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Plasma Science, IEEE Transactions on

Issue 3  Part 1 • Date June 2008

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Displaying Results 1 - 25 of 27
  • Table of contents

    Page(s): C1 - 565
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  • IEEE Transactions on Plasma Science publication information

    Page(s): C2
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  • The Twelfth Special Issue on High-Power Microwave Generation

    Page(s): 566 - 568
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  • Space Applications of High-Power Microwaves

    Page(s): 569 - 581
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1179 KB) |  | HTML iconHTML  

    Schemes have been suggested for transferring energy from Earth-to-space, space-to-Earth, and space-to-space using high-power microwave (HPM) beams. All use power beaming. Microwave beams have been studied for propelling spacecraft for launch to orbit, orbit raising, launch from orbit into interplanetary and interstellar space, and deployment of large space structures. The microwave thermal rocket, called the ldquomicrowave thermal thruster,rdquo is a reusable single-stage vehicle that uses an HPM beam to provide power to a heat-exchanger propulsion system, with double the specific impulse of conventional rockets. Orbital missions include orbit raising and space solar power. Microwave-propelled sails are a new class of spacecraft that promises to revolutionize future space probes. Experiments and simulations have verified that sails riding beams can be stable on the beam for conical sail shapes. Beam-driven sail flights have now demonstrated the basic features of the beam-driven propulsion. Beams can also carry angular momentum and communicate it to a sail to help control it in flight. An early mission for microwave space propulsion is dramatically shortening the time needed for sails to escape Earth's orbit. A number of missions for beam-driven sails have been quantified for high-velocity mapping of the outer solar system, Kuiper Belt, the Heliopause, and the penultimate interstellar precursor mission. For large HPM systems at fixed effective isotropic radiated power, minimum capital cost is achieved when the cost is equally divided between antenna gain and radiated power. This is a driver when considering design of power-beaming systems such as interstellar Beacons, which the Search for Extraterrestrial Intelligence is searching for. Much of the technical means for these applications are already in hand. Microwave and millimeter-wave array antennas are already in use for astronomy; sources at high frequencies are being developed for fusion and the military. Develo- - pment of high-power arrays is needed. A synergistic way to develop a space power-beaming infrastructure is incremental buildup, addressing lower power applications first, and then upgrading. View full abstract»

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  • Self-Consistent Electromagnetic–Thermal Model for Calculating the Temperature of a Ceramic Cylinder Irradiated by a High-Power Millimeter-Wave Beam

    Page(s): 582 - 590
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (654 KB) |  | HTML iconHTML  

    The high-power millimeter-wave beams that can be generated by CW gyrotrons represent a promising energy source for rapid high-temperature processing of materials. A program is under way at the Naval Research Laboratory to investigate the heating of ceramic tubes and cylinders using an 83-GHz beam for joining and sintering applications. In this paper, we discuss the scattering and absorption of microwave power by a ceramic cylinder and calculate the resulting temperature profile. The analysis accounts for the temperature dependence of the dielectric properties, an effect that can dramatically alter the microwave coupling during the heating process. In the process under investigation, the cylinder is rotated to promote azimuthally uniform heating so that only the radial dependence of the dielectric properties needs to be included. View full abstract»

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  • Design of a Subterahertz, Third-Harmonic, Continuous-Wave Gyrotron

    Page(s): 591 - 596
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (273 KB) |  | HTML iconHTML  

    The design of a 400-GHz gyrotron operating at the third cyclotron harmonic is presented. The gyrotron is designed to operate at the TE6!4-mode, which allows one to produce about 1 kW of output power with the density of ohmic losses acceptable for continuous operation. The dependence of performance characteristics on various gyrotron parameters (beam voltage, current, pitch-ratio, and velocity spread) is analyzed. It is shown that the desired mode is significantly distinct from competing modes. Special attention is given to the effect of imperfections in resonator fabrication on gyrotron performance. It is found that to keep the gyrotron performance close to the designed data obtained for an ideal resonator shape, the resonator should be fabricated with tolerance of about 1 mum. In view of the recent experimental data, such fabrication seems feasible. Therefore, the development of 1 kW, continuous-wave gyrotrons operating at the third harmonic in this frequency range looks possible. View full abstract»

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  • Observation of Mode Competition in an 11.4-GHz Magnicon Amplifier

    Page(s): 597 - 605
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (572 KB) |  | HTML iconHTML  

    This paper describes the observation of pulse shortening in an 11.4-GHz magnicon amplifier due to competition with a parasitic gyrotron mode. This effect was observed following the installation of a new electron beam collector. The parasitic mode occurred only at high operating powers, when the beam transverse momentum was high, and the growth of the parasitic mode caused the power in the output pulse to drop substantially. We analyze the competition between the gyrotron and magnicon modes in the output cavity using a time-dependent multimode gyrotron simulation code that has been specially modified to model competition between synchronous magnicon and nonsynchronous gyrotron interactions, and compare the results to experimental observations. We also analyze the effect due to the change in the collector. View full abstract»

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  • MAGY Simulations of Mode Interaction in a Coaxial Gyrotron

    Page(s): 606 - 619
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1610 KB) |  | HTML iconHTML  

    Mode interactions in coaxial gyrotrons are studied numerically using the Maryland gyrotron code (MAGY), which has recently been modified to treat coaxial structures. Simulations are focused on the study of the FZK 170 GHz coaxial gyrotron. This device is being considered for electron cyclotron plasma heating in International Thermonuclear Experimental Reactor; however, current performance is below expectations based on previous simulations. The mode competition process during the voltage rise includes at least six modes in two groups (corotating and counterrotating with an electron beam). Simulations show that the sequence of modes achieving a measurable level of output power during start-up depends on several electron beam parameters: voltage, current, beam radius, beam thickness, pitch angle, and spread in transverse velocity. MAGY simulations made with nominal parameters confirm the results of previous simulations. Two beam parameters are not well characterized: pitch angle and spread in transverse velocity. We found that the measured results are consistent with a decrease in the pitch angle and a 3% transverse velocity spread. Also, the effect of modes at the cyclotron harmonic on the fundamental cyclotron harmonic modes is studied and discussed. View full abstract»

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  • Improved Magnetron Injection Guns for Gyrotrons

    Page(s): 620 - 630
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    Recent gyrotron operations indicate that nonuniform cathode emission is prevalent in many, if not most, magnetron injection guns. A nonuniform emission can result in degradation of the RF performance and increase heating in the collector. This paper describes research to improve cathode emission by addressing temperature uniformity and work function issues. A new cathode design is proposed, and a facility for measuring both temperature and emission uniformity is described. View full abstract»

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  • RF Behavior of a 200-kW CW Gyrotron

    Page(s): 631 - 636
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (591 KB) |  | HTML iconHTML  

    The RF behavior of a 42-GHz 200-kW continuous-wave (CW) gyrotron for plasma heating in a small experimental tokamak is presented in this paper. The operating mode, as a matter of technical convenience, is the mode, as is required by the end user. Design constraints are carefully investigated, and starting currents are computed. Cold-cavity and self-consistent calculations are carried out; power and efficiencies are computed for a typical set of beam parameters. In addition, a triode-type magnetron injection gun (MIG) has been designed, and the realistic beam parameters obtained from these MIG calculations are used in time-dependent self-consistent calculations which are carried out before and after space-charge neutralization. These studies on RF behavior suggest that it is feasible to realize CW powers in excess of 200 kW at 42 GHz with as the operating cavity mode. View full abstract»

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  • Self-Fields in a Planar Orotron

    Page(s): 637 - 646
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (786 KB) |  | HTML iconHTML  

    The goal of producing terahertz radiation from miniature electron beam devices has refocused interest in orotrons. The efficiency of these devices improves with increasing current density. However, with increasing current density, self-fields become more important. In this paper, the theory of self-fields in a planar orotron is developed. We find that the parameters of the grating, which provides the slow wave fields that interact with the beam, also affect the self-fields, which give rise to the slow space-charge wave. Thus, the optimization of the grating parameters requires consideration of their impact on the dispersive properties of the slow space-charge wave. We present a sample structure design that is appropriate for a planar orotron. View full abstract»

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  • Controlled Amplification in a TWT Using the Guide Magnetic Field

    Page(s): 647 - 654
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (564 KB) |  | HTML iconHTML  

    The interaction of the fast cyclotron wave of a linear electron beam guided by a magnetic field with a counter- propagating electromagnetic wave leads to the appearance of a stop-band over a wide range of the magnetic field near its resonance. Suppression of generation in backward wave oscillators and the resonant-cyclotron method of mode selection are based on this effect, termed "cyclotron absorption." In this paper, we analyze the possibility of controlling regenerative amplification in such oscillators as a traveling wave tube (TWT) by suppressing parasitic feedback using the guide magnetic field in the region of cyclotron absorption (RCA). Approaching the magnetic field to values that border this region, which contain thresholds of self-excitation, leads to a decrease in suppression of the reflected wave that is responsible for the positive feedback; in other words, this leads to an increase in gain. We illustrate amplification in the RCA using two approaches: the theory of stationary operation of a TWT accounting for the cyclotron resonance of electrons with a reflected wave, and particle-in-cell computer simulations. View full abstract»

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  • Repetitive Production of Nanosecond Gigawatt Microwave Pulses

    Page(s): 655 - 660
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    This paper presents the results of the theoretical and experimental studies of an efficient and stably operating microwave source with a nanosecond high-current electron beam in an extended backward-wave-oscillator-type slow-wave structure. The possibilities for stabilization of the RF field phase and for minimization of the pulse-to-pulse peak power spread have been demonstrated. Possible mechanisms of the stabilization of peak microwave power are considered, with emphasis placed on the mode in which a part of the particles are reflected in an intense RF field. View full abstract»

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  • Measurement of Parameters of X-Band High-Power Microwave Superradiative Pulses

    Page(s): 661 - 664
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    This paper describes the waveguide antenna, the detector based on the thermionic microwave diode, and the alcohol-filled calorimeter developed at the Institute of High Current Electronics. The techniques were used to measure parameters of X-band microwave pulses with a peak power of approximately 1 GW and a pulse length from 0.7 to 1 ns. The error of the peak power measurement was about 15%. View full abstract»

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  • Design of an Electron Optics System for a W -Band Sheet Beam Klystron

    Page(s): 665 - 669
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (284 KB) |  | HTML iconHTML  

    The design of an electron optics system for a W-band sheet beam klystron was described. An elliptically cylindrical electron gun and wiggler focusing structure were adopted to produce and guide a 80-kV 4-A sheet beam with an elliptical cross section of 10 times 0.4 mm. The wiggler focusing principle was reviewed and a practical structure was presented. MAFIA was used to simulate the structure. The simulation showed that the electron beam transmission attained 100% over 100 mm in distance with a fill factor that is less than 0.6. View full abstract»

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  • Parallel Simulation of Independent Beam-Tunnels in Multiple-Beam Klystrons Using TESLA

    Page(s): 670 - 681
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1185 KB) |  | HTML iconHTML  

    We present an extension of the klystron simulation code TESLA to model multiple-beam klystrons (MBKs) in which interaction parameters may vary significantly from beam-tunnel to beam-tunnel. In earlier work, the single-beam code was applied to model the MBK by assuming that all electron beams and beam-tunnels were identical and all electron beams interacted identically with the fields of the resonant cavities, using averaged values of R/Q to represent interaction with each resonant cavity. To overcome the limitations of this approach and to take into account the effects from nonidentical beams and/or beam-tunnels, we have modified the code to use a parallel algorithm for multiple beams. The implementation of the parallel version of TESLA is based on the latest Fortran-95 version of the serial code and uses the message-passing interface library for communication. For testing and verification purposes, the new version of the code is applied to simulate an experimental four-cavity, eight-beam klystron amplifier, which was designed and successfully tested last year at the Naval Research Laboratory. The results of modeling using the new parallel TESLA and their comparison with experimental data are discussed in detail. View full abstract»

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  • Simulation Studies of a Relativistic Klystron With Strong Input Power

    Page(s): 682 - 687
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (623 KB) |  | HTML iconHTML  

    As one of the potential high-power microwave devices on the level of gigawatts, relativistic klystron amplifier (RKA) can be used for power combination to further improve the radiation microwave power. Because of self-excited oscillation of the intense relativistic electron beam, the frequency and phase characteristics of general relativistic klystron devices are independent with the driven microwave pulse. In order to obtain frequency and phase locking, a method of improving the input power is put forward to inhibit these parasitic oscillations. This paper reports a particle-in-cell simulation study of the RKA's characteristics under the condition of strong power feeding. By making use of the 500-keV 6-kA electron beam, the simulation results show that strong input power can inhibit the parasitical oscillations in cavity and modulate the beam very well with only one cavity. About 5.4-kA modulation current and a microwave with power of 1.4 GW, bandwidth of 5%, and efficiency of 50% are obtained. The new amplifier driven by the strong input power proves to be a potential device to attain high amplitude stability, high efficiency, high spectral purity, wide bandwidth, and low level of phase and amplitude noise. View full abstract»

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  • Experimental Studies of Anode and Cathode Materials in a Repetitive Driven Axial Vircator

    Page(s): 688 - 693
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (761 KB) |  | HTML iconHTML  

    Repetitive use of a high-power-microwave radiation source implies strong erosion on cathode and anode materials. Electrode-material endurance has been studied in a series of experiments with an axial virtual cathode oscillator powered by a compact Marx generator. The Marx generator is operated in a 10-Hz repetitive mode with a burst of ten pulses. Velvet and graphite was used as electron-emitting materials, and they showed markedly different pulse characteristics. The following three different anode materials were used: stainless-steel mesh, stainless-steel wires, and molybdenum wires, which all had different influence on the pulse characteristics. View full abstract»

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  • Secondary Virtual-Cathode Formation in a Low-Voltage Vircator: PIC Simulations

    Page(s): 694 - 700
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (308 KB) |  | HTML iconHTML  

    We have performed 2-D relativistic electromagnetic axisymmetric particle-in-cell simulations for an axially extracted vircator. During periods of significant microwave emission, we observe the formation of a secondary smaller virtual cathode (VC) at some distance from the main VC. For a given vircator geometry, this appears only during low-voltage operation. The electron density in this secondary structure tends to increase with the microwave emission. We have also provided a qualitative explanation for the creation of this secondary structure and for its appearance during low-voltage operation. We find that electron trajectories in the vircator can be divided into four broad categories, based on their shapes and also on the temporal variation of electron kinetic energy. Three of these trajectories are those reported earlier by Alyokhin, while the fourth appears to be a new one. The fourth type is linked to the appearance of the secondary VC and, hence, becomes significant only at times of significant power emission. View full abstract»

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  • Ion Noise in the Plasma-Assisted Slow-Wave Oscillator

    Page(s): 701 - 709
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (328 KB) |  | HTML iconHTML  

    The theory describing the effect of ion oscillations on the spectrum of outgoing microwave radiation in plasma-assisted slow-wave oscillators (pasotrons) is developed. It is shown that the most important are the variations of ion density in the potential well formed by electron beam in the space between the plasma gun and an aperture installed at the entrance to the interaction space. These fluctuations cause temporal variations in the Budker parameter that is responsible for the ion focusing of the beam. After the focal plane, the beam electrons radially diverge and are intercepted by the wall of a slow-wave structure. In the presence of oscillations in ion density, the beam interception also becomes time dependent, which affects the spectrum of microwave radiation. The results obtained allow one to interpret experimental data and can also be used for minimizing the ion sidebands in the spectrum of pasotron radiation. View full abstract»

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  • Magnetic Priming at the Cathode of a Relativistic Magnetron

    Page(s): 710 - 717
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (819 KB) |  | HTML iconHTML  

    Experiments have been performed in testing magnetic priming at the cathode of a relativistic magnetron to study the effects on high-power microwave performance. Magnetic priming consists of N/2 azimuthal magnetic perturbations applied to an N-cavity magnetron for rapid generation of the desired number of electron spokes for the pi-mode. Magnetic perturbations were imposed by utilizing three high-permeability nickel-iron wires embedded beneath the emission region of the cathode, spaced 120 apart. Magnetic priming was demonstrated to increase the percentage of pi-mode shots by 15% over the baseline case. Mean peak power for -mode shots was found to be higher in the magnetically primed case by almost a factor of two. Increases in mean microwave pulsewidth were also observed in the magnetically primed case when compared to the unprimed case (66-ns primed versus 50-ns unprimed). Magnetron starting current for the magnetically primed pi-mode exhibited a reduction to 69% of the unprimed baseline starting current. View full abstract»

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  • Review of Cold Cathode Research at the Air Force Research Laboratory

    Page(s): 718 - 728
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1141 KB) |  | HTML iconHTML  

    Over the last decade, the Air Force Research Laboratory, Directed Energy Directorate (AFRL/DE) has engaged in a high current density field emission cathode research program. This program explored the aspects of cathode materials as well as the details of cathode geometries and emission physics. This paper summarizes the results of this ongoing research effort to date. We review the history and motivation for the program, which provide insight into the physics issues of concern for various vacuum electronic sources. One important aspect of the program consists of the investigation of new cathode materials. For many high power microwave (HPM) sources, neutral out-gassing, which ties critically with cathode materials, plays a key role in the effective operation of the source. These material properties influence plasma formation, which in turn dictates the operation of an HPM device. For a cathode material, AFRL chose to focus on cesium-iodide-coated carbon fiber cathodes, which we discuss in detail here. A second important aspect of the program consists of understanding emission physics and the optimum geometries for a cathode. This aspect couples closely with electron beam quality, which in turns effects the electron beam interaction with microwaves in the HPM structure. This paper concludes with a discussion of the implementation of the cathode material on both a Magnetically Insulated transmission Line Oscillator and a relativistic magnetron. View full abstract»

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  • Off-Axis Space-Charge Limit for a Bunched Electron Beam in a Coaxial Conducting Structure

    Page(s): 729 - 734
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (237 KB) |  | HTML iconHTML  

    We derive a space-charge limit for a circularly symmetric bunched electron beam that has its center-of-mass slightly offset from the axis of a circularly symmetric coaxial conducting structure. The limit is a necessary condition for beam stability resulting from the following two forces acting on the center-of-mass of the electron bunch: (1) the radial deflecting force due to the induced surface charges and currents on the conducting structure and (2) the confining force due to the presence of an external solenoidal magnetic-focusing field. We show explicit calculations of the space-charge limits for beam-charge distributions, which in the radial direction have zero thickness, i.e., thin annular beams, and in the axial direction have either zero longitudinal thickness or Gaussian like distributions. Finally, we show how this limit is applicable to a previous design study of the University of California, Davis/Stanford Linear Accelerator Center 2.8-GHz coaxial ubitron oscillator. View full abstract»

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    Page(s): 735
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    Freely Available from IEEE
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    Page(s): 736
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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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Editor-in-Chief
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Senior Scientist, US Civilian Research & Development Foundation
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