Y.F. Wu

Edge shear flows and particle transport near the density limit of the HL-2A tokamak

Edge shear flow and its effect on regulating turbulent transport have long been suspected to play an important role in plasmas operating near the Greenwald density limit n G. In this study, equilibrium profiles as well as the turbulent particle flux and Reynolds stress across the separatrix in the HL-2A tokamak are examined as is approached in ohmic L-mode discharges. As the normalized line-averaged density is raised, the shearing rate of the mean poloidal flow drops, and the turbulent drive for the low-frequency zonal flow (the Reynolds power ) collapses. Correspondingly, the turbulent particle transport increases drastically with increasing collision rates. The geodesic acoustic modes (GAMs) gain more energy from the ambient turbulence at higher densities, but have smaller shearing rate than low-frequency zonal flows. The increased density also introduces decreased adiabaticity which not only enhances the particle transport but is also related to reduction in the eddy-tilting and the Reynolds power. Both effects may lead to cooling of edge plasmas and therefore the onset of MHD instabilities that limit the plasma density.

Development of beam emission spectroscopy diagnostic on EAST.

Beam Emission Spectroscopy (BES) diagnostic based on Neutron Beam Injection (NBI) on the Experimental Advanced Superconducting Tokamak has been developed. This system consists of 16 × 8 channels which can diagnose the density fluctuation in a rectangular area of about 20 × 10 cm2 in the cross section, whose radial position is adjustable from the core to edge just by means of changing the angle of the rotation mirror. The spatial resolution is about 1-3 cm according to the diagnosed radial position. The temporal resolution is 1 μs. Space calibration of the diagnostic system is done based on the reversibility of the optical path. The NBI modulation experiment shows the success of BES development.

Calibration of phase contrast imaging on HL-2A Tokamak

Phase contrast imaging (PCI) has recently been developed on HL-2A tokamak. In this article we present the calibration of this diagnostic. This system is to diagnose chord integral density fluctuations by measuring the phase shift of a CO2 laser beam with a wavelength of 10.6 μm when the laser beam passes through plasma. Sound waves are used to calibrate PCI diagnostic. The signal series in different PCI channels show a pronounced modulation of incident laser beam by the sound wave. Frequency-wavenumber spectrum is achieved. Calibrations by sound waves with different frequencies exhibit a maximal wavenumber response of 12 cm−1. The conversion relationship between the chord integral plasma density fluctuation and the signal intensity is 2.3 × 1013 m−2/mV, indicating a high sensitivity.

Optics of beam emission spectroscopy diagnostic on EAST tokamak

128-channel Beam Emission Spectroscopy (BES) diagnostic basing on neutral beam injection (NBI) has recently been developed on EAST tokamak. It can diagnose plasma density fluctuation with a sample rate of 1 MHz and a spatial resolution of 1–3 cm, according to the diagnosing spatial positions. The Doppler-shifted beam emission line is led through prisms, lens groups and mirrors, and finally divided into two detection branches. By means of rotating the rotation mirror in the optical path, the viewing area, which is a 20 cm × 10 cm rectangle, can be moved from plasma core to edge. Three-cavity-interference filter with a center frequency of 659 nm and a bandwidth of 1.59 nm is used to eliminate the interference background Dα signal and carbon radiation. First experimental results show high performance of this diagnostic.

Electron cyclotron resonance plasma excitation in a toroidal plasma

In this article, Electron Cyclotron Resonance (ECR) absorption, Upper-Hybrid Resonance (UHR) absorption and Electron Bernstein Wave (EBW) conversion are systematically confirmed in magnetically confined KT-5D plasma which is sole-excited by a magnetron source. A 2.45 GHz ECR system has been developed on the toroidal helimak KT-5D to produce and sustain a steady-state plasma. 0.98 kW electron cyclotron wave produced by the magnetron is injected into the vacuum chamber through rectangular waveguides with a power absorption efficiency of 40∼50%. A steady-state plasma is excited with a density of several 1016/m3 and electron temperature of up to 30 eV. The radial profile of plasma density shows that ECR absorption dominates the power deposition with a higher hydrogen pressure of at the order of 10-1 Pa, while UHR absorption dominates with a lower hydrogen pressure of at the order of 10-2 Pa. Plasma density in the discharge with a superimposed magnetic shear has demonstrated the wave conversion from ECR to EBW.In this article, Electron Cyclotron Resonance (ECR) absorption, Upper-Hybrid Resonance (UHR) absorption and Electron Bernstein Wave (EBW) conversion are systematically confirmed in magnetically confined KT-5D plasma which is sole-excited by a magnetron source. A 2.45 GHz ECR system has been developed on the toroidal helimak KT-5D to produce and sustain a steady-state plasma. 0.98 kW electron cyclotron wave produced by the magnetron is injected into the vacuum chamber through rectangular waveguides with a power absorption efficiency of 40∼50%. A steady-state plasma is excited with a density of several 1016/m3 and electron temperature of up to 30 eV. The radial profile of plasma density shows that ECR absorption dominates the power deposition with a higher hydrogen pressure of at the order of 10-1 Pa, while UHR absorption dominates with a lower hydrogen pressure of at the order of 10-2 Pa. Plasma density in the discharge with a superimposed magnetic shear has demonstrated the wave conversion from ECR to EBW.

The construction of a steady-state upgraded KT-5

In this article we present the main idea to construct a steady-state upgraded KT-5, with a conductive ring placed in the vacuum chamber center along the axis. It has an externally controllable poloidal magnetic field and a tokamak-like magnetic configuration. Some main parameters, such as the poloidal magnetic field and safety factor, are carefully discussed. The plasma density is significantly increased as compared to helimak configuration discharges.

Co-current toroidal rotation-driven and turbulent stresses with resonant magnetic perturbations in the edge plasmas of the J-TEXT tokamak

Author(s): Zhao, KJ; Shi, Y; Liu, H; Diamond, PH; Li, FM; Cheng, J; Chen, ZP; Nie, L; Ding, YH; Wu, YF; Chen, ZY; Rao, B; Cheng, ZF; Gao, L; Zhang, XQ; Yang, ZJ; Wang, NC; Wang, L; Jin, W; Xu, JQ; Yan, LW; Dong, JQ; Zhuang, G | Abstract: