Recent results in high power gyrotron development for W7-X at FZK

Summary form only given. A 10 MW ECRH system is currently under construction for the stellarator W7-X which will be built up and operated by IPP in Greifswald, Germany. The RF power will be provided by 10 gyrotrons. A European collaboration has been established to develop and build the 10 gyrotrons each with an output power of 1 MW for continuous wave (CW) operation. Nine gyrotrons are being manufactured by Thales Electron Devices (TED), Velizy, France, one gyrotron was produced by CPI, Palo Alto, CA and has passed the acceptance tests at IPP. The acceptance tests of the TED gyrotrons are performed at the test stand at FZK and on site at IPP. The first series tube yielded a total output power of 0.98 MW, with an efficiency of 31 % (with non-depressed collector) in short pulse operation and of 0.92 MW in pulses of 1800 s (efficiency of almost 45 % at a depression voltage of 29 kV). The Gaussian mode output power was 0.91 MW. The RF power, measured in a calorimetric load at the end of a 25 m long quasi-optical transmission line with seven mirrors, was 0.87 MW. In this contribution topical results of the series gyrotrons will be reported.