Update on the development of a 10 MW, 91 GHz gyroklystron

Summary form only given. Calabazas Creek Research, Inc. (CCR) is funded by the U.S. Department of Energy to develop a high efficiency gyroklystron amplifier for W-Band linear collider applications. In particular, this program supports development of a W-Band accelerator now underway at the Stanford Linear Accelerator Center. CCR is developing a 91.392 GHz gyroklystron to produce 10 MW of RF power with efficiency greater than 40% and a gain of 55 dB. Achievement of 10 MW of peak power would advance the state of the art for W-Band amplifiers by two orders of magnitude and potentially lead to other applications, including land- and ship-based radar, medical accelerators, and materials processing. The design uses the second-harmonic mode to reduce the magnetic field requirements and use available TWT drivers. The current circuit design employs six cavities consisting of an input cavity, three buncher cavities and a final output cavity. The input cavity is a fundamental cavity operating with the TE011 mode and uses radial coupling to the input rectangular waveguide. The following buncher cavities operate with the TE021 mode and are stagger-tuned to improve efficiency and bandwidth. The output cavity operates in the TE021 mode and has smooth-wall transitions. A conventional, double anode, magnetron injection gun generates the electron beam. Following the circuit, a large radial gap is introduced in the output waveguide to allow voltage depression of the beam collector to increase the overall efficiency. A hybrid mode is used (TE01/02) to maximize transmission across the gap. An internal elbow is included to prevent beam bombardment of the output window. All major subassemblies of the gyroklystron have been fabricated and the cavity sections are currently being cold-tested. Completion of tube assembly is expected by the end of January with testing scheduled to begin in March 2002 at the Stanford Linear Accelerator Center.