Inertia-Centric Stability Analysis of a Planar Uniform Dust Molecular Cloud with Weak Neutral-Charged Dust Frictional Coupling
This paper adopts an inertia-centric evolutionary model to study the excitation mechanism of new gravito-electrostatic eigenmode structures in a one-dimensional (1-D) planar self-gravitating dust molecular cloud (DMC) on the Jeans scale. A quasi-neutral multi-fluid con- sisting of warm electrons, warm ions, neutral gas and identical inertial cold dust grains with partial ionization is considered. The grain-charge is assumed not to vary at the fluctuation evolution time scale. The neutral gas particles form the background, which is weakly coupled with the collapsing grainy plasma mass. The gravitational decoupling of the background neutral particles is justifi- able for a higher inertial mass of the grains with higher neutral population density so that the Jeans mode frequency becomes reasonably large. Its physical basis is the Jeans assumption of a self-gravitating uniform medium adopted for fiducially analytical simplification by neglecting the zero-order field. So, the equilibrium is justifiably treated initially as “homogeneous”. The efficacious inertial role of the thermal species amidst weak collisions of the neutral-charged grains is taken into account. A standard multiscale technique over the gravito-electrostatic equilibrium yields a unique pair of Korteweg-de Vries (KdV) equations. It is integrated numerically by the fourth-order Runge-Kutta method with multi-parameter variation for exact shape analyses. Inter- estingly, the model is conducive for the propagation of new conservative solitary spectral patterns. Their basic physics, parametric features and unique characteristics are discussed. The results go qualitatively in good correspondence with the earlier observations made by others. Tentative applications relevant to space and astrophysical environments are concisely highlighted.
On-Line Measurement of Ion Density in Atmospheric Nitrogen Discharge Filaments via Radiation Signals from Plasma Oscillation Hot!
Diagnosis of the particle number density of plasma plays an important role in the understanding of plasma sources and processing. Regular radiation signals from plasma oscillation in filaments of atmospheric nitrogen discharge, which were excited by the injection of secondary electron beams during the propagation of the streamer, are employed to determine the ion density of plasma and its evolution in the filaments. Results show that the density of N + 4 in a filament of atmospheric nitrogen discharge is of the order of 10 13 cm −3 . It is also found that the re- combination processes play a dominant role in plasma decay, and that the ion density decreases non-monotonically with time during streamer propagation.
Motion and Splitting of Vacuum Arc Column in Transverse Magnetic Field Contacts at Intermediate-Frequency
Arc motion and splitting of vacuum arc at intermediate frequency (400-800 Hz) were investigated under transverse magnetic field (TMF). The experiment was performed on cup-type TMF contacts with contact diameter of 40 mm and a contact gap of 4 mm in a single-frequency circuit. With high-speed photography we characterized the arc appearance at different arc cur- rents from 3.3 kA-rms to 10 kA-rms at intermediate frequencies. As arc current increases from 3.3 kA-rms to 10 kA-rms the arc appearance changes obviously. When current value is 3.3 kA- rms (current frequency 400-800 Hz), there is almost no splitting arc; when the current exceeds 5 kA-rms (current frequency 400-800 Hz), the arc rotates at a speed above 20 m/s, accompanied by an observable splitting arc. The splitting arc could be observed at different frequencies and the arc-voltage had no noises when splitting occurred. The motion direction and the velocity of arc column were studied. Finally, the formation of a split arc was discussed.
Optimization Study of Pulsed DC Nitrogen-Hydrogen Plasma in the Presence of an Active Screen Cage
A glow discharge plasma nitriding reactor in the presence of an active screen cage is optimized in terms of current density, filling pressure and hydrogen concentrations using optical emission spectroscopy (OES). The samples of AISI 304 are nitrided for different treatment times under optimum conditions. The treated samples were analyzed by X-ray diffraction (XRD) to explore the changes induced in the crystallographic structure. The XRD pattern confirmed the formation of iron and chromium nitrides arising from incorporation of nitrogen as an interstitial solid solution in the iron lattice. A Vickers microhardness tester was used to evaluate the surface hardness as a function of treatment time (h). The results showed clear evidence of improved surface hardness and a substantial amount of decrease in the treatment time compared with the previous work.
Discharge Characteristics of SF6 in a Non-Uniform Electric Field Under Repetitive Nanosecond Pulses
The characteristics of high pressure sulphur hexafluoride (SF 6 ) discharges in a highly non-uniform electric field under repetitive nanosecond pulses are investigated in this paper. The influencing factors on discharge process, such as gas pressure, pulse repetition frequency (PRF), and number of applied pulses, are analyzed. Experimental results show that the corona intensity weakens with the increase of gas pressure and strengthens with the increase of PRF or number of applied pulses. Spark discharge images suggest that a shorter and thicker discharge plasma channel will lead to a larger discharge current. The number of applied pulses to breakdown descends with the increase of PRF and ascends with the rise of gas pressure. The reduced electric field (E/p) decreases with the increase of PRF in all circumstances. The experimental results provide significant supplements to the dielectric characteristics of strongly electronegative gases under repetitive nanosecond pulses.
Formation of a 40 A DC Current Arc During the Opening of Silver Contacts
The erosion of silver contacts due to break arcs with length proportional to time and of variable duration has been measured by weighing the contacts following 5000 openings at a constant current equal to 40 A. The experimental results show that, for arc durations shorter than 60 µs, the transfer of metal from the anode to the cathode occurs, but after passing this stage, when the two electrodes are separated by greater distances, each will display erosion. This is the result of the diffusion of material outside the space between the two electrodes. In order to interpret these results, we have applied a classical model of the physical phenomena occurring at the root of the arc. Analysis of the experimental results shows that for an arc duration of less than 15 µs, no distinct cathode root is seen to exist, but beyond this, several spots appear gradually on the cathode for arc duration up to 50 µs, after which they merge into a single spot. The comparison between experiment results and theoretical interpretation is reasonable up to 60 µs.
Characteristics of Electrode-Water-Electrode Discharge and its Application to Water Treatment Hot!
Atmospheric air discharge above the surface of water is an effective method for water treatment. The leakage current and Joule heating of water are reduced by the air gap, which raises the energy efficiency of the water treatment. However, the application of this kind of discharge is limited by a pair of conflicting factors: the chemical efficiency grows as the discharge gap distance decreases, while the spark breakdown voltage decreases as the gap distance decreases. To raise the spark breakdown voltage and the chemical efficiency of atmospheric pressure water surface discharge, both the high-voltage electrode and the ground electrode are suspended above the water surface to form an electrode-water-electrode discharge system. For this system, there are two potential discharge directions: from one electrode to another directly, and from the electrodes to the water surface. The first step in utilizing the electrode-water-electrode discharge is to find out the discharge direction transition criterion. In this paper, the discharge direction transition criterions of spark discharge and streamer discharge are presented. By comparing the discharge characteristics and the chemical efficiencies, the discharge propagating from the electrodes to the water surface is proved to be more suitable for water treatment than that propagating directly between the electrodes.
Tarnish Testing of Copper-Based Alloys Coated with SiO 2 -Like Films by PECVD
The tarnishing test in the presence of hydrogen sulfide (H 2 S) vapors has been used to investigate the tarnish resistance capability of copper-based alloys coated with SiO 2 -like films by means of plasma-enhanced chemical vapor deposition (PECVD) fed with a tetraethoxysi- lane/oxygen mixture. The chemical and morphological properties of the films have been char- acterized by using infrared absorption spectroscopy (IR) and scanning electron microscopy (SEM) with energy disperse spectroscopy (EDS). The corrosion products of the samples after the tarnish- ing test have been identified by X-ray diffraction analysis (XRD). It has been found that SiO 2 -like films formed via PECVD with a high O 2 flow rate could protect copper-based alloys from H 2 S vapor tarnishing. The alloys coated at the O 2 flow rate of 20 sccm remain uncorroded after 54 days of H 2 S vapor tarnish testing. The corrosion products for the alloys deposited at a low O 2 flow rate after 54 days of tarnish testing are mainly composed of brochantite.
Design of a Prototype EHD Air Pump for Electronic Chip Cooling Applications
This paper presents the design, optimization and fabrication of an EHD air pump intended for high-power electronic chip cooling applications. Suitable high-voltage electrode con- figurations were selected and studied, in terms of the characteristics of the generated electric field, which play an important role in ionic wind flow. For this purpose, dedicated software is used to implement finite element analysis. Critical design parameters, such as the electric field intensity, wind velocity, current flow and power consumption are investigated. Two different laboratory prototypes are fabricated and their performances experimentally assessed. This procedure leads to the fabrication of a final prototype, which is then tested as a replacement of a typical fan for cooling a high power density electronic chip. To assist towards that end, an experimental ther- mal testing setup is designed and constructed to simulate the size of a personal computer’s CPU core of variable power. The parametric study leads to the fabrication of experimental single-stage EHD pumps, the optimal design of which is capable of delivering an air flow of 51 CFM with an operating voltage of 10.5 kV. Finally, the theoretical and experimental results are evaluated and potential applications are proposed.
High Growth Rate of Microcrystalline Silicon Films Prepared by ICP-CVD with Internal Low Inductance Antennas
The plasma parameters in ICP-CVD system with internal low inductance antennas (LIA) were diagnosed by Langmuir probe. The ions density (N i ) reached 10 11 -10 12 cm −3 , and the electron temperature (T e ) was below ca. 2 eV, which was slightly decreased with applied power. A p-type hydrogenated microcrystalline silicon (µc-Si:H) film was prepared on glass substrate. After optimization of the processing parameters in flow ratio of SiH 4 :B 2 H 6 :H 2 , a high quality µc-Si:H film with deposition rate above 1.0 nm/s was achieved in this work.
Experimental Research of ZnO Surface Flashover Trigger Device of Pseudo-Spark Switch
Pseudo-spark switch (PSS) is one of the most widely used discharge switches for pulse power technology. It has many special characteristics such as reliability in a wide voltage range, small delay time, as well as small delay jitter. In this paper, the measuring method for the initial plasma of ZnO surface flashover triggering device of PSS is studied and the results of the measurement show that the electron emission charge is mainly influenced by trigger voltage, gas pressure and DC bias voltage. When the bias voltage increases from 2 kV to 6 kV with the gap distance fixed at 3 mm, the electron emission charge changes from 2 μC to about 6 μC. When the gap distance changes from 3 mm to 5 mm with the bias voltage fixed at 2 kV, the electron emission charge increases from 1.5 μC to 2.5 μC. When the gap distance is 4 mm, the hold-off voltage of PSS is 45 kV at gas pressure of 2 Pa, the minimum operating voltage is less than 1 kV. So, the operating scope is from 2.22% to 99% of its self-breakdown voltage. The discharging delay time decreases from 450 ns to 150 ns when the trigger pulse voltage is 1 kV and the discharging voltage is changed from 1 kV to 12 kV. When the trigger pulse voltage is 6 kV, the discharging delay time is less than 100 ns and changes from 100 ns to 50 ns, and the delay jitters are less than 30 ns.
Numerical Simulation of Subcooled Boiling Inside High-Heat-Flux Component with Swirl Tube in Neutral Beam Injection System
In order to realize steady-state operation of the neutral beam injection (NBI) system with high beam energy, an accurate thermal analysis and a prediction about working conditions of heat-removal structures inside high-heat-flux (HHF) components in the system are key issues. In this paper, taking the HHF ion dump with swirl tubes in NBI system as an example, an accurate thermal dynamic simulation method based on computational fluid dynamics (CFD) and the finite volume method is presented to predict performance of the HHF component. In this simulation method, the Eulerian multiphase method together with some empirical corrections about the inter-phase transfer model and the wall heat flux partitioning model are considered to describe the subcooled boiling. The reliability of the proposed method is validated by an experimental example with subcooled boiling inside swirl tube. The proposed method provides an important tool for the refined thermal and flow dynamic analysis of HHF components, and can be extended to study the thermal design of other complex HHF engineering structures in a straightforward way. The simulation results also verify that the swirl tube is a promising heat removing structure for the HHF components of the NBI system.
Construction and Implementation of the Online Data Analysis System on EAST
In order to obtain diagnostic data with physical meaning, the acquired raw data must be processed through a series of physical formulas or processing algorithms. Some diagnostic data are acquired and processed by the diagnostic systems themselves. The data processing pro- grams are specific and usually run manually, and the processed results of the analytical data are stored in their local disk, which is unshared and unsafe. Thus, it is necessary to integrate all the specific process programs and build an automatic and unified data analysis system with shareable data storage. This paper introduces the design and implementation of the online analysis system. Based on the MDSplus event mechanism, this system deploys synchronous operations for differ- ent processing programs. According to the computational complexity and real-time requirements, combined with the programmability of parallel algorithms and hardware costs, the OpenMP par- allel processing technology is applied to the EAST analysis system, and significantly enhances the processing efficiency.
The Application and Improvement of Helium Turbines in the EAST Cryogenic System
The helium cryogenic system supplies supercritical helium cooling capacity at 4.5 K for the superconducting magnets in the EAST superconducting tokamak. Four low-temperature helium turbines are used in the 2 kW helium refrigeration system, and their performance and reliability are critical for the continuous operation of the tokamak. The turbines were made by the Helium Mechanics Company in Russia. The start-up process is very unstable, easily broken, and thus testing and improvements are needed. In this paper, we analyze the structure of the helium turbine, make improvements, and describe the testing process and results of the improved helium turbines. Some of the operational experiences during the start-up process and tests are also presented.
A Nickel Coating Removal Process for ITER Superconducting Cables
A new method is developed for removing the nickel coating on ITER superconduct- ing cables by mechanical polishing. The obvious advantage of the mechanical method, which uses a nylon brush, is that there is no chemical residual left in the cable, which would otherwise result in passive effects on the joint resistance. The coating resistance test results of this newly devel- oped method are compared with those of the two other methods that can meet the requirements of ITER. An automatic polishing machine is designed and manufactured for the procedure to provide quality under precise control. This new technique can replace the conventional manual method due to its improved efficiency.
R&D of High Current Balance Reactors
The design of high current balance reactors used in the ITER DC testing platform is presented, which is verified by simulations with finite element method software, and the reactors are fabricated and tested according to the design output. These reactors are chosen as multilayer multi-turn structure and cooled by water. The multilayer multi-turn structure is usually selected by some high voltage reactors, but is seldom used in high current situations. The analysis and testing results indicate that the multilayer multi-turn structure is also feasible for high current reactors with many advantages, and is of considerable significance to similar applications.