Ac Glow Discharge Research Articles

Measurement of controlled metastable oxygen atom concentration from nitric oxide AC glow discharge plasma

Measurement of controlled metastable oxygen atom concentration from nitric oxide AC glow discharge plasma

Thickness dependent thermal and optical properties of plasma polymerized N-benzylaniline thin films

Thermally stable, smooth and highly transparent plasma polymerized (N-benzylaniline) thin films are deposited onto glass substrates under ac (50 Hz) glow discharge plasma. Thermal stability and optical absorbance of the films are very high, indicate conjugation in the films, which depends on their thickness. Other optical parameters such as band energy gaps, steepness, Urbach energy, dielectric constant, etc. are also observed to vary with film thickness. The small value of extinction coefficient and high value of refractive index confirms that the films are very smooth highly transparent, and therefore suitable for anti-reflecting coating and infrared applications.

High-rate growth of single crystal diamond in AC glow discharge plasma

The detailed experimental behavior of an AC abnormal glow discharge plasma assisted chemical vapor deposition reactor for single crystal diamond (SCD) synthesis operating within the wide-range (20–250 Torr) pressure regime was presented. Within the discharge operating window absorbed power densities of 250–9000 W/cm3 were achieved and high quality SCD synthesis with growth rate up to 80 μm/h was demonstrated. At the power densities over 2500 W/cm3 the diamond substrates were located directly on water-cooled substrate holder without any intermediate molybdenum holder. The influence of several input experimental variables including pressure, N2 and Ar concentration, CH4 percentage, and discharge current on SCD deposition was explored. The quality of synthesized crystals approved competitive purity level of glow discharge CVD process.

The essential role of redox potential/equilibrium constant in the ability of non-equilibrium plasma for nano-synthesis in liquids

In this study, we investigated the role of redox potential in the ability of nano-synthesis by plasma–liquid interactions. From redox potential, a parameter featured the standard Gibbs free energy, and the equilibrium constant of a reduction reaction can be determined. Our calculation showed that the reactions of AuCl4−/Au0 with a redox potential of 1.0 V and Cu2+/Cu0 of 0.34 V have equilibrium constants of approximately 1050 and 1011, respectively. The results are significant to explain the failure in the copper nanoparticle synthesis in the process of nucleation through the Lamer theory. To compare these results to experimental data, the nanoparticles synthesized in a mixed solution of AuCl4− and Cu2+ by AC glow discharge were characterized. The experimental results showed that there were only gold nanoparticles synthesized even though the concentration of gold ions is 200 times smaller. Other results of silver and platinum nanoparticles were also agreeable to the theory. Our findings provide a prediction to explain the ability in the nano-synthesis by plasma in contact with liquid for any noble metals.

Comparison of electron temperature in DC glow discharge and AC glow discharge plasma

Knowing electron temperature and electron density is important for any plasma related applications. In this research, the electron temperature and electron density of argon plasma generated by low frequency AC power supply and a high voltage DC power supply were investigated. The measurements were compared, both experimentally and theoretically. For the experiment, a long glass cylindrical tube was used as a chamber where the electrodes were placed at 37.5 cm apart. A high voltage function generator power supply was operated at various frequencies and it was also used for DC operation. The electron temperatures were measured by Optical Emission Spectroscopy (OES) technique for different operating pressures of 0.1 mbar, 0.6 mbar and 1.1 mbar. For the simulation, both plasma theory and finite element method were used to simulate dynamics of the plasma in the cylindrical setup. From the experiment, the range of breakdown voltage was found to be between 0.80 to 2.3 kV. The length of DC glow discharge dark regions of the plasma decreases due to increasing in both operating pressure and voltage. AC glow discharge shows positive charge and negative charge swing. From the DC discharge, the maximum value of electron temperature was found to be 0.810 eV and the minimum value was 0.610 eV under the operating pressure 0.1 and 0.6 mbar respectively. From AC glow discharge plasma, the maximum electron temperature was 0.907 eV and the minimum was 0.540 eV under operating pressure 0.1 and 1.1 mbar respectively. Collision loss between ions and electrons causes this variation in the results.

New set up for diamond coatings deposition in AC glow discharge plasma on WC-Co milling cutters of complex shape

In the current work, we developed a new type of CVD reactor for high-speed deposition of uniform diamond coatings on WC-Co milling cutters in AC glow discharge plasma with two plasma channels in the Ar/H2/CH4 atmosphere. This CVD system successfully allowed one to deposit well-adherent MCD, UNCD and Multilayer diamond coatings with a thickness up to 60 μm on WC-Co milling cutters of various geometries and with a diameter up to 14 mm. We found that to minimize the edge effect, the optimal energy input for each plasma cord should be set in the range of 1.4–2.5 kW. We also found that diluting the H2/CH4 atmosphere with argon in the range of 45–80% vol. is one of the necessary conditions to control the deposition process. Diamond deposition rate has been achieved up to 2.5–3 μm/h with a uniformity of deposition over 50% from maximum thickness. Presented CVD system is very promising due to sufficiently high deposition rate and ease of implementation, and it also has great potential for industrial scaling.

Measurement of Microwave Propagation in Weakly Ionized Dusty Plasma

An experimental method of producing dusty plasma with high dusty particle density is proposed and implemented. Microdusty particles are immersed into an ac glow discharge plasma with large scale by applying electronically controlled vibratory screen mesh and continuous equidistributional dusty environment is formed. The impact of dusty particles on microwave propagation in a laboratory plasma device can be observed. The gigahertz microwave transmittance through the dusty plasma region is measured with vector network analyzer and horn antenna placed in the sides of plasma region. The results show that the dusty particles can synergize the influence on propagation of microwave in plasma.

Pectin modification assisted by nitrogen glow discharge plasma

This study is concerned with modification of high methoxy pectin (HMP) assisted by nitrogen AC glow discharge plasma. Intrinsic viscosity of plasma treated pectin (PTP) was measured as primary index for structural changes in pectin molecules at different plasma conditions. The intrinsic viscosity of pectin increased within 7 min of exposure to plasma treatment and then remained constant. According to Fourier Transform Infrared Spectrometry (FT-IR) analysis, the intensity of carboxylate peaks increased in PTP samples due to de-esterification of pectin. Moreover, by decreasing the degree of esterification (DE) in PTP samples, the results of FT-IR were confirmed. Based on high performance size-exclusion chromatography (HPSEC) analysis, the molecular weight of PTP reduced. PTP gel had higher storage and loss modulus and shorter linear viscoelastic region. Moreover, X-ray diffraction (XRD) studies indicated an increase of crystallinity in PTP due to the formation of hydrogen bonds. Results revealed that nitrogen AC glow discharge plasma had significant influence on physicochemical and functional properties of pectin. The result of this study showed AC glow discharge plasma has promising potential towards modification of pectin.

Achieving reactive species specificity within plasma‐activated water through selective generation using air spark and glow discharges

Plasma‐activated liquids (PAL) attract increasing interest with demonstrated biological effects. Plasma exposure in air produces stable aqueous reactive species which can serve as chemical diagnostics of PAL systems. Here, we tailor aqueous reactive species inside plasma‐activated water (PAW) through treating water with AC air spark and glow discharges in contact with water. Chemical probing demonstrated species specificity between two types of PAW. Spark discharge PAW contains and , while and are generated in glow discharge PAW. Species formation in different PAWs have been discussed in terms of discharge mechanisms and liquid phase chemistry process. Species specificity can provide richer parametric spaces for producing PALs with controlled impact and dosage achievable by combining discharge modes or mixing different PALs.

Research on the Plasma Anemometer Based on AC Glow Discharge

A new plasma anemometer based on AC glow discharge is designed in this article. Firstly, theoretical analysis of plasma anemometer working principle is introduced to prove the feasibility of the experimental measurement method. Then the experiments are carried out to study the effects of different parameters on the static discharge characteristics of the plasma anemometer system, by which the system optimization methods are obtained. Finally, several groups of appropriate parameters are selected to build the plasma anemometer system based on resistance capacitance coupling negative feedback AC glow discharge, and different airflow speeds are applied to obtain the achievable velocity measurement range. The results show that there is a linear relationship between airflow velocity and discharge current in an allowable error range, which can be applied for airflow velocity measurement. Negative feedback coupling module, which is composed of the coupling resistance and the coupling capacitance, has good effects on improving the system stability. The measurement range of the airflow velocity is significantly increased when the electrode gap is 3 mm, coupling resistance is 470 Ω, and coupling capacitance is 220 pF.

Numerical and Experimental Diagnostics of Dusty Plasma in a Coaxial Gridded Hollow Cathode Discharge

This paper presents the results of experimental and numerical investigation of the influence of dust nanoparticles on glow discharge plasma properties. A special apparatus was developed to provide a steady input of dust nanoparticles into ac glow discharge plasma. The plasma was created in a large-volume coaxial gridded hollow cathode. A novel simulation approach of dusty plasma was developed specifically for the experimental conditions. An extended fluid approach with drift-diffusion approximation for the electron and ion fluxes was modified to account for charged dust nanoparticles' contribution to net charge and for ion and electron loss on the surface of particles. Uniform distribution of dust particles in plasma and instantaneous charging process were assumed during simulations. Experimental measurements were carried out using Langmuir probe. Simulations and probe measurements were carried out before and after input of dust particles into plasma. Under the conditions studied both methods showed a decrease by a factor of 5 in electron density caused by input of dust nanoparticles.

AC plasma anemometer—characteristics and design

The characteristics and design of a high-bandwidth flow sensor that uses an AC glow discharge (plasma) as the sensing element is presented. The plasma forms in the air gap between two protruding low profile electrodes attached to a probe body. The output from the anemometer is an amplitude modulated version of the AC voltage input that contains information about the mean and fluctuating velocity components. The anemometer circuitry includes resistance and capacitance elements that simulate a dielectric-barrier to maintain a diffuse plasma, and a constant-current feedback control that maintains operation within the desired glow discharge regime over an extended range of air velocities. Mean velocity calibrations are demonstrated over a range from 0 to 140 m s−1. Over this velocity range, the mean output voltage varied linearly with air velocity, providing a constant static sensitivity. The effect of the electrode gap and input AC carrier frequency on the anemometer static sensitivity and dynamic response are investigated. Experiments are performed to compare measurements obtained with a plasma sensor operating at two AC carrier frequencies against that of a constant-temperature hot-wire. All three sensors were calibrated against the same known velocity reference. An uncertainty based on the standard deviation of the velocity calibration fit was applied to the mean and fluctuating velocity measurements of the three sensors. The motivation is not to replace hot-wires as a general measurement tool, but rather as an alternative to hot-wires in harsh environments or at high Mach numbers where they either have difficulty in surviving or lack the necessary frequency response.

Self-organized pattern formation of an atmospheric-pressure, ac glow discharge with an electrolyte electrode

An atmospheric-pressure plasma sustained by an ac power supply was generated using electrolyte solution as one of the electrodes. By altering the power supply, ring-like patterns, double-ring patterns and plasma-spot patterns were observed at the electrolyte–electrode surface. Synchronous current–voltage characteristics and time-resolved images were measured. Important factors for the self-organized patterns, including the electrode gap, power, frequency and electrolyte concentration, were explored. The optical spectrum characteristics of the device were investigated. The pH of the solution after discharge was also explored and the results show that the pH of the solution is evidently reduced after the discharge, implying that acidic components are produced in the solution. This study provides an alternative discharge method for producing patterns on a water surface.

Absolute number densities of helium metastable atoms determined by atomic absorption spectroscopy in helium plasma-based discharges used as ambient desorption/ionization sources for mass spectrometry

The absolute number densities of helium atoms in the 2s 3S1 metastable state were determined in four plasma-based ambient desorption/ionization sources by atomic absorption spectroscopy. The plasmas included a high-frequency dielectric barrier discharge (HF-DBD), a low temperature plasma (LTP), and two atmospheric-pressure glow discharges, one with AC excitation and the other with DC excitation. Peak densities in the luminous plumes downstream from the discharge capillaries of the HF-DBD and the LTP were 1.39×1012cm−3 and 0.011×1012cm−3, respectively. Neither glow discharge produced a visible afterglow, and no metastable atoms were detected downstream from the capillary exits. However, densities of 0.58×1012cm−3 and 0.97×1012cm−3 were measured in the interelectrode regions of the AC and DC glow discharges, respectively. Time-resolved measurements of metastable atom densities revealed significant random variations in the timing of pulsed absorption signals with respect to the voltage waveforms applied to the discharges.

Diamond film synthesis in high-alternating-current glow discharge

Results of experiments with the deposition of polycrystalline diamond films onto silicon, titanium, and molybdenum substrates in a specially designed ac glow discharge system are presented. The phase composition and morphology of deposited films have been studied using the atomic force microscopy and X-ray diffraction techniques. It is established that the obtained diamond films possess high purity and degree of crystallinity. Inclusions of non-diamond carbon phases are absent. The rate of diamond film growth in the proposed system is 6–7 μm/h.

Atmospheric pressure glow discharge in air

In this study, an atmospheric pressure glow discharge (APGD) in air using 50Hz power supply was experimentally investigated by means of electrical characterization. The discharge has been generated in a specially designed hemispherical–plane electrode system. The main objective of the study was to identify the conditions to generate AC glow at atmospheric pressure air using 50 Hz power supply. The mode of discharge was characterized by observing the number of current pulses per half cycle in the current waveform of the discharge for different values of applied voltage for different electrode spacing. It was found that with 3mm gap and 18.75 kV of applied voltage, the current waveforms consist of a single pulse per half cycle indicating the formation of AC glow discharge. An attempt to study the effect of dielectric on the mode of the discharge was also made by using three types of materials namely Polycarbonate, Polyethylene and Glass as barrier between the electrodes.

The absorption spectrum study of the (4, 0) band in the b4Σ--a4Πi system of NO

The absorption spectrum of NO is analyzed in a range of 12530-12850 cm-1 using optical heterodyne concentration modulation spectroscopy in an AC glow discharge of He/NO mixture. Among all the spectral lines, 324 lines are assigned to the (4, 0) band and 267 ones are fitted to the Hamiltonians of the b4Σ--a4Πi system by a non-linear least-square fitting procedure. A residual (0.0071 cm-1) comparable to system error (0.0071 cm-1) is obtained. The main molecular constants are consistent with those reported in the literature and the fine structure constants are fitted.

Observation of (1, 0) band in the b4Σ −– a4Π 5/2 system of SO + cation

The (1, 0) band in the b 4Σ −– a 4Π 5/2 system of the SO + cation ion has been observed in the range of 12 600–12 800 cm −1 using optical heterodyne velocity modulation spectroscopy in an AC glow discharge of He/SO 2 mixture. Rotational analysis results in close to a three orders of magnitude improvement in the molecular constants.

An Application of AC Glow Discharge Stabilized by Fast Air Flow for Water Treatment

A scheme for a plasma-solution reactor on the basis of a glow discharge stabilized by a fast air flow is suggested as a novel water treatment technique. The discharge ignition voltage is about 2.7 kV, and the input power can be as low as 3 W. It is found that plasma is generated in pulsed mode where the duration of each individual pulse is 15-20 mus. A maximal destruction rate of methylene blue dye of 3.27 times 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> mol/l middots has been received in an acidic medium at a discharge power level of 6 W. A comparison of the efficiency of plasma interaction in different solutions has been carried out. The chemical effectiveness of the plasma treatment decreases with an increase of solution pH. It is shown that the developed glow discharge two phase reactor can be effectively used for destruction of water pollutants.

Deuterium retention in tungsten oxide under low energy [formula omitted] plasma exposure

W is a candidate for plasma facing material and oxide layers are highly anticipated on W surface. We have studied deuterium (D) retention in tungsten oxide (WO 3) films and thermal release of deuterium. WO 3 films, prepared by oxidation of W metal sheet, were exposed to D 2 plasma under AC glow discharge at the applied voltage V up to a few kV and DC discharge. D-retention in W has been studied for comparison. The amount of D retained in the WO 3 films and W were analyzed by detecting α particles from the nuclear reaction, D( 3He, α)p, using 0.7 MeV 3He + ions. We find that D-uptake in WO 3 film is much larger than in W. According to thermal desorption, release of D 2 occurs at ∼180 and 450 °C.