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Plasma Science, IEEE Transactions on

Issue 3  Part 1 • Date June 2006

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Displaying Results 1 - 25 of 32
  • Table of contents

    Publication Year: 2006 , Page(s): c1 - c4
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  • IEEE Transactions on Plasma Science publication information

    Publication Year: 2006 , Page(s): c2
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  • Guest Editorial The Eleventh Special Issue on High-Power Microwave Generation

    Publication Year: 2006 , Page(s): 498 - 499
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  • A Tribute to Robert K. Parker (1942-2005)

    Publication Year: 2006 , Page(s): 500 - 501
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  • On potentials of gyrotron efficiency enhancement: measurements and simulations on a 4-mm gyrotron

    Publication Year: 2006 , Page(s): 502 - 511
    Cited by:  Papers (12)
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    In a 74.2-GHz 100-kW pulse gyrotron, the characteristics of parasitic low-frequency oscillations and their influence on electron energy spread have been determined. A method for suppressing parasitic oscillations by varying the magnetic field distribution in the beam compression region is studied. The results of measurements demonstrate the influence of azimuthal inhomogeneity of electron emission on the excitation of parasitic oscillations and on the gyrotron output parameters. Obtained data allows one to determine the ways of gyrotron efficiency enhancement by improved quality of the helical electron beam View full abstract»

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  • Influence of background plasma on electromagnetic properties of "Cold" gyrotron cavity

    Publication Year: 2006 , Page(s): 512 - 517
    Cited by:  Papers (9)
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    A simple approximate theory of background plasma influence on the electromagnetic properties of high-power gyrotron cavities is presented. It is shown that a background plasma slightly reduces the operational frequency of gyrotrons, increases the quality factors of operational and neighbouring modes, and modifies the longitudinal field distribution in the gyrotron cavity. The calculated downshift of the operational frequency is compared with long-pulse measurements performed in 140-GHz 1-MW continuous wave gyrotron experiments at Forschungszentrum Karlsruhe View full abstract»

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  • Operational characteristics of a 14-W 140-GHz gyrotron for dynamic nuclear polarization

    Publication Year: 2006 , Page(s): 518 - 523
    Cited by:  Papers (26)
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    The operating characteristics of a 140-GHz 14-W long pulse gyrotron are presented. The device is being used in dynamic nuclear polarization enhanced nuclear magnetic resonance (DNP/NMR) spectroscopy experiments. The gyrotron yields 14 W peak power at 139.65 GHz from the TE(0,3) operating mode using a 12.3-kV 25-mA electron beam. Additionally, up to 12 W peak has been observed in the TE(2,3) mode at 136.90 GHz. A series of mode converters transform the TE(0,3) operating mode to the TE(1,1) mode. Experimental results are compared with nonlinear simulations and show reasonable agreement. The millimeter-wave output beam was imaged in a single shot using a pyroelectric camera. The mode patterns matched reasonably well to theory for both the TE(0,1) mode and the TE(1,1) mode. Repeatable mode patterns were obtained at intervals ranging from 0.8 s apart to 11 min apart at the output of the final mode converter View full abstract»

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  • Continuous-wave operation of a 460-GHz second harmonic gyrotron oscillator

    Publication Year: 2006 , Page(s): 524 - 533
    Cited by:  Papers (33)
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    We report the regulated continuous-wave (CW) operation of a second harmonic gyrotron oscillator at output power levels of over 8 W (12.4 kV and 135 mA beam voltage and current) in the TE0,6,1 mode near 460 GHz. The gyrotron also operates in the second harmonic TE2,6,1 mode at 456 GHz and in the TE2,3,1 fundamental mode at 233 GHz. CW operation was demonstrated for a one-hour period in the TE 0,6,1 mode with better than 1% power stability, where the power was regulated using feedback control. Nonlinear simulations of the gyrotron operation agree with the experimentally measured output power and radio-frequency (RF) efficiency when cavity ohmic losses are included in the analysis. The output radiation pattern was measured using a pyroelectric camera and is highly Gaussian, with an ellipticity of 4%. The 460-GHz gyrotron will serve as a millimeter-wave source for sensitivity-enhanced nuclear magnetic resonance (dynamic nuclear polarization) experiments at a magnetic field of 16.4 T View full abstract»

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  • Design of a ka-band second harmonic gyroklystron amplifier by using a self-consistent nonlinear simulation

    Publication Year: 2006 , Page(s): 534 - 540
    Cited by:  Papers (3)
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    The self-consistent nonlinear simulation of a Ka-band, second harmonic two-stage gyroklystron amplifier is presented in this paper. The beam-wave interaction in the gyroklystron is studied by using a self-consistent nonlinear simulation code GKLSC, and the electron bunching pictures of the different positions in phase space are demonstrated in detail. The effects of various parameters, such as drift tube length, input power, frequency, velocity ratio, guiding center radius, magnetic field strength, velocity spread and beam current on the electronic efficiency, gain, and output power are discussed. The simulated results show that the designed gyroklystron amplifier can obtain about 21% electronic efficiency, 43 dB gain, and 0.6% bandwidth, respectively. The performance of the designs is also confirmed by a particle-in-cell code View full abstract»

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  • Analysis of a tapered disc-loaded waveguide for a wideband gyro-TWT

    Publication Year: 2006 , Page(s): 541 - 546
    Cited by:  Papers (3)
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    The solution of the dispersion relation of a disc-loaded circular waveguide for the propagation constant, obtained by the cold (beam-absent) field analysis, was fed back into the small-signal gain equation of a gyro-traveling wave tube (TWT) to assess the technique of tapering the structure cross section for widening the bandwidth of the device, a technique that is known to broadband the device in a smooth-wall waveguide, usually at the cost of the device gain. The disc-to-disc distance of a nontapered disc-loaded circular waveguide, reportedly the most effective structure parameter for widening the bandwidth of a gyro-TWT, becomes an insignificant parameter for tapering the structure for wide bandwidths of a gyro-TWT, while simultaneous tapering of the waveguide-wall and disc-hole radii led to wide bandwidths at reasonably large gains View full abstract»

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  • Phase stability of a two-stage W-band TE/sub 01/ gyro-traveling-wave-tube with distributed loss and tapered magnetic field

    Publication Year: 2006 , Page(s): 547 - 553
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    Phase stability of a W-band TE01 gyro-traveling-wave-tube (Gyro-TWT) with distributed loss and tapered magnetic field is studied in this paper. The phase sensitivity of electron beam voltage, current, and magnetic field is analyzed by using nonlinear theory. The influences on phase stability of important factors such as distributed loss, tapered magnetic field, and input frequency are presented. The results show that relations between phase deviation and electron beam parameters may be expressed by a linear equation. In addition, to maintain phase stability with a maximum accuracy of plusmn20deg, it is necessary to stabilize beam current with an accuracy of plusmn8.3%, beam voltage with an accuracy of plusmn4.65%, and external magnetic fields to within an accuracy of plusmn0.092% View full abstract»

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  • Gain-frequency response of nearby waveguide modes in vane-loaded gyro-TWT

    Publication Year: 2006 , Page(s): 554 - 558
    Cited by:  Papers (2)
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    In this paper, the behavior of a gyro-traveling wave tube (gyro-TWT) amplifier, in which an axis-encircling electron beam synchronously interacts with the azimuthal modes of the vane-loaded cylindrical waveguide interaction structure, has been analyzed. The dispersion characteristics and gain-frequency response of the nearby waveguide modes (TE01, TE21, and TE41) for the vane-loaded gyro-TWT amplifier have been presented. The gain-frequency response of the device has been studied for both the small-orbit and large-orbit configurations. It has been observed that the TE41 mode of the device is well separated on the frequency scale for both these configurations. In addition, it has higher device gain in the large-orbit configuration when compared with the same obtained for the TE01 and TE21 modes View full abstract»

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  • Enhancement of frequency-tunability for a Smith-Purcell free-electron laser oscillator in the millimeter-wave region

    Publication Year: 2006 , Page(s): 559 - 562
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    The frequency-tunability for a Smith-Purcell free-electron laser oscillator in the millimeter wave region is enhanced with the aid of a quasi-periodic distributed Bragg reflector (DBR) made of metallic waveguide gratings with rectangular grooves. For a quasi-periodic DBR, the grating parameters are adjusted by means of genetic algorithms to get the desired reflection coefficient, thus compensating for the frequency dependence of the overall output characteristics. For a typical numerical example, flat output characteristics have been obtained over 10% bandwidth around the center frequency 121 GHz View full abstract»

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  • Modeling of T-shaped vane loaded helical slow-wave structures

    Publication Year: 2006 , Page(s): 563 - 571
    Cited by:  Papers (2)
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    In this paper, the finite-size vane (FSV) sheath-helix model is proposed to calculate the cold-test characteristics of T-shaped vane loaded helical slow-wave structures (SWSs), in which the effects of the finite number and dimensions of the T-shaped vanes are taken into account, and also the angular harmonics generated due to the angular periodicity of the vanes are considered. Based on this model, the dispersion relation and the interaction impedance are derived and then are applied to an actual structure. The theoretical predictions are also compared with the MAFIA simulation results, and the error are analyzed and interpreted. In the end, the influences of the inner radius and inner width of the T-shaped vanes on the cold-test characteristics are illustrated View full abstract»

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  • Development of an S-band klystron with bandwidth of more than 11%

    Publication Year: 2006 , Page(s): 572 - 575
    Cited by:  Papers (10)
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    The development of an S-band klystron with bandwidth of more than 11% is introduced in this paper. At the peak power level of 800 kW, the efficiency of more than 30%, the gain of more than 40 dB, the equal-driving (constant input power across the bandwidth) relative instantaneous bandwidth of 11.2%, the average power of larger than 8.8 kW, and the power fluctuation within bandwidth of less than 1.5 dB are obtained in this klystron. The design considerations, simulation, and test results are presented and the techniques adopted to extend the bandwidth of the klystron are described View full abstract»

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  • Bandwidth extension of an S-band, fundamental-mode eight-beam klystron

    Publication Year: 2006 , Page(s): 576 - 583
    Cited by:  Papers (15)
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    We present a general discussion of multiple-gap cavity characteristics and stability issues along with the detailed design of a five-cavity, broadband, high-power multiple-beam klystron (MBK). The predicted performance characteristics of this S-band fundamental-mode klystron circuit include a 3-dB bandwidth of 6.7% with peak power ~600 kW and an electronic gain of 33 dB. The circuit is powered by a 32 A, 45 kV eight-beam electron gun (Nguyen , 2004) whose design has been successfully tested in a previous narrowband MBK circuit (Nguyen , 2004), (Abe , 2005). The present circuit was designed and optimized with the three-dimensional particle-in-cell code MAGIC View full abstract»

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  • Two-dimensional theoretical analysis of the dominant frequency in the inward-emitting coaxial vircator

    Publication Year: 2006 , Page(s): 584 - 589
    Cited by:  Papers (7)
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    Two-dimensional steady-state analysis for the electron flow in an inward-emitting coaxial virtual cathode oscillator is presented. Based on the relativistic-fluid-Maxwell equations, the relativistic plasma frequency characteristics and its dependence on the geometric parameters are derived. The resulting plasma frequency solution scales linearly with the diode current. The exact dominant frequency is solved numerically, which gives the theoretical support for the simulation result that the microwave frequency in a coaxial vircator is similar to that produced by a planar vircator with the same small anode-cathode gap distance. Numerical result shows that higher frequency can be achieved in the coaxial vircator for higher applied voltage and smaller anode-cathode gap distance. The numerical solutions of the dominant frequencies predict the measured and simulated values within 10% View full abstract»

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  • Particle-in-cell simulations of start-up dynamics in a grounded cathode magnetron

    Publication Year: 2006 , Page(s): 590 - 605
    Cited by:  Papers (1)
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    Simulations results of a relativistic magnetron using the MAGIC particle-In-cell (PIC) code are reported. The time evolution of the buildup process for different magnetron azimuthal modes is studied for a variety of initial voltages, with and without a second, oscillatory small voltage in addition to the drive. The self-field is seen to evolve so that the anode-cathode voltage nears the Buneman-Hartree voltage of a particular mode. Simulations show that the output power is larger in the case where the voltage dynamically approaches the Buneman-Hartree value from above than when it is approached from below. The time evolution of a pure mode (without mode competition) resembles the time evolution of some autoresonant systems. An oscillatory voltage, of relatively small amplitude, fixed or chirped in frequency is seen to modify mode competition. The frequency of the first occurring mode is shown to follow the external drive with small phase deviations. This appears to be the beginning of an autoresonance process driven by the external drive, which stops abruptly at the mode transition. Small changes in the azimuthal structure are seen to lead to different mode dynamics; when the pi-mode symmetry is enforced other competing modes are suppressed to some extent View full abstract»

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  • Improvement of the output characteristics of magnetrons using the transparent cathode

    Publication Year: 2006 , Page(s): 606 - 619
    Cited by:  Papers (20)  |  Patents (1)
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    The output characteristics of magnetrons can be significantly improved by using a cathode that is transparent to the synchronous electromagnetic fields thereby providing improved conditions for fast conversion of the electrons' potential energy into electromagnetic energy. The transparent cathode consists of separate longitudinal metal strips, arranged to form a cylindrical surface, that act as individual electron emitters. Favorable prebunching of electrons to excite the desired operating mode is provided by a suitable choice of the number and azimuthal position of the cathode strips. The strong azimuthal wave field in the cathode region rapidly captures the prebunched electrons into rotating spokes forming the anode current. This process provides faster start-of-oscillations than priming using a solid cathode. The strong wave field in the electron sheath over the cathode, for any sheath thickness, gives the possibility of improving the efficiency by concomitantly increasing the applied voltage and magnetic field. Computer simulations of the A6 magnetron driven both by a solid and transparent cathode demonstrate the advantages of this approach View full abstract»

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  • Mode conversion in a magnetron with axial extraction of radiation

    Publication Year: 2006 , Page(s): 620 - 626
    Cited by:  Papers (21)  |  Patents (1)
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    We demonstrate the ability to form simple radiation patterns from a relativistic magnetron with axial extraction. This is achieved by tapering onto a conical antenna only those cavities of the anode block that correspond to the symmetry of the radiated modes. The efficiency of mode conversion of the operating pi-mode into a radiated mode using this method is demonstrated using computer simulations of a six-cavity magnetron View full abstract»

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  • Radio frequency priming of a long-pulse relativistic magnetron

    Publication Year: 2006 , Page(s): 627 - 634
    Cited by:  Papers (9)
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    Rapid startup, increased pulsewidth, and mode locking of magnetrons have been explored experimentally on a relativistic magnetron by radio frequency (RF) priming. Experiments utilize a -300 kV, 2-8 kA, 300-500-ns electron beam to drive a Titan six-vane relativistic magnetron (5-100 MW output power in each of the three waveguides). The RF priming source is a 100-kW pulsed magnetron operating at 1.27-1.32 GHz. Tuning stubs are utilized in the Titan structure to adjust the frequency of the relativistic magnetron to match that of the priming source. Experiments are performed on rising sun as well as standard anode configurations. Magnetron start-oscillation time, pulsewidth, and pi-mode locking are compared with RF priming versus the unprimed case. The results show significant reductions in microwave output delay and mode competition even when Adler's Relation is not satisfied View full abstract»

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  • Optimal synthesis of quasi-optical launchers for high-power gyrotrons

    Publication Year: 2006 , Page(s): 635 - 641
    Cited by:  Papers (21)
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    Quasi-optical launcher designs for high-power gyrotrons use perturbations of the waveguide surface following the cavity to convert the high order cavity mode to a Gaussian-like beam, which is then radiated from a spiral cut of the waveguide. The design technique of these launchers is based on an analytic theory that specifies the mode amplitudes to obtain a Gaussian-like distribution of the field in the azimuthal and longitudinal directions. This approach can generate a beam with high Gaussian content and low diffraction losses. However, by adjusting the mode amplitudes to obtain a Gaussian-like distribution of the field in the radial (instead of the azimuthal) direction, designs with significantly less diffraction loss, reduced beam divergence angles, and higher Gaussian beam content can be achieved View full abstract»

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  • Secondary electron yield measurements from materials with application to collectors of high-power microwave devices

    Publication Year: 2006 , Page(s): 642 - 651
    Cited by:  Papers (4)
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    An experimental test facility has been established for measuring the secondary electron yield (SEY) of materials thought to be suitable for low yield vacuum electronic applications such as collectors in high-power microwave (HPM) tubes. Experiments can be broadly divided into two energy-regimes: a high-energy (1-50 keV) and a low-energy (10 eV-1 keV) regime. Measurements of SEY at high energies are presented for the following materials: copper, titanium, and Poco graphite. Observation of time-dependent SEY behavior in these samples suggests that surface processes play an important role during measurements. In addition, SEY at low energies and as a function of the angle of incidence of primary electrons has been measured for plasma sprayed boron carbide (PSBC). The experimental results presented here are benchmarked with existing SEY data in the literature, empirically and to first principle formulae View full abstract»

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  • Progress toward optimization of phase-correcting mirrors for a multifrequency 1-MW gyrotron

    Publication Year: 2006 , Page(s): 652 - 658
    Cited by:  Papers (3)
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    Due to the requirement of a newly designed ultra-broadband chemical vapour deposition (CVD)-diamond window for a multifrequency 1-MW short-pulse gyrotron at Forschungszentrum Karlsruhe (FZK), the existing beam-forming mirror system inside the gyrotron tube has to be modified. This paper describes the design scheme for shaping the output beams from the launching antenna waveguide into the desired fundamental Gaussian profile by using adapted phase-correcting mirrors with nonquadratic surface contour function. Simulation results show these phase-correcting mirrors can be used for broadband operation of a frequency step-tunable gyrotron, which operates in nine modes from the TE17,6 mode at the frequency of 105 GHz to the TE23,8 mode at 143 GHz. Further calculations predict that efficiencies of more than 94% can be obtained for converting the high-order cylindrical cavity modes into the usable fundamental Gaussian mode View full abstract»

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  • Analysis and design of wideband reflector gratings in rectangular waveguide

    Publication Year: 2006 , Page(s): 659 - 665
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    Optimized designs for wideband reflector gratings in rectangular waveguide are presented for application in microwave electron beam devices. A moment method procedure for a general dual-plane step in rectangular waveguide and a generalized scattering matrix approach are used to analyze the reflector gratings. A least squares optimization method is used to determine optimized dimensions for reflector gratings which have a constant power reflection coefficient for the TM11 mode over a wide bandwidth 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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Meet Our Editors

Editor-in-Chief
Steven J. Gitomer, Ph.D.
Senior Scientist, US Civilian Research & Development Foundation
Guest Scientist, Los Alamos National Laboratory
1428 Miracerros Loop South
Santa Fe, NM  87505  87505  USA
tps-editor@ieee.org
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