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Title: Factors influencing the temporal growth rate of the high order TM{sub 0n} modes in the Ka-band overmoded Cherenkov oscillator

Abstract

When the wavelength of overmoded Cherenkov oscillator goes into Ka-band, power handling capacity becomes an essential issue. Using the TM{sub 02} mode or higher order TM{sub 0n} modes as the operating mode is a potential solution. This paper is aimed to find some proper parameters to make the temporal growth rate of the TM{sub 02} mode higher in our previously studied Gigawatt (GW)-class Ka band oscillator. An accurate and fast calculation method of the “hot” dispersion equation is derived for rectangular corrugated SWSs, which are widely used in the high frequency Cherenkov devices. Then, factors that affect the temporal growth rate of the high order TM{sub 0n} modes are analyzed, including the depth of corrugation, the radius of drift tube, and the diode voltage. Results show that, when parameters are chosen properly, the temporal growth rate of the TM{sub 02} mode can be as high as 0.3 ns{sup −1}.

Authors:
; ;  [1]
  1. College of Photoelectric Science and Engineering, National University of Defense Technology, Changsha 410073 (China)
Publication Date:
OSTI Identifier:
22410445
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 22; Journal Issue: 6; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; CALCULATION METHODS; CHERENKOV RADIATION; DISPERSION RELATIONS; DRIFT TUBES; ELECTRIC POTENTIAL; OSCILLATION MODES; OSCILLATORS; WAVELENGTHS

Citation Formats

Wu, Dapeng, E-mail: vipbenjamin@163.com, Shu, Ting, and Ju, Jinchuan. Factors influencing the temporal growth rate of the high order TM{sub 0n} modes in the Ka-band overmoded Cherenkov oscillator. United States: N. p., 2015. Web. doi:10.1063/1.4921932.
Wu, Dapeng, E-mail: vipbenjamin@163.com, Shu, Ting, & Ju, Jinchuan. Factors influencing the temporal growth rate of the high order TM{sub 0n} modes in the Ka-band overmoded Cherenkov oscillator. United States. doi:10.1063/1.4921932.
Wu, Dapeng, E-mail: vipbenjamin@163.com, Shu, Ting, and Ju, Jinchuan. Mon . "Factors influencing the temporal growth rate of the high order TM{sub 0n} modes in the Ka-band overmoded Cherenkov oscillator". United States. doi:10.1063/1.4921932.
@article{osti_22410445,
title = {Factors influencing the temporal growth rate of the high order TM{sub 0n} modes in the Ka-band overmoded Cherenkov oscillator},
author = {Wu, Dapeng, E-mail: vipbenjamin@163.com and Shu, Ting and Ju, Jinchuan},
abstractNote = {When the wavelength of overmoded Cherenkov oscillator goes into Ka-band, power handling capacity becomes an essential issue. Using the TM{sub 02} mode or higher order TM{sub 0n} modes as the operating mode is a potential solution. This paper is aimed to find some proper parameters to make the temporal growth rate of the TM{sub 02} mode higher in our previously studied Gigawatt (GW)-class Ka band oscillator. An accurate and fast calculation method of the “hot” dispersion equation is derived for rectangular corrugated SWSs, which are widely used in the high frequency Cherenkov devices. Then, factors that affect the temporal growth rate of the high order TM{sub 0n} modes are analyzed, including the depth of corrugation, the radius of drift tube, and the diode voltage. Results show that, when parameters are chosen properly, the temporal growth rate of the TM{sub 02} mode can be as high as 0.3 ns{sup −1}.},
doi = {10.1063/1.4921932},
journal = {Physics of Plasmas},
number = 6,
volume = 22,
place = {United States},
year = {Mon Jun 15 00:00:00 EDT 2015},
month = {Mon Jun 15 00:00:00 EDT 2015}
}
  • Particle simulation and experimental results are presented about a Ka-band overmoded Cherenkov-type high power millimeter wave generator in this paper. The relativistic electron beam with peak current of 8.4 kA was generated by a pulsed power accelerator working at the voltage of 625 kV, which was guided by an axial magnetic field of 1.05 T and transported through the beam-wave interaction structures. After careful calibration, the microwave power radiated in the far field was as high as about 500 MW, with a frequency of 32.1 GHz and a pulse width of 20 ns. The radiation mode was well controlled tomore » be TM{sub 0n} mode.« less
  • By combining the Cerenkov-type generator with the cascaded resonators, this paper proposes a Ka-band relativistic backward wave oscillator operating under the guide magnetic field 1.0 T with high power handling capability and high conversion efficiency. It is found that TM{sub 02} can be selected as the operation mode in order to increase the power handling capability and provide sufficient coupling with the electron beam. In slow wave structure (SWS), ripples composed of semicircle on top of the rectangle enhance the wave-beam interaction and decrease the intensity of the electric field on the metallic surface. Taking advantage of the resonator cascades, themore » output power and the conversion efficiency are promoted greatly. The front cascaded resonators efficiently prevent the power generated in SWS from leaking into the diode region, and quicken the startup of the oscillation due to the premodulation of the beam. However, the post cascade slightly postpones the startup because of the further energy extraction from the electron beam. The numerical simulation shows that generation with power 514 MW and efficiency 41% is obtained under the diode voltage 520 kV and current 2.4 kA. And the microwave with the pure frequency spectrum of 29.35 GHz radiates in the pure TM{sub 01} mode.« less
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  • Overmoded O-type Cerenkov generators using annular electron beams are facing the problem of multi-modes output due to the inevitable structural discontinuities. A simple but effective method to achieve the pure TM{sub 01} mode output is applied on the 0.14 THz overmoded surface wave oscillator (SWO) in this paper. In spite of still using an overmoded slow wave structure to ensure the easy fabrication, the followed smooth circular waveguide is shrinkingly tapered to the output waveguide with appropriate radius that it cuts off other higher modes except TM{sub 01} mode. Moreover, the modified device here has the same power capacity as themore » previous one according to the numerical analysis. By optimized lengths of the transition waveguide and tapered waveguide, particle-in-cell simulation results indicate that the subterahertz wave with output power increased 14.2% at the same frequency is obtained from the proposed SWO under the previous input conditions, and importantly, the output power is all carried by TM{sub 01} mode as expected. Further simulation results in the pulse regime confirm the feasibility of the optimized structure in the actual experiments. This simple and viable design is also applicable to overmoded devices in the lower frequency band of subterahertz wave.« less
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