Pulsed Discharge Mode Research Articles

Effect of Silver Vanadate Additions on the Electrochemical Characteristics of the Fluorocarbon Electrode

An original method for the synthesis of silver vanadate was developed. It includes mechanical activation of the precursor in the course of plastic deformation on a high-pressure apparatus of the Bridgman anvil type, which is significantly time- and energy-saving. It was shown that the addition of silver vanadate to fluorocarbon improves the electrochemical characteristics of the electrodes, especially in pulsed discharge modes.

Structure and properties of titanium after nitriding in a plasma of pulsed hollow cathode glow discharge

The paper reports on a study of the structure, phase composition and mechanical characteristics of a modified surface layer of VT1-0 titanium after nitriding in the plasma of pulsed and stationary non-self-sustained glow discharge. It was revealed that after nitriding in a pulsed glow discharge, the volume fraction of nitride phase (Ti2N, TiN) in the surface layer of VT1-0 titanium is higher than that in the nitrited layer obtained by exposure to a plasma of steady glow discharge at the same nitriding temperatures, average ion current density at the surface and ion energy. As a result, the hardness of the surface layer of samples obtained by nitriding in pulsed discharge mode exceeds that of samples treated in steady glow discharge mode. Wear resistance of titanium after nitriding in the plasma of a pulsed glow discharge is approximately four times higher than that of titanium without treatment and 1.5 times higher than that achieved by nitriding in a steady glow discharge plasma.

The spatial and temporal evolution characteristics of the density field near wall region actuated by plasma

Using the dielectric barrier discharge plasma actuating model and high speed schlieren technique, the spatial and temporal characteristics of the density field near wall region actuated by plasma has been investigated in the different discharge modes and electrical parameters. Experimental results indicate that the initiation, development and dissipation of the induced vortex is an unsteady start-up process. After the equilibrium of body force and atmospheric damp is reached, the induced vortex stops accelerating and reaches maximum speed. The induced flow propagates downstream with the intermittent pulsed pattern in the pulsed discharge mode. However, in the steady discharge mode, plasma aerodynamic actuation cannot generate the closed vortex and the flow develops in a continuous turbulent form. Carrier voltage and the duty cycle are the key parameters that affect the vortex start position and maximum flow speed. With the increase of duty ratio, the start position of induced vortex moves downstream. There is a positive correlation between the excitation voltage maximum speed and the location of the maximum speed is pushed back with the rise of voltage. Pulse frequency is the dominant factor which determines the vortex generation frequency and the vortex generation frequency and pulse frequency is strictly consistent. We also find that the jumping change of flow speed resulted from pulsed discharge is the formation mechanism of induced vortex. Switching moment of actuator is the zero hour of vortex growth and duty ratio dominates the spatial structure and developmental pattern of induced vortex.

Parametric Study of Paraelectric and Peristaltic Pulsed DBD Plasma Actuation for Aerodynamic Flow Control Based on PIV

Using single and multiple dielectric barrier discharge plasma actuators, the velocity fields induced by steady, pulsed, asynchronous, and duty cycle plasma actuation are studied based on Particle Image Velocimetry (PIV). First, the flow fields induced by a single dielectric barrier discharge with different discharge models and actuation parameters are investigated. According to the velocity distributions, a parametric study on the influence of excitation voltages, carrier frequencies, pulse frequencies, and duty ratios on plasma actuation is presented and the optimum actuation parameters are provided. Emphatically, through double actuators alternating discharge, the peristaltic acceleration plasma actuation, a new plasma actuation mode, has been proposed and studied. The efficiency of the plasma actuators in steady and pulsed discharge modes is explored. The velocity field induced by plasma actuation with different phase angles and duty cycle ratios is acquired and the momentum transfer characteristics of the flow field were discussed. Finally, based on the above-mentioned results, the technical superiority and mechanism of the peristaltic acceleration induced by multiple dielectric barrier discharge plasma actuators are analyzed.

Optical emission spectroscopy observations of fast pulsed capillary discharge plasmas

We present time resolved optical emission spectroscopic (OES) observations of a low energy, pulsed capillary discharage (PCD). The optical emission from the capillary plasma and plasma jets emitted from the capillary volume was recorded with with a SpectraPro 275 spectrograph, fitted with a MCP gated OMA system, with 15 ns time resolution. The discharge was operated with different gases, including argon, nitrogen, hydrogen and methane, in a repetitive pulsed discharge mode at 10-50 Hz, with, 10-12 kV pulses applied at the cathode side. The time evolution of the electron density was measured using Stark broadening of the Hβ line. Several features of the capillary plasma dynamics, such as ionization growth, wall effects and plasma jet evolution, are inferred from the time evolution of the optical emission.

High-beta plasma effects in a low-pressure helicon plasma

In this work, high-beta plasma effects are investigated in a low-pressure helicon plasma source attached to a large volume diffusion chamber. When operating above an input power of 900W and a magnetic field of 30G a narrow column of bright blue light (due to Ar II radiation) is observed along the axis of the diffusion chamber. With this blue mode, the plasma density is axially very uniform in the diffusion chamber; however, the radial profiles are not, suggesting that a large diamagnetic current might be induced. The diamagnetic behavior of the plasma has been investigated by measuring the temporal evolution of the magnetic field (Bz) and the plasma kinetic pressure when operating in a pulsed discharge mode. It is found that although the electron pressure can exceed the magnetic field pressure by a factor of 2, a complete expulsion of the magnetic field from the plasma interior is not observed. In fact, under our operating conditions with magnetized ions, the maximum diamagnetism observed is ∼2%. It is observed that the magnetic field displays the strongest change at the plasma centre, which corresponds to the maximum in the plasma kinetic pressure. These results suggest that the magnetic field diffuses into the plasma sufficiently quickly that on a long time scale only a slight perturbation of the magnetic field is ever observed.

Sputtering of graphite in pulsed and continuous arc and spark discharges

The environment that leads to the sputtering of graphite electrodes and formation of carbonaceous discharge has been studied with emission spectroscopy. Population level densities, excitation & vibrational temperatures and electron densities have been obtained from a set of three ion sources. The sources operate in continuous and pulsed discharge modes. The sputtered species include monatomic, diatomic and higher carbon clusters. The main sputtered species are excited and ionized C 1 (CI, CII, respectively) and C 2. In the continuous arc discharge the vibrational temperature derived from the Swan band of C 2 is ∼10,000 K, whereas, in the pulsed arc the excitation temperature of Neon is ∼11,000 K. The spark discharge yields an average excitation temperature of CI and NI ∼ 5500 K.

Inverted-magnetron cold-cathode gauge in hybrid-discharge mode

In high-vacuum measurement, cold-cathode ionization gauges have been widely used due to their unique advantages such as being simple and robust, low outgassing, x-ray effects, and so on. But during the measuring process, they show that a considerable pump effect, contamination buildup, and the heating and sputtering of the electrode surface from discharge can also become a serious problem at higher measured pressures. In such circumstances, pulsed operation is a good solution. However, the lowest measurable pressure of cold-cathode ionization gauges in pulsed operation is hard to extend, which limits its application. But if the measurable range of the cold-cathode gauge is divided into two regions, the low-pressure region where it is operated in dc discharge mode to ensure its lowest measurable pressure and the high-pressure region where it is operated in pulsed-discharge mode to reduce its above disadvantages at high pressures, the problem can be well solved. This article describes a pulsed high-voltage generating circuit controlled by a single-chip CPU to perform such a hybrid discharge in an inverted-magnetron gauge. With this circuit, the following problems of an inverted-magnetron gauge were investigated: the difference between pulsed-discharged mode and dc discharge mode, one method of extending the low measurable pressure limit in pulsed-discharge mode, the volt-current characteristics at different pressures, and constant-current pulsed-discharge measurement at pressures above 2×10−2Pa.

The characterization of structure-tailored plasma films deposited from the pulsed RF discharge

Pulsed RF plasma polymerization using vinyl acetic acid as a prototype precursor was investigated in order to evaluate the applicability of the pulsed RF discharge to obtain plasma polymers with less cross-linked structure and high degree retention of the groups in the starting monomer. The chemical structure and the surface morphology of the polymerized vinyl acetic acid were characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscope (XPS) and scanning electron microscope (SEM). At all other plasma parameters remaining constant, the chemical structure was observed to vary with the plasma duty cycles. The FTIR results showed that more carboxylic groups could be ‘retained’ with the decreasing of the duty cycles. The XPS results were consistent with the FTIR measurements. Surface energy measurements indicated that the plasma films were hydrophilic. The plasma polymerized films at continuous discharge mode show higher thermal stability than the films polymerized at pulsed discharge mode. But the later is less cross-linked. So it is possible to control the chemical composition of the plasma film with the same surface functional groups as its monomer being ‘retained’ by pulse plasma technologies. Some regular graft ‘lightning’ network patterns were interestingly found in the plasma films kept at room temperature for some time by SEM. It was estimated that the mechanism of the plasma polymerization is different along the ‘lightning’ network and on the valley of the pattern.

Optical emission diagnostics of permanent and pulsed microwave discharges in H2–CH4–N2 for diamond deposition

A microwave plasma of H2–CH4–N2 gas mixture used for diamond film deposition has been characterized by optical emission spectroscopy in the continuous and in the pulsed modes. In the continuous mode, a dynamic form of actinometric optical emission spectroscopy was used to determine temporal trends in the concentrations of H, CH and CN species following the cut-off of either the CH4 or N2 flows. These data show that the gas-phase reactions play a major role in the production of the above-mentioned species, but also the plasma–diamond surface reactions contribute significantly to the production of the CN radical. In the pulsed-discharge mode, time-resolved optical emission spectroscopy was used to determine the evolution of the relative concentrations of reactive species H, CH, CN and Ar with time. This evolution during the discharge, post-discharge and transient stages gives information on the processes leading to the population of excited states.

Discharge impedance variations in large area radio frequency excited CO2 lasers

Some results from a systematic study on the impedance matching conditions and on the longitudinal power distributions in planar rf discharges for CO2 lasers, are given. They show that both plasma impedance and voltage distribution are different in cw and pulsed discharge modes revealing the importance of parameters such as the interelectrode temperature distribution and the local gas density and composition. These parameters have to be taken into account when designing matching networks and voltage smoothing schemes.

Some Characteristics of the Hollow Cathode Discharge Source from Hollow Cathodes of Different Sizes and Shapes

The empirical evaluation of several types of two-piece hollow cathodes for the analysis of microsamples using both dc and pulsed discharge modes of the hollow cathode discharge is reported. The discharge parameters used are similar to those that have given good precision and sensitivity for microsamples in this laboratory. Both optical microscopy and scanning electron microscopy were used to follow sputtering effects on the cathode geometry. The sputtering patterns in the flat-bottom, two-piece cylindrical hollow cathode revealed directly the cathode dark space on the cathode cavity bottom. The temporal emission profiles from the spherical cathode cavity are similar to those observed in cylindrical cathode cavities. The temporal emission profile changes with the diameter of the cylindrical cathode cavity and is characteristic of the analyte.

Selective detection of emission lines from sputtered particles in glow discharge plasma with a modulated hollow cathode lamp

A modulated hollow cathode lamp which consists of three electrodes is investigated and discussed. A discharge operating power supplied between the intermediate electrode and the anode generates the hollow cathode plasma in the intermediate electrode with a pulsed discharge mode. The number of sample atoms sputtered from the cathode surface is controlled with a bias voltage supplied between the cathode (sample) and the intermediate electrode. Emission intensities from the sputtered particles strongly depend on the variation in the bias voltage, whereas those from gas species hardly change. It is suggested from this effect that the emission lines of the sample atoms are selectively detected from the total emission signals.

The 4X Source

Our Penning surface-plasma source (SPS) discharge chamber was enlarged 4X in two dimensions. To date, three pulsed discharge modes have been studied: two with noisy arc (#x02273;20% H- current fluctuations) and one with quiescent arc (≲1% H- current fluctuations). Lower arc magnetic field and higher H2 gas flow allow switching from the noisy to the quiescent mode. The noisy modes yield up to 120 mA of 29-keV H- beam; for 110 mA at 29 keV, the two-dimensional normalized rms emittance is 0.017 x 0.018 π·cm·mrad. The quiescent mode yields 75 mA of 29-keV H- beam; for 67 mA at 24 keV, the emittance is 0.011 x 0.012 π·cm·mrad.

Excitation Mechanisms in Pulsed Ar-Kr Discharges

Excitation mechanisms of Ar–Kr ion lasers have been investigated by observing time sequences of spontaneous emissions from upper laser levels in the pulsed discharge mode. The experimental results show that a dominant excitation mechanism of Ar gas in Ar–Kr mixtures changes, with increasing Kr content, from direct electron collisions into excitation transfer collisions between Kr ion and Ar atom. The excitation mechanism of Kr gas is predominantly due to a direct electron excitation and no appreciable change with the gas composition is found.