The Experts below are selected from a list of 300 Experts worldwide ranked by ideXlab platform
Gregory S. Nusinovich - One of the best experts on this subject based on the ideXlab platform.
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Wave coupling in sheet and multiple beam Traveling Wave Tubes
Physics of Plasmas, 2009Co-Authors: Gregory S. Nusinovich, S J Cooke, M Botton, Baruch LevushAbstract:To increase the power level of the sources of coherent electromagnetic radiation at frequencies from 100 GHz up to the terahertz range it makes sense to develop devices with a spatially extended interaction space. Sheet-beam and multiple-beam devices belong to the category. In the present paper the small-signal theory of Traveling-Wave Tubes with sheet-beam and multiple sheet-beam configurations is developed. It is shown that in such Tubes the Wave coupling on electron beams may occur even in small-signal regimes. The Wave coupling and its role for amplification of forward and excitation of backward Waves in such amplifiers is studied. Also the effect of transverse nonuniformity of the electromagnetic field on the device operation is analyzed and illustrated by several examples.
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analytical theory of frequency multiplying gyro Traveling Wave Tubes
Physics of Plasmas, 2001Co-Authors: Gregory S. Nusinovich, W Chen, Victor L. GranatsteinAbstract:The theory is developed which describes analytically the gain and bandwidth in frequency-multiplying gyro-Traveling-Wave-Tubes. In this theory the input Waveguide is considered in the small-signal approximation. Then, in the drift region separating the input and output Waveguides, the electron ballistic bunching evolves which causes the appearance in the electron current density of the harmonics of the signal frequency. The excitation of the output Waveguide by one of these harmonics is considered in a specified current approximation. This makes the analytical study of a large-signal operation possible. The theory is illustrated by using it to analyze the performance of an existing experimental tube.
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Phase stability in gyro-Traveling-Wave-Tubes
IEEE Transactions on Electron Devices, 2001Co-Authors: Gregory S. Nusinovich, JIMMIE RODGERS, W Chen, Victor L. GranatsteinAbstract:This paper describes theoretical and experimental studies of the\nphase stability in frequency-multiplying gyro Traveling-Wave-Tubes\n(gyro-TWTs). The theory is developed under assumptions that 1) an input\nWaveguide operates in a small-signal regime; 2) a drift region is free\nof microWaves; and 3) an output Waveguide can be analyzed in a specified\ncurrent approximation. By using these assumptions, one can develop an\nanalytical theory describing the phase sensitivity of\nfrequency-multiplying gyro-TWTs. The calculations were done for the\nparameters of a frequency-doubling gyro-TWT which was studied\nexperimentally. In the experiments, the beam voltage and magnetic field\nphase pushing factors were measured. The experimental results are in\nreasonable agreement with theoretical predictions. These results can be\nused for evaluating the restrictions on fluctuations in the beam voltage\nand current and the magnetic field which should be fulfilled for\nproviding a required level of phase stability in gyro-TWTs
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chaotic oscillations enhanced by magnetosonic Waves in plasma filled Traveling Wave Tubes
Physics of Plasmas, 1998Co-Authors: Yu P Bliokh, Gregory S. Nusinovich, M G Liubarskii, V O Podobinskii, Ya B Fainberg, S Kobayashi, Y Carmel, Victor L. GranatsteinAbstract:A theory of plasma-filled Traveling-Wave Tubes (TWTs) is developed in which the effect of magnetosonic Waves excited in plasma by the operating Wave is taken into account. These Waves are excited by the ponderomotive force caused by the radial inhomogeneity of the axial component of the electric field of the operating Wave. In the simplest case considered in the paper, this effect leads to an additional reactive nonlinearity in the Wave envelope equation. This leads to a shrinkage of the region of stable oscillations in TWTs with the feedback causing the self-excitation; at the same time, the region of stochastic oscillations becomes larger. The radiation spectrum of stochastic oscillations in plasma-filled TWTs in which magnetosonic Waves are excited is much wider and more continuous than the spectrum of stochastic oscillations in vacuum TWTs with the same feedback.
S.t. Blunk - One of the best experts on this subject based on the ideXlab platform.
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Gain stability of Traveling Wave Tubes
IEEE Transactions on Electron Devices, 1999Co-Authors: D.m. Goebel, W L Menninger, J.g. Keller, S.t. BlunkAbstract:The long-term gain stability of Traveling Wave Tubes (TWT's) with helix slow-Wave structures is examined. A major variable in the gain of TWT's is the stability of the attenuator material that is placed in the tube to damp oscillations and improve input-to-output isolation. Thin carbon layers are often used for this purpose in TWT's and are deposited onto the helix support rods by several different techniques that produce a variability in the material structure and properties. The carbon layers are also susceptible to physical damage due to the environment in the tube during conditioning and long-term operation. Modification of the electrical conductivity of the layer by energetic particle bombardment and chemical erosion decreases the net RF loss in the tube and causes the gain to increase with time. The presence of impurity gases and rapid conditioning procedures produce gain increases due to the lattice damage of the attenuator material of up to 10 dB in a TWT in the first several hundred hours of operation. Properly designed attenuator loss-patterns and minimization of the gas evolution in the TWT causes these effects to saturate and the gain to stabilize quickly. Techniques to ensure long-term stability of these layers are discussed.
D.m. Goebel - One of the best experts on this subject based on the ideXlab platform.
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improved model of long term gain increases in Traveling Wave Tubes
IEEE Transactions on Electron Devices, 2015Co-Authors: Ryan W Conversano, D.m. GoebelAbstract:An improved model to predict the gain increases in Traveling-Wave Tubes (TWTs) during long-term operation is presented. The conventional gain growth model describes the pressure variation in a TWT over its life using an exponential decrease from the initial outgassing level to a constant base pressure. This model often shows an inability to capture the gain change behavior of many Tubes during the transition between early life burn-in and long-term operation, leading to a significant underprediction of long-term gain increases. The model is improved here first through the introduction of another pressure-related term associated with desorption of gas from the tube’s inner surfaces that exhibits a $t^{\mathrm {\mathbf {-1/2}}}$ time dependence. This new pressure dependence is governed by the behavior of a Langmuirian adsorption isotherm. Second, the exponential pressure decay term is separated into two terms associated with early life and long-term operation with different outgassing time constants. The improved model shows a significantly better matching of long-term TWT gain growth data compared to the conventional model. In addition, the improved model predicts a more physical pressure behavior in the TWT with time.
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development of linear Traveling Wave Tubes for telecommunications applications
IEEE Transactions on Electron Devices, 2001Co-Authors: D.m. Goebel, W L Menninger, Ronglin Liou, Xiaoling Zhai, E A AdlerAbstract:Traveling Wave Tubes (TWTs) designed for telecommunications applications in multichannel power amplifiers (MCPAs) are required to have high linearity, low intermodulation distortion, high efficiency and high power outputs. The linearity of the TWT can be greatly improved by operation of the tube significantly backed off from saturation and by optimization of the design of the helix circuit. This results in two tone intermodulation products that are 25 to 40 dB below the carrier level, depending on the amount of back-off selected. However, operation backed off from saturation results in a greatly reduced efficiency of the TWT, which must be compensated for by optimal circuit and collector design. Several L-band and S-band Hughes TWTs have been developed for telecommunications applications and feature saturated power levels of up to 2 kW and average power of over 600 W with overall efficiencies of over 20% at 10 dB back-off and 40% at 6 dB back-off. These Tubes provide high average power, high efficiency amplification with modest size and reduced cooling requirements compared to solid state amplifiers.
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Gain stability of Traveling Wave Tubes
IEEE Transactions on Electron Devices, 1999Co-Authors: D.m. Goebel, W L Menninger, J.g. Keller, S.t. BlunkAbstract:The long-term gain stability of Traveling Wave Tubes (TWT's) with helix slow-Wave structures is examined. A major variable in the gain of TWT's is the stability of the attenuator material that is placed in the tube to damp oscillations and improve input-to-output isolation. Thin carbon layers are often used for this purpose in TWT's and are deposited onto the helix support rods by several different techniques that produce a variability in the material structure and properties. The carbon layers are also susceptible to physical damage due to the environment in the tube during conditioning and long-term operation. Modification of the electrical conductivity of the layer by energetic particle bombardment and chemical erosion decreases the net RF loss in the tube and causes the gain to increase with time. The presence of impurity gases and rapid conditioning procedures produce gain increases due to the lattice damage of the attenuator material of up to 10 dB in a TWT in the first several hundred hours of operation. Properly designed attenuator loss-patterns and minimization of the gas evolution in the TWT causes these effects to saturate and the gain to stabilize quickly. Techniques to ensure long-term stability of these layers are discussed.
Sheel Aditya - One of the best experts on this subject based on the ideXlab platform.
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wideband power combining of four microfabricated w band Traveling Wave Tubes
IEEE Transactions on Electron Devices, 2017Co-Authors: Shaomeng Wang, Sheel AdityaAbstract:Wideband power combining of four W-band microfabricated Traveling-Wave Tubes (TWTs) is presented. The proposed TWTs are based on a planar helix slow-Wave structure (SWS) with straight-edge connections (PH-SEC) that can be microfabricated with stripline input–output feed. A novel 1:4 WR-10 Waveguide-to-stripline power divider–combiner is designed that covers the frequency range of 92–104 GHz. The simulation results show that ${S}_{{11}}$ is less than −20 dB and the magnitude and phase differences among the four output signals are less than 0.01 dB and 0.41°, respectively, indicating a power combining efficiency as high as 99.9%. The power divider, four PH-SEC SWSs, and the power combiner are assembled and the performance of the overall assembly is checked by simulation. The overall ${S}_{{11}}$ is better than −15 dB in the frequency range of 91.7–100.7 GHz and ${S}_{{21}}$ is better than −12.3 dB. Effects of power and phase variation of individual TWTs have also been considered. With four 5-kV and 10-mA sheet electron beams, particle-in-cell simulations show that the combined TWTs can give 25-W saturation peak power at 94 GHz with a gain of 18 dB.
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vane loaded planar helix slow Wave structure for application in broadband Traveling Wave Tubes
IEEE Transactions on Electron Devices, 2015Co-Authors: Krithi Swaminathan, Chen Zhao, Ciersiang Chua, Sheel AdityaAbstract:Dispersion control of a planar helix slow-Wave structure (SWS) using vane loading for applications in Traveling-Wave Tubes has been studied. The addition of metal vanes and coplanar ground planes to the planar helix structure has been investigated with the help of simulations aimed at achieving low or negative dispersion. It is shown that, similar to the case of circular helix, the addition of metallic vanes to the planar helix can produce a flatter dispersion curve or negative dispersion characteristics. Furthermore, it is shown that even stronger dispersion control can be achieved by the use of metal vanes together with extended coplanar ground planes on the dielectric substrates that support the planar helix. As a proof of concept, one of the designs of the planar helix SWS including metal vanes and operating at S-band frequencies has been fabricated and tested; the measured phase velocity results match the simulation results very well.
Baruch Levush - One of the best experts on this subject based on the ideXlab platform.
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large signal 2 d modeling of folded Waveguide Traveling Wave Tubes
IEEE Transactions on Electron Devices, 2016Co-Authors: Igor A Chernyavskiy, David Chernin, Thomas M. Antonsen, K T Nguyen, Alexander N Vlasov, Baruch LevushAbstract:A new computationally efficient 2-D large-signal code TESLA-FW has been developed to model Traveling Wave Tubes (TWTs) using folded (or serpentine) Waveguide (FW) slow-Wave structures. The code incorporates a recently published shunt-loaded transmission line model of the structure and takes advantage of a new time advance algorithm recently implemented in the code TESLA-CC. The new code has been applied to modeling $G$ -band (220 GHz) serpentine and FW TWTs. Results compare very favorably with those obtained from the 3-D particle-in-cell (PIC) code MAGIC3D and with experimental data. Typical running times of TESLA-FW are 1–2 orders of magnitude less than those of 3-D PIC codes.
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Wave coupling in sheet and multiple beam Traveling Wave Tubes
Physics of Plasmas, 2009Co-Authors: Gregory S. Nusinovich, S J Cooke, M Botton, Baruch LevushAbstract:To increase the power level of the sources of coherent electromagnetic radiation at frequencies from 100 GHz up to the terahertz range it makes sense to develop devices with a spatially extended interaction space. Sheet-beam and multiple-beam devices belong to the category. In the present paper the small-signal theory of Traveling-Wave Tubes with sheet-beam and multiple sheet-beam configurations is developed. It is shown that in such Tubes the Wave coupling on electron beams may occur even in small-signal regimes. The Wave coupling and its role for amplification of forward and excitation of backward Waves in such amplifiers is studied. Also the effect of transverse nonuniformity of the electromagnetic field on the device operation is analyzed and illustrated by several examples.
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Recent advances in modeling of Traveling Wave Tubes
2009 IEEE International Conference on Microwaves Communications Antennas and Electronics Systems, 2009Co-Authors: David Chernin, John Petillo, Thomas M. Antonsen, Baruch LevushAbstract:Traveling Wave Tubes (TWTs) remain the amplifiers of choice in many ground and space-based applications requiring the production of broadband high frequency microWave and millimeter Wave power with high efficiency. All modern TWTs are designed using sophisticated computer-based design tools that are based on the fundamental physical laws governing the emission, transport, interaction, and collection of electron beams. This paper provides an overview of a state-of-the-art suite of modeling and design tools for the end-to-end simulation of coupled-cavity and helix Traveling Wave Tubes.
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nonlinear time domain analysis of coupled cavity Traveling Wave Tubes
International Vacuum Electronics Conference, 2002Co-Authors: H P Freund, Thomas M. Antonsen, Baruch Levush, E G Zaidman, J LegarraAbstract:Coupled-cavity Traveling Wave Tubes are used for radar and communication applications. The interaction structure is composed of a series of cavities that are connected via slots and a beam tunnel. Typically, the beam tunnel radius is a small fraction of the transverse cavity dimensions and is a negligible contributor to the cold circuit dispersion of the structure. As in many slow-Wave devices, the flow of power in the structure is predominantly near the cavity walls and propagates from cavity to cavity through the slots. We describe a 2.5-D, hybrid, time-domain formulation where the structure is modeled by an equivalent circuit, but the electron beam is treated using models for the RF and magnetostatic fields and a Poisson solver for the space-charge fields. Electron dynamics are adapted from a previously-described time-domain helix TWT simulation code and are fully 3-D. The formulation implicitly includes several important physical processes needed to simulate CCTWTs.
