Development of a Collector with Multistage Recuperation for Gyrotron
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TRON AND ION OPTICS
Development of a Collector with Multistage Recuperation for Gyrotron O. I. Loukshaa, * and P. A. Trofimova aPeter
the Great St. Petersburg Polytechnic University, St. Petersburg, 195251 Russia *e-mail: [email protected] Received July 19, 2019; revised July 19, 2019; accepted November 21, 2019
Abstract—A four-stage collector system is developed for the experimental gyrotron at the Peter the Great St. Petersburg Polytechnic University based on spatial separation of electrons with different energies in crossed electric and magnetic fields. The conditions of use of this system for the efficient recuperation of electron residual energy in a spent beam are determined. The numerical simulation of the recuperator and the analysis of the electric and magnetic field distribution in the gyrotron collector region are accomplished. Theoretical estimations and trajectory analysis of the helical electron beam show that the system developed provides the electron residual energy recuperation necessary to achieve total gyrotron efficiency over 70%. DOI: 10.1134/S1064226920080082
INTRODUCTION Nowadays, gyrotrons are the most efficient powerful devices operating in the millimeter and submillimeter wavelength ranges. These devices occupy a special niche between traditional vacuum devices and optical devices, which are limited in output power and efficiency in these ranges. Gyrotrons are applied for heating plasma in controlled nuclear fusion facilities, high-resolution spectroscopy, thermal material processing, and some other applications (see, for example, [1]). A gyrotron is a maser that operates using cyclotron resonance and the energy of transverse electron motion in a helical electron beam (HEB) to generate high-frequency electromagnetic radiation. Gyrotron electronic efficiency ηel determined by the efficiency of the electron energy transfer to high-frequency radiation usually does not exceed 30–40% [2]. The energy of the spent beam remained after electron interaction with the high-frequency field in the resonator is dissipated in the form of heat on the collector of the device. Using collectors with recuperation of the beam residual energy is a promising way to improve the total efficiency of gyrotrons and other vacuum RF-frequency devices. In these devices, the collector voltage is negative in respect to the device body; therefore, before deposition on metal walls, electrons are decelerated in the electric field and consequently give up part of their energy to the electric circuit. Presently, collector systems with single-stage energy recuperation are widely introduced in powerful gyrotrons. The total efficiency of these gyrotrons attains 50–55% [1–3]. A further increase in the effi-
ciency can be achieved by implementing collector systems with multistage energy recuperation. In systems of this kind, spatial separation of fractions of electrons with different kinetic energies occurs with subsequent deposition of these fractions on collector electrodes with different retarding potentials. In the gyrot
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