fractions for the CXRS applications. A magnet ring is used to improve the magnetic property of the ion source. The result shows that the full-energy component fractions increase from 19 to 25 percent with optimization of the beam operation, but with a dramatic increase of the water component. There are nine optical fiber channels observing one section of the beam simultaneously for this spectroscopy, which provides information of the power profiles of the beam. The full width at half maximum (FWHM) of the beam profile is 8 cm, as measured by using the spectroscopy.