Design, simulation and experiment of a cusp electron beam for millimeter wave gyro-devices

The design, simulation and experiment of a thermionic cusp electron gun that is to be used for millimeter wave generation will be presented. A cusp gun uses a non-adiabatic magnetic field reversal to obtain azimuthal motion on an electron beam resulting in an annular shaped, axis-encircling beam. The cusp gun was designed to generate a beam of 1.5A at 40kV with an adjustable velocity ratio of up to 3.0. The beam had a simulated axial velocity spread of 7.4% and alpha spread of 10.1%. The beam had an averaged radius of 0.35mm and beam thickness of 0.05mm which is ideal to drive sub-mm wave gyro-devices under investigation

Bandwidth study of the microwave reflectors with rectangular corrugations

The mode-selective microwave reflector with periodic rectangular corrugations in the inner surface of a circular metallic waveguide is studied in this paper. The relations between the bandwidth and reflection coefficient for different numbers of corrugation sections were studied through a global optimization method. Two types of reflectors were investigated. One does not consider the phase response and the other does. Both types of broadband reflectors operating at W-band were machined and measured to verify the numerical simulations

A cusp electron gun for millimeter wave gyrodevices

The experimental results of a thermionic cusp electron gun, to drive millimeter and submillimeter wave harmonic gyrodevices, are reported in this paper. Using a "smooth" magnetic field reversal formed by two coils this gun generated an annular-shaped, axis-encircling electron beam with 1.5 A current, and an adjustable velocity ratio alpha of up to 1.56 at a beam voltage of 40 kV. The beam cross-sectional shape and transported beam current were measured by a witness plate technique and Faraday cup, respectively. These measured results were found to be in excellent agreement with the simulated results using the three-dimensional code MAGIC

Theory and simulations of a gyrotron backward wave oscillator using a helical interaction waveguide

A gyrotron backward wave oscillator (gyro-BWO) with a helically corrugated interaction waveguide demonstrated its potential as a powerful microwave source with high efficiency and a wide frequency tuning range. This letter presents the theory describing the dispersion properties of such a waveguide and the linear beam-wave interaction. Numerical simulation results using the PIC code MAGIC were found to be in excellent agreement with the output measured from a gyro-BWO experiment

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

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

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

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

Demonstration of a high power broadband mm-wave gyro-TWA

Design and experimental results of a broadband, high power, millimetre-wave gyrotron traveling wave amplifier (gyro-TWA) operating in the 75-110 GHz frequency band and based on a helically corrugated interaction region (HCIR) and cusp electron beam source are presented. The second harmonic cyclotron mode of the electron beam was used to match the dispersion of an eigenwave in the HCIR, achieving energy transfer from the electrons to waves over a large frequency range. The gyro-TWA was measured to generate a maximum power of a few kWs with an unsaturated gain of 36-38 dB in the driving frequency band of 91-96.5 GHz