Status of the Series Production of 1-MW, 140-GHz, CW Gyrotrons for W7-X

The first series tube of the gyrotrons for W7-X has been tested at the FZK and yielded a total output power of 980 kW with an efficiency of 31% in short pulse operation and of 920 kW in pulses of 180 s (efficiency of 43% with depression voltage). At reduced electron beam current, it is possible to operate the tube at FZK in longer pulses. At an output power of 570 kW (electron beam current of 29 A), the pulse length was 1893s. The pressure increase during the pulse was less than a factor of two and ended up in the 10
^-9
mbar range. The tube was delivered to IPP Greifswald for tests at full power and designed pulse lengths (30 min.). The output power yielded 920 kW. Again, no indications for a limitation in pulse length was found. The 2
^nd
series tube has been tested in short pulse operation and showed a limitation of the pulse length even in short pulse operation (ms) at full power. The 3
^rd
series tube is presently under test.