arXiv subjects

R. Ke

Publications and source records attributed to R. Ke.

3 recordsLinked to original sources

arXiv2025

Impact of edge turbulence spreading on broadening the heat flux width with plasma approaching the density limit

This paper investigates the impact of edge turbulence spreading on broadening the heat flux width in Ohmic-plasma approaching the density limit of the J-TEXT tokamak. At the plasma edge, the EXB shear flow collapses while turbulence transport and spreading enhances significantly when approaching the density limit. The heat flux width increases with normalized density. An energy production ratio model is used to quantify the contribution of edge turbulence spreading to the origin of the SOL turbulence. Experimental data show that the energy production ratio is much larger than 1, indicating that turbulence spreading at separatrix is the origin of the SOL turbulence. The heat flux widths increase with edge turbulence spreading as well as the energy production ratio. The impact of blob-induced transport on the heat flux width is investigated in detail. Especially, the average blob-induced spreading is about 81% of the total edge spreading in the high-density scenario. Blobs with larger radial scales enhance edge spreading into the SOL, thus dominating the SOL turbulence and consequently broadening the heat flux width. These results suggest that edge turbulence spreading plays a crucial role in broadening the heat flux width as plasma approaches the density limit.

physics.plasm-ph↗

arXiv2017

Development of a New Gas Puff Imaging Diagnostic on the HL-2A Tokamak

A new gas puff imaging (GPI) diagnostic has been developed on the HL-2A tokamak to study two-dimensional plasma edge turbulence in poloidal vs. radial plane. During a discharge, neutral helium or deuterium gas is puffed at the edge of the plasma through a rectangular multi-capillary nozzle to generate a gas cloud on the observing plane. Then a specially designed telescope and a high-speed camera are used to observe and photograph the emission from the neutral gas cloud. The brightness and contrast in the 2-D poloidal vs. radial frames reveal the structures and movements of the turbulence. The diagnostic was put into the first experiment during the latest campaign and successfully captured blob structures of different shapes and sizes in scrape-off layer (SOL).

physics.plasm-ph↗

arXiv2017

Edge Shear Flows and Particle Transport near the Density Limit in 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 $ n_G $ is approached in ohmic L-mode discharges. As the normalized line-averaged density $ \bar{n}_e/n_G $ is raised, the shearing rate of the mean poloidal flow $ \omega_{\rm sh} $ drops, and the turbulent drive for the low-frequency zonal flow (the Reynolds power $ \mathcal{P}_{Re} $) 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 a reduction in the eddy-tilting and the Reynolds power. Both effects may lead to the cooling of edge plasmas and therefore the onset of MHD instabilities that limit the plasma density.

physics.plasm-ph↗