D. A. Constable

A novel cylindrical TE2,1 mode converter

A novel, compact arrangement for Ka-band mode couplers, which convert a rectangular waveguide TE(1,0) to cylindrical waveguide TE(2,1) mode, has been designed, constructed, and tested. The design features a set of longitudinal slots, positioned in regions of negligible current flow for the TE(2,1) mode, allowing its propagation to be preferentially favored, by suppression of the fundamental TE(1,1) mode. Numerical simulations and experimental measurements display good agreement, showing transmission of the intended TE(2,1) mode at levels of better than -5 dB, from a frequency of ∼37.5 to 41 GHz. Subsequent farfield measurements confirm the presence of the TE(2,1) mode, demonstrating good agreement when compared with analytical expectations. Such a device would be an ideal candidate for an application where mode purity, bandwidth, and ease of construction are of primary importance and where the transmission efficiency is of limited concern.

A co-harmonic gyro-oscillator with a novel interaction cavity

A novel interaction cavity has been designed for a gyro-oscillator, allowing co-harmonic generation at the 2nd and 4th harmonic resonances of the cyclotron frequency. The output aperture of the cavity has been designed to trap the lower harmonic, whilst allowing output of the upper harmonic. Results from recent numerical simulations, performed using MAGIC 3-D, are presented. The intended co-harmonic behaviour is observed, with simultaneous excitation of the 2nd and 4th harmonics. Refinement of the output structure is now being undertaken to ensure only the 4th harmonic signal is emitted.

Recent progress on a co-harmonic gyrotron

Results from numerical simulations have demonstrated the principle of a co-harmonic gyrotron, operating with a novel cavity. Such a cavity is capable of generating coherent radiation at both the 2nd and 4th harmonics of the electron cyclotron frequency simultaneously, at frequencies of 37.5 GHz and 75 GHz. Further results are presented here, including refinements to the output section of the cavity, as well as on the on-going testing of the cavity and its associated components, which are required to generate the operating modes of interest.

A Millimeter-Wave Klystron Upconverter With a Higher Order Mode Output Cavity

Manufacturing of klystrons in the millimeter-wave frequency range is challenging due to the small size of the cavities and the ratio of the maximum gap voltage to the beam energy. The small dimensions also make difficult to produce devices with the output power required by a number of applications at millimeter wave, such as communications and spectroscopy. Operating with a higher order mode can be a potential solution, as a larger transverse size structure can be used. Unfortunately, high-order mode cavities have a lower impedance than in fundamental mode. In this paper is proposed a novel solution to overcome the reduced impedance by utilizing an upconverter, where all cavities except the output cavity are designed to work in high-order mode. To demonstrate the effectiveness of the approach, two klystron upconverters were designed. One has six cavities aiming to achieve a maximum output power of ~90 W at 105 GHz. The second klystron upconverter was a simpler three-cavity structure designed for quick prototype. Millimeter-wave measurements of the three-cavity klystron upconverter are presented.

2-D particle-in-cell simulations of high efficiency klystrons

Currently, klystrons employing monotonic bunching offer efficiencies on the order of 70%. Through the use of the core oscillation electron bunching mechanism, numerical simulations have predicted klystrons with efficiencies up to 90%. In this paper, we present PIC simulations of such geometries operating at a frequency of 800 MHz, with efficiencies up to 83% predicted thus far.

Numerical investigation of gyro-multiplier schemes

Numerical simulations using the PiC code Magic 3-D have investigated two distinct gyro-multiplier schemes. Subsequent results have predicted the operation of a single cavity device operating at the 2nd and 4th harmonics, at frequencies of 37.5 GHz and 75 GHz, respectively. As a result, this device is currently under experimental investigation. Additionally, a sectioned cavity device has shown promising output, delivering 4th harmonic output at ~1.36 THz. Results of both schemes will be presented.

submitter : Particle-in-cell simulation of second and third harmonic cavity klystron

This paper outlines the results obtained from Magic software for the CSM_23 (Core Stabilization Method) klystron. This klystron implements the use of a second and third harmonic klystron to increase the efficiency. From the PIC simulation an efficiency of 78.1% was achieved.

MAGIC2-D simulations of high efficiency klystrons using the core oscillation method

Klystrons employing traditional monotonic electron bunching are capable of efficiencies up to ∼70%. The use of the core oscillation method (COM) of electron bunching has predicted a significant improvement in efficiency towards 90%. Here, we document refinements on previously presented geometries, with PIC simulations predicting efficiencies up to 85%.

Particle-in-cell simulation of the third harmonic cavity F-Tube klystron

Use of a second harmonic and third harmonic cavity within a klystron to increase efficiency has been studied using particle-in-cell (PIC) code, MAGIC 2D. The six cavity device has a drive frequency of 1GHz, a predicted efficiency of 88%, 39 dB gain and an output power of 833 kW. The preliminary simulation results have revealed indications of bunching with bunch core oscillations. The initial results and analysis of the F-Tube PIC study are presented.

Magic 3-D simulations of a 1.37 THz gyro-multiplier

Results are presented of recent numerical simulations of a high frequency, gyrotron oscillator based on the principle of frequency multiplication, where the high frequency waves are excited as a consequence of a strong non-linear interaction at a lower harmonic. The model strongly supports 1D non-linear predictions of the systems performance.