Performance of ECR heating during the first operational phase of W7-X

Wendelstein 7-X is an optimised stellarator designed for steady-state operation. The only steadystate capable heating system is electron cyclotron resonance heating (ECRH) launching microwaves at 140GHz into the vessel corresponding to the 2nd harmonic of the electron cyclotron frequency at 2.5 T. A quasi optical transmission line is used to bring the power into the machine. The power is launched into the vessel by front steerable quasi-optical launchers from the low field side in Xor O-mode. Fig 1 (a) shows a photo of the launcher with respect to the vacuum flux surfaces. The launching angle can be varied both in toroidal as well as in poloidal direction allowing to run advanced heating scenarios like electron cyclotron current drive or off axis heating. During the first operational phase of W7-X (OP 1.1) 6 gyrotrons providing up to 4.3MW microwave power were available as the sole heating system. The total injected energy was limited to 4MJ in order to protect in vessel components, especially the five poloidal limiters, from overheating. For the next operational phases 4 additional gyrotrons will be brought into operation and the control system will be optimised aiming to provide 9MW port through heating power. In this paper we present an overview of the plasma performance during OP 1.1 with respect to ECRH physics. A set of diagnostics is installed to characterise the efficiency of ECRH absorp-