UC davis experimental second-harmonic CUSP GUN driven peniotron

Summary form only given. There is an increasing need for compact millimeter-wave transmitters, specifically at 95 GHz. However, the current state-of the-art is defined by fundamental mode gyrotrons requiring superconducting magnets and relatively high beam voltages, both of which add size and weight. The only physical means to eliminating the superconducting magnet is harmonic operation, realistically at cyclotron harmonics of n=3 or more. This has been problematic for MIG driven gyrotrons in the past as efficiency drops significantly at these higher harmonics. As a possible remedy, UC Davis has been preparing experiments using an axis-encircling beam - a beam more conducive to high efficiency harmonic interaction. The beam is generated by a novel cusp gun. Furthermore, the peniotron interaction has been proven capable of high conversion efficiency, even at harmonic operation and reduced beam voltage. Using the cusp gun, the UC Davis peniotron experiment is designed to maximize device efficiency and usable power out. As a first step, the experimental device is designed to operate at the second cyclotron harmonic at around 34 GHz with the goal of a follow-on device at higher harmonics (but not higher magnetic field) and 95 GHz. The device incorporates a slotted circular (magnetron-like) circuit designed for mode stability and efficiency. Large signal simulations predict 125 kW peak output power at 47% (device) efficiency with higher efficiency possible with a depressed collector. The device has been designed, simulated, fabricated, assembled and successfully cold-tested. The experimental magnets have been designed and tested with excellent agreement to design simulations. A modulator, intended specifically for these experiments has been built and is in operation. The peniotron, with the circuit replaced by a smooth-bore "beamstick" has been placed under vacuum and mounted in the magnet. Testing is underway and the status of experiment along with preliminary results - ill be reported