skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Design of a high efficiency relativistic backward wave oscillator with low guiding magnetic field

Abstract

A high efficiency relativistic backward wave oscillator working at a low guiding magnetic field is designed and simulated. A trapezoidal resonant reflector is used to reduce the modulation field in the resonant reflector to avoid overmodulation of the electron beam which will lead to a large momentum spread and then low conversion efficiency. The envelope of the inner radius of the slow wave structure (SWS) increases stepwise to keep conformal to the trajectory of the electron beam which will alleviate the bombardment of the electron on the surface of the SWS. The length of period of the SWS is reduced gradually to make a better match between phase velocity and electron beam, which decelerates continually and improves the RF current distribution. Meanwhile the modulation field is reduced by the introduction of nonuniform SWS also. The particle in cell simulation results reveal that a microwave with a power of 1.8 GW and a frequency of 14.7 GHz is generated with an efficiency of 47% when the diode voltage is 620 kV, the beam current 6.1 kA, and the guiding magnetic field 0.95 T.

Authors:
; ; ; ; ; ; ; ; ;  [1]
  1. Science and Technology on High Power Microwave Laboratory, Northwest Institute of Nuclear Technology, Xi'an 710024 (China)
Publication Date:
OSTI Identifier:
22600045
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 23; Journal Issue: 7; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; BEAM CURRENTS; EFFICIENCY; ELECTRIC POTENTIAL; ELECTRON BEAMS; ELECTRONS; GHZ RANGE 01-100; LENGTH; MAGNETIC FIELDS; MICROWAVE RADIATION; MODULATION; OSCILLATORS; PHASE VELOCITY; RELATIVISTIC RANGE; SIMULATION; SURFACES

Citation Formats

Li, Xiaoze, Song, Wei, Tan, Weibing, Zhang, Ligang, Su, Jiancang, Zhu, Xiaoxin, Hu, Xianggang, Shen, Zhiyuan, Liang, Xu, and Ning, Qi. Design of a high efficiency relativistic backward wave oscillator with low guiding magnetic field. United States: N. p., 2016. Web. doi:10.1063/1.4954903.
Li, Xiaoze, Song, Wei, Tan, Weibing, Zhang, Ligang, Su, Jiancang, Zhu, Xiaoxin, Hu, Xianggang, Shen, Zhiyuan, Liang, Xu, & Ning, Qi. Design of a high efficiency relativistic backward wave oscillator with low guiding magnetic field. United States. doi:10.1063/1.4954903.
Li, Xiaoze, Song, Wei, Tan, Weibing, Zhang, Ligang, Su, Jiancang, Zhu, Xiaoxin, Hu, Xianggang, Shen, Zhiyuan, Liang, Xu, and Ning, Qi. Fri . "Design of a high efficiency relativistic backward wave oscillator with low guiding magnetic field". United States. doi:10.1063/1.4954903.
@article{osti_22600045,
title = {Design of a high efficiency relativistic backward wave oscillator with low guiding magnetic field},
author = {Li, Xiaoze and Song, Wei and Tan, Weibing and Zhang, Ligang and Su, Jiancang and Zhu, Xiaoxin and Hu, Xianggang and Shen, Zhiyuan and Liang, Xu and Ning, Qi},
abstractNote = {A high efficiency relativistic backward wave oscillator working at a low guiding magnetic field is designed and simulated. A trapezoidal resonant reflector is used to reduce the modulation field in the resonant reflector to avoid overmodulation of the electron beam which will lead to a large momentum spread and then low conversion efficiency. The envelope of the inner radius of the slow wave structure (SWS) increases stepwise to keep conformal to the trajectory of the electron beam which will alleviate the bombardment of the electron on the surface of the SWS. The length of period of the SWS is reduced gradually to make a better match between phase velocity and electron beam, which decelerates continually and improves the RF current distribution. Meanwhile the modulation field is reduced by the introduction of nonuniform SWS also. The particle in cell simulation results reveal that a microwave with a power of 1.8 GW and a frequency of 14.7 GHz is generated with an efficiency of 47% when the diode voltage is 620 kV, the beam current 6.1 kA, and the guiding magnetic field 0.95 T.},
doi = {10.1063/1.4954903},
journal = {Physics of Plasmas},
number = 7,
volume = 23,
place = {United States},
year = {Fri Jul 15 00:00:00 EDT 2016},
month = {Fri Jul 15 00:00:00 EDT 2016}
}
  • A klystron-like relativistic backward wave oscillator with a ratio of transverse dimension to free-space wavelength being about four is presented. In the beam-wave interaction region, the electron beam interacts with surface wave and volume wave simultaneously. The cathode holder plays an important role in the reflection of backward waves. A guard electrode, an electron collector ring, and a reflection ring are used to optimize the beam-wave interaction. The particle in cell simulation results reveal that microwaves with a power of 2 GW and a frequency of 12.3 GHz are generated with an efficiency of 42% when the diode voltage ismore » 400 kV, the beam current 12 kA, and the magnetic field 0.48 T.« less
  • A V-band overmoded relativistic backward wave oscillator (RBWO) guided by low magnetic field and operating on a TM{sub 03} mode is presented to increase both the power handling capacity and the wave-beam interaction conversion efficiency. Trapezoidal slow wave structures (SWSs) with shallow corrugations and long periods are adopted to make the group velocity of TM{sub 03} mode at the intersection point close to zero. The coupling impedance and diffraction Q-factor of the RBWO increase, while the starting current decreases owing to the reduction of the group velocity of TM{sub 03} mode. In addition, the TM{sub 03} mode dominates over themore » other modes in the startup of the oscillation. Via numerical simulation, the generation of the microwave pulse with an output power of 425 MW and a conversion efficiency of 32% are achieved at 60.5 GHz with an external magnetic field of 1.25 T. This RBWO can provide greater power handling capacity when operating on the TM{sub 03} mode than on the TM{sub 01} mode.« less
  • Backward wave oscillators (BWO`s) driven by high-current relativistic electron beams are capable of producing high-power coherent radiation in the centimeter and millimeter wavelength regions. However, the efficiency of these devices is usually limited to 15--20% when a homogeneous slow-wave structure is used. Utilizing a two-section slow-wave structure, where the spatial period of the second section is larger than that of the first section, a BWO efficiency of greater than 50% was calculated. A conceptual design of a high-efficiency S-band BWO driven by a 500-kV 5-kA electron beam has been developed and analyzed.
  • A linear theory of the excitation of electromagnetic waves in a plasma filled backward wave oscillator driven by an intense relativistic electron beam is presented. It is found that the spatial growth rate of backward wave instability exhibits a resonant increase for a particular value of fill plasma density. The authors compare the results to the experimental by Minami et al. on a high power backward wave oscillator.
  • The klystron-like relativistic backward wave oscillator (RBWO) combines the transition radiation with Cerenkov radiation and has demonstrated microwave output of high power and high efficiency. The coaxial slow wave structure device can produce microwave with a lower frequency in a smaller cross section. For the purpose of high efficiency, low frequency, and miniaturization, a coaxial klystron-like RBWO with a premodulation cavity is presented. Particle-in-cell simulations show that a microwave with power of 1.15 GW and frequency of 2.1 GHz is generated with conversion efficiency of 48%, whereas for the device with a reflector, the efficiency is 38%.