A 1.5-MW, 140-GHZ, TE28,16-COAXIAL CAVITY GYROTRON

The design of a 1,5-MW, 140-GHz, TE28,16-coaxial cavity gyrotron is pr esented and results of experimental operation are given, A cavity with a cylindrical outer wall and a radially tapered inner rod with longit udinal corrugations was used, A maximum output power of 1.17 MW has be en measured in the design mode with an efficiency of 27.2%. Single-mod e operation has been found over a wide range of operating parameters, The experimental values agree well with the results of multimode calcu lations, Frequency-step tuning has been performed between 115.6 and 16 4.2 GHz. In particular, an output power of 0.9 MW has been measured in the TE25,14 mode at 123.0 GHz and 1.16 MW in the TE32,18 mode at 158. 9 GHz, At frequencies with strong window reflections the parameter ran ge for which stable operation is possible is reduced significantly. In order to obtain results relevant for a technical realization of a con tinuously operated gyrotron, a tube with a radial radio frequency (rf) -beam output through two output windows and a single-stage depressed c ollector has been designed and is under fabrication, A two-step mode c onversion scheme-TE-(28,16) to TE+76,2 to TEM00-which generates two na rrowly directed (60 degrees at the launcher) output wavebeams has been chosen for the a quasioptical (q.o.) mode converter system, A convers ion efficiency of 94% ss expected.