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Plasma Science, IEEE Transactions on

Issue 4 • Date Aug 2001

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Displaying Results 1 - 12 of 12
  • High-power microwave generation using a ferroelectric cathode electron gun

    Publication Year: 2001 , Page(s): 599 - 603
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (92 KB) |  | HTML iconHTML  

    A two-stage 500 kV 200-A ferroelectric electron gun has been designed, fabricated, tested, and used in a high power microwave amplifier experiment. We report on the operational characteristics of the gun including measurements of the beam dynamics. The optimum conditions for application of the trigger and its timing are also reported. Faraday cup measurement shows that the beam radius is 4.1 mm, in good agreement with simulation. The gun is designed for use in traveling-wave tube amplifiers, and testing of an X-band amplifier driven by the gun is reported. A peak output power of 5.9 MW has been observed from a single stage amplifier driven by a 100 A. 450 kV beam. This corresponds to energy converging efficiency of 13.1% and is the first observation of high power (~MW) microwave generation using the beam generated from a ferroelectric cathode, View full abstract»

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  • Microwave-generated plasma in air under standard conditions

    Publication Year: 2001 , Page(s): 604 - 608
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (96 KB) |  | HTML iconHTML  

    The possibility and feasibility of microwave-excited plasmas in air under standard conditions, as well as under moderate pressures of up to 5 bar, is demonstrated by using a quarter-wave coaxial resonator. The microwave energy is coupled into the resonator by an inductive loop attaining a match of better -15 dB. The equivalent circuit of the resonator allows to determine intrinsic resistance, inductance, and capacitance, additionally, the quality factor and, finally, the field strength inside the resonator can be deduced. By using this approximation a breakdown field of 300 kV/m is computed. The power levels used for exciting microwave plasmas are low enough to be manageable, e.g., 35 W View full abstract»

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  • Uniform plasma model of shot noise in gyroklystrons

    Publication Year: 2001 , Page(s): 639 - 648
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (212 KB) |  | HTML iconHTML  

    Theoretical estimates of electron cyclotron shot noise in gyroklystrons have recently been confirmed at low currents. However at high beam current, the noise temperature is always reduced. We examine the effect of transverse collective effects on the shot noise. There are two collective effects; shielding, which reduces the noise; and instability, which increases it. It is shown that the effect of transverse shielding is negligible unless the gyrotron beam is extremely cold. Regarding instability, if the bare shot noise amplitude is denoted Ξ, then the shot noise, including the effect of instability, can be expressed as Ξ(1+A exp Γ), where Γ is the integrated growth. The effect of instability is then measured by two parameters, Γ and A. For a cold gyrotron beam, A is about 0.3, meaning about 10 dB of power growth is needed for the instability to manifest itself. Thermal effects both reduce A and Γ. For realistic gyrotron beams, about 20-25 dB of power e folds would be necessary for instability to manifest itself. To summarize, the theory developed explains the absence of instability in the measurements, but indicates that phenomena other than transverse shielding are responsible for the noise reduction View full abstract»

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  • Electrothermal-chemical synthesis of nanocrystalline aluminum nitride using a metal vapor pulsed plasma jet

    Publication Year: 2001 , Page(s): 649 - 652
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (76 KB) |  | HTML iconHTML  

    A relatively new process, electrothermal-chemical (ETC) synthesis, is proposed and tested for synthesizing nanocrystalline aluminum nitride (AlN) and aluminum powders. The ETC synthesis employed a plasma gun especially adapted for material synthesis. The plasma gun is powered by high magnitude current pulse (100 kA flowing for 1.2 ms) and produces pulsed, high-velocity metal vapor plasma jets. The pulsed plasma jet is directed into a reaction chamber which is filled with room temperature atmospheric pressure nitrogen (N2) or helium (He) gas reacting with the metal vapor plasma jet. Transmission electron microscopy and X-ray diffraction have been applied to characterize the synthesized materials and confirmed that the material contained nanocrystalline aluminum (Al) and AlN whose particle size ranging 30-120 nm View full abstract»

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  • Observation of reflex klystron oscillation phenomena in a plasma

    Publication Year: 2001 , Page(s): 569 - 572
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (112 KB) |  | HTML iconHTML  

    Reflex klystron electron oscillation, occurring in a plasma potential well formed in a system consisting of plasma and two electrodes (filaments and a mesh grid which is at floating potential), was observed in a very simple device with only filaments and a mesh grid. This oscillation mechanism consists of three elements: 1) an acceleration region on the side in which filaments are located, which accelerates primary electron beams emitted from filaments; 2) a deceleration region on the side in which the mesh grid is located, which causes the reflection of the beams; and 3) a plasma region. In addition, the velocity modulation of primary electron beams is given by the electron plasma oscillation at the presheath on the filament side. The maximum amplitude and frequency of an oscillation obtained by this mechanism were Vpp=210 mV 210 mV and f=200 MHz, respectively. These values can be controlled by the discharge potential View full abstract»

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  • Experimental study of CRM with simultaneous excitation of traveling and near-cutoff waves (CARM-gyrotron)

    Publication Year: 2001 , Page(s): 609 - 612
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (64 KB) |  | HTML iconHTML  

    A new variety of RF sources is studied experimentally. In the cyclotron autoresonance maser (CARM)-gyrotron with an open “gyrotron-type” cavity, two regimes of operation are observed: the conventional high-harmonic gyrotron regime, and the CARM-gyrotron regime with effective radiation of the traveling CARM mode. The two-mode character of the electron-wave interaction in the CARM-gyrotron regime was proved experimentally View full abstract»

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  • Shadowgraphy and interferometry using a CW laser and a CCD of a laser-induced plasma in atmospheric air

    Publication Year: 2001 , Page(s): 613 - 616
    Cited by:  Papers (22)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (100 KB) |  | HTML iconHTML  

    We present a new application of a charged coupled device (CCD), where a continuous-wave (CW) laser is used as a probe beam in shadowgraphy and interferometric diagnosis of transparent media where the refractive index varies in time. The time resolution is obtained by gating the CCD. This configuration has the advantage that the temporal resolution of both techniques can be changed according to the evolution of the process under study and no stability setup is required, as usual, in CW interferometric techniques. We applied this method to the diagnosis of a laser induced plasma (LIP) in air measuring the evolution of plasma, shock wave, electron density, and hot core air expansion from the ns to the ms time scale View full abstract»

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  • Inhomogeneity of currents in a wire array during its exploding phase

    Publication Year: 2001 , Page(s): 632 - 638
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (140 KB) |  | HTML iconHTML  

    The current in a wire array during its exploding phase has been studied. The wire array consisting of many thin wires is used as a plasma source in a z-pinch X-ray radiation system. The current distribution in the exploding wire array plays an important role in producing an initial symmetrical plasma. In the present experiment, four tungsten wires of 0.1 mm in diameter were exploded in a vacuum. The experiment was carried out with an inductive voltage adder pulsed power generator providing a current of 160 kA at quarter period of 1.8 μs The currents through and the voltage across the wires were measured simultaneously. It was found that the currents in the wires were inhomogeneous, especially after the wires became plasma. Once the currents became inhomogeneous, the inhomogeneity remained throughout the discharge. It was also studied how the dimensions of the wires affected the homogeneity of the currents. Wires of different lengths or different cross sectional areas resulted in strong inhomogeneities of the currents. The wires with shorter length or smaller cross-sectional area became plasmas earlier than other wires. Thus, the resistances of the wires were not equal. These differences in the resistance caused the inhomogeneity of the currents View full abstract»

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  • Influence of gas flow rate and reactor length on NO removal using pulsed power

    Publication Year: 2001 , Page(s): 592 - 598
    Cited by:  Papers (24)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (136 KB) |  | HTML iconHTML  

    A short duration of 100-ns pulsed power has been used to remove nitric oxide (NO) in a mixture of nitrogen, oxygen, water vapor, and NO, simulating flue gases from a power station. The effects of the gas flow rate, the reactor length, and the pulse repetition rate on the percentage of NO removal and its energy efficiency are reported. The percentage of NO removal at a fixed gas flow rate increased with increasing pulse repetition rate due to the increased energy into the discharge. At a fixed pulse rate, the removal of NO increased with decreasing gas flow rate due to the increased residence time of the gas in the discharge reactor, thus facilitating the creation of increased radicals of O and N which then decreased NO. The energy removal efficiency of NO (in mol/kWh) decreased with increasing gas flow rate and increasing removal ratio of NO. The removal of NO increased with increasing energy density (J/I), input into the discharge at different reactor length View full abstract»

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  • A characterization of plasma fluctuations within a Hall discharge

    Publication Year: 2001 , Page(s): 582 - 591
    Cited by:  Papers (24)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (524 KB) |  | HTML iconHTML  

    Experimental results are presented for studies of low (2-20 kHz) and intermediate-frequency (20-100 kHz) oscillations in crossed-field closed electron-drift Hall discharges. Conditional sampling using two electrostatic probes is used to identify and extract properties of coherent structures associated with the propagation of azimuthal and longitudinal instabilities within the discharge channel. The azimuthal component phase velocities are determined for a wide range of wave frequencies and over characteristic regimes of operation of these devices. A variety of propagation modes are observed and analyzed, including the appearance of an induced mode due to the presence of the probes themselves. This later result is believed to be the first direct evidence of how fluctuations can be influenced in these Hall discharges using relatively simple actuation methods View full abstract»

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  • Electrical behavior of a simple helical flux compression generator for code benchmarking

    Publication Year: 2001 , Page(s): 573 - 581
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (180 KB) |  | HTML iconHTML  

    A variety of basic magnetic flux compression (MFC) generator geometries have been tested during the last three decades. Though size and operating regimes differ widely, it is apparent that the helical flux compression generator is the most promising concept with respect to current amplification and compactness. Though the geometry of the helical generator (dynamically expanding armature in the center of a current carrying helix) seems to be basic, it turns out that the understanding of all involved processes is rather difficult. This fact is apparent from the present lack of a computer model that is solely based on physical principles and manages without heuristic factors. A simple generator was designed to address flux and current losses of the helical generator. The generator's maximum current amplitude is given as a function of the seed current and the resulting “seed-current” spread is compared to the output of state-of-the-art computer models. Temporally resolved current and current time derivative signals are compared as well. The detailed generator geometry is introduced in order to facilitate future computer code bench marking or development. The impact of this research on the present understanding of magnetic flux losses in helical MFC generators is briefly discussed View full abstract»

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  • The structure of chaotic magnetic field lines in a tokamak with external nonsymmetric magnetic perturbations

    Publication Year: 2001 , Page(s): 617 - 631
    Cited by:  Papers (20)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (532 KB) |  | HTML iconHTML  

    We consider the effects of external nonsymmetric magnetostatic perturbations caused by resonant helical windings and a chaotic magnetic limiter on the plasma confined in a tokamak. The main purpose of both types of perturbation is to create a region in which field lines are chaotic in the Lagrangian sense: two initially nearby field lines diverge exponentially through many turns around the tokamak. The equilibrium field is obtained from the equations of magneto-hydrodynamic equilibrium written down in a polar toroidal coordinate system. The magnetic fields generated by the resonant helical windings and the chaotic magnetic limiter are obtained through an analytical solution of Laplace equation. The magnetic field line equations are integrated to give a Hamiltonian mapping of field lines that we use to characterize the structure of chaotic field lines. In the case of resonant windings, we obtained the map by both numerical integration and a Hamiltonian formulation. For a chaotic limiter, we analytically derived a symplectic map by using a Hamiltonian formulation 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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