Confinement in Wendelstein 7-X limiter plasmas

摘要

Observations on confinement in the first experimental campaign on the optimized Stellarator Wendelstein 7-X are summarized. In this phase W7-X was equipped with five inboard limiters only and thus the discharge length restricted to avoid local overheating. Stationary plasmas are limited to low densities <2-3 • 10~(19) m~(-3). With the available 4.3 MW ECR Heating core T _e ∼ 8 keV, T _i ∼ 1-2 keV are achieved routinely resulting in energy confinement time τ _E between 80 ms to 150 ms. For these conditions the plasmas show characteristics of core electron root confinement with peaked T _e-profiles and positive E _r up to about half of the minor radius. Profiles and plasma currents respond to on- and off-axis heating and co- and counter ECCD respectively.