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 acti- vated 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 emerg- ing 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.

Microstructure and Properties of the Cr–Si–N Coatings Deposited by Combining High-Power Impulse Magnetron Sputtering(HiPIMS) and Pulsed DC Magnetron Sputtering

The Cr–Si–N coatings were prepared by combining system of high-power impulse magnetron sputtering and pulsed DC magnetron sputtering. The Si content in the coating was adjusted by changing the sputtering power of the Si target.By virtue of electron-probe microanalysis, X-ray diffraction analysis and scanning electron microscopy, the influence of the Si content on the coating composition, phase constituents, deposition rate, surface morphology and microstructure was investigated systematically. In addition, the change rules of micro-hardness, internal stress, adhesion, friction coefficient and wear rate with increasing Si content were also obtained. In this work, the precipitation of silicon in the coating was found.With increasing Si content, the coating microstructure gradually evolved from continuous columnar to discontinuous columnar and quasi-equiaxed crystals; accordingly, the coating inner stress first declined sharply and then kept almost constant. Both the coating hardness and the friction coefficient have the same change tendency with the increase of the Si content, namely increasing at first and then decreasing. The Cr–Si–N coating presented the highest hardness and average friction coefficient for an Si content of about 9.7 at.%, but the wear resistance decreased slightly due to the high brittleness.The above phenomenon was attributed to a microstructural evolution of the Cr–Si–N coatings induced by the silicon addition.

Modeling for V–O_2 reactive sputtering process using a pulsed power supply

In this article, we present a time-dependent model that enables us to describe the dynamic behavior of pulsed DC reactive sputtering and predict the film compositions of VOx prepared by this process. In this modeling, the average current J is replaced by a new parameter of Jeff. Meanwhile, the four species states of V, V2O3, VO2, and V2O5 in the vanadium oxide films are taken into consideration. Based on this work, the influences of the oxygen gas supply and the pulsed power parameters including the duty cycle and frequency on film compositions are discussed. The model suggests that the time to reach process equilibrium may vary substantially depending on these parameters. It is also indicated that the compositions of VOx films are quite sensitive to both the reactive gas supply and the duty cycle when the power supply works in pulse mode. The ＇steady-state＇ balance values obtained by these simulations show excellent agreement with the experimental data, which indicates that the experimentally obtained dynamic behavior of the film composition can be explained by this time-dependent modeling for pulsed DC reactive sputtering process. Moreover, the computer simulation results indicate that the curves will essentially yield oscillations around the average value of the film compositions with lower pulse frequency.

Nitriding molybdenum: Effects of duration and fill gas pressure when using 100-Hz pulse DC discharge technique

Molybdenum is nitrided by a 100-Hz pulsed DC glow discharge technique for various time durations and fill gas pressures to study the effects on the surface properties of molybdenum. X-ray diffractometry （XRD）, scanning electron microscopy （SEM）, and atomic force microscopy （AFM） are used for the structural and morphological analysis of the nitrided layers. Vickers＇ microhardness tester is utilized to investigate surface microhardness. Phase analysis shows the formation of more molybdenum nitride molecules for longer nitriding durations at fill gas pressures of 2 mbar and 3 mbar （1 bar = 105 Pa）. A considerable increase in surface microhardness （approximately by a factor of 2） is observed for longer duration （10 h） and 2-mbar pressure. Longer duration （10 h） and 2-mbar fill gas pressure favors the formation of homogeneous, smooth, hard layers by the incorporation of more nitrogen.

Self-Consistent Model for Pulsed Direct-Current N_2 Glow Discharge

A self-consistent analysis of a pulsed direct-current (DC) N2 glow discharge is presented. The model is based on a numerical solution of the continuity equations for electron and ions coupled with Poisson's equation. The spatial-temporal variations of ionic and electronic densities and electric field are obtained. The electric field structure exhibits all the characteristic regions of a typical glow discharge (the cathode fall, the negative glow, and the positive column). Current-voltage characteristics of the discharge can be obtained from the model. The calculated current-voltage results using a constant secondary electron emission coefficient for the gas pressure 133.32 Pa are in reasonable agreement with experiment.

Influences of working pressure on properties for TiO_2 films deposited by DC pulse magnetron sputtering

TiO2 films were deposited at room temperature by DC pulse magnetron sputtering system.The crystalline structures,morphological features and photocatalytic activity of TiO2 films were systematically investigated by X-ray diffraction（XRD）,atomic force microscopy（AFM） and ultraviolet spectrophotometer,respectively.The results indicated that working pressure was the key deposition parameter in？uencing the TiO2 film phase composition at room temperature,which directly affected its photocatalytic activity.With increasing working pressure,the target self-bias decreases monotonously.Therefore,low temperature TiO2 phase（anatase） could be deposited with high working pressure.The anatase TiO2 films deposited with 1.4 Pa working pressure displayed the highest photocatalytic activity by the decomposition of Methyl Orange solution,which the degradation rate reached the maximum（35%） after irradiation by ultraviolet light for 1 h.

Design and Simulation for the Pulse High-Voltage DC Power Supply (HVPS) of 1.2 MW/2.45 GHz HT-7U Lower Hybrid Current Drive System

The superconducting tokamak HT-7U [1] has been designed by the Institute of Plasma Physics since 1998 and will be set up before 2003. The 1.2 MW /2.45 GHz HT-7U LHCD (Lower hybrid current drive) system which being the most efficient non-induction device can heat the plasma and drive the plasma current has been efficiently in operation 'owl and a particular design of the 2.8 MW/-35 kV high-voltage DC power supply has been already completed and will apply to the klystron of LHCD on HT-7 and the future HT-7U, and the project of the power supply has been examined and approved professionally by an authorized group of high-level specialist in the institute of Plasma Physics. The detailed design of the power supply and the simulation results are referred in the paper.

Effect of Pulse and dc Formation on the Performance of One-Transistor and One-Resistor Resistance Random Access Memory Devices

We investigate the effect of the formation process under pulse and dc modes on the performance of one transistor and one resistor （1 T1R） resistance random access memory （RRAM） device. All the devices are operated under the same test conditions, except for the initial formation process with different modes. Based on the statistical results, the high resistance state （FIRS） under the dc forming mode shows a lower value with better distribution compared with that under the pulse mode. One of the possible reasons for such a phenomenon originates from different properties of conductive filament （CF） formed in the resistive switching layer under two different modes. For the dc forming mode, the formed filament is thought to be continuous, which is hard to be ruptured, resulting in a lower HRS. However, in the case of pulse forming, the filament is discontinuous where the transport mechanism is governed by hopping. The low resistance state （LRS） can be easily changed by removing a few trapping states from the conducting path. Hence, a higher FIRS is thus observed. However, the HRS resistance is highly dependent on the length of the gap opened. A slight variation of the gap length will cause wide dispersion of resistance.

Resonance-Enhanced Photon Excitation Spectroscopy of the Even-Parity 3p^5（2P1/2）nl′ [K′]J （l′=1, 3） Autoionizing Rydberg States of Ar

Metastable 40Ar＊ atoms are produced in the two metastable states 3p54s [3/2]2 and 3p5 4s′ [1/2]0 in a pulsed DC discharge in a beam, and are subsequently excited to the even-parity autoionizing resonance series 3pSnp′[3/2]1,2, 3p5 np′ [1/2]1, and 3p5nf′[5/2]3 using single photon excitation with a pulsed dye laser. The excitation spectra of the even-parity autoion- izing resonance series from the metastable 40Ar＊ are obtained by recording the autoionized Ar＋ ions with time-of-flight ion detection in the photon energy range of 32500-35600 cm-1 with an experimental bandwidth of 〈0.1 cm-1. A wealth of autoionizing resonances are newly observed, from which more precise and systematic spectroscopic data of the level energies and quantum defects are derived.

Investigation on the shockwave induced by surface arc plasma in quiescent air

The shockwave induced by surface direct-current （DC） arc discharge is investigated both experimentally and numer- ically. In the experiment, the shockwave generated by rapid gas heating is clearly observed from Schlieren images. The peak velocity of the shockwave is measured to be over 410 m/s; during its upright movement, it gradually falls to about 340 m/s; no remarkable difference is seen after changing the discharge voltage and the pulse frequency. In the modeling of the arc plasma, the arc domain is not simulated as a boundary condition with fixed temperature or pressure, but a source term with a time-varying input power density, which could better reflect the influence of the heating process. It is found that with a reference power density of 2.8× 1012 W/m2, the calculated peak velocity is higher than the measured one, but they quickly （in 30 Its） become agreed with each other. The peak velocity also rises while increasing the power density, the maximum velocity acquired in the simulation is over 468 m/s, which is expected to be effective for high speed flow control.

Low-Temperature Plasma-Catalytic Reduction of NO_x by C_2H_2 in the Presence of Excess Oxygen

Synergistic effects of pulsed DC dielectric barrier discharge （DBD） plasma and Indium modified HZSM-5 （In/HZSM-5） catalyst for C2H2 selective reduction of NOx at 200℃, in the presence of enriched oxygen by using a one-stage plasma-over-catalyst （POC） reactor, are reported. With a reactant gas mixture of 480 ppm NO, 500 ppm C2H2, 13.0% O2 in N2 and gas hourly space velocity （GHSV） = 10000 h^-1, pure catalytic, pure plasma-induced （discharges over fused silica pellets） and plasma-catalytic NOx conversion percentages are 45.0%, 4.0% and 92.2%, respectively. NOx conversion rates and energy costs were also compared for pulsed DC DBD and AC DBD reactors.

Resonance-Enhanced Photon Excitation Spectroscopy of the Even-Parity Autoionizing Rydberg States of Xe

Xenon atoms were produced in their metastable states 5p^56s[3/2]2 and 5p^56s＇[1/2]0 in a pulsed DC discharge in a beam, and subsequently excited to the even-parity autoionizing Rydberg states 5p^5np＇ [3/2] 1,[1/2] 1, and 5p^5nf＇ [5/2] 3 using single photon excitation. The excitation spectra of the even-parity autoionizing resonance series from the metastable 129Xe were obtained by recording the autoionized Xe＋ with time-of-flight ion detection in the photon energy range of 28000-42000 cm-1. A wealth of autoionizing resonances were newly observed, from which more precise and systematic spectroscopic data of the level energies and quantum defects were derived.

Biologic Waste： Consistent Performance with an Alternating Field

Biomass plants often struggle to capture flow measurements reliably. High amounts of dry solids and fats complicate the measurement with an MID （Magnetic-Inductive） flowmeter and make it susceptible to faults. To overcome this impediment, the waste water treatment plant in Innsbruck, Austria, relies on electromagnetic pulsed AC （Alternating Current） flowmeters. Compared to pulsed DC （Direct Current） devices, AC devices are able to build up magnetic fields that are ten times stronger. Equipped with this capability, the Sitrans Transmag 2 is able to guarantee a constant and also high measuring accuracy, zero point stability and signal strength regardless of impurities in the medium or fluctuations in the magnetic field.

Characterization of Microstructural and Morphological Properties in As-deposited Ta/NiFe/IrMn/CoFe/Ta Multilayer System

Surface morphology and its relationship with microstructure in Ta/NiFe/IrMn/CoFe/Ta multilayer system deposited by pulsed DC magnetron sputtering have been investigated in dependence of Ta buffer and NiFe seed layer thicknesses using atomic force microscopy. The structural parameters such as grain size, dislocation density, texture and strain were calculated. For each surface, a self-affinity behavior with mean fractal dimensions in the range of 2.03-2.18 was found. Additionally, it was also observed that the surface of all samples has locally smooth textured surface structure in the short range. The texture aspect parameter and texture direction index have been obtained for isotropy/anisotropy surface texture. A significant relationship between the surface texture and the strength of the 〈111〉 texture in IrMn layer has been found. The analysis indicated that the surface roughness is strongly affected by the thicknesses of the NiFe seed and Ta buffer layers.