Study of High-Power Ka-Band Rectangular Double-Grating Sheet Beam BWO
TL;DR: In this article, a double-grating rectangular waveguide is used as the slow wave structure (SWS) for high power Ka-band electron beam backward wave oscillator, in which a high power sheet beam is used with a cross section of 30 mm.
Abstract: It is attractive to use sheet beam vacuum devices to generate high frequency, high-power microwave radiation. In this paper, we present the numerical and experimental studies of a high-power Ka-band sheet electron beam backward wave oscillator (BWO), in which the double-grating rectangular waveguide is used as the slow wave structure (SWS) for its thermal and mechanical robustness. The fundamental mode of this kind of SWS is an antisymmetric mode which has an antisymmetric longitudinal field distribution and will nonsynchronously interact with the electron beam on two sides of the electron channel along the vertical direction. We put forward a method to overcome this trouble in this paper. To drive this BWO, a high-power sheet beam is used with a cross section of 30 mm $\times\,$ 1 mm. A thin graphite cathode is used for its superiority in producing a high current, high-quality electron beam. For an experimental electron beam of 141 kV and 1668 A, the output power of over 46.8 MW at 31.68 GHz is obtained, which corresponds to a beam–wave interaction efficiency of 19.9%. Compared with the conventional hollow beam BWO and the single-grating rectangular waveguide sheet beam BWO, the double-grating sheet beam BWOs efficiency is higher, which indicates that the double-grating sheet beam device is promising for producing millimeter wave radiation with high power and high efficiency.
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TL;DR: In this article, a slow-wave structure (SWS) was proposed to enhance the performance of high-power backward wave oscillators (BWOs). The design features a periodic metallic ring insertion and a deeply corrugated cylindrical waveguide, serving to improve interaction impedance and flexibility in dispersion curve engineering.
Abstract: We present a novel slow-wave structure (SWS) to significantly enhance the performance of high-power backward wave oscillators (BWOs). The design features a periodic metallic ring insertion and a deeply corrugated cylindrical waveguide. Both serving to improve interaction impedance and flexibility in dispersion curve engineering. A new technique for mode control in waveguides is also introduced. In addition to demonstrating mode control in SWSs, the key aspects of the presented design are mode dominance reversal and a 100% improvement in interaction impedance that can be exploited to achieve greater power conversion efficiency and output mode purity. Performance comparisons on group velocity, phase velocity and interaction impedance of the new SWS versus the conventional corrugated waveguide are provided. We extend the concept of inhomogeneous SWSs by designing a three-section inhomogeneous SWS. Further simulations using a Particle in Cell code of a highly efficient three-section inhomogeneous K
a
-band BWO generates a peak output power of a 5.92 MW at 27 GHz with a 58% peak efficiency.
21 citations
Additional excerpts
...7% [8] and 35% [2] have been reported....
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TL;DR: A Ka-band overmoded Cherenkov-type high power millimeter wave generator that was well controlled to be TM(0n) mode and the microwave power radiated in the far field was as high as about 500 MW.
Abstract: 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 to be TM(0n) mode.
20 citations
TL;DR: In this article, a novel slow-wave structure called quasi-parallel-plate (QPP) is proposed for terahertz (THz) backward-wave oscillator BWO design.
Abstract: In this paper, a novel slow-wave structure (SWS), called quasi-parallel-plate (QPP), is proposed for terahertz (THz) backward-wave oscillator BWO design. Compared with the conventional SWSs, the novel SWS has a wider “cold” bandwidth and higher interaction impedance. The Particle-in-cell (PIC) results show that the BWO can produce over 0.82 W output power in the operating frequency range from 0.82 to 1 THz by utilizing an operating voltage range from 5 to 10 kV. The interaction efficiency over the entire operating frequency band is above 2.8%. This SWS, which employing a circular electron beam of 3 mA, can be considered as a promising THz SWS for BWO design with characteristics of moderate operating voltage, wide tunable bandwidth, high efficiency, and compact structure.
10 citations
TL;DR: In this paper, a high-power Ka-band traveling-wave tube (TWT) driven by a sheet electron beam is proposed and demonstrated by means of the simulation and experimental methods.
Abstract: In this paper, a high-power Ka-band traveling-wave tube (TWT) driven by a sheet electron beam is proposed and demonstrated by means of the simulation and experimental methods. The single grating rectangular waveguide with large width-to-height ratio is used as the slow-wave structure (SWS). An $E$ -plane bend energy coupler is put forward to feed this wide SWS. An irregular transition structure between the input waveguide and the SWS is suggested and designed, which is beneficial to suppress the self-excited oscillation. For a practical electron beam (20 mm $\times \,\, 1$ mm, 150.1 kV, 850 A, and 20-ns), the output power of this single rectangular grating sheet beam TWT is larger than 750 kW from 34.5 to 35.4 GHz. The maximum power is 1.21 MW at 35 GHz, corresponding to a gain of 20.4 dB.
9 citations
Cites background from "Study of High-Power Ka-Band Rectang..."
...frequency can be calculated out [1], [2], [23]...
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TL;DR: In this paper, a high-power 200-GHz extended interaction oscillator (EIO) was designed by large-signal analysis, where the authors calculated the mode called, here, as ${L}_{{1}} $ to be the most efficient one for our structure.
Abstract: A high-power 200-GHz extended interaction oscillator (EIO) is designed by large-signal analysis. Analyzing different resonant modes, we calculated the mode called, here, as ${L}_{{1}} $ to be the most efficient one for our structure. From eigenmode analysis, it was predicted that the resonator-slow wave structure (SWS) coupling region has a considerable effect on resonant RF mode due to a ${L}_{{1}} \rightarrow {L}_{-{1}} $ mode transformation, where ${L}_{-{1}} $ is a parasitic low-output power resonant mode of the resonator. Using the eigenmode outcomes in addition to large-signal results, we found the optimum dimensions for the coupling region. The designed oscillator was then simulated by Particle-in-Cell (PIC) solver, leading to approximately the same results as those predicted by the mentioned procedure. The observed mode competition of different modes of the oscillator is analyzed and then removed by inserting a lossy layer at a proper location. By properly introducing a stub mode tuner near the output coupler, we could selectively excite the ${L}_{{1}} $ mode and maximize the RF output power to values even higher than those observed in the absence of mode tuner. Stable RF powers up to 2 kW are predicted to be obtainable by the sheet electron beams with beam densities lower than the state of the art.
7 citations
Cites background from "Study of High-Power Ka-Band Rectang..."
...Development of the sheet electron beams has also affected other high-power MMW sources such as traveling-wave tube amplifiers [13], [14] and backward-wave oscillators [15]....
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References
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TL;DR: In this paper, the capabilities for vacuum electronic device (VED) sources of powerful terahertz (THz) and near-THz coherent radiation, both CW or average and pulsed, were evaluated.
Abstract: Recent research and development has been incredibly successful at advancing the capabilities for vacuum electronic device (VED) sources of powerful terahertz (THz) and near-THz coherent radiation, both CW or average and pulsed. Currently, the VED source portfolio covers over 12 orders of magnitude in power (mW-to-GW) and two orders of magnitude in frequency (from ; 10 THz). Further advances are still possible and anticipated. They will be enabled by improved understanding of fundamental beam-wave interactions, electromagnetic mode competition and mode control, along with research and development of new materials, fabrication methods, cathodes, electron beam alignment and focusing, magnet technologies, THz metrology and advanced, broadband output radiation coupling techniques.
860 citations
"Study of High-Power Ka-Band Rectang..." refers background or methods in this paper
...A great many laboratories, such as the Los Alamos National Laboratory, the Stanford Linear Accelerator Center, the Naval Research Laboratory, the University of California-Davis, the University of Wisconsin-Madison, and IECAS have published reports on the design of sheet beam VEDs [2], [3], [7]–[15]....
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...VACUUM electron devices, with high power, high frequency are a nature choice for spectroscopy of materials [1], high-data communications, concealed weapon or threat detection [2], high-resolution radar [3], and so on....
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TL;DR: In this article, the contemporary plasma physics and other related issues of compact, high power mmw-to-THz sources are compared and contrasted to those of classic HPM generation, and future research challenges and opportunities are discussed.
Abstract: Homeland security and military defense technology considerations have stimulated intense interest in mobile, high power sources of millimeter-wave (mmw) to terahertz (THz) regime electromagnetic radiation, from 0.1 to 10THz. While vacuum electronic sources are a natural choice for high power, the challenges have yet to be completely met for applications including noninvasive sensing of concealed weapons and dangerous agents, high-data-rate communications, high resolution radar, next generation acceleration drivers, and analysis of fluids and condensed matter. The compact size requirements for many of these high frequency sources require miniscule, microfabricated slow wave circuits. This necessitates electron beams with tiny transverse dimensions and potentially very high current densities for adequate gain. Thus, an emerging family of microfabricated, vacuum electronic devices share many of the same plasma physics challenges that are currently confronting “classic” high power microwave (HPM) generators including long-life bright electron beam sources, intense beam transport, parasitic mode excitation, energetic electron interaction with surfaces, and rf air breakdown at output windows. The contemporary plasma physics and other related issues of compact, high power mmw-to-THz sources are compared and contrasted to those of HPM generation, and future research challenges and opportunities are discussed.
533 citations
"Study of High-Power Ka-Band Rectang..." refers background or methods in this paper
...A great many laboratories, such as the Los Alamos National Laboratory, the Stanford Linear Accelerator Center, the Naval Research Laboratory, the University of California-Davis, the University of Wisconsin-Madison, and IECAS have published reports on the design of sheet beam VEDs [2], [3], [7]–[15]....
[...]
...VACUUM electron devices, with high power, high frequency are a nature choice for spectroscopy of materials [1], high-data communications, concealed weapon or threat detection [2], high-resolution radar [3], and so on....
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TL;DR: In this article, two rectangular cross-section magnetic configurations capable of focusing in both transverse dimensions are investigated: (i) a closed-side two-plane PCM configuration that is topologically equivalent to conventional round-cross-section PPM focusing; and (ii) an open-side configuration that uses ponderomotive PCM focusing in the vertical plane and simple vzBy Lorentz force focusing in horizontal plane.
Abstract: Sheet electron beams focused by periodically cusped magnetic (PCM) fields are stable against low‐frequency velocity‐shear instabilities (such as diocotron mode). This is in contrast to more familiar unstable behavior in uniform solenoidal magnetic fields. Two rectangular‐cross‐section magnetic configurations capable of focusing in both transverse dimensions are investigated: (i) a closed‐side two‐plane PCM configuration that is topologically equivalent to conventional round‐cross‐section PPM focusing; and (ii) an open‐side configuration that uses ponderomotive PCM focusing in the vertical plane and simple vzBy Lorentz force focusing in the horizontal plane. Both configurations are capable of stable sheet beam confinement. The open‐side configuration appears more practical both for focusing and for realizing matched (cold) beam conditions in which the beam envelope is free from oscillations. For realistic beams with finite emittance, the existence of a matched cold beam solution implies less emittance grow...
139 citations
TL;DR: In this paper, a half-period-staggered double-vane array and a high-aspect ratio sheet electron beam were designed for high-power wideband submillimeter-wave generation.
Abstract: A novel slow-wave vacuum electron device circuit, consisting of a half-period-staggered double-vane array and a high-aspect ratio sheet electron beam, has been conceived for a high-power wideband submillimeter-wave generation. A particle-in-cell simulation, which is based on a finite-difference time-domain algorithm, has shown that this circuit has a very wide intrinsic bandwidth (in excess of 50 GHz around the operating frequency of 220 GHz) with a moderate gain of 13 dB/cm. Moreover, the saturated conversion efficiency is predicted to be 3%-5.5% over the operating band corresponding to an output power of 150-275 W, assuming a beam power of 5 kW. Of particular importance, this structure is based on the TE-fundamental mode interaction, thereby avoiding the complex over moding instabilities that usually cause spurious signal oscillation in conventional high-aspect-ratio structures. This planar circuit has simple 2-D geometry that is thermally and mechanically robust as well as being compatible with conventional microfabrication techniques. This concept is expected to open numerous opportunities in potential applications of versatile electronic devices in the low-millimeter- and submillimeter-wave regions.
132 citations
"Study of High-Power Ka-Band Rectang..." refers background in this paper
...However, unlike the staggered double-grating structure, the fundamental mode of the double-grating rectangular waveguide is an antisymmetric mode [16], [17]....
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TL;DR: In this article, the beam matching and side focusing for sheet beams of finite width is discussed and a review of past and present theoretical and experimental investigations of sheet beam transport is presented.
Abstract: Sheet electron beams focused by periodically cusped magnetic (PCM) fields are stable against low‐frequency velocity‐shear instabilities (such as the diocotron mode). This is in contrast to the more familiar unstable behavior in uniform solenoidal magnetic fields. A period‐averaged analytic model shows that a PCM‐focused beam is stabilized by ponderomotive forces for short PCM periods. Numerical particle simulations for a semi‐infinite sheet beam verify this prediction and also indicate diocotron stability for long PCM periods is less constraining than providing for space‐charge confinement and trajectory stability in the PCM focusing system. In this article the issue of beam matching and side focusing for sheet beams of finite width is also discussed. A review of past and present theoretical and experimental investigations of sheet‐beam transport is presented.
64 citations