Jason R. Garner

Design and Measurement of a Broadband Sidewall Coupler for a W-Band Gyro-TWA

The input coupler is an important component for a microwave amplifier. In this paper, a sidewall single-hole input coupler for a W-band gyrotron traveling-wave amplifier that operates at the frequency range of 90-100 GHz was designed and measured. Instead of using a cutoff waveguide, a broadband Bragg-type reflector with a small spread in phase was optimized for use as part of the input coupler. The minimum radius of the reflector was two times the size of a cutoff waveguide, which reduced the possibility for some of the beam electrons being collected in this section and lost to the amplifier interaction region.

Design Study of a Fundamental Mode Input Coupler for a 372-GHz Gyro-TWA I: Rectangular-to-Circular Coupling Methods

The design of two fundamental mode rectangular-to-circular waveguide input couplers for a low-terahertz gyrotron-traveling wave amplifier (gyro-TWA) is presented. A T-junction input coupler with a Bragg reflector and a multiple-hole directional coupler were optimized for operation between 360 and 384 GHz, the proposed gyro-TWA bandwidth. The T-junction coupler and the multiple-hole coupler achieved the respective bandwidths of 10% and 35%. The benefits and potential limitations of the low-terahertz wave coupler topologies are discussed alongside the challenging manufacturing methods of the submillimeter-wave components.

Design Study of a 372-GHz Higher Order Mode Input Coupler

The design of a higher order mode (HOM) input coupler for a low-terahertz gyrotron travelling wave amplifier is presented. A two-branch waveguide coupler based on the even distribution of incident power is designed to couple the rectangular TE10 mode to the circular TE61 mode. The optimised tapered waveguide input coupler achieved an operating frequency range of 359-385 GHz, equating to a bandwidth of 7%. A prototype waveguide coupler scaled to W-band (75-110 GHz) was manufactured. The vector network analyser measured return loss of the HOM coupler is shown to be <;10 dB at 90-96 GHz. A transmission and phase measurement is presented to analyse TE61 mode conversion in the coupler.

Measurement of a W-band gyro-TWA experiment based on a helically corrugated interaction region

Measurements of an upgraded W-band gyro-TWA with a helically corrugated waveguide and a cusp electron gun are presented. With upgraded input coupler and output systems a gain of ∼37 dB was measured from the experiment with a maximum output power of over 2 kW. The amplification from the gyro-TWA was measured in the frequency range of 90 GHz to 96 GHz.

Input coupling systems for mm-wave amplifiers

Input couplers for mm-wave gyrotron traveling wave amplifiers (gyro-TWAs) were designed. A W-band input coupler composed of a T-junction and a broadband reflector was constructed and measured in W-band. It achieved a transmission coefficient of −2.2 dB including the pillbox window and a waveguide bend. A multiple-hole coupler was designed and simulated at 372 GHz. Without considering the Ohmic loss, in simulations the 372GHz coupler achieved a transmission coefficient of −0.5 dB.

Numerical modelling of rectangular TE 10 to circular TE 11 terahertz mode couplers

The design of two fundamental mode rectangular to circular waveguide mode converters are presented. The waveguide transitions are optimized for operation as an input coupler on a 372 GHz gyro-TWA for Dynamic Nuclear Polarization (DNP) enhancement of NMR imaging. A T-junction input coupler and a multiple hole directional coupler were optimized for operation between 360–384 GHz. The T-junction coupler and the multiple hole coupler exhibited bandwidths of 10% and 35% respectively with a high coupling factor of > −1 dB.

Development of high power broadband gyro-TWAs towards the terahertz range

In this paper gyrotron travelling wave amplifiers (gyro-TWAs) based on helically corrugated interaction regions will be presented. Their operating principle and the first experiment in X-band will be reviewed. The present experiment in W-band using a cusp electron beam source with the capability of a high pulse repetition frequency of 2 kHz will also be presented. The design and performances of the amplifiers for kilowatt output and broadband operation in the millimeter-wave and terahertz frequency ranges will also be presented.

TE10R–TE11c input coupler for a low-THz gyro-TWA

The design of a fundamental rectangular-to-circular coaxial cavity input coupler for a low-THz gyro-traveling wave amplifier (TWA) is presented. Theoretical and numerical approaches to the design of the coaxial cavity input coupler are introduced. The design is optimized for operation between 360-384 GHz, achieving a transmission bandwidth of 7.5% (358-386 GHz). A comment on the manufacturability of sub-mm waveguide channels is included.

Developments of a W-band gyro-TWA for high PRF operation

Latest developments of a gyrotron travelling wave amplifier (gyro-TWA) with a helically corrugated waveguide and a cusp electron gun for operation over a bandwidth of 90-100 GHz at a high pulse repetition rate (5 kHz) are presented. Performance upgrades of the input coupler, pulsed power system and beam collector with water-cooling capability were realized for the high power wide band gyro-TWA.

Development of a novel W-band side-wall coupler for a gyro-TWA

This paper presents the development of an input coupler for a W-band gyro-TWA which is currently been built in the University of Strathclyde.