Overview of W7-X ECRH Results.

In its second operation phase (OP1.2a) W7-X was equipped with full 3d island divertor and an upgraded ECRH-system of 10 gyrotrons with a total port through power of 7 MW. The combination of pellet fueling and high density ECRH enabled to explore density above 1 10²⁰ m^-3. In particular with the O2-polarisation combined with a multi-pass reflector tile system a density of up to 1.4 10²⁰ m^-3 was achieved. At slightly lower densities high core beta values and record values of the fusion tripple product of 0.66 10²⁰ m^-3 keVs for stellarators were reached. In addition routine plasma start-up and ECRH wall conditioning were performed. The island divertor enables to demonstrate the intrinsic steady state capabilities of W7-X, where stationary discharges of up to 30s were demonstrated being only limited by the heat capacity of the uncooled divertor. With the flexible ECRH launch system current density profile variations were used for MHD stability investigations. Here by fine-tuning of the ECCD profile different MHD activity could be triggered. [ABSTRACT FROM AUTHOR]