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Impurity transport was investigated at both edge and core regions in large helical device (LHD) with developed spectroscopic instruments which can measure one- and two-dimensional distributions of impurities. The edge impurity behavior was studied recently using four carbon resonant transitions in different ionization stages of CIII (977?), CIV (1548?), CV (40.3?) and CVI (33.7?). When the line-averaged electron density, ne, is increased from 1 to 6 ? 1013 cm?3, the ratio of (CIII+CIV)/ne increases while the ratio of (CV+CVI)/ne decreases. Here, CIII+CIV (CV+CVI) expresses the sum of CIII (CV) and CIV (CVI) intensities. The CIII+CIV indicates the carbon influx and the CV+CVI indicates the emissions through the transport in the ergodic layer. The result thus gives experimental evidence on the impurity screening by the ergodic layer in LHD, which is also supported by a three-dimensional edge particle simulation. The core impurity behavior is also studied in high-density discharges (ne ? 1? 1015 cm?3) with multi H2-pellets injection. It is found that the ratio of V/D (V: convection velocity, D: diffusion coefficient) decreases after pellet injection and Zeff profile shows a flat one at values of 1.1?1.2. These results confirm no impurity accumulation occurs in high-density discharges. As a result, the iron density, nFe, is analyzed to be 6 ? 10?7 ( = nFe/ne) of which the amount can be negligible as radiation source even in such high-density discharges. One- and two-dimensional impurity distributions from space-resolved VUV and EUV spectrometers newly developed for further impurity transport study are also presented with their preliminary results.

Energy confinement time taken from 135 discharges of the 2006 campaign in HL-2A is studied. The data obtained from the measurements are verified by comparing diamagnetic energy with the electronic kinetic energy calculated from both the electron temperature and density profiles. Two data sets for supporting the ITER L-Mode confinement database are generated from the 2006 campaign. The dependence of ?E on the line-averaged electron density during ohmic phases is analysed. The comparison of ?E in electron cyclotron resonance heating (ECRH) plasma as well as the existing ITER L-mode scalings is made. The results show that the energy confinement time is consistent with the ITER L-mode scalings.

A method for the identification and analysis of magnetic islands is presented based on the calculation of the perturbative current and magnetic field in plasmas. A cylindrical approximation is adopted and the toroidal effect on plasma equilibrium is also included. This method has been used on the HL-2A tokamak for analysing the magnetic island structures.

A new criterion has been proposed to predict the major disruptions caused by tearing mode instabilities. According to the HL-2A experimental results, the statistical analyses are employed to investigate the relationships between MHD activities and the plasma disruptions. Two kinds of the tearing mode activities can finally cause the disruption on HL-2A operations. By introducing a new parameter, i.e. an integral of poloidal magnetic field over time, as the criterion of disruption precursor, almost all of the disruptions can be predicted.

In this paper, we describe the behavior of impurity transport in the HL-2A electron cyclotron resonance heating (ECRH) L-mode plasma. The neon as a trace impurity is injected by the supersonic molecular beam injection (SMBI) technique, which is used for the first time to study the impurity transport in HL-2A. The progression of neon ions is monitored by the soft X-ray camera and bolometer arrays with good temporal and spatial resolutions. The convection and diffusion process of the neon ions are investigated with the one-dimensional impurity transport code STRAHL. The results show that the diffusion coefficient D of neon ions is a factor of four larger than the neoclassical value in the central region. The value of D is larger in the outer region of the plasma (ρ > 0.6) than in the central region of the plasma (ρ < 0.6). The convective velocity directs inwards with a value of ~ −1.0 m/s in the Ohmic discharge, but it reverses to direct outwards with a value of ~ 8.0 m/s in the outer region of the plasma when ECRH is applied. The result indicates that the impurity transport is strongly enhanced with ECRH.