Fengping Li

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 α 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.

Design and Numerical Optimization of a Cusp-Gun-Based Electron Beam for Millimeter-Wave Gyro-Devices

A novel thermionic cusp electron gun operating in the temperature-limited regime that produces a large-orbit electron beam through a nonadiabatic magnetic-field reversal was designed, analyzed, and optimized to give an electron-beam ideal for driving gyro-devices, particularly in the millimeter-to-submillimeter-wavelength range due to its small cross-sectional size. The annular-shaped axis-encircling electron beam had a beam current of 1.5 A at an acceleration potential of 40 kV, a tunable velocity ratio alpha (= vperp/vz) between one and three, an optimized axial velocity spread A.vx/vz of ~8%, and a relative alpha spread Deltakappa/alpha of ~10% at an alpha value of 1.65.

W-band gyro-devices using helically corrugated waveguide and cusp gun : design, simulation and experiment

This paper presents the design and simulation of W-band Gyro-devices using helically corrugated waveguides as the beam-wave interaction region and a cusp gun as the electron beam source. The electron beam system and the beam-wave interaction were optimized through numerical simulations by using a particle-in-cell (PIC) code MAGIC to predict (calculate) the output power and frequency bandwidth. The beam cross sectional measurement using a scintillator plate confirmed that an axis encircling electron beam was achieved with the designed beam parameters of current 1.5 A and energy 40 keV. The W-band helically corrugated interaction region for the gyrotron backward wave oscillator (Gyro-BWO) was manufactured with a dispersion from 80 GHz to 110 GHz measured using a vector network analyser which was found to be in good agreement with simulations and theory. The Gyro-BWO achieved frequency-tuneable operation by adjusting the magnetic field in the interaction cavity. A -3 dB bandwidth of ~84-104 GHz and output power ~10 kW were simulated using the electron beam from the cusp gun. The gyrotron travelling wave amplifier (Gyro-TWA) is designed to have a -3 dB frequency bandwidth of 90-100 GHz, output power of 10 kW and saturated amplification gain of 40 dB.

Design and simulation of a ~390?GHz seventh harmonic gyrotron using a large orbit electron beam

A similar to 390 GHz harmonic gyrotron based on a cusp electron gun has been designed and numerically modelled. The gyrotron operates at the seventh harmonic of the electron cyclotron frequency with the beam interacting with a TE71 waveguide mode. Theoretical as well as numerical simulation results using the 3D particle-in-cell code MAGIC are presented. The cusp gun generated an axis-encircling, annular shaped electron beam of energy 40 keV, current 1.5 A with a velocity ratio alpha of 3. Smooth cylindrical waveguides have been studied as the interaction cavities and their cavity Q optimized for 390 GHz operation. In the simulations similar to 600W of output power at the design frequency has been demonstrated.

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.

Updates on a W-band Gyro-BWO using a helically corrugated waveguide experiment

The experimental demonstration of a W-band gyrotron backward-wave oscillator (gyro-BWO) using both thermionic cusp electron gun and helically corrugated waveguide will be presented. The cusp gun is designed to generate an axis-encircling electron beam of 1.5 A at 40 kV with an adjustable velocity ratio of up to 3.0. The beam had a simulated axial velocity spread (Δvz/vz) of ~8% and alpha spread (Δ α /α) of ~10%. The beam had an averaged radius of 0.35 mm and beam thickness of 0.05 mm which is ideal to drive sub-mm wave gyro-devices under investigation. The gyro-BWO has been experimentally measured and the latest results will be presented.

10.4: Experimental demonstration of a W-band gyro-BWO using a helically corrugated waveguide

The experimental demonstration of a W-band gyro-BWO using both thermionic cusp electron gun and helically corrugated waveguide 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 ∼8% and alpha spread of ∼10%. 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. The gyro-BWO has been constructed and designed to produce pulsed millimeter wave output radiation in the frequency range 84GHz to 104GHz.

The simulation of an high power 390GHz large-orbit harmonic gyrotron

This paper presents the design and simulation of a 390 GHz harmonic gyrotron operating with a TE71 mode at the 7th electron cyclotron harmonic of a large orbit electron beam from a cusp electron gun. The electron beam has an energy of 40 keV, beam current of 1.5 A, an adjustable pitch alpha from 1 to 2 with a minimum beam velocity spread and scalloping in the beam trajectory. Interaction region based on cylindrical waveguide with smooth inner surface and slotted structures have been studied. Theoretical analysis and numerical simulation results of this source operating at THz frequencies are presented.

A ∼10kW W-Band Gyro-BWO using a helically corrugated waveguide

Presented in this paper are the results of a 10 kW W-Band Gyro-BWO based on a helically corrugated interaction region and novel cusp electron gun. Microwave measurements of the helically corrugated interaction region are shown to give a low loss of 1dB over the frequency region of interest (84-104 GHz). The measured dispersion was found in good agreement with the analytically calculated and numerically simulated dispersions. The design and simulation results of the cusp electron gun of the Gyro-BWO device are given in this paper.

A W-Band Gyro-BWO using a helically corrugated waveguide

Presented in this paper is the design of a W-Band Gyro-BWO with a helically corrugated waveguide and a cusp electron gun. The interaction region has been constructed with good accuracy and microwave results measured using a vector network analyzer are given. The microwave dispersion agrees well with analytical and numerical theory. The transmission loss of this helically corrugated waveguide was measured to be ~1dB over the frequency range (84 - 104GHz). A cusp electron gun has been designed to generate a 1.5A, 40kV electron beam with an adjustable pitch angle (α) of up to 3. The beam was optimized through numerical simulation with an axial velocity spread, ΔVz/Vz, of 7% and Δα/α, of 10.4% at α=1.65. From simulation of the beam-wave interaction the maximum output power from the Gyro-BWO was predicted to be 10kW (CW) at 17% efficiency, with a 3dB frequency tuning range of ~84-104GHz.