Theory of gyro-backward wave oscillators with tapered magnetic field and waveguide cross section

Nusinovich, Gregory S.; Dumbrajs, O.

doi:10.1109/27.532945

Cited by 61 publications

(14 citation statements)

References 20 publications

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“…Following experiments with moderate energy electron beam and high energy electron beam were performed to obtain kilowatt-level 2,8-10 to megawatt-level [11][12][13] millimeter wave sources, but the fast tuning bandwidth was less than expected. Theoretical and simulation works were then motivated by experiments for studying the essential properties of gyro-BWO, e.g., the start oscillation criteria (linear properties), [14][15][16] the saturation efficiency of the beamwave interaction, [17][18][19][20][21][22][23] and the nonstationary oscillation of the gyro-BWO (nonlinear properties). 24,25 The theoretical analysis and numerical simulation formed the basis of the experimental design and have been extensively applied on the study of the efficiency enhancement of gyro-BWO induced by the magnetic field tapering 18,19,21 or the tapering of waveguide wall radius.…”

Section: Introductionmentioning

confidence: 99%

Linear and nonlinear behaviors of gyrotron backward wave oscillators

Chen

2012

Physics of Plasmas

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Linear and nonlinear behaviors of gyrotron backward wave oscillators (gyro-BWO) were investigated by both analytical theories and direct numerical calculations. Employing two-scale-length expansion, an analytical linear dispersion relation corresponding to absolute instabilities in a finite-length system has been derived. Detuning from the beam-wave resonance condition due to the finite amplitude radiation fields, meanwhile, was found to play the crucial roles in the nonlinear physics. Near the start oscillation of the gyro-BWO, the radiation field amplitude saturates when the resonance broadening is comparable to the linear growth rate. Far beyond the start oscillation threshold, the beam-wave resonance detuning effectively shortens the interaction length toward that corresponding to the critical oscillation length for the given beam current. The theoretically predicted scaling laws for the linear stability properties and nonlinear stationary states of the gyro-BWO are in good agreement with numerical results.

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Section: Introductionmentioning

confidence: 99%

Linear and nonlinear behaviors of gyrotron backward wave oscillators

Chen

2012

Physics of Plasmas

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“…On the other hand, a gyro-device operating with a traveling-wave and a nonresonant-microwave structure can provide a broadband smooth frequency tuning by variation of the magnetic field or the electron beam energy. The gyro-BWO operation has been theoretically analyzed in detail (see, e.g., [1]- [4]) and successfully realized in a number of experiments [5]- [7]. In the experimental studies at the Naval Research Laboratory [5] and the National Tsing Hua University [6], pulsed Ka-band gyro-BWO operation at the fundamental cyclotron harmonic and fundamental mode of a smooth cylindrical waveguide was demonstrated with voltage-and magnetic-frequency tuning of up to 5% and 13%, respectively, a very high efficiency (for BWO) of nearly 20% and a pulsed power up to 100 kW.…”

Section: Introductionmentioning

confidence: 99%

Frequency-Tunable CW Gyro-BWO With a Helically Rippled Operating Waveguide

Самсонов

Денисов

Bratman

et al. 2004

IEEE Trans. Plasma Sci.

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Operation of a continuous wave gyrotron backward-wave oscillator (gyro-BWO) with a helically rippled operating waveguide has been experimentally studied. The gyro-BWO exploits a dc oil-cooled magnet with magnetic field up to 0.5 T and utilizes a weakly relativistic (20 keV) electron beam produced by a magnetron injection gun. Stable generation at the second cyclotron harmonic with a maximum power of 7 kW and an efficiency of 15% at a frequency of 24.7 GHz was achieved. Smooth oscillation frequency tuning by varying the magnetic field was measured to be as wide as 5% at the half-power level. The first gyro-BWO operation with a single-stage energy recovery system was realized. The use of a depressed collector provided an efficiency increase up to 23% and an opportunity for reduction of the main power supply voltage down to 10 kV.Index Terms-Continuous wave (CW) high-power microwave device, cyclotron-resonance maser, gyrotron backward-wave oscillator (gyro-BWO), smooth-frequency tuning.

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“…12,13 Either cylindrical or rectangular waveguides are usually used as the interaction structures of gyro-BWOs. [1][2][3][4][5][6][7][8][9][10][11][12][13] Various transverse waveguide modes may be resonantly excited by matching the beam-wave resonance condition when the beam current exceeds their start-oscillation currents.…”

Section: Introductionmentioning

confidence: 99%

“…1 Start oscillation conditions were analyzed using the linear theory. [2][3][4] Nonlinear analysis revealed that properly tapering the magnetic field can enhance the efficiency of the gyro-BWO from 10-15% to 25-30%.…”

Section: Introductionmentioning

confidence: 99%

Effects of tapering structures on the characteristics of a coaxial-waveguide gyrotron backward-wave oscillator

2011

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This study analyzes the characteristics of a gyrotron backward-wave oscillator (gyro-BWO) with a longitudinally tapered coaxial-waveguide by using a single-mode, self-consistent nonlinear code. Simulation results indicate that although tapering the inner wall or the outer wall can significantly raise the start-oscillation current, the former is more suitable for mode selection than the latter because an increase of the start-oscillation current by a tapered inner wall heavily depends on the chosen C value (i.e., the average ratio of the outer radius to the inner radius over the axial waveguide length). Selective suppression of the competing mode by tapering the inner wall is numerically demonstrated. Moreover, efficiency of the coaxial gyro-BWO is increased by tapering the outer wall. Properly down-tapering the outer wall ensures that the coaxial gyro-BWO can reach a maximum efficiency over twice that with a uniform one.

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Theory of gyro-backward wave oscillators with tapered magnetic field and waveguide cross section

Cited by 61 publications

References 20 publications

Linear and nonlinear behaviors of gyrotron backward wave oscillators

Linear and nonlinear behaviors of gyrotron backward wave oscillators

Frequency-Tunable CW Gyro-BWO With a Helically Rippled Operating Waveguide

Effects of tapering structures on the characteristics of a coaxial-waveguide gyrotron backward-wave oscillator

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