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Plasma Science, IEEE Transactions on

Issue 3 • Date June 2002

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Displaying Results 1 - 25 of 63
  • Amplification mechanism in the output section of the harmonic multiplying gyrotron traveling-wave amplifier

    Publication Year: 2002 , Page(s): 931 - 937
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (536 KB) |  | HTML iconHTML  

    Particle-in-cell (PIC) code simulations have been carried out to investigate the physical mechanism responsible for the wave amplification in the output section of a harmonic-multiplying gyrotron traveling-wave tube. Simulation results demonstrate that the injected signal frequency plays an important role in determining the wave growth process. This is because the initial frequency mismatch in the input section influences the extent of bunching at the entrance of the output section and the slope of the electron phase trajectory. For a small frequency mismatch, the amplification arises entirely from the second harmonic generation due to the bunching at the fundamental frequency. As the mismatch is increased, the bunched electrons start to disperse early in the output section, and the wave amplification is then dominated by the cyclotron maser instability. The electron axial velocity spread is observed to substantially degrade the device performance. View full abstract»

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  • A gyrotron-traveling-wave tube amplifier experiment with a ceramic loaded interaction region

    Publication Year: 2002 , Page(s): 885 - 893
    Cited by:  Papers (61)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (508 KB) |  | HTML iconHTML  

    The design and experimental study of a 35-GHz gyrotron-traveling-wave tube (gyro-TWT) amplifier operating in the circular TE01 mode at the fundamental cyclotron harmonic are presented. The interaction circuit in this experiment consisted of a new type of ceramic loading that provided the required loss for stable operation. A saturated peak power of 137 kW was measured at 34.1 GHz, corresponding to a saturated gain of 47.0 dB and an efficiency of 17%, with a -3-dB bandwidth of 1.11 GHz (3.3%). Peak output powers in the range of 102.1 to 148.6 kW with -3-dB bandwidths of 1.26 and 0.94 GHz, respectively, were measured by varying the operating parameters. The gyro-TWT was found to be zero-drive stable at these operating points, demonstrating that ceramic loading is a highly effective means of suppressing spurious oscillations in gyro-TWTs. This type of ceramic loading has the added advantage of being compatible with high average power operation. View full abstract»

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  • Particle-in-cell code simulations on a rising-sun magnetron oscillator

    Publication Year: 2002 , Page(s): 956 - 961
    Cited by:  Papers (15)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (854 KB)  

    A high-power rising-sun magnetron oscillator (AX-9) operating at 9.50 GHz is examined by the use of a three-dimensional particle-in-cell (PIC) code, MAGIC3D. A mode spectrum of the 18 vanes rising-sun magnetron cavity is obtained from both an analytic field theory and the numerical code MAGIC3D. A large mode separation in the vicinity of a π-mode is observed in the rising-sun configuration. A time evolved electron flow exhibits nine space charge spokes in the PIC simulations, which confirms the π-mode oscillation in the 18 vanes rising-sun magnetron. When space charge spokes build up in the interaction region, a single frequency RF oscillation starts to grow and the leakage current escaping from the interaction region reduces to zero. Simulations predict that the saturated radiation power measured at the output waveguide is 250 kW at 9.50 GHz, corresponding to a magnetron efficiency of 53% where the external magnetic field is 0.52 T and the beam voltage and current are 28 kV and 17 A, respectively. View full abstract»

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  • Possibilities for multifrequency operation of a gyrotron at FZK

    Publication Year: 2002 , Page(s): 828 - 835
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (471 KB) |  | HTML iconHTML  

    We investigate the possibility of multifrequency operation of a 140-GHz gyrotron, which is designed to operate in the TE22,8 mode at 140 GHz and the TE19,6 mode at 111 GHz or the TE17,6 mode at 105 GHz, for which existing equipment can be used. The present calculations compute beam properties for a given set of coil currents, accelerating voltage and current, and then use these beam properties to compute the output power and efficiency. These calculations are performed separately for each mode. View full abstract»

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  • Crossed-field amplifier simulations using a moving wavelength computer code

    Publication Year: 2002 , Page(s): 962 - 979
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1654 KB)  

    A moving wavelength particle in cell computer code has been used to study the interaction in emitting sole crossed-field amplifiers (CFAs). Results of the study of magnetrons using a related code have been published previously. The CFA results echo many of the features of the magnetron results. Application of the code to a cold cathode, pulsed CFA showed the existence of chaotic fluctuations in the space charge which we believe are related to noise in experimental CFAs. A major feature of these fluctuations is voids in the charge above the cathode which propagate slower than the RF wave (and, hence, travel backward in the moving reference frame). As the voids pass beneath the base of the spokes they modulate the amount of charge entering the spokes and enhance the chaotic behavior. The spokes recirculate from output to input becoming partially debunched in the process. Differing amounts and distributions of the space charge recirculated result in the computed power and phase pushing varying from pass-to-pass of the moving wavelength around the CFA anode. The fluctuations in field at the cathode and the pass-to-pass fluctuations are used as a measure of the fluctuation of the simulation. Two alternative designs have been investigated in an attempt to reduce CFA noise. A nonreentrant design eliminates the pass-to-pass fluctuations. However, the simulations show internal fluctuations commencing shortly after the space charge has built up. Experimentally, noise of this CFA was improved over the baseline design by from 4 to 8 dB depending on the operating frequency. Simulation of an alternate reentrant design with a thermionic cathode capable of a current density which will support a "Slater" solution of the sheath trajectories, showed elimination of the internal space-charge fluctuations. Experimentally, noise of this CFA was improved by 10-30 dB over that of the baseline CFA. Fluctuations observed in the simulations are believed to be a qualitative model of noise generation phenomenon and may help point the way to future reduction of such noise. View full abstract»

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  • Design of a linear C-band helix TWT for digital communications experiments using the CHRISTINE suite of large-signal codes

    Publication Year: 2002 , Page(s): 1053 - 1062
    Cited by:  Papers (18)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (661 KB)  

    A set of optimization goal functions designed to improve the efficiency and linearity performance of helix traveling-wave tubes (TWT) is described. These goal functions were implemented in the CHRISTINE suite of large-signal helix TWT codes along with a steepest-descent optimization algorithm to automate the process of circuit parameter variation and to facilitate the rapid exploration of alternative TWT designs. We compare the predicted power, efficiency, and linearity of four different helix TWT circuits, each developed according to a different set of optimization criteria. Out of these designs, a single design was selected to be further developed for use in C-band high-data-rate communications experiments. The detailed design of this linearized TWT with a predicted 1-dB small-signal bandwidth of 1.2 GHz, small-signal centerband gain of 35.7 dB (fc=5.5 GHz), and centerband saturated output power of 52 dBm (158.5 W) is presented. View full abstract»

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  • Axisymmetric waves in dielectric corrugated rods and systems of periodic dielectric rings

    Publication Year: 2002 , Page(s): 1082 - 1088
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (623 KB) |  | HTML iconHTML  

    A method for simulating axisymmetric waves of electric and magnetic type in dielectric or magnetic corrugated rods and systems of rings are developed. Such electrodynamic systems are attractive for application in relativistic microwave electronics and fiber optics devices and systems. The method described in this article is based on one-dimensional integral equations of the second kind with kernels having logarithmic singularities. A method is suggested for separating desired solutions from others, whose appearance is typical for problems pertaining to finding the eigenvalues for the integral equations under consideration. The results of the simulation of dispersion properties for dielectric rods with sinusoidal corrugation and a series of dielectric circular rings are presented. View full abstract»

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  • The influence of an axial magnetic field on the performance of a coaxial vircator

    Publication Year: 2002 , Page(s): 1186 - 1195
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (902 KB) |  | HTML iconHTML  

    It is shown, using a plane magnetic diode as a model, that an axial magnetic field tends to interfere unfavorably with the operation of a coaxial vircator. When the magnetic field reaches its near cutoff value, the operation of the vircator should cease altogether. View full abstract»

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  • Smooth-bore magnetron simulations using a moving wavelength computer code

    Publication Year: 2002 , Page(s): 980 - 983
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (309 KB) |  | HTML iconHTML  

    A moving wavelength computer code developed for crossed-field amplifier simulations has been used to simulate the operation of a smooth-bore magnetron. Simulations using thermionic emission and a mixture of thermionic and secondary emission have been conducted. The simulations were run for about 24 000 cyclotron periods and were stationary for at least the last 18 000 of these periods. The results show the space charge does not settle to an approximation of a Brillouin state, but instead a charge distribution of lower density extends well beyond the edge of a theoretical Brillouin sheath. A small current reaches the anode. Trajectories extracted from the simulation show a mixture of shapes-some with substantial cycloiding, others with little cycloiding. View full abstract»

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  • Development of a 140-GHz 1-MW continuous wave gyrotron for the W7-X stellarator

    Publication Year: 2002 , Page(s): 808 - 818
    Cited by:  Papers (43)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1877 KB) |  | HTML iconHTML  

    The development of high-power gyrotrons (118 GHz, 140 GHz) in continuous-wave (CW) operation for heating nuclear fusion plasmas has been in progress for several years in a joint collaboration between different European research institutes and industrial partners. The 140-GHz gyrotron being under development for the installation at the W7-X stellarator now under construction at the IPP Greifswald, Germany, operates in the TE28,8 mode and is equipped with a diode type magnetron injection electron gun, an improved beam tunnel, a high mode-purity low-Ohmic loss cavity, an optimized nonlinear up-taper, a highly efficient internal quasi-optical mode converter, a single-stage depressed collector and an edge-cooled, single disk CVD-diamond window. RF measurements at pulse duration of a few milliseconds yielded an RF output power of 1.15 MW at a beam current of 40 A and a beam voltage of 84 kV. Depressed collector operation has been possible up to decelerating voltages of 33 kV without any reduction of the output power. Long pulse operation (10 s at 1 MW) was possible without any signs of a limitation caused by the tube. For this output power the efficiency of the tube could be increased from about 30% without to about 50% with depression voltage. The best performance reached so far has produced an energy per pulse as high as 90 MJ (power 0.64 MW, pulse length 140 s) which is the highest value achieved in gyrotrons operating at this frequency and power level. The pulse-length limitations so far are mainly due to the external system. View full abstract»

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  • The multifrequency spectral Eulerian (MUSE) model of a traveling wave tube

    Publication Year: 2002 , Page(s): 1063 - 1075
    Cited by:  Papers (17)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (849 KB) |  | HTML iconHTML  

    We derive from Eulerian electron beam equations the multifrequency spectral Eulerian (MUSE) model, a new one-dimensional (1-D) nonlinear multifrequency model of a traveling wave tube (TWT). We also derive from the same equations a Lagrangian "disk" model, LATTE, so that MUSE may be directly compared to a Lagrangian approach. The models are compared to the large signal code Christine 1-D on a set of TWT parameters which are based on a single section of the Hughes 8537H L-band TWT. Aspects of the physics, nonlinearities, and simulation dimensions of the MUSE model are discussed, as well as its relation to the method of collective variables. A simplified MUSE model S-MUSE useful for analysis is also presented and its applications are discussed. View full abstract»

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  • Linear dispersion relation of backward-wave oscillators with finite-strength axial magnetic field

    Publication Year: 2002 , Page(s): 1134 - 1146
    Cited by:  Papers (15)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (850 KB) |  | HTML iconHTML  

    The linear dispersion relation of backward wave oscillators (BWOs) with finite strength axial magnetic field is derived and calculated numerically. Axisymmetric mode radiation in a slow wave structure (SWS) with corrugated metal wall including a column of relativistic electron beam streaming along the lines of a finite strength axial magnetic field is analyzed. Three theoretical achievements viz. (1) the dielectric tensor derived by Bogdankevich et al. (1981), (2) the formulation of EM waves in the beam column that are expressed as a linear combination of extraordinary and ordinary modes elucidated by Antonsen et al., and (3) a consideration of boundary conditions in the beam-SWS system initiated by Swegle et al. (1985) are combined in our numerical code to be exact and universal under the scope of linear treatment. Our dispersion relation can include effects of interaction between a structure mode and electron cyclotron modes in addition to conventional beam space charge modes. Numerical analysis is carried out using the parameters of a BWO experiment at the University of Maryland. The results show the well-known cyclotron absorption of radiation from the BWO at a particular value of magnetic field that was previously analyzed in various ways different from ours. View full abstract»

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  • Full-wave analysis of the field distribution of natural modes in the rectangular waveguide grating based on singular integral equation method

    Publication Year: 2002 , Page(s): 1151 - 1159
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (659 KB) |  | HTML iconHTML  

    The full-wave analysis based on the singular integral equation method is developed to correctly investigate dispersion properties and field distributions inside a rectangular waveguide grating used in low-voltage traveling wave amplifiers. Simplified treatments of periodic structures with rectangular grating are widely used in the analysis of microwave electron beam devices, providing an actually good accuracy for the calculation of dispersion curves of natural modes in a wide range of grating parameters. However, they do not guarantee the correct field distributions in a close proximity to the grating just where an electron beam is usually passed to get more effective beam-wave coupling. The amplitude of the minus-first spatial harmonic, which is mostly responsible for the resonant beam-wave interaction, can be substantially larger than that predicted by the simplified analysis. In addition, the contribution of the higher spatial harmonics to the total field is shown to be significantly larger than that evaluated from the simplified treatment. Consequences of the enhanced influence of higher harmonics on beam-wave interaction are discussed. View full abstract»

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  • Stability of traveling-wave amplifiers with reflections

    Publication Year: 2002 , Page(s): 1089 - 1107
    Cited by:  Papers (23)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1583 KB) |  | HTML iconHTML  

    The maximum achievable gain in individual sections of helix-type traveling-wave amplifiers is limited by the requirement that the device be stable with respect to the excitation of spurious modes. The excited modes may be of two types: backward waves, which are absolutely unstable, or forward waves, which are unstable in the presence of reflections and regenerative amplification. Whether a specific device is unstable depends on a number of details that must be computed numerically. We will present a model, used in the traveling-wave tube simulation code CHRISTINE, in which stability is determined including a number of important effects. These are: the placement of severs, their reflection and transmission coefficients, the profile of attenuation along the interaction length, the presence of a driven signal, and the coupling of forward and backward waves due to asymmetries in the helix support structure. Asymmetries result in a stopband near the "π" point formed by the coupling of the forward and backward waves. For this case, a model is developed to evaluate the maximum stable length. View full abstract»

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  • Dependence on axial magnetic field of radiation from a high-power gas-filled backward wave oscillator

    Publication Year: 2002 , Page(s): 1196 - 1202
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (366 KB) |  | HTML iconHTML  

    Microwave output power from a high-power helium-filled backward wave oscillator (BWO) operating at X band is measured as a function of the strength of guiding magnetic field B and helium gas pressure. Tenuous helium gas filling the slow wave structure is ionized by an injected electron beam with typical parameters of energy 100 keV and current 0.5 kA. The enhancement of output power from the present gas-filled BWO is less than those reported in some previous publications. Near B=0.8 T, we observe the minimum value of output that is judged to result from cyclotron absorption caused by resonant interaction of the fast electron cyclotron mode with the Cherenkov radiation. On both sides of the absorption, two peak outputs near B=0.5 and 1.0 T are measured. In the former case, the output is enhanced compared with vacuum case by the presence of helium gas with pressure of a few mtorr. In the latter case, on the other hand, the output monotonously decreases with the gas pressure. The output powers for the latter case are larger than those of the former case. Both cases are observed repeatedly for various experimental conditions. The physical reasons for the observed results are discussed. View full abstract»

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  • CARM-amplifier in the regime of "nonresonant" trapping of the electron beam

    Publication Year: 2002 , Page(s): 927 - 930
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (291 KB) |  | HTML iconHTML  

    A new version of the regime of electron trapping is proposed for gyro-amplifiers. The use of this regime in the cyclotron resonance maser with a weakly relativistic electron beam can simultaneously provide efficiency as high as 50%, a very broad (tens of percent) frequency band, and very weak sensitivity to the spread in electron velocity. View full abstract»

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  • Nonlinear time-domain analysis of coupled-cavity traveling-wave tubes

    Publication Year: 2002 , Page(s): 1024 - 1040
    Cited by:  Papers (21)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1087 KB) |  | HTML iconHTML  

    A time-dependent nonlinear analysis of a coupled-cavity traveling-wave tube (CCTWT) is presented. The coupled-cavity structure is modeled by a set of equivalent circuit equations where the equations for currents and voltages are coupled to the nearest neighbor cavities. Input and output coupler models as well as sever cavities are included in the formulation. The electron dynamics are treated using the three-dimensional Lorentz force equations although the RF field representation is an analytic model based on cylindrically symmetric geometry. The magnetic focusing fields are also cylindrically symmetric and can be either a solenoid or a periodic permanent magnet stack. The space-charge fields are found by mapping charge to a two-dimensional grid (r, z) and solving Poisson's equation by a finite difference grid formulation. The circuit and Lorentz force equations are integrated in time in a self-consistent manner. The formulation is capable of treating multiple drive frequencies and the associated intermodulation products as well as oscillations and backward wave instabilities. Hence, the model can be used to perform stability analyses. Furthermore, the cavity parameters can be varied to model dynamic velocity tapering for efficiency enhancement. The simulation is applied to the analysis of a sample C-Band CCTWT, and comparisons with measured performance of a Ka-Band CCTWT at Communications and Power Industries, Palo Alto, CA, are made. View full abstract»

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  • A note on current modulation from nonlinear electron orbits

    Publication Year: 2002 , Page(s): 1176 - 1178
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (289 KB)  

    Current modulation on an electron beam, including the effects of charge overtaking, harmonics, and intermodulation products, may be calculated exactly in a one-dimensional geometry once the electron orbit is given. This paper provides a simple proof together with a numerical example in a model that is commonly used in the klystron literature. View full abstract»

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  • Dispersion relation of the electromagnetic waves propagating through a helix inserted into a magnetron-type conducting cylinder

    Publication Year: 2002 , Page(s): 1076 - 1081
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (493 KB) |  | HTML iconHTML  

    The dispersion relation of the electromagnetic waves propagating through a helix is obtained for the helix inserted into a magnetron-type cylindrical conductor. The resultant dispersion relation consists of a combination of helix and magnetron dispersion relations. In special cases, they decouple from each other and recover the previous results. For example, in the case when the magnetron vane structures disappear, the dispersion relation recovers the typical helix dispersion relation. On the other hand, the resultant dispersion relation recovers the magnetron-transverse electric mode when the helix pitch angle φ approaches π/2. View full abstract»

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  • Initial studies of a long-pulse relativistic backward-wave oscillator utilizing a disk cathode

    Publication Year: 2002 , Page(s): 1112 - 1119
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (481 KB)  

    One of the major issues in high-power microwave device operation is pulse shortening, which often limits microwave pulses to less than 100 ns. This has been the focus of many studies on the long-pulse backward-wave oscillator (BWO) at the University of New Mexico. Previous diagnostics have indicated that significant plasma is produced by a graphite knife-edge or "cookie cutter" geometry cathode. This plasma caused the beam to expand radially to match the dimensions of the cutoff neck upon entrance into the slow-wave structure. This effect led to an impedance collapse at which point the microwave production ceased. In recent studies by Loza and colleagues, they have produced intense annular relativistic electron beams that maintain a stable cross section for 1-μs duration utilizing a disk cathode. Whereas the beams produced by Loza and colleagues were not used in microwave sources, we have incorporated such a disk cathode in a long-pulse relativistic BWO to study its effort on pulse shortening. This simple solution has led to an increase in pulselength and radiated microwave power up to a factor of two as compared to the "cookie cutter" cathode. View full abstract»

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  • Selective multichannel feedback

    Publication Year: 2002 , Page(s): 1147 - 1150
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (344 KB)  

    A simple and effective method of mode selection in oversized electrodynamic systems is described. The method is based on forming a solitary resonant combination of eigenmodes by a system of Bragg reflectors having a different azimuthal symmetry at the ends of the electrodynamic system. Application of this method to a resonant traveling-wave tube is considered. View full abstract»

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  • Use of the Kompfner dip effect in multistage gyro-TWTs of high average power

    Publication Year: 2002 , Page(s): 922 - 926
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (358 KB) |  | HTML iconHTML  

    Very often, in order to realize a high-gain operation of gyro-traveling-wave tubes (gyro-TWTs), the tubes are designed as multistage amplifiers, in which each section is short enough and thus, stable. In such tubes, the wave amplified in the input and intermediate stages should be absorbed at their ends by matching loads, which often limits the average power capability of these devices. This limitation can be avoided if these stages operate in the regime of the wave absorption by an electron beam. A long time ago, such a regime in conventional TWTs driven by linear electron beams was studied by Kompfner (1950), so the effect of wave attenuation in the gain curve is known as the Kompfner dip. In the present paper, we consider a two-stage (gyro-)TWT in which the first section operates in the Kompfner dip regime. The small-signal theory is developed, which allows one to analyze the tradeoffs in the small-signal gain and bandwidth associated with this kind of operation. The large-signal simulations indicate that such a two-stage gyro-TWT can operate with the orbital efficiency of 40% (total efficiency of 15%) and the gain over 40 dB. View full abstract»

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  • A simulation study of beam loading on a cavity

    Publication Year: 2002 , Page(s): 1160 - 1168
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (656 KB)  

    Beam loading exerts a strong influence on the operation of high-power and medium-power microwave sources. This paper reports a simulation study of beam loading on a cavity using the two-dimensional particle-in-cell code, MAGIC. We vary the beam voltage, the beam current, the degree of current modulation on the dc beam before the beam enters the cavity, and the degree of charge neutralization on the beam. We deduce the beam-loaded quality factor Q and the beam-loaded resonant frequency from a Lorentzian fit of the numerical data on the gap voltage response as a function of the driving frequency. The MAGIC simulations have revealed several unanticipated results. The beam loading is observed to be a function of perveance. Constant perveance beams, of varying voltage and current, exercise about the same degree of beam loading on the model klystron cavity (except, of course, for the cases with very small beam current). The inclusion of an ac component on the dc beam current has no effect on the degree of beam loading; neither does the neutralization of the electron beam. Many of these simulation results cannot be explained by existing theories that ignore ac space charge effects. View full abstract»

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  • Analysis of a broadband Q band folded waveguide traveling-wave tube

    Publication Year: 2002 , Page(s): 1017 - 1023
    Cited by:  Papers (18)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (553 KB) |  | HTML iconHTML  

    A highly reproducible, low-cost folded waveguide traveling-wave-tube amplifier is designed using the Pierce theory and a three-dimensional (3-D) particle-in-cell (PIC) code. The amplifier is designed to operate at 40-48 GHz with peak output radiation power of 200 W. Initial circuit parameters are obtained from the Pierce theory and circuit dispersion relations. A nonlinear large-signal performance of the amplifier is predicted from 3-D PIC simulations. Simulations show that the amplifier produces a saturated radiation power of 200 W at 44 GHz, corresponding to 5.6% electronic efficiency where the beam voltage and current are 21 kV and 0.17 A, respectively. A saturated 3-dB bandwidth is found to be 16% (40.5-47.5 GHz). View full abstract»

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  • The dependence of microwave radiation from a beam-driven turbulent plasma on the beam-to-plasma density ratio

    Publication Year: 2002 , Page(s): 1203 - 1210
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (680 KB)  

    When an intense relativistic electron beam is injected into an unmagnetized plasma, the plasma develops into a strong Langmuir turbulence state, and high-power broadband microwave radiation is emitted. The emission source has been confirmed to be the modulated beam interacting with the caviton fields. Total power of this radiation depends on the beam-to-plasma density ratio almost in the same way as the level of the beam modulation. The present paper indicates that by performing two and a half-dimensional particle-in-cell simulations, this dependence comes from the dependence of activity or the beam electron-plasma electron two-stream instability on the beam-to-plasma density ratio. View full abstract»

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IEEE Transactions on Plasma Sciences focuses on plasma science and engineering, including: magnetofluid dynamics and thermionics; plasma dynamics; gaseous electronics and arc technology.

 

 

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