New Advanced Operational Regime on the W7-AS Stellarator

Abstract

A promising new plasma operational regime on the Wendelstein stellarator W7-AS has been discovered. It is extant above a threshold density and characterized by flat density profiles, high energy and low impurity confinement times, and edge-localized radiation. Impurity accumulation is avoided. Quasistationary discharges with line-averaged densities ${\overline{n}}_{e}$ to $4\ifmmode\times\else\texttimes\fi{}{10}^{20}{\mathrm{m}}^{\ensuremath{-}3}$, radiation levels to $90%$, and partial plasma detachment at the divertor target plates can be simultaneously realized. Energy confinement is up to twice that of a standard scaling. At ${B}_{t}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.9\mathrm{T}$, an average $\ensuremath{\beta}$ value of $3.1%$ is achieved. The high ${\overline{n}}_{e}$ values allow demonstration of electron Bernstein wave heating using linear mode conversion.