Ignition Of Glow Discharge Research Articles

On the slow ionization waves forming the breakdown in a long capillary tube with helium at low pressure

The results of studies of an electrical breakdown leading to the glow discharge ignition in a long capillary quartz tube are presented. Under such conditions, the breakdown completion is preceded by the development of direct, backward, and counter slow ionization waves (IWs) traveling in the tube. The initiation of the waves was created in helium at low pressure (P = 10 Torr) by the high-voltage pulses of positive and negative polarity with amplitude of several kilovolts. In the beginning, the regime without the breakdown completion in the tube was studied. In this regime, the propagation of only direct positive and direct negative IWs happens. The research on dynamics of the direct, backward, and counter positive and negative waves followed by a complete breakdown was done as well. The influence of the pre-existing plasma on the IWs propagation was also studied. The plasma was created in advance by low-current glow discharge being formed in the tube. The instant images of IWs were correlated with the electrical currents formed by the waves, that is, with the displacement current through the dielectric wall and the conductive current through the plasma column. In the experiments, the fine-sectioned electrode wrapped around the lateral tube surface was used. The usage of such electrode allowed one to study the dynamics of the surface charge deposition and deletion happening during the direct and backward wave propagation, respectively. Finally, a strong difference in the spatial structure and velocity of positive and negative direct waves traveling through non-ionized gas was revealed. Contrary, both the positive and negative backward waves traveling through the plasma formed by previous direct waves have the parameters close to each other.

Features of glow discharge ignition through a small hole in the hollow cathode of a large volume

The influence of the size of a cathode gap on the initiation of the effect of a hollow cathode in a glow discharge system with an extended hollow cathode in the forevacuum pressure range is shown. It was found that the threshold current for the transition of the discharge to the burning mode with a hollow cathode is determined by the ratio of the longitudinal and transverse dimensions of the cathode slit. With a decrease in the width of the slot, the threshold current increases disproportionately; at the same time, with an increase in the length of the slot, this current sharply decreases.

Numerical simulation of atmospheric pulse-modulated radio-frequency glow discharge ignition characteristics assisted by a pulsed discharge

A one-dimensional self-consistent fluid numerical model was developed to study the ignition characteristics of a pulse-modulated (PM) radio-frequency (RF) glow discharge in atmospheric helium assisted by a sub-microsecond voltage excited pulsed discharge. The temporal evolution of discharge current density and electron density during PM RF discharge burst was investigated to demonstrate the discharge ignition characteristics with or without the pulsed discharge. Under the assistance of pulsed discharge, the electron density in RF discharge burst reaches the magnitude of 1.87 × 1017 m−3 within 10 RF cycles, accompanied by the formation of sheath structure. It proposes that the pulsed discharge plays an important role in the ignition of PM RF discharge burst. Furthermore, the dynamics of PM RF glow discharge are demonstrated by the spatiotemporal evolution of the electron density with and without pulsed discharge. The spatial profiles of electron density, electron energy and electric field at specific time instants are given to explain the assistive role of the pulsed discharge on PM RF discharge ignition.

Double-hole anode glow discharge in axial magnetic field at low pressures

The influence of magnetic field on glow plasma was studied by the self-designed double-hole anode discharge device, and the relationship between ignition voltage and gas pressure under different magnetic fields is obtained. In addition, the influence of magnetic field on the spatial distribution of plasma density is studied by changing different magnetic field configurations. The results show that under the same pressure, the magnetic field can effectively reduce the glow discharge ignition voltage and increase the plasma density; the enhancement of magnetic field is similar to the increase in air pressure in the double-hole anode glow discharge structure; the hole anode and magnetic field are indispensable conditions for glow generation at low pressure; and different magnetic field configurations control the plasma density distribution.

Dynamics of Breakdown in a Low-Pressure Argon–Mercury Mixture in a Long Discharge Tube

Breakdown dynamics in the course of glow discharge ignition in a long discharge tube (80 cm in length and 25 mm in diameter) filled with argon at a pressure of 3–4 Torr and mercury vapor at room temperature was studied experimentally. Rectangular voltage pulses with amplitudes from 1 to 2.5 kV were applied to the tube anode, the cathode being grounded. Complex electrical and optical measurements of the breakdown dynamics were carried out. Breakdown begins with a primary discharge between the anode and the tube wall. In this stage, a jump in the anode current and a sharp decrease in the anode voltage are observed and prebreakdown ionization wave arises near the anode. The cathode current appears only after the ionization wave reaches the cathode. The wave propagation velocity was measured at different points along the tube axis. The wave emission spectrum contains Hg, Ar, and Ar+ lines. The intensities of these lines measured at a fixed point exhibit very different time behaviors. The effect of the tube shielding on the breakdown characteristics was examined. It is found that, at a sufficiently narrow gap between the shield and the tube, this effect can be substantial.

Structure and Properties of Parts with Coatings After Heat Treatment

Microstructures of combined coatings deposited under radiation heating in vacuum with pulsed ignition of glow discharge are presented. The effect of the heat treatment on the structure and properties of the coatings is studied.

Generation of Large Volume Atmospheric Pressure Air Plasma

Atmospheric pressure large volume air plasma was generated by applying 100 ns, 1-kHz high voltage pulse between two parallel electrodes separated by 48-mm gap. The high voltage power electrode has uniformly distributed pens and ground electrode shaped as a flat disc. Glow discharge ignition is initialized at the outer pens to form luminousness circle. By applying higher voltage, the glow expands to ignite the internal pens and to fill the gap between the two electrodes. Each pen forms glow discharge plasma with the ground electrode. The increase in voltage or frequency enhances the plasma intensity and homogeneity. The generated plasma showed efficiency against the fruit borne fungi of grapes.

Features of glow discharge ignition in a gap partially filled with dielectric beads

603 Recently, the electrical discharges in structured and heterogeneous media have evoked increased fun damental scientific interest and are widely applied in various technologies. Here, we mean by heterogeneous media (HM) media such as the powder of granulated par ticulate masses [1, 2], foamed liquids [3, 4], pored dielec trics [5, 6], dusted gases and aerosols [7–9], etc. Numer ous experiments have shown that the discharge modes in such media might differ cardinally from those of the well studied discharges in uniform gases and liquids.

Wave Packet Excitation and its Development in Supersonic Boundary Layer

A method of exciting of artificial disturbances localized in space and time (wave packets) in a supersonic boundary layer is developed. Experimental investigations are carried out in the low noise supersonic wind tunnel T-325 at Mach M = 2. A model of a flat steel plate with a sharp leading edge is used. Measurements of mean flow and fluctuations are performed by using a constant temperature anemometer. To generate controlled fluctuations the short time surface glow discharge is used. Measurements of controlled disturbances are synchronized in time with glow discharge ignition. To increase the signal-to-noise ratio the time trace averaging technique is applied. Electrical power and polarity of the glow discharge initiation are changed to see their influence on the initial wave packet amplitude. Optimal glow discharge parameters for generation of artificial disturbances are found. The experimental data on the localized disturbances evolution in boundary layer are received. It is obtained that the velocity of the wave packet propagation has speed close to the free stream for the leading wave edge. The trailing edge of the wave packet spreads with subsonic speed relatively the supersonic flow. The wave packet propagates in both the streamwise and spanwise directions. Half-angle of this spreading is approximately equal to 10 degrees relative to the free stream direction. It has been found, that the wave packet is developed inside the boundary layer near of the artificial pulsations source. However the evolution of controlled disturbances leads to their radiation into free flow

Simulation of the glow-to-arc discharge transition due to the cathode heating by ion bombardment

A model of gas-discharge transition from glow to diffuse arc, involving the equations of the discharge cathode sheath and the cathode heat balance equation, has been built. Time dependences of the cathode temperature and voltage drop from the moment of glow discharge ignition to the transition from glow to arc have been calculated.

Discharge characterization in plasma electrolytic oxidation of aluminium

Digital video imaging of the plasma electrolytic oxidation (PEO) of aluminium has been performed, which allowed evaluation of both dimensional characteristics of individual microdischarges appearing at the oxide–electrolyte interface and their collective behaviour throughout the oxidation process. It has been shown that the microdischarge cross-sectional dimensions vary within the range 0.01–1.35 mm2. In the course of PEO processing, small localized events (<0.03 mm3) always dominate in the microdischarge spatial distribution and the relative proportion of medium-sized to very large microdischarges is gradually redistributed in favour of the latter. Temporal dependences have been found for the fraction of surface area instantaneously experiencing the discharge, as well as for the spatial and current densities of the microdischarge. Discharge mechanisms occurring during PEO are discussed and a model of microdischarge formation is suggested, assuming the possibility of free-electron generation and glow discharge ignition in the gaseous media developed at the oxide–electrolyte interface. First approximation evaluations of thermal processes in the oxide layer under the discharge conditions have been considered. The estimated ranges of the microdischarge current density (50–18 kA m−2) and duration (0.25–3.5 ms) sufficient for initiating phase transitions (e.g. γ–α transformation and melting) in the surface oxide layer are shown to be in good agreement with experimental data.

Time-dependent O2 mass balance change and target surface oxidation during mode transition in Ti–O2 reactive sputtering

Time-dependent O2 mass balance change among the amounts injected into the chamber, pumped out from the chamber, gettered by sputtered Ti metal, residing in the chamber, and consumed to oxidize the target surface has been investigated as a function of time elapsed after the discharge ignition in Ti–O2 reactive sputtering. From the mass balance results obtained, target surface coverage has been estimated. In the period of up to 10 s after discharge ignition, the gettering of O2 by sputtered Ti dominated the process change. In this period, the target surface oxidation rate was low. In the period of 20–50 s, the amount of O2 consumed to target surface oxidation surpassed the amount of O2 gettered by deposited Ti, resulting in a drastic increase in the target coverage. After the target surface oxidation was completed, the process became stable. In this period, the amount of O2 pumped out without causing any process changes increased and a very small amount of O2 was consumed to oxidize the target surface. The equilibrium in the balance between the formation and sputter etching of the oxide layer on the target surface resulted in the stable condition. Calculated target coverage achieved more than 250 monolayers at 600 s after the glow discharge ignition. This value equated with the oxide thickness of about 100 nm. It is concluded that the nonlinear target surface oxidation process causes a nonlinear process change occurring during the mode transition.

Investigation of the effects of pumping speed and Ar/O 2 ratio on the transient time at mode transition in Ti-O 2 reactive sputtering

The effects of the pumping speed and the Ar/O 2 flow rate ratio on the transient time needed to reach a steady-state, after glow discharge ignition in Ti−O 2 reactive sputtering, were investigated. It was shown that the O 2 partial pressure, deposition rate, discharge voltage and the Ti emission intensity change continuously after glow discharge ignition until the process reaches a steady-state. The transient time increases as the pumping speed increases or as the Ar/O 2 ratio increases. The results suggest that a low pumping speed or a low Ar/O 2 ratio shortens the transient time for process operation parameter changes such as a reactive gas flow rate change.

Initiation and propagation of flame fronts in lean CH 4-air mixtures by the three modes of the ignition spark

The initiation and subsequent propagation of flame fronts by breakdown, are and glow discharge ignition devices have been investigated by time resolved interferometry in CH4-air mixtures (1/Ф=1.0, 1.11, 1.25, 1.4) at 4 bar. Based on size, effective expansion velocity, and radial temperature profiles across the flame fronts as functions of time after spark onset, it is shown that the breakdown controls the inflammation process up to ≈1 ms. The breakdown is far better suited for inflaming combustible mixtures than are or glow discharge due to very high energy transfer efficiency (≈95%), large double sided contact areas with the unburnt mixture, very steep gradients of temperature and particle density, and reignition capabilities at ≈300 μs. Thus extremely lean (1/Φ≈1.6) mixtures ignited at high flow velocities with high inflammation probabilities.