Magnetron-Injection Gun with Increased Current for Frequency Tunable Medium Power Sub-THz Gyrotron
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Magnetron-Injection Gun with Increased Current for Frequency Tunable Medium Power Sub-THz Gyrotron V. N. Manuilov 1 & A. E. Fedotov 1 & I. V. Zotova 1 S. Mitsudo 2 & M. Yu. Glyavin 1
1
2
& R. M. Rozental & T. Idehara &
Received: 21 April 2020 / Accepted: 17 September 2020/ # Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract
A magnetron-injection gun able to provide very high ratio tj≈ 0.5 of the beam current to the Langmuir current has been designed, while maintaining good enough quality and stability of a formed helical electron beam. The specific feature of the gun is the shape of the cathode with two singular points of the electric field distribution which ensure close to uniform electric field profile within the emitter ring for wide range of operating currents. The gun provides the smoothed dependence of the beam parameters for currents up to 1.5–2 A and is suitable for wide (~ 10 GHz) frequency range gyrotron operation with the central frequency of 0.2 THz and output power ~ 1 kW within the whole tuning band. Such approach for the magnetron-injection gun design can be used for development of other promising high power sub-THz gyrotrons. Keywords Gyrotron . Positronium . Wide frequency tuning . Electron beam optics . Magnetroninjection gun
1 Introduction Development of medium power (0.1–1 kW) frequency tunable sub-THz gyrotrons with the tuning band of at least a few percent is highly demand for a large number of modern applications. In particular, one of such applications is related to direct measurement of positronium hyperfine structure (Ps-HFS) which is promising for experimental testing of some
* I. V. Zotova [email protected]
1
Institute of Applied Physics of the Russian Academy of Sciences, Nizhny Novgorod, Russia
2
Research Center for Development of Far-Infrared Region, University of Fukui (FIR UF), Fukui, Japan
Journal of Infrared, Millimeter, and Terahertz Waves
predictions given by quantum electrodynamics [1–6]. Hyperfine transition of Ps-HFS can be provided in a Fabry-Perot cavity pumped by radiation with frequency near 203.4 GHz and power of 0.5–1 kW which in this frequency band can be provided by gyrotrons only [7–9]. At the same time, for high-accuracy Ps-HFS measurements, the radiation source with an operating frequency near 203.4 GHz should be smoothly tunable by about 3–6 GHz with maintaining the high power level within the whole tuning band [6]. A well-known method for electronic frequency tuning in gyrotrons is excitation of high-order axial modes in relatively long cavities with a small frequency difference between neighboring modes [10–13]. However, the gyrotron efficiency and the output power under described conditions drop dramatically with increasing the axial index q of the operating mode due to the influence of the electron velocity spread. At the same time, significant reduction of sensitivity of high-order (q > 1) axial modes to the velocity spread can be provided with using specially shortened gyrotron cavities with a normalized length severa
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