Aspects of steady-state operation of the Wendelstein 7-X stellarator

The objective of Wendelstein 7-X is to demonstrate steady-state operation at β -values of up to 5%, at ion temperatures of several keV and plasma densities of up to 2 × 10 20 m −3 . The second operational phase foresees a fully steady-state high heat flux (HHF) divertor. Preparations are underway to cope with residual bootstrap currents, either by electron cyclotron current drive or by HHF protection elements. The main steady-state heating system is an electron cyclotron resonance heating facility. Various technical improvements of the gyrotrons have been implemented recently. They enable a reliable operation at the 1 MW power level. Some of the technical issues preparing plasma diagnostics for steady-state operation are exemplified. This includes the protection against non-absorbed microwave radiation.