Constricted Discharges in the Rare Gases. I. Spectroscopic and Electrical Measurements

Abstract

A description of the visual characteristics of some constricted discharges in the rare gases using dc, rf, and microwave excitation is given. These discharges require power inputs of from 20 to greater than 100 W/cc. The results of a series of spectroscopic and electrical measurements made on these discharges indicate the range of plasma parameters encountered. Gas temperatures were measured using the intensity distribution of the spectra of several diatomic molecules. The gas temperature falls in the range from 2000° to 3000°K, but atomic excitation levels are not in equilibrium at this temperature. The charge density is around 1014/cc from continuum intensity, line broadening, and electrical measurements. The electron energy distribution is Maxwellian with an average electron energy which falls between 1 and 2 eV. Thus, these plasmas lie between ``thermal'' and ``cold'' plasmas in their properties. The recombination process probably has contributions from both dissociative recombination and dielectronic recombination with an over-all recombination coefficient of about 2×10−11 cm3/sec.

Radial contraction of microwave-sustained plasma columns at atmospheric pressure

“…An interesting variant of our experiment is one in which the discharge tube is in the horizontal position ͑Massey 31,32 and Rogers 61 ͒. In this case, a single plasma filament is not axially centered and is unstable unless the gas is static.…”

“…Since most of the experimental data on contracted discharges were obtained with the positive column of dc discharges, 30,31,[35][36][37][38][39][40] the majority of the theoretical models published to date have aimed at explaining the transition of this type of discharge from a radially uniform diffuse glow to a radially contracted bright filament as current and pressure are increased. 32,35,[41][42][43][44][45][46][47][48][49][50][51][52][53][54] This phenomenon was interpreted mainly on the basis of a radially nonuniform heating of the discharge gas, as will be discussed later.…”

“…As a rule, the more contracted the discharge, the brighter it is. 31 In comparison, the glow of a noncontracted discharge is faint, and one often speaks of a diffuse glow. However, in contrast to dc discharges, in which the contracted column always takes the form of a single, axially centered, straight filament, hf discharges can yield one, two or more filaments depending on discharge operating conditions.…”

Abatement of perfluorinated compounds using microwave plasmas at atmospheric pressure

“…[39][40][41][42][43][44][45][46] In contrast to dc discharges where the contracted discharge always takes the form of a single straight filament, rf and microwave discharges can also yield two or more plasma filaments depending on dis- charge operating conditions. 26 The plasma-free region, resulting from the contraction effect, limits the abatement efficiency, as will be discussed in Sec.…”

Effect of Microparticles on Acousto-Optic Diffraction in Water

“…From experiments, in particular with rare gases, it is known that, under medium pressure the positive column can exist in a diffuse state and in a contracted state [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]. The transition between the states occurs abruptly if the discharge current is varied [7,[11][12][13][14][15][16][17][18][19][20][21][22][23][24].…”