Investigation on the optimal magnetic field of a cusp electron gun for a W-band gyro-TWA

High efficiency and broadband operation of a gyrotron traveling wave amplifier (gyro-TWA) requires a high-quality electron beam with low-velocity spreads. The beam velocity spreads are mainly due to the differences of the electric and magnetic fields that the electrons withstand the electron gun. This paper investigates the possibility to decouple the design of electron gun geometry and the magnet system while still achieving optimal results, through a case study of designing a cusp electron gun for a W-band gyro-TWA. A global multiple-objective optimization routing was used to optimize the electron gun geometry for different predefined magnetic field profiles individually. Their results were compared and the properties of the required magnetic field profile are summarized

A pillbox window with impedance matching sections for a W-band gyro-TWA

A mode-matching method was developed to design a pillbox-type millimeter wave window for a W-band gyrotron traveling wave amplifier. With additional impedance matching sections, the pillbox window was able to achieve -40 dB reflection over a 10% frequency bandwidth. The manufactured pillbox window achieved a maximum reflection of -15 dB. The reasons for the difference between the simulated and measured reflections were investigated

Design of a multilayer output window for a 372 GHz gyro-TWA

An output window for application in a gyrotron traveling-wave amplifier (gyro-TWA) operating at a center frequency of 372 GHz is designed and simulated. The window is based on the multilayer design and has the requirement of greater than -30 dB reflection over 24 GHz bandwidth

Simulation and experiments of a W-band extended interaction oscillator based on a pseudospark-sourced electron beam

This paper presents the first experimental results of an extended interaction oscillator (EIO) based on a pseudospark-sourced electron beam, which produced a peak output power over 38 W at W-band. The advantages of the newly developed device are: 1) transport of the electron beam by the positive-ion focusing channel without the need of an external magnetic field and 2) high interaction impedance and high gain per unit length of the EIO circuit. The experimental results agree well with the 3-D particle-in-cell simulations

Multi-mode coupling wave theory for helically corrugated waveguide

Helically corrugated waveguide has been used in various applications such as gyro-backward wave oscillators, gyro-traveling wave amplifier and microwave pulse compressor. A fast prediction of the dispersion characteristic of the operating eigenwave is very important when designing a helically corrugated waveguide. In this paper, multi-mode coupling wave equations were developed based on the perturbation method. This method was then used to analyze a five-fold helically corrugated waveguide used for X-band microwave compression. The calculated result from this analysis was found to be in excellent agreement with the results from numerical simulation using CST Microwave Studio and vector network analyzer measurements

A multiple-hole input coupler for a 372 GHz gyro-travelling wave amplifier

The design of a multiple-hole coupler that operates at a center frequency of 372 GHz for use in a gyrotron travelingwave amplifier (gyro-TWA) is presented. In simulations, the coupler achieved 35% bandwidth from 289GHz to–410 GHz with transmission losses of -0.5 dB predicted

Input coupling systems for millimetre-wave gyrotron travelling wave amplifiers

Input couplers for millimetre-wave gyrotron travelling wave amplifiers are presented in this study. A W-band input coupling system composed of a pillbox window, a smoothly curved waveguide bend, a T-junction and a broadband reflector was numerically optimised, constructed and measured. An average transmission coefficient of −2.0 dB over a designed operating frequency range was measured. Additionally, a higher-frequency input coupler for operation at a central frequency of 372 GHz was also designed based on a multiple-hole coupling configuration. The simulated transmission coefficient was −0.5 dB if the ohmic loss is not considered

Amplification of frequency-swept signals in a W-band gyrotron travelling wave amplifier

The frequency agility of a W-band gyrotron travelling wave amplifier (gyro-TWA) was demonstrated by the amplification of a frequency-swept input signal (chirp signal). The gyro-TWA was developed to provide high output power and wide bandwidth by using a helically corrugated interaction region. In the experiment a ~0.5 W signal of linearly swept frequency bandwidth of 1 GHz was amplified and a gain of over 30 dB was measured when driven by a 40 keV, 1.5 A, axis-encircling electron beam

Measurement of an upgraded input coupling system for W-band gyro-TWA

A gyrotron traveling-wave amplifier (gyro-TWA) operating at W-band has been upgraded and experimentally measured. In this paper, the design and measurement of the upgraded input coupling system for the gyro-TWA is presented. In the measurement, the transmission coefficient of the coupler is at an optimal level of about -1 dB

TE10 R-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