Simulation of low-frequency collective processes in gyrotron electron beams

Abstract

UDC 621.385We simulate collective processes in an electron space charge trapped between the cathode and the magnetic mirror in gyrotron-type systems using the particle-in-cell method. Threshold conditions of excitation and frequency-amplitude characteristics of low-frequency oscillations connected with the development of an instability in a space charge in the trap are determined using a gyrotron with an output power of 100 kW and a radiation wavelength of 4 mm as an example. The mechanism of the instability development in an ensemble of anharmonic electron oscillators is proposed and used to analyze the method of oscillation suppression based on varying the magnetic-field distribution in the region of the beam compression. The influence of low-frequency oscillations on the parameters of the electron beam entering the cavity is studied. The obtained calculation data are compared with the results of the experiments studying the parameters of low-frequency collective processes in gyrotrons.

Simulation of high-efficiency gyrotron with the system of multistage energy recovery

“…The increased velocity spreads limits the possibilities of gyrotron operations at high average pitch ratio because realization of electron beam with high  and δv  can lead to high percentage of electron reflection from the magnetic mirror resulting in development of the parasitic low-frequency oscillations in the trap between the cathode and the resonator [4,6,22,23]. Based on the experimental data obtained in the SPbPU gyrotron, the threshold coefficient of electron reflection from the mirror R th corresponding to excitation of these oscillations was determined to be approximately 1.7•10 -3 [10].…”

Improvement of the helical electron beam quality and the gyrotron efficiency by controlling the electric field distribution near a magnetron injection gun

“…Among the mech anisms underlying low frequency (LF) oscillations in an HEB, one can separate out an instability that devel ops in the space charge captured by a specific trap between the cathode and a magnetic mirror (the final part of the region where the beam compresses magnet ically before it enters into the cavity). RF fields due to parasitic oscillations add to the spread of the electron velocity longitudinal and transverse components in the HEB, cause a spread in the total velocity (energy spread), change the transverse configuration of the beam, result in electron bombardment of the cathode surface, and generate secondary electrons [4][5][6][7][8][9]. A desired quality of the beam entering into the cavity can be achieved by suppressing parasitic oscillations in the electron space charge.…”

Simulation on the interaction between particles and fields for gyroklystron amplifier

“…As one of the most important high power millimeter wave source, gyroklystron amplifier has been largely studied over years. In order to improve the performance of gyroklystron amplifier, numerical simulations (Yan et al , 1999; Luksha, 2009; Glyavin et al , 2009; Liu et al , 2010; Li et al , 2003; Latham et al , 1994) of the interaction between particles and fields play an important role in this aspect as they can predict some nonlinear effects that decide the performance of the device (e.g. saturated output power, electronic efficiency, saturated 3‐dB bandwidth) and therefore facilitate the design of devices.…”