High efficiency Ka-band second-harmonic peniotron

A second-harmonic peniotron has been designed for high efficiency and immunity to mode competition from gyrotron interactions. A peniotron experiment at Tohoku University recently achieved an electron efficiency of 70% at the third harmonic, but since the cavity was only critically coupled, the device efficiency was a more modest 35%. In order to achieve high device efficiency, the UC Davis peniotron will employ an overcoupled interaction cavity. To ensure stability from competing gyrotron interactions, the peniotron will operate in the lowest order mode of a slotted four-vane circuit, the π/2 mode. The cavity is strongly diffraction coupled with a circuit efficiency of 84%. The 33 GHz, slotted second-harmonic peniotron with a 70 kV, 3.5 A, v⊥/vZ = 1.5, ΔvZ/vZ = 10%, axis-encircling electron beam is predicted to yield 130 kW with an electron efficiency of 63% and a device efficiency of 52%. The device is being constructed at UC Davis and will be driven by a recently developed Northrop Grumman Cusp gun.