Experimental studies of high-power harmonic gyroklystrons

At the University of Maryland, we have developed several gyroklystron configurations, the characteristics of which are approaching the predicted requirements for the next generation linear collider. These studies have revolved around a test bed capable of producing a 450 kV, 160–260 A, 1 µs beam immersed in a 5.5 kG (nominal) axial magnetic field with an average ratio of electron perpendicular to parallel velocities near one. We present results for a series of second-harmonic two-cavity tubes that culminated in a peak power of 32 MW at 19.7 GHz with an efficiency of 28% and a large-signal gain of 27 dB. The experience gained from these tubes has been incorporated into the design of a 17.136 GHz, 100 MW, coaxial, second-harmonic, two-cavity gyroklystron. We conclude the paper by detailing the design of the new test bed, the single-anode magnetron injection gun, and the microwave circuit.