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Plasma Science, IEEE Transactions on

Issue 1 • Date Feb. 1998

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Displaying Results 1 - 19 of 19
  • Comments on "The time evolution of the resistances and inductances of the discharges in a pulsed gas laser through its current waveforms" [with reply]

    Publication Year: 1998 , Page(s): 119 - 121
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (48 KB)  

    Persephonis et al. (see ibid., vol.24, p.1208-14 (1996)) present a method for calculating the time evolution of the resistance and inductance from the measured current and voltage waveforms of a circuit. As it was pointed out by Fridman (1997), from those measurements, it is impossible to obtain a unique time evolution of the resistance and inductance; further hypothesis are needed to solve the problem. In this comment we analyze the results presented in the above paper and find several contradictory features, like violations to the Kirchoff's law. Finally, we stress the fact that during the fast breakdown of a gas gap characterized by large, fast varying values of the resistivity, it is impossible to meaningfully and separately define a resistance and an inductance as lumped parameters of a circuit. View full abstract»

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  • Author's reply

    Publication Year: 1998 , Page(s): 121
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (21 KB)  

    First Page of the Article
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  • PASP Plus solar array parasitic current collection flight results

    Publication Year: 1998 , Page(s): 46 - 58
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (324 KB)  

    Exposed positive potential surfaces of spacecraft solar cells (interconnects and cell sides) collect electrons from the surrounding plasma. In low-Earth-orbit, this current is a drain on the array power that can be significant for high-power arrays, and this current influences the floating potential of the spacecraft. One objective of the Air Force PASP Plus (Photovoltaic Array Space Power Plus Diagnostics) experiment is an improved understanding of parasitic current collection. We examined the flight data for the arrays facing the ram direction. Overall, the effective current collection area rises about two orders of magnitude as the applied bias rises one order of magnitude, as is typical when snapover plays a role. The collecting area has a weak dependence on plasma density, with larger collecting areas corresponding to lower densities (longer debye length). This dependence on plasma density is stronger for lower densities and weaker for higher densities. There is a large amount of scatter in the measurements, with the current collected under similar conditions varying by up to a factor ten. Further laboratory and flight experiments are needed to determine the cause of the scatter. Even with this ambiguity, PASP Plus results can be used to quantify this effect by spacecraft designers and have already been used to validate an analytic model of this process View full abstract»

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  • Ion charge state distributions of pulsed vacuum arcs-interpretation of their temporal development

    Publication Year: 1998 , Page(s): 118 - 119
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (52 KB)  

    Ion charge states of vacuum arcs are enhanced at the beginning of each arc pulse. The ion charge states drop with time and become steady-state after about 100 μs, with some dependence on the cathode material. A reduction of ion charge states has been observed at the end of each are pulse. In this note it is shown that the charge-state-dependent ion drift velocity in the plasma expansion zone contributes to the effect measured by the time-of-flight method, although it is not solely responsible for it. A quantitative evaluation as well as literature data of other measuring methods prove the physical significance of the effects observed View full abstract»

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  • Kinetic theory of stochastically heated RF capacitive discharges

    Publication Year: 1998 , Page(s): 59 - 68
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (336 KB)  

    Stochastic sheath heating is the dominant heating mechanism at low pressures for radio frequency (RF) capacitive discharges. It produces an electron energy probability distribution function (EEPF) that approximates a two-temperature Maxwellian, as seen in both experiments and numerical simulations. We have used the fundamental kinetic equation to obtain a space- and time-averaged kinetic equation. We assume that electrons with the x component kinetic energy lower than a certain threshold Φ are prevented from interacting with the sheath heating fields. With these approximations and either a knowledge of the central density or an ansatz on Φ, we obtain a self-consistent solution for the quasiequilibrium discharge parameters valid for low pressures in argon. The results are compared to those found in experiments, yielding reasonable agreement View full abstract»

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  • Simulation of a Helicon plasma source using a multivariable fuzzy model

    Publication Year: 1998 , Page(s): 104 - 112
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (232 KB)  

    This paper reports work on the development of an automatic control system for a Helicon plasma processing source. The lack of a definitive physical model for the plasma physics of the source and the power coupling mechanism to the plasma precludes the use of traditional control algorithms. This paper develops a fuzzy model that simulates the behavior of the plasma source using the process of genetic algorithms to identify and optimize the parameters of the fuzzy model. This type of model will eventually be used to test a fuzzy control system for the plasma source. In this work, an extensive set of experimental data was acquired where the magnetic field and input power to the plasma source were varied over a wide range while the electron number density was measured. From this learning dataset, the genetic algorithm derived the values of the parameters for the difference equation that describes the system. The fuzzy model so constructed was used to predict the behavior of the source from known input parameters. Comparing the predictions with experimental observations showed that the fuzzy model was generally able to predict the behavior of the plasma as its input parameters were varied with a precision of better than 10% View full abstract»

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  • Experimental studies on isentropic efficiency of a nonequilibrium MHD disk generator

    Publication Year: 1998 , Page(s): 69 - 78
    Cited by:  Papers (3)
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    Isentropic efficiency of the nonequilibrium MHD power generator was studied by a shock tube driven disk generator. Cesium seeded helium was used as a working gas. From the measurements of Faraday current density distribution, it was possible to estimate the general tendency of Joule dissipation in the generator. The Joule dissipation did not decrease due to the occurrence of nonuniformity of the plasma when external load resistance was low, although it decreased with the decrease in the load resistance when the load resistance was high. The electrical efficiency increased with the increase in applied magnetic flux density. This fact is thought to be caused by high Hall parameter and the stabilization of the plasma due to high degree of seed ionization View full abstract»

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  • Wave propagation in a transient plasma-development of a Green's function

    Publication Year: 1998 , Page(s): 19 - 25
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (272 KB)  

    The effect of a transient plasma on a source wave, when the rise time of the electron density profile is comparable to the source wave period, is considered. The problem is not amenable to a sudden-switching approximation or an adiabatic approximation. It is investigated by developing a causal Green's function for temporally unlike media. A perturbation series based on the Green's function gives the solution to the desired accuracy. As compared to the numerical methods that give the total fields, this method has the intrinsic advantage of processing the forward propagating and backward propagating waves explicitly. The validity of the method is illustrated by comparing the perturbation solution to the exact solution of a linear profile. The scattering coefficients for a “hump profile,” which has no obvious exact solution, are obtained to illustrate the general applicability of the new approach View full abstract»

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  • Two-dimensional modeling of positive streamer propagation in flue gases in sphere-plane gaps

    Publication Year: 1998 , Page(s): 41 - 45
    Cited by:  Papers (16)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (116 KB)  

    The results of two-dimensional numerical simulation of positive streamer dynamics in flue gases in sphere-plane electrode configuration are presented. The G-values (numbers of radicals produced per 100 eV of input electrical energy) for the production of chemically active particles participating in flue gas cleaning from toxic components are calculated. Obtained G-values are almost independent on the discharge conditions. Simple estimates for G-values, based on analytical streamer theory, are shown to agree with the results of numerical simulation View full abstract»

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  • Analysis of the nitrogen ion beam generated in a low-energy plasma focus device by a Faraday cup operating in the secondary electron emission mode

    Publication Year: 1998 , Page(s): 113 - 117
    Cited by:  Papers (27)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (112 KB)  

    The energy distribution and flux of fast nitrogen particles generated in a Mather-type plasma focus device operating at 0.4 Torr of N2 pressure is reported. A Faraday cup operating in the secondary electron emission mode was employed. To determine the total number of beam particles, multiple scattering of the ions was taken into account. It has been possible to register the ion energy up to a lower kinetic energy threshold of ≈50 keV, which is a value much lower than that obtained with a Thomson spectrometer in a previous work View full abstract»

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  • Instrumental and process considerations for the fabrication of silicon-on-insulators (SOI) structures by plasma immersion ion implantation

    Publication Year: 1998 , Page(s): 79 - 84
    Cited by:  Papers (36)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (164 KB)  

    Plasma immersion ion implantation (PIII) has recently been shown to be a viable method to fabricate silicon-on-insulator (SOI) materials using either the SPIMOX (separation by plasma implantation of oxygen) or the ion cut/wafer bonding method. We have recently modified and characterized a new generation plasma immersion ion implanter for SOI fabrication, and this paper will discuss some of the instrumental and processing issues, including the plasma source, mean free path consideration, and dc sheath characteristics View full abstract»

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  • Radiation properties of ICRF waveguide couplers

    Publication Year: 1998 , Page(s): 26 - 35
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    The radiation spectra of a dielectric-filled waveguide (DWG) and a folded waveguide (FWG) antenna in the ion cyclotron range of frequencies are evaluated for tokamaks with the waveguide codes, which model the coupling of the waveguide modes to the plasma waves with outward radiating boundary conditions. The codes provide a self-consistent calculation of the fields across the waveguide apertures for various antenna phasings taking into account a complete set of waveguide eigenmodes including the reflected modes and, in the case of DWG, an arbitrary orientation of the antenna to the plasma magnetic field. In the studied cases, the spectra are found to be well described by a model which is based on a simplified wave field pattern determined by the antenna aperture geometry. Comparison to the corresponding loop antenna is carried out View full abstract»

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  • Regime of trapping and adiabatic deceleration of electrons in a sectioned electron RF generator

    Publication Year: 1998 , Page(s): 36 - 40
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (128 KB)  

    As a method for the realization of the regime of trapping and adiabatic deceleration of particles in relativistic RF electron autooscillators, the scheme of the twystron with a self-exciting input section and an output section where the deceleration of electrons is provided by profiling the parameters of the system is suggested. It is shown that for a wide range of parameters, almost total trapping of the particles and, therefore, high-efficiency stable RF generation, can be achieved View full abstract»

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  • Variation of focus action with electrode length for an inner electrode of negative polarity

    Publication Year: 1998 , Page(s): 14 - 18
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (124 KB)  

    A 2.3 kJ plasma focus (PF) device was used to investigate the variation of focus action with electrode length using argon, air, and nitrogen as filling gases. It was observed that for an inner electrode (IE) of negative polarity, the focus action improved tremendously as the electrode lengths were reduced from 80 to 40 mm. The high voltage (HV) pulse width also decreased with the decrease in electrode lengths. Third, the best focus peak of the HV pulse was shifted toward higher focus pressures, and the range for good focus action was broader. There is a tendency toward improvement of focus action toward significantly shorter IE lengths (about 40 mm) for negative polarity as compared to positive polarity, where the optimum IE length is 150 mm. This suggests that plasma contamination due to ablated IE material is minimized with shorter electrode length for negative IE. This could provide part of the solution to the polarity riddle of PF devices in relation to neutron production View full abstract»

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  • Ion-acoustic surface waves on a dielectric-dusty plasma interface

    Publication Year: 1998 , Page(s): 100 - 103
    Cited by:  Papers (35)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (156 KB)  

    The theory of ion-acoustic surface wave propagation on the interface between a dusty plasma and a dielectric is presented. Both the constant and variable dust-charge eases are considered. It is found that massive negatively charged dust grains can significantly affect the propagation and damping of the surface waves. Application of the results to surface-wave generated plasmas is discussed View full abstract»

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  • Nonlinear development of the dust acoustic instability in a collisional dusty plasma

    Publication Year: 1998 , Page(s): 92 - 99
    Cited by:  Papers (24)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (240 KB)  

    We study the nonlinear behavior of the low-frequency dust acoustic instability in a collisional dusty plasma by means of particle simulations. The instability arises due to the streaming of plasma ions and neutrals relative to charged dust grains. According to linear theory, the presence of collisions between the plasma ions and a neutral gas background reduces the growth rate of the instability. Nonlinearly, however, the presence of drifting neutrals maintains the initial relative drift between plasma and dust ions until the unstable waves grow to large amplitude and collisions due to wave-particle interactions exceed the neutral collisions. As a result, stronger nonlinear effects, as manifested by enhanced fluctuations, larger amounts of plasma and dust heating, and a temporary reduction of the relative drift velocity, can occur in the presence of collisions View full abstract»

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  • Numerical simulation of axisymmetric anode spot formation in glow discharge at elevated pressure

    Publication Year: 1998 , Page(s): 7 - 13
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (292 KB)  

    A two-dimensional nonstationary fluid model is used to simulate dc elevated pressure glow discharges to describe the growth of the instability near an anode inside a cylindrically symmetric parallel plane surface geometry. This model is based on a fluid description of electron and ion transport coupled with Poisson's equation. Numerical results for the case of a glow discharge in nitrogen gas are presented. The transition of a radially uniform glow discharge into a state with spots or ring structures is obtained from the two-dimensional simulations without any special initiating perturbation. The influence of diffusion, full current through spot, and volume recombination on the normal current density effect in the near-anode region of the glow discharge has been investigated. The applicability of the similarity principle to the anode spot development processes is analyzed. Prerequisites to the existence of the complex shape current structure in the form of a ring with a central spot are discussed View full abstract»

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  • Modification of an electromagnetic wave by a time-varying switched magnetoplasma medium: transverse propagation

    Publication Year: 1998 , Page(s): 1 - 6
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (252 KB)  

    The modification of frequency and field amplitudes of an extraordinary wave (X-wave) by a time-varying magnetoplasma medium is considered. An explicit expression for the amplitude of the electric and magnetic fields in terms of the magnetoplasma parameters and the new frequency is obtained View full abstract»

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  • Mode-selective amplification in a waveguide free electron laser with a two-sectioned wiggler

    Publication Year: 1998 , Page(s): 85 - 91
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (168 KB)  

    One important issue in waveguide free electron lasers (FELs) involves an interaction of the electron beam with one waveguide mode at two different resonant frequencies. Since the low-frequency mode often has a higher pain, the usually preferred high-frequency mode is suppressed as a result of mode competition. In this paper, possible control of this mode competition is considered using a nonstandard wiggler magnet consisting of two cascaded wiggler sections with different periods and field strengths. It is demonstrated that with an appropriate differentiation between the two wiggler sections the high-frequency mode may be amplified preferentially. This mode-selective amplification may be used to suppress the low-frequency mode. A small signal gain formulation is developed for a waveguide FEL with such a two-sectioned wiggler arrangement and numerical examples are used to demonstrate its applicability to mode control in waveguide FELs. Effects of wiggler field errors and electron energy spread are also considered. It is shown that the requirement for wiggler field errors and electron energy spread in the two-sectioned wiggler arrangement is similar to that in the usual straight wiggler configuration 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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