W7-X commissioning: Progress and lessons learned for future devices

Commissioning of the stellarator Wendelstein 7-X (W7-X) at the Max-Planck-Institute for Plasma Physics in Greifswald, Germany, started in April 2014, simultaneously with final assembly work. First, individual components and their local control systems were put into operation. The subsequent cryostat evacuation was then the first large system commissioning. Before the final room temperature vacuum of ≈10-4 mbar was reached, the electrical insulation of the superconducting coil system had been successfully tested with voltages up to 2.5 kV under Paschen conditions. Partly in parallel, all power supplies, the trim and most of the control coils, CoDaC, and the diagnostic as well as ECRH - as far as possible without plasma - were put into operation. Next major achievements were the magnet system cool-down to 3.8 K, and the first operation of individual coil groups. Evacuation of the plasma vessel has been delayed due to leaks at vacuum pump manifold flanges which are currently being repaired. The large system commissioning steps and problems encountered as well as remedies are described, and an outlook for remaining work to be done until the first plasma is given.