Confinement in Wendelstein 7-X limiter plasmas.

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 · 10¹⁹ 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. [ABSTRACT FROM AUTHOR]