T.A. Spencer

Slotted W-band sixth-harmonic gyrotron with axis-encircling electrons

A high-harmonic slotted gyrotron is under construction at UCD that will be driven by a 70 kV, 3.5 A, axis-encircling electron beam from a Northrop Grumman Cusp gun. The 94 GHz, slotted sixth-harmonic gyrotron is predicted to generate 40 kW with a device efficiency of 16%.

Highly efficient 34 GHz peniotron

While high conversion efficiency has been demonstrated in peniotrons, practical application of the device requires that power be efficiently extracted from the cavity. The UCD peniotron is designed to achieve high overall device efficiency and power output (130 kW peak) by employing an over-coupled cavity driven by a Northrop Grumman Cusp gun. Stability is insured through the use of a fundamental-mode interaction with the second cyclotron harmonic of the axis-encircling electron beam.

Highly efficient Ka-band second-harmonic slotted peniotron

A harmonic peniotron has been designed for high efficiency and relative immunity to mode competition from gyrotron interactions. The device employs a 70 kV, 3.5 A, axis-encircling electron beam. To ensure stability from competing gyrotron interactions, the peniotron will operate in the lowest order mode of a slotted four-vane circuit, the /spl pi//2 mode. The 33 GHz, slotted second-harmonic peniotron is predicted to yield 125 kW with an electron efficiency of 58% and a device efficiency of 52%. The device is being constructed at UCD and will be driven by a recently developed Northrop Grumman Cusp electron gun.

Cusp gun driven peniotron

The UCD peniotron has been designed for optimum device efficiency and output power in second-harmonic operation at a 34 GHz fundamental-mode resonance. Key to the design is interaction with the axis-encircling electron beam. The UCD device incorporates over-coupling of the cavity to achieve the desired increased device efficiency. The predicted efficiency and power have been calculated from our large signal code.

34 GHz cusp gun driven peniotron

Summary form only given. A peniotron designed for optimum device efficiency is currently being assembled at UC Davis. The peniotron incorporates a four-vane slotted (magnetron-like) cavity operating in the fundamental waveguide mode, the /spl pi//2 mode. Interaction is at approximately 34 GHz with the second-harmonic beam mode. This interaction provides good separation from possible competing gyrotron modes. The cavity incorporates an output coupling iris which is required to achieve the desired loaded Q of 375 necessary for overcoupling of the device and optimum power output. The predicted output power is approximately 125 kW (at 47% device efficiency as predicted with our large-signal code). Cold test of the cavity/iris combination shows good agreement with predictions from simulation with HFSS. The interaction is powered by a Northrop-Grumman cusp gun which provides the high quality axis-encircling electron beam required for efficient interaction. For the device to operate as predicted, the gun will supply 3.5 amps at 70 kV. The spent beam should be suitable for recovery with a single-stage depressed collector, raising the total device efficiency to 57%.

Efficient 34 GHz second-harmonic peniotron with cusp gun drive

A 34 GHz peniotron, operating in the fundamental-mode of a slotted circuit, is under construction at UC Davis. The device is designed for second-harmonic interaction with the axis-encircling beam produced by a Northrop Grumman cusp gun. Recent efforts have concentrated on improving the magnetic field design and beam quality. Consequently, the cryogenic magnet of the initial design has been replaced with conventional coils and pole pieces. Measurement of the new magnet indicates that design goals for the magnetic field have been achieved and simulation of the beam predicts greatly improved quality.

Simulation and modeling of a 34 GHz cusp gun driven peniotron

A comprehensive review of the simulation and modeling work done to insure optimal realization of the design, including recent progress on the magnetic field design using the subsequent effect on beam quality were presented in this paper. However, the beam quality was critically dependent on the magnetic field in gun region, which has been the most difficult aspect of the design.

Cusp gun driven 34 GHz peniotron

Summary form only given, as follows. The peniotron has demonstrated an electronic conversion efficiency as high as 75 %, making the device attractive as a source of high frequency RF power, especially in harmonic operation. However, practical realization of the device is dependant on 1) selection of a stable operating mode, free of competition from gyrotron modes, 2) a high quality axis-encircling beam to increase the interaction efficiency, and 3) extraction of sufficient power to provide high device efficiency. This is the objective of the UCD peniotron.

Second-harmonic fundamental-mode slotted peniotron

Summary form only given. The harmonic peniotron has been demonstrated to be a highly efficient generator of millimeter-wave power (Ishihara et al., 1999). Since a practical peniotron design must provide immunity to mode competition from gyrotron interactions as well as high device efficiency, the UC Davis peniotron design (McDermott et al., 2000) employs an overcoupled interaction cavity for a predicted device efficiency of 47% at 34 GHz. Stability will be ensured by operation in the lowest order mode of a slotted four-vane (magnetron type) circuit, the pi/2 mode. The TE11-like pi/2 mode couples well to the TE11 mode of the circular output waveguide through the 2.5 mm radius iris at the end of the cavity. The output diffraction coupling configuration results in heavy loading of higher order axial modes and avoids mode conversion in the output waveguide. For diagnostic purposes, the experimental device will also incorporate side-wall coupling to the cavity. The peniotron will operate with a 70 kV, 3.5 A, vt/vz=1.5, axis-encircling electron beam generated by a recently developed Northrop Grumman Cusp gun (Gallagher et al., 2000). Large-signal simulation of the interaction predicts an electronic efficiency of 58% and an extracted power output of 120 kW (47% device efficiency). The overall efficiency can be raised to 57% by use of a depressed collector.

W-band sixth-harmonic slotted gyrotron

A high-harmonic slotted gyrotron is under construction at UCD that will be driven by a 70 kV, 3.5 A, axis-encircling electron beam from a Northrop Grumman Cusp gun. The 94 GHz, slotted sixth-harmonic gyrotron is predicted to generate 40 kW with a device efficiency of 16%.