1,720,961 research outputs found
Dispersion relation in plasmas generated by a sheath-helix antenna
No full textA theoretical model of the plasmas generated by a sheath-helix antenna is developed for axisymmetric perturbations. The system configuration consists of a cylindrical plasma column inside a dielectric tube of radius R-c. The eigenvalue equation is obtained and the eigenfunction is identified as the Bessel function J(0)(x) of the first kind of order zero. The radial wave numbers xi and eta for the eigenfunction are described in terms of the rf frequency and plasma density. A full dispersion relation is analytically obtained, including influence of the finite plasma size, antenna effects, the electron inertia, and ion mass contributions. It is shown from the dispersion relation that the radial mode number xi approaches infinity at the lower-hybrid frequency, exhibiting a resonance condition. Meanwhile, the radial wave number eta approaches 3.83/R-c at the lower-hybrid frequency. A cross-sectional view of the light emission in experiment indicates that the helicon-plasma density at the lower-hybrid frequency has a hollow profile. The azimuthal component E-theta(r) of the perturbed electric field observed experimentally is very similar to the theoretical model of J(1)(3.83r/R-c) at the lower-hybrid frequency. The emission peak coincides with the radial location of the strongest electric-field intensity. (C) 2002 American Institute of Physics
Electron temperature analysis of two-gas-species inductively coupled plasma
No full textThe electron energy distribution functions and electron temperatures are measured in Ar/He and Ar/Xe inductively coupled plasma with various mixing ratios. The electron temperature does not change linearly with the mixing ratios; instead it increases abruptly near P-He/PAr+He=1 and decreases rapidly near P-Xe/PAr+Xe=0. A simple model using a two-ion-species fluid model is suggested to explain the electron temperature variations, and it agrees well with the experimental results. (C) 2001 American Institute of Physics
Plasmas Generated by Axisymmetric Helicon Antenna
No full textA theoretical model of the plasmas generated by a sheath-helix antenna is developed for axisymmetric perturbations. The system configuration consists of a cylindrical plasma column inside a dielectric tube of radius Rc. The eigenvalue equation is obtained inside the plasma column and the eigenfunction is identified as the Bessel function of the first kind of order zero. The radial wave numbers for the eigenfunction are described in terms of the rf frequency and plasma density. An algebraic dispersion relation is analytically obtained. Several eigenmodes are identified from the dispersion relation. They are the low-frequency whistler-like mode, the Trivelpiece-Gould mode (TG), and the lower-hybrid mode. Properties of the plasmas and perturbed fields excited by a single-loop antenna are experimentally investigated. A cross-sectional view of the light emission indicates that the helicon-plasma density generated at the lower-hybrid frequency has a hollow profile. The azimuthal component of the perturbed electric field is obtained experimentally and its radial profile is found to be similar to the theoretical model. The emission peak coincides with the radial location of the strongest electric-field intensity. The experimental observations of the field profiles agree remarkably well with theoretical predictions
Properties of Plasmas generated by a Sheath-Helix Antenna
No full textSummary form only given. A theoretical model of the plasmas generated by a sheath-helix antenna is developed for axisymmetric perturbations. The system configuration consists of a cylindrical plasma column inside a dielectric tube of radius R. The eigenvalue equation is obtained inside the plasma column and the eigenfunction is identified as the Bessel faction Jo(x) of the first kind of order zero. The radial wave numbers for the eigenfunction are described in terms of the rf frequency and plasma density. An algebraic dispersion relation is analytically obtained. Several eigenmodes are identified from the dispersion relation. They are the low-frequency whistler-like mode, the Trivelpiece-Gould mode (TG), and the lower-hybrid mode. Properties of the plasmas and perturbed fields excited by a single-loop antenna are experimentally investigated. A cross-sectional view of the light emission indicates that the helicon-plasma density generated at the lower-hybrid frequency has a hollow profile. The azimuthal component of the perturbed electric field is obtained experimentally and its radial profile is found to be similar to the theoretical model. The emission peak coincides with the radial location of the strongest electric-field intensity. The experimental observations of the field profiles agree remarkably well with theoretical prediction
Characteristics of an atmospheric microwave-induced plasma generated in ambient air by an argon discharge excited in an open-ended dielectric discharge tube
No full textParametric observations on an atmospheric-pressure plasma sustained in ambient air by an argon discharge excited by 2.45 GHz microwaves in an open-ended dielectric discharge tube are reported. Microwave power, discharge tube dimensions, and argon flow rate were the major operating parameters. Three distinctive plasma regions were observed: plasma filaments exiting from the discharge tube, converging point of these filaments, and a plasma flame. At the filament-converging point, argon atom excitation temperature, rotational temperature, and electron density were measured by optical emission spectroscopy (OES) in the operating range of (3.0-5.0) liters per minute of gas flow rate and (650-950) W of microwave power. The measured excitation temperature and rotational temperature were (5000-5800) K and (2800-3400) K, respectively. The electron density obtained by Stark broadening width of the H-beta line showed (5.0-8.0)x10(14) cm(-3). It was observed that the volume of the plasma flame and the gas temperature were increased with increasing the microwave power. On the other hand, higher gas flow rates increased the electron density. In the plasma flame, the gas temperature measured by a thermocouple and OES was in the range of (1030-2200) K, which showed an exponential decrease in the axial direction away from the converging point. (C) 2002 American Institute of Physics.This work was supported by Grant No. R01-2000-00254
from the Korea Science and Engineering Foundation, and the
BK21 Project
Plasma parameters analysis of various mixed gas inductively coupled plasmas
No full textThe electron energy distribution functions and plasma parameters in various gas mixture discharges (N-2,O-2,CF4/He,Ar,Xe) are measured. When He is mixed, the electron temperature increases but the electron density is almost constant. The electron temperature increases rapidly near a He mixing ratio of 1, but it is almost constant when the mixing ratio is small. In Ar mixture discharge, the electron temperature is almost constant; the electron density increases rapidly near a mixing ratio of 1, but increases slightly when the mixing ratio is small. Mixing Xe increases the electron density and decreases the electron temperature. The electron density varies in a similar way with that of the Ar mixing case. A simple two-ion-species global model is used to analyze the plasma parameter variations as a function of mixing ratio, and it agrees well with the experimental results. (C) 2002 American Institute of Physics
Characteristics of plasma generated by polysilicon semiconductor bridge (SCB)
No full textIn an effort to elucidate the plasma generation mechanism of the semiconductor bridge (SCB), currents were forced to flow through a polysilicon bridge with a resistance of 1 Omega, while the voltage drop was measured to obtain the in situ power dissipation through the bridge. The energy stored in a 25 muF capacitor was used to activate the plasma. The typical behavior of two peaks in the voltage-time curve was observed. It is inferred from the photodiode signal that the second peak in the voltage curve results from the plasma generation of the bridge material. The breakdown voltage of the electrical discharge at high pressure proved that the SCB is an effective plasma generator. The experimental data for the no-fire condition, directly related to the safety of the explosive system, is compared with the analytical results from a theoretical model. (C) 2002 Elsevier Science B.V. All rights reserved.This research was supported in part by the Dual Use Technology Program of Ministry of National Defense
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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