Studies Of An X-Band Three-Cavity Gyroklystron System

The University of Maryland is developing a 10 GHz, three-cavity, gyroklystron to demonstrate the feasibility of this type of device as an RF source for future 1 TeV linear colliders. Our system uses a beam produced by a magnetron injection gun. This system is designed to operate in the TE
₀₁₁
mode. The design beam parameters are 500 kV, 160 A, α=l.5, with a velocity spread of about 7%, for a pulse length of 1 μs. Until now our experimental effort has focused on testing a two-cavity system1 which has produced peak powers of about 20 MW at a gain of 28 dB and an efficiency of 32%. These results were obtained operating at 85% of the design beam voltage. Higher power operation has been hampered by parasitic oscillations in the system. Due to the Larmor radius of the beam electrons it is not possible to reduce the size of the drift regions enough to cutoff all modes. Suppression of unwanted modes in the drift regions and the cavities is accomplished by using liners of lossy dielectric material. The geometry and dielectric constant of these lossy dielectric liners is first optimized for maximum mode suppression using numerical techniques, and then fine adjustments are made based on microwave transmission and reflection measurements.