The klystrino: a high power W-band amplifier

High average power millimeter wave sources are being developed in a collaboration between SLAC and CPI. CPI has developed a number of high-power, broadband, millimeter-wave, CCTWT amplifiers. The coupled cavity technology is now approaching the limits for generating power at millimeter wave frequencies. To generate significant increases in power, other technologies need to be considered. At SLAC, compact, lightweight, PPM-focused, klystrons, nicknamed ´klystrinos´ are being developed, using lithographic fabrication methods (LIGA). These devices will operate at 100 kW peak power and 1 kW average power at 95 GHz. Two design areas are critical to the success of the klystrino. First is the electron beam optics and beam focusing. A beam tester is being built to evaluate the electron gun and the PPM focusing system. Results of the beam tests are presented. CPI has analyzed the electron gun and is investigating the addition of a control electrode for improved modulator efficiency. The second significant design area is the modeling of the klystrino. The combination of the rectangular LIGA structure and the multiple gap output section make modeling the klystrino difficult. MAFIA and MAGIC have been used to develop an equivalent 2D model of the 3D LIGA circuit. Thermal capacity of the circuit is also investigated at CPI using the ANSYS 3D FEA code. The analysis included both the expected RF losses and beam interception. The calculations include both transient response and steady state. The thermal analysis is used to predict the maximum allowable beam interception and duty cycle that the circuit can withstand without major problems.