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Plasma Science, IEEE Transactions on

Issue 4  Part 2 • Date Aug 2002

 This issue contains several parts.Go to:  Part 1 

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Displaying Results 1 - 7 of 7
  • Numerical model of thermoelectric phenomena leading to cathode-spot ignition

    Publication Year: 2002 , Page(s): 1561 - 1567
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (391 KB) |  | HTML iconHTML  

    This paper deals with the results of a numerical model of the predischarge heating process encountered by a microprotrusion on the cathode surface of a vacuum gap, due to the field-effect current density flowing throughout the protrusion. The model is one-dimensional and nonstationary. The protrusion is sketched as a truncated cone and the material considered is tungsten, whose physical and thermal properties have been assumed temperature dependent. Electron current density emitted by the tip and the Nottingham effect have been calculated solving the integral of the energy distribution of the emitted electrons. In all other existing models, these two quantities are approximated by algebraic equations, valid in a limited temperature range. Results seem to confirm the experimental evidence that breakdown starts from the explosion of microprotrusions in a time of the order of 1-10 ns. In order to induce the explosion, current densities could be as high as 1013 A/m2, while the corresponding electric field at the tip can reach the value of 1010 V/m, slightly higher than the value found by others. Numerical results confirm that the more slender the protrusion, the more likely its explosion. Investigation of the role of the surface work function shows that decreasing its value at the cathode surface favors the explosion of a larger number of protrusions, inducing the distribution of the arc current among more spots, with a cathode damage reduction, especially on electrodes operating at high current and low temperature. View full abstract»

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  • On the potential for direct or MHD conversion of power from a novel plasma source to electricity for microdistributed power applications

    Publication Year: 2002 , Page(s): 1568 - 1578
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (530 KB) |  | HTML iconHTML  

    The generation of electricity using direct electrostatic and magnetohydrodynamic (MHD) conversion of the plasma-particle energy of small to midsize chemically assisted microwave or glow discharge plasma (CA-plasma) power sources in the range of a few hundred Watts to several tens of kilowatts for microdistributed commercial applications (e.g., household, automotive, light industry, and space-based power) is studied for the first time. In the determination of the effect of plasma parameters on conversion efficiency, careful attention was paid to the unique plasma conditions of low-pressure, low-ionization fraction, and nonthermal ion energies that are much greater than that of the thermal ions of traditional MHD but much lower than those of a fully ionized plasma typically generated for fusion experiments. The density of plasma ions and neutrals and their cross sections for processes such as charge exchange were also considered. The most important parameters were found to be charged-particle density and energy, as well as the large inventory of neutral gas atoms and molecules. Momentum and charge exchange of plasma ions with the large background fraction of neutrals represents a limitation to conversion efficiency. Two conversion technologies were examined in some detail. We considered the possibility of converting a CA-plasma using adaptations of a member of the broad category of electromagnetic direct converters previously developed for recovery and conversion of the high energy particles lost from tandem mirror and magnetically confined plasmas, and an MHD converter previously developed for conversion of high pressure combustion gases to electricity. While it was found that both conversion techniques performed well under ideal conditions for conversion of plasma to electricity showing conversion efficiencies of >50%, the tight coupling of plasma cell and converter, size limitations, particle energy, and the substantial inventory of relatively low energy neutrals may substantially reduce the efficacy of direct electrostatic converters under these conditions. However, MHD conversion of CA-plasmas appears feasible at ∼50% efficiency with a simple compact design. View full abstract»

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  • Plasma-etching profile model for SiO2 contact holes

    Publication Year: 2002 , Page(s): 1579 - 1586
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (563 KB) |  | HTML iconHTML  

    A theoretical plasma-etching model for contact holes (vias) is presented. The significant feature of this model is that the etch and deposition rates are given by analytical equations. The etch-profile simulations for the contact holes are computed from the trajectory equations of the surface-evolution equation by using a computer package of MATLAB. The ion and neutral etch rates are proportional to the energy and particle fluxes, respectively. A new approximate analytic expression for the ion-energy flux is reported for contact holes; the neutral flux expressions were found previously. The scanning-electron microscopy micrographs of SiO2 contact holes etched in a gas mixture of CF4/CHF3/Ar in a magnetically enhanced reactive ion etching reactor are fitted well using the developed model. View full abstract»

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  • Breakdown-voltage memory effect in a neon-filled diode at 1 mbar

    Publication Year: 2002 , Page(s): 1597 - 1601
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (348 KB) |  | HTML iconHTML  

    Results of the investigation of the breakdown-voltage distribution dependence on the relaxation time of the diode [the curve U~b~=f(τ)], i.e., memory effect, in neon at p=1 mbar are presented in this paper. The memory effect is determined for the diode-relaxation times 0.1-100 s. The applied voltage was linearly increased with the increasing rate 10 V/s. For each value of the relaxation time, the series of 200 successive and independent measurements were done. The numerical fitting of the theoretical expression of the breakdown-voltage distribution on the histograms of the experimentally established data was used to determined relative yield in the diode for the different relaxation times Y/Y0=f(τ). Results show that the yield in the diode decreased in that time interval in one order of magnitude. Quantitative parameters for two-step decreasing and qualitative explanation of these dependencies are given. View full abstract»

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  • Enthalpy-probe diagnostics of an atmospheric-pressure unleaded petrol exhaust-gas microwave-induced plasma

    Publication Year: 2002 , Page(s): 1587 - 1591
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (273 KB) |  | HTML iconHTML  

    An unleaded petrol exhaust-gas microwave-induced plasma (MIP) at atmospheric pressure was generated in a TE101 resonant-mode cavity. The microwave discharges were generated at three incident microwave power levels: 500 W, 700 W, and 1500 W. An enthalpy probe was used to characterize the exhaust-gas MIP discharge, yielding values of enthalpy, velocity, and heavy-particle temperature along the microwave-discharge axis. The heavy-particle temperature was found to be 710 K, 940 K, and 1065 K, with velocities of 140 m s-1, 148 m s-1, and 155 m s-1, at the exit plane of the discharge tube for an exhaust-gas flow rate of 3.5 l min-1 at 500 W, 700 W, and 1500 W respectively. The assumption of local thermodynamic equilibrium is required in the calculation of temperature and velocity in the microwave discharge from the enthalpy-probe data. In microwave-induced plasmas, the electron temperature is significantly higher than the heavy-particle temperature. We present arguments that indicate that the calculated heavy-particle temperature and velocity values are nevertheless accurate. View full abstract»

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  • Optimal duct bias for transport of cathodic-arc plasmas

    Publication Year: 2002 , Page(s): 1602 - 1605
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (294 KB) |  | HTML iconHTML  

    Carbon and titanium plasmas are used to investigate the effects of duct bias on the plasma transport through the magnetic duct of a cathodic-arc plasma source as a function of the magnetic-field strength and arc current so as to determine the optimal duct bias, at which the magnetic duct produces the maximum efficiency for plasma transport. The influence of the guiding magnetic field and arc current on the optimal duct bias is investigated. The optimal duct bias increases with the plasma density for carbon plasma, while the relationship is the opposite for the titanium plasma. The carbon-plasma behavior can be explained by a plasma-diffusion model presented in this paper, since the electron-ion collision frequency νei is less than the electron-cyclotron frequency νc,e. On the other hand, in a titanium plasma, νei is larger than νc,e, so this model is inaccurate. Our result shows that different kinds of plasmas have different transport behavior through the magnetic duct and thus, the duct parameters must be carefully chosen in order to achieve the optimal transport efficiency. View full abstract»

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  • Emission uniformity and emittance of explosive field-emission cathodes

    Publication Year: 2002 , Page(s): 1592 - 1596
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (525 KB) |  | HTML iconHTML  

    Explosive field-emission cathodes as well as plasma-flashover cathodes are important for high-power microwave tubes. These cathodes have the advantage of being lightweight as well as requiring no heater for electron emission. However, this class typically suffers from large amounts of outgassing, nonuniform emission, and very high emittance. In this paper, we review research into the uniformity and emittance of tufted carbon-fiber cathodes that have been coated with cesium iodide (CsI) salt. The CsI cathode is compared to polymer velvet, metal-dielectric, and carbon-slat cathodes. We find the uniformity and emittance are related for all of these cathodes. In general, the more uniform the electron emission, the lower the emittance of the cathode. This article shows that given proper diode design, the tufted carbon-fiber cathode with CsI has some promise as an electron emitter producing a good quality electron beam. 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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