Advanced high power gyrotrons

A 1 MW, 140 GHz gyrotron with diamond window for continuous wave (CW) operation and with a single-stage depressed collector for energy recovery and improvement of efficiency has been designed and constructed in collaboration with CRPP Lausanne and TTE Velizy. It operates in the TE/sub 28.8/ cavity mode and provides a linearly polarized TEM/sub 0.0/ Gaussian RF beam. The gyrotron consists of a magnetron injection gun (diode type), an improved beam tunnel, an improved cavity with rounded corners and low surface loss densities (<2 kW/cm/sup 2/), an optimized non-linear up-taper and an improved launcher. First RF power measurements at pulse lengths of 1 ms gave 0.65 MW output power at 40 A and 82 kV. With pulse lengths up to 150 ms an output power of 0.6 MW was measured. Despite careful optimization it has not been possible, to improve the output power for this beam current. With the 165 GHz coaxial cavity gyrotron which has been developed at Forschungszentrum for higher output power due to reduced mode competition problems an output power of 2.2 MW with an efficiency of 28% has been measured recently in short pulse operation (1 ms).