Boda Yuan

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.

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.