Positive Column Of Dc Discharge Research Articles

Ion accumulation by a dust cloud in a dc discharge

The ion accumulation within the negatively charged dust cloud embedded in a plasma of dc glow discharge has been studied numerically under the conditions corresponding to recent experiments. The characteristics of neon plasma in a positive column of dc discharge with various densities of micron-sized particles have been simulated by a diffusion-drift model with the use of experimental values of parameters of dust clouds. The model considers an additional gas heating associated with the presence of a dust component. It has been shown that the injection of dust particles into a plasma can either reduce the density of ions due to their recombination on dust particles or increase it due to the formation of an ion concentrator. Conditions under which the plasma-dust cloud represents an ion concentrator have been found; the density of ions in this trap can be several times higher than that in a discharge without dust particles. The method of elevating the ion density with dust particles has been shown to be more efficient than increasing the discharge current without dust particles and the value of relative overheating of the discharge with dust particles is many times less. The possibility of obtaining the desired ion density in a dust cloud at different neon pressures and the same discharge current has been demonstrated; it should be emphasized that this is impossible in a discharge without dust particles.

Measurement of the electron energy distribution in moving striations at low gas pressures

The time-resolved Electron Energy Distribution Functions (EEDFs) have been measured at different phases of moving striations in a positive column of DC discharge in argon gas. A very low gas pressure of 10 mTorr, a high energy resolution (to resolve the low energy part of the EEDF), and the dynamic range up to 3–4 orders of magnitude (to resolve the EEDF tail) with a temporal resolution of 2.5 μs distinguish our work from previous publications. The measured EEDFs reveal drastic changes in time of their low energy parts with the formation of a low energy peak. The observed EEDF dynamics is explained in the framework of nonlocal electron kinetics as electric field reversals and the trapping of low-energy electrons in potential wells propagating with striation along the discharge tube. The formation of the low energy peak in the EEDF is similar to that in rf capacitive and inductive discharges at low gas pressures where the low-energy electrons are trapped in the potential well created by the ambipolar electric field and cannot penetrate into the areas of electron heating by strong rf electric fields.

Influence of dust particles on the neon spectral line intensities at the uniform positive column of dc discharge at the space apparatus “Plasma Kristall-4”

Influence of the elongated dust cloud on the intensities of different neon spectral lines in visible and near ir spectral ranges in the uniform positive column has been experimentally investigated using the Russian-European space apparatus “Plasma Kristall-4” (SA PK-4) on board of the International Space Station (ISS). The investigation was performed in the low pressure (0.5 mbar) direct current (dc, 1 mA) gas discharge in neon. Microgravity allowed us to perform experiments with a large dust cloud in the steady-state regime. To avoid the dust cloud drift in the dc electric field a switching dc polarity discharge mode has been applied. During the experiment a dust cloud of 9 mm in diameter in the discharge tube of 30 mm in diameter with the length of about 100 mm has been observed in the steady-state regime. In this regard, the intensities of neon spectral lines corresponding to 3p → 3s electronic transitions have increased by a factor of 1.4 times, while the intensities of neon spectral lines corresponding to 3d → 3p electronic transitions have increased by a factor of 1.6 times. The observed phenomenon is explained on the basis of the Schottky approach by a self-consistent rising dc electric field in the dusty plasma cloud resulting in an increase of the electron temperature.

Validating the Goldstein–Wehner law for the stratified positive column of dc discharge in an undergraduate laboratory

In this paper we suggest a simple technique for validating the Goldstein–Wehner law for a stratified positive column of dc glow discharge while studying the properties of gas discharges in an undergraduate laboratory. To accomplish this a simple device with a pre-vacuum mechanical pump, dc source and gas pressure gauge is required. Experiments may be performed in nitrogen or even in air. First you need to photograph the discharge tube with striations at different gas pressure values and then you need to determine the thickness of the first striation on a computer monitor.

A nonlocal model of spatially nonuniform positive column of DC discharge

A self-consistent kinetic model is given of the positive column of low-pressure low-current dc discharge in neon in a tube of circular cross section, which is nonuniform in both the radial and longitudinal directions. The model is based on the solution of kinetic equation for the electron distribution function in nonlocal approximation, of drift equation for ions, of diffusion equation for metastable ions, and of Poisson equation for electric field. Calculations are performed for the case where the longitudinal nonuniformity of discharge is caused by a jumpwise variation of the discharge tube radius.

Electron thermal diffusion instability and standing striations in the plasma of a dc discharge in molecular gases

A linear theory of waves in the positive column of dc discharge in molecular gases is presented. Full account is taken of local electron hydrodynamics (s.c. quasi-homogeneous equations), which is derived on the basis of a local non-equilibrium distribution of the electron gas. The production term on the right-hand-side of the ion balance equation gives the familiar ionization wawes, but the ion drift enhanced by the high value of the logitudinal field strength, together with the modification of the pertubed electric field incurred by the electron thermal diffusion, causes the dispersion curve to inersect thek-axis. This provides a natural explanation of the amplified low frequency anode directed wave commonly observed in molecular gas discharges as well as of the standing striation pattern. Numerical examples are given for the case of nitrogen.