Pulsed Direct Current Discharge Research Articles

Observation of ring–shaped pulsed DC discharge plasma source using single pole magnet setups for material processing

ABSTRACTA pulsed direct current (DC) discharge ring–shaped plasma source has been proposed using single pole magnet arrangements, including a center magnet, with magnets in the setups (a): one circle, (b): two circles, and (c): three circles. The three-dimensional (3D) magnetic flux lines profiles, gyro–radii and Hall parameters of the electrons and ions, the electrical discharge characteristics, the temporal evolutions of the ion saturation currents were investigated to characterize the proposed plasma source. The calculated electron gyro–radii, re were 0.17, 1.64, 5.82 mm for setups (a), (b), and (c), respectively. The strong ring–shaped plasma discharges was observed for all setups. The typical discharge voltages were 1.0, 0.6, and 0.6 kV for setups (a), (b), and (c), respectively. The ion saturation currents, Iisat were 1.44, 2.88, and 2.2 mA for setups (a), (b), and (c), respectively at r = 45 mm and t = +10 μs. The Iisat of setup (b) is less fluctuating, whereas Iisat of setup (a) and (c) is highly variable in all positions, so that setup (b) has the best profile among the setups.

Development and application of network virtual instrument for emission spectrum of pulsed high-voltage direct current discharge

Network virtual instrument (VI) is a new development direction in current automated test. Based on LabVIEW, the software and hardware system of VI used for emission spectrum of pulsed high-voltage direct current (DC) discharge is developed and applied to investigate pulsed high-voltage DC discharge of nitrogen. By doing so, various functions are realized including real time collection of emission spectrum of nitrogen, monitoring operation state of instruments and real time analysis and processing of data. By using shared variables and DataSocket technology in LabVIEW, the network VI system based on field VI is established. The system can acquire the emission spectrum of nitrogen in the test site, monitor operation states of field instruments, realize real time face-to-face interchange of two sites, and analyze data in the far-end from the network terminal. By employing the network VI system, the staff in the two sites acquired the same emission spectrum of nitrogen and conducted the real time communication. By comparing with the previous results, it can be seen that the experimental data obtained by using the system are highly precise. This implies that the system shows reliable network stability and safety and satisfies the requirements for studying the emission spectrum of pulsed high-voltage discharge in high-precision fields or network terminals. The proposed architecture system is described and the target group gets the useful enlightenment in many fields including engineering remote users, specifically in control- and automation-related tasks.

Kinetics of high pressure argon-helium pulsed gas discharge

Simulations of a pulsed direct current discharge are performed for a 7% argon in helium mixture at a pressure of 270 Torr using both zero- and one-dimensional models. Kinetics of species relevant to the operation of an optically pumped rare-gas laser are analyzed throughout the pulse duration to identify key reaction pathways. Time dependent densities, electron temperatures, current densities, and reduced electric fields in the positive column are analyzed over a single 20 μs pulse, showing temporal agreement between the two models. Through the use of a robust reaction rate package, radiation trapping is determined to play a key role in reducing Ar(1s5) metastable loss rates through the reaction sequence Ar(1s5)+e−→Ar(1s4)+e− followed by Ar(1s4)→Ar+ℏω. Collisions with He are observed to be responsible for Ar(2p9) mixing, with nearly equal rates to Ar(2p10) and Ar(2p8). Additionally, dissociative recombination of Ar2+ is determined to be the dominant electron loss mechanism for the simulated discharge conditions and cavity size.

Time-resolved measurements of NO2 concentration in pulsed discharges by high-sensitivity cavity ring-down spectroscopy

To describe the complex kinetics of formation and destruction mechanism of nitrogen dioxide (NO2), there is an increasing demand for real-time and in situ analysis of NO2 in the discharge region. Pulsed cavity ring-down spectroscopy (CRDS) provides an excellent diagnostic approach. In the present paper, CRDS has been applied in situ for time evolution measurement of NO2 concentration which is rarely investigated in gas discharges. In pulsed direct current discharge of NO2/Ar mixture at a pressure of 500 Pa, a peak voltage of −1300 V and a frequency of 30 Hz, for higher initial NO2 concentration (3.05 × 1014 cm−3, 8.88 × 1013 cm−3), the NO2 concentration sharply decreases at the beginning of the discharge afterglow and then becomes almost constant, and the pace of decline increases with pulse duration; however, for lower initial NO2 concentration of 1.69 × 1013 cm−3, the NO2 concentration also decreases at the beginning of the discharge afterglow for 200 ns and 1 μs pulse durations, while it slightly increases and then declines for 2 μs pulse duration. Thus, the removal of low-level NO2 could not be promoted by a higher mean energy input.

Surface modification of polyacrylonitrile co-polymer membranes using pulsed direct current nitrogen plasma

Low temperature plasma treatment using pulsed direct current discharge of nitrogen gas was employed to enhance hydrophilicity of the polyacrylonitrile co-polymer membranes. The membranes were characterized in terms of morphology, structure, hydrophilicity, and membrane performance. Properties and functional groups on the surface of polyacrylonitrile co-polymer membranes were investigated by contact angle, scanning electron microscopy, Fourier transform infrared and X-ray photoelectron spectroscopy. Effects of plasma conditions, namely, pulsed voltage, duty cycle and treatment time on increase in membrane hydrophilicity were studied. Permeability of treated membrane was increased by 47% and it was retained up to 70days. Surface etching due to plasma treatment was confirmed by weight loss of the treated membranes. Due to surface etching, average pore size increased and rejection of 200kDa polyethylene glycol decreased to about 70% for the treated membrane. Oxygen and nitrogen functional groups were responsible for surface hydrophilicity.

Ozone kinetics in low-pressure discharges: vibrationally excited ozone and molecule formation on surfaces

A combined experimental and modeling investigation of the ozone kinetics in the afterglow of pulsed direct current discharges in oxygen is carried out. The discharge is generated in a cylindrical silica tube of radius 1 cm, with short pulse durations between 0.5 and 2 ms, pressures in the range 1–5 Torr and discharge currents ∼40–120 mA. Time-resolved absolute concentrations of ground-state atoms and ozone molecules were measured simultaneously in situ, by two-photon absorption laser-induced fluorescence and ultraviolet absorption, respectively. The experiments were complemented by a self-consistent model developed to interpret the results and, in particular, to evaluate the roles of vibrationally excited ozone and of ozone formation on surfaces. It is found that vibrationally excited ozone, , plays an important role in the ozone kinetics, leading to a decrease in the ozone concentration and an increase in its formation time. In turn, the kinetics of is strongly coupled with those of atomic oxygen and O2(a 1Δg) metastables. Ozone formation at the wall does not contribute significantly to the total ozone production under the present conditions. Upper limits for the effective heterogeneous recombination probability of O atoms into ozone are established.

IR emission from the target during plasma magnetron sputter deposition

In this article, energy flux measurements at the substrate location are reported. In particular, the energy flux related to IR radiation emanating from the titanium (10cm in diam.) target surface is quantified during magnetron sputter deposition processes. In order to modulate the plasma–target surface interaction and the radiative energy flux thereof, the working conditions were varied systematically. The experiments were performed in balanced and unbalanced magnetic field configurations with direct current (DC), pulsed DC and high power impulse magnetron sputtering (HiPIMS) discharges. The power delivered to the plasma was varied too, typically from 100 to 800W. Our data show that the IR contribution to the total energy flux at the substrate increases with the supplied sputter power and as the discharge is driven in a pulse regime. In the case of HiPIMS discharge generated with a balanced magnetic field, the energy flux associated to the IR radiation produced by the target becomes comparable to the energy flux originating from collisional processes (interaction of plasma particles such as ions, electron, sputtered atoms etc. with the substrate). From IR contribution, it was possible to estimate the rise of the target surface temperature during the sputtering process. Typical values found for a titanium target are in the range 210°C to 870°C.

Cavity Ringdown Spectroscopy of PH2 Radical in 465–555 nm

Absorption spectra of jet-cooled PH2 radicals were recorded in the wavelength range of 465–555 nm using cavity ringdown spectroscopy. The PH2 radicals were produced in a supersonic jet by pulsed direct current discharge of a mixture of PH3 and SF6 in argon. Seven vibronic bands with fine rotational structures have been observed and assigned as 000, 2n0, and 2n1 (n = 1–3) bands of the Ã2A1−X̃2B1 electronic transition. Rotational assignments and rotational term values for each band were re-identified, and the molecular parameters including rotational constants, centrifugal distortion constants, and spin-rotation interaction constants were also improved with reasonably high precision. In addition, large perturbations observed in each quantum number of total angular momentum of the a axis level of the excited vibronic states were briefly discussed.

Characteristics of High Speed Electro-thermal Jet Activated by Pulsed DC Discharge

Experimental study of synthetic jet produced by pulsed direct current (DC) discharge is presented. High velocity jet is activated electro-thermally by high frequency pulsed DC discharge in small cavity. A cavity of 2.38 mm diameter cylinder bounded by circular electrode is made in a ceramic plate and a small orifice of 1.78 mm diameter is drilled in the middle of cavity. High frequency pulsed DC discharge instantaneously heats air in the cavity and produces high velocity jet at the exit of the orifice. Schlieren imaging at high framing rate of 100 kHz reveals the presence of supersonic precursor shock followed by the jet emerging from the orifice. The jet velocity reaches as high as about 300 m/s. Jet with smaller cavity volume produces lesser effect and jet velocity reaches maximum at certain cavity volume with given discharge current and orifice size. As duty time of pulse increases from 5 to 20 μs at fixed frequency of 5 kHz, the jet velocity also increases and becomes nearly constant with further increase in duty time. At fixed duty time of 20 μs, higher frequency pulsing of 10 kHz produces degradation of the jet as the discharge pulse continues. The jet developed in this study is demonstrated to be strong enough to penetrate deep into supersonic boundary layer and to produce a bow shock when the jet is issued into Mach 3 supersonic flow.

Cathode-sheath driven low-speed aerodynamic flow actuation using direct-current surface glow discharges

Flow actuation by a continuous/pulsed, direct-current (DC) surface glow discharge is explored. The discharge comprises an array of pin electrode pairs flush mounted on a dielectric actuator surface that lies adjacent to stagnant air. Strong electrostatic fields produced in the cathode sheath region of the discharge provides a motive force on the ions which in turn drag the background gas resulting in directed air flow from the anode to the cathode. The induced flow velocity is estimated by particle image velocimetry (PIV) at 10 Hz with TiO 2 seeding. For a pulsed DC discharge with peak power of 5 W per electrode pair, the induced flow velocity reaches peak values of about 1.7 m/s which is comparable to dielectric-barrier discharge (DBD) or corona discharge actuators. The actuation effect quantified by the magnitude of induced velocity increases as the pulse frequency increases from 0 to 1 kHz. The actuation effect decreases for further increase in frequency above 1 kHz. Decreased actuation effect at high frequency is accompanied by structural change in the discharge. At fixed frequency of 1 kHz, flow actuation effect is highest for a square wave pulse with a duty cycle of 50% indicating that pulsed DC discharges produces better actuation than continuous DC with a corresponding reduction in energy consumption.

MHD Flow Control of Oblique Shock Waves Around Ramps in Low-temperature Supersonic Flows

This article is devoted to experimental study on the control of the oblique shock wave around the ramp in a low-temperature supersonic flow by means of the magnetohydrodynamic(MHD) flow control technique. The purpose of the experiments is to take advantage of MHD interaction to weaken the oblique shock wave strength by changing the boundary flow characteristics around the ramp. Plasma columns are generated by pulsed direct current(DC) discharge, the magnetic fields are generated by Nd-Fe-B rare-earth permanent magnets and the oblique shock waves in supersonic flow are generated by the ramp. The Lorentz body force effect of MHD interaction on the plasma-induced airflow velocity is verified through particle image velocimetry(PIV) measurements. The experimental results from the supersonic wind tunnel indicate that the MHD flow control can drastically change the flow characteristics of the airflow around the ramp and decrease the ratio of the Pitot pressure after shock wave to that before it by up to 19. 66%, which leads to the decline in oblique shock wave strength. The oblique shock waves in front of the ramp move upstream by the action of the Lorentz body force. The discharge characteristics are analyzed and the MHD interaction time and consumed energy are determined with the help of the pulsed DC discharge images. The interaction parameter corresponding to the boundary layer velocity can reach 1. 3 from the momentum conservation equation. The velocity of the plasma column in the magnetic field is much faster than that in the absence of magnetic field force. The plasma can strike the neutral gas molecules to transfer momentum and accelerate the flow around the ramp.

Effect of Methane Pressure on the Size of Carbon Nanoparticles Deposited by Pulsed Plasma Enhanced Chemical Vapor Deposition

AbstractThe nanoparticles of carbon were deposited from methane under the potential of a pulsed direct current discharge. The deposition was carried without external heating. The size, chemistry, and structure of carbon nanoparticles were characterized using transmission electron microscopy (TEM), X‐ray diffraction (XRD), Raman and Fourier transform infrared (FTIR) spectroscopy. The minimum size of the nanoparticles was as low as 10 nm as shown by TEM. The nanocrystalline or amorphous structure of the particles was revealed by XRD. Raman spectroscopy indicated on the sp2 bonds of carbon and FTIR spectroscopy identified the other bonds of carbon.

Time-Resolved Ionisation Studies of the High Power Impulse Magnetron Discharge in Mixed Argon and Nitrogen Atmosphere

Magnetron sputtering technology is widely used to grow thin films on a range of substrate materials. High power impulse magnetron sputtering (HIPIMS) technology differentiates itself from other types of magnetron sputtering by the high degree of ionisation of the sputtered material achieved by applying high peak powers of 3 kW · cm−2 (4 A · cm−2) at duty cycles of <1%. The current paper discusses HIPIMS of Ti in mixed argon and nitrogen atmosphere, commonly used for hard coatings deposition. Estimation of the composition of the ion deposition flux arriving at the substrate position is extracted from energy-resolved mass spectrometry data. The measured time-resolved ion mass and ion energy distribution functions were compared for the HIPIMS discharge and industry-standard direct current (DC) and medium frequency pulsed DC magnetron discharges operated at the same average power of 2 W · cm−2. In inert Ar atmosphere, HIPIMS produced a metal-dominated ion flux with Ti1+ concentration of 46%, compared to 10% in DC operation. In reactive atmosphere of Ar and 10% N2 the HIPIMS discharge produced an ion flux with significantly increased content of ionised film-forming species such as Ti1+, Ti2+ and N1+. The atomic ion N1+ was the most abundant species representing 40% of the total flux with Ti1+ 19% and Ar1+ 19%. In contrast, the ion flux in DC and pulsed DC discharges was dominated by Ar1+ and molecular ion N.

Experimental and theoretical studies of the electron temperature in nitrogen afterglow

In this paper, results of joint experimental and theoretical studies of the electron temperature in nitrogen afterglow at pulse-periodical excitation are presented. Electron energy distribution function (EEDF) in an afterglow of a pulsed direct current discharge has been measured by means of a time-resolved Langmuir probe technique. Electron concentration, vibrational temperature, and population of lower metastable electronic state of N/sub 2/ molecules have also been experimentally estimated at different delays after the discharge pulse. The results show that electron temperature in afterglow decreases with time, while the vibrational temperature remains almost constant. The EEDF has been calculated numerically from a steady-state Boltzmann equation, taking into account electron-electron collisions as well as superelastic collisions with vibrationally and electronically excited molecules. The vibrational distribution function was found numerically by solving a system of kinetic equations. Calculations show that the vibrational distribution function weakly varies within a cycle and is controlled by an average discharge power. Electron temperature in nitrogen afterglow for given populations of vibrational levels and of lower electronic level essentially depends on the electron concentration. Finally, a comparison of the theoretical and experimental results is performed.

Is there a way to improve the uniformity of TiN deposition conditions in large pulsed d.c. plasma CVD reactors?

Recent investigations of the dynamics of pulsed direct-current discharges relevant for the production of titanium nitride coatings by plasma-assisted chemical vapour deposition in large reactors have shown that, when titanium tetrachloride is used as a feed stock gas, the spreading of the discharge is slow, reaching some parts of the reactor with substantial delay. The result is a non-uniform plasma power density in front of the substrates as well as a spatially varying exposure time of the surface to the plasma. These problems can be solved by measures, which increase the conductivity of the plasma at the beginning of the pulses. One way to achieve this goal is the use of synchronized additional short high-voltage pulses. The present study investigates the dependence of the evolution of the discharge on parameters of the additional short high-voltage pulses.

Jumps and bi-stabilities in electron energy distribution in Ar-N2post discharge plasma

The electron energy distribution function (EEDF) in an afterglow ofa pulsed direct current discharge has been measured in an Ar:N2mixture by means of a time-resolved Langmuir probe technique. The vibrationaltemperature, Tv, of N2 molecules has also been experimentallyestimated. The results show that a correlation between an effective electrontemperature, Te, and Tv strongly varies with experimental conditions. Inparticular the conditions exist under which the rapid decrease from high tolow Te values is observed at some moment after the discharge pulse, whilethe vibrational temperature remains almost constant.The theoretical study of the EEDF in Ar:N2 afterglow plasma hasalso been made by the numerical solution of an appropriate Boltzmann equationby taking into account electron-electron collisions as well as superelasticvibrational and superelastic electronic collisions. Calculations show that fora given Tv the value of Te depends on the electron concentration, ne.Moreover, the ranges of ne and Tv exist, where two different solutions ofBoltzmann equations can be obtained.Finally, the comparison of the theoretical and experimental results isperformed and an explanation of the experimentally observed phenomenon is given.