New Advanced Operational Regime on the W7-AS Stellarator

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 n̄ₑ to 4×10²⁰m^-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 Bₜ0ex0ex=0ex0ex0.9T, an average β value of $3.1%$ is achieved. The high n̄ₑ values allow demonstration of electron Bernstein wave heating using linear mode conversion.