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Plasma Science, IEEE Transactions on

Issue 4 • Date Aug 1992

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Displaying Results 1 - 13 of 13
  • Effect of the inside profile of a hollow cathode on the plasma plume

    Publication Year: 1992 , Page(s): 410 - 412
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (232 KB)  

    The effect of the inside profile of a hollow cathode on the intensity of plasma plume has been studied in a low-pressure (~3-torr) argon discharge. The effectiveness of three different `inside' profiles of a hollow cathode was compared by performing emission spectroscopy on the plasma plume in each case. A conical-profile hollow cathode produced a plasma plume that was much more intense than the one in a commonly used cylindrical-profile hollow cathode View full abstract»

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  • Radial distribution of plasma density in the positive column of the high-current stationary glow discharge

    Publication Year: 1992 , Page(s): 413 - 418
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (364 KB)  

    A model is presented which describes the radial distributions of the plasma density, electric potential, current density, and magnetic field in the positive column of a stationary glow discharge not in contact with the longitudinal walls of the discharge chamber. In this model, the compression of the positive column is provided by the azimuthal magnetic field created by the discharge current. The value of, the discharge current is obtained for the case where charged-particle diffusion is balanced by the actions of the radial electric field and the magnetic pinch effect. The radial distributions of plasma parameters are also calculated for the case of high-current glow discharges where charged-particle diffusion can be ignored View full abstract»

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  • The theory of long waveguide structures radiating lower hybrid waves into a plasma

    Publication Year: 1992 , Page(s): 425 - 431
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    It is shown that the radiation into a plasma from the structures composed of many waveguides is well described by the theory of the infinite structures. This theory results in the efficient numerical code which is appropriate for the study of the nonlinear response of the plasma ill front of the grill. Both the infinite conventional grill and the structure built up from the infinite series of identical N-waveguide multijunction sections are investigated. It is proved that the spectrum of the last structure is the superposition of N spectra of the infinite conventional grills with the specially selected phase shifts. The theoretical results for three long structures (24-waveguide conventional grill on ASDEX and two multijunction arrays, namely a 32-waveguide grill on JET and a 30-waveguide grill proposed for T15) are compared with the predictions of the theory for the corresponding infinite structures. and the agreement is good View full abstract»

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  • Parasitic oscillation in and suppression of a gyrotron backward wave mode in a low-Q 8 GHz gyrotron

    Publication Year: 1992 , Page(s): 458 - 465
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (620 KB)  

    The parasitic oscillation of the TE°21 gyrotron backward-wave (gyro BW) mode is observed in a low-Q, 8 GHz TE°011, gyrotron. At low power (PBW<5 kW), the oscillation of the gyro BW mode, simultaneously with the gyrotron mode, results in a maximum TE°011, mode efficiency of less than 0.25. The parasitic oscillation is suppressed by operating the gyrotron with a negative magnetic field gradient along the electron beam, which allows the maximum efficiency to reach 0.40 and the output power to be multiplied by a factor varying from 1.4 to 1.7. The optimum efficiency curve of the TE°011 mode indicates that the low-Q cavity behaves as a much higher Qdiff cavity. Excessive values of magnetic field gradient and α favor the TE°012 , longitudinal mode, which oscillates in place of the TE°011 mode and limits its maximum output power. This competitive process is responsible for the high-Q-like behavior of the optimum efficiency curve View full abstract»

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  • Measurements of the perpendicular width of ionization-produced double layers

    Publication Year: 1992 , Page(s): 476 - 479
    Cited by:  Papers (1)
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    Measurements of the perpendicular (to B) double-layer widths of ionization-produced (anode) double layers are presented. These widths were determined from measurements of the double-layer charge separations. The variations of the transverse-to-B widths with plasma density and magnetic field strength are given View full abstract»

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  • Pulsed dye laser diagnostics of vacuum arc cathode spots

    Publication Year: 1992 , Page(s): 466 - 472
    Cited by:  Papers (42)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (540 KB)  

    The ignition and arc phases of vacuum arcs were investigated using differential dye laser absorption photography with simultaneous high spatial (micrometer) and temporal (nanosecond) resolution. The discharge duration was 800 ns, the current 50-150 A, the electrode material copper, and the cathode-anode distance less than 50 μm. A 0.4 ns laser pulse (tunable, γ=480-530 nm) was used to obtain momentary absorption photographs of the cathode region. During ignition, an optically thick anode plasma expanded toward the cathode, decaying within 25 ns after bridging the electrode gap. In the arc phase, a fragmentary structure of the cathode spots was observed in situ for the first time. The microspots have a characteristic size of 5-10 μm. They appear and disappear on a nanosecond time scale. The plasma density of the microspots was estimated to be greater than (3-6)×1026 m-3 View full abstract»

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  • Experimental characterization of arc instabilities and their effect on current chopping in low-surge vacuum interrupters

    Publication Year: 1992 , Page(s): 439 - 446
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (544 KB)  

    In low-current vacuum arcs, short (<500-ns) peaks in arc voltage (instabilities), with a height of up to ten times the normal arc voltage, are abundantly present. The instabilities are thought to be caused by ion starvation near the anode. A number of parameters of these instabilities, occurring in vacuum interrupters with AgWC (low-surge) and CuCr (conventional) contact material, have been analyzed statistically in a practical AC circuit. A striking difference in median rate of rise and height is found. It is found plausible that these parameters reflect important switching characteristics such as recovery (peak rate of rise) and current chopping level (peak height). Also, the dependence of the parameters on momentary arc current and contact distance is studied and explained qualitatively View full abstract»

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  • Observation of enhanced prebreakdown electron beams in a vacuum spark with a hollow-cathode configuration

    Publication Year: 1992 , Page(s): 405 - 409
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (368 KB)  

    The generation of prebreakdown electron beams in a low-energy vacuum spark with a hollow-cathode configuration is observed under a range of experimental conditions. The vacuum spark studied is powered by either a 25-kV, 3.3-nF single capacitor discharge or a two-stage, 50-kV, 1.65-nF Marx. The electron beams are detected by observing the X-ray emission from the anode tip produced by electron impact. Results show that an electron beam is formed well before the onset of the electrical breakdown. This prebreakdown electron beam has an initial slow buildup phase followed by an exponential rise, leading to the breakdown of the discharge. This behavior of the electron beam evolution is in good qualitative agreement with the model simulation of the pseudospark phenomenon obtained for a transient hollow-cathode discharge View full abstract»

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  • Determining railgun plasma current distribution using Jansson's method to deconvolve B-dot probe signals

    Publication Year: 1992 , Page(s): 432 - 438
    Cited by:  Papers (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (552 KB)  

    The authors present a method of determining the plasma armature current distribution from B-dot probe signals. This method utilizes the knowledge that the B-dot probe signal can be shown to be a convolution of the plasma armature current distribution with the impulse response function of the B-dot probe. Jansson's (1984) relaxation-based nonlinear deconvolution technique is developed for use with recorded B-dot probe data. Results obtained with this technique indicate that significant improvement in estimations can be obtained over previously used linear deconvolution methods View full abstract»

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  • Plasma erosion opening switch using laser-produced plasma

    Publication Year: 1992 , Page(s): 447 - 451
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (328 KB)  

    In order to construct a practical inductive energy storage pulsed power generator, an opening switch which can repeatedly conduct a large current and then rapidly interrupt this current is necessary. Though the plasma erosion opening switch (PEOS) can interrupt a large current rapidly, the effective number of switch operations is limited because of the decrease of the carbon sprayed on the insulator with each shot. A PEOS using a laser-produced plasma, which can possibly be operated for hundreds of thousands of shots without maintenance, is proposed, and its operation as an opening switch is confirmed experimentally View full abstract»

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  • Theory of a frequency-step-tunable gyrotron for optimum plasma ECRH

    Publication Year: 1992 , Page(s): 452 - 457
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (476 KB)  

    A theory is presented which describes the dependence of the multimode operation of a gyrotron on the modulation and beam voltages. Nonlinear nonstationary processes are considered. An approximate start-up scenario of a gyrotron is determined which makes it possible to achieve single-mode excitation and high-efficiency operation in a desired mode, as well as to switch the tube to a similar operation in other modes View full abstract»

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  • Multidimensional models for the analysis of linear MHD generator channel plasma flows

    Publication Year: 1992 , Page(s): 473 - 476
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (288 KB)  

    Mathematical models for the analysis of the linear MHD generator channel operation are described. The local phenomena are analyzed through a steady-state two-dimensional model which is based on a description of both the fluid dynamic and the electrodynamic behavior of the plasma. The transients caused by variations of the loading and by faults are studied by means of a time-dependent quasi-one-dimensional model View full abstract»

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  • A numerical study of the transient behaviors of solitary waves in relativistic plasmas

    Publication Year: 1992 , Page(s): 419 - 424
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (392 KB)  

    The authors study the transient behaviors of solitary waves in a relativistic plasma with nonisothermal electrons. In particular, the modified Korteweg-de Vries (K-dV) equation is solved numerically with a Gaussian function as the initial condition. In addition, it is found that the time evolution of solitons from the initial profile is quite similar to that of a K-dV equation with the exception that the soliton speeds are faster. It is also found that the relativistic ions and the nonisothermal electrons tend to have a similar effect on the soliton behavior of the wave, making nonisothermal electrons more noticeable 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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