Advanced high power gyrotrons for ECRH applications

Summary form only given. Recently the 165 GHz coaxial cavity gyrotron has been equipped with a new diode type electron gun with dispenser cathode to be operated at a cathode voltage of 90 kV and a beam current of 50 A. The advanced quasi-optical mode converter for transforming the TE/sub 31.17/-cavity mode into a single rf-output wave beam consists of a simple launcher and two phase correcting mirrors. First measurements resulted in 1.8 MW output power at 91 kV and 70 A with an efficiency of 28%. The maximum efficiency of 30% has been achieved at an output power of about 1.5 MW without depressed collector. The measurements will be continued, including single-stage depressed collector operation in order to increase the efficiency. Fast stepwise frequency-tunability within 1 s time steps has been demonstrated with the TE/sub 22.6/ gyrotron. For that purpose two small auxiliary normal conducting magnets have been added to the superconducting magnet system. The fast change of the magnetic field by /spl plusmn/300 mT results in a fast frequency change of about /spl plusmn/7 GHz with the center frequency at 140 GHz. The measurements were carried out at a power level of 1 MW with a cathode voltage of 85 kV and a beam current of 40 A. The gyrotron was tuned within 1 sec time steps between the TE/sub 20.6/ mode at 132.8 GHz via the TE/sub 21.6/, TE/sub 22.6/, TE/sub 23.6/ mode and the TE/sub 24.6/ mode at 147.5 GHz.