Interelectrode Breakdown Research Articles

The interelectrode breakdown mechanism and discharge characteristics of the electrospray thruster

In the actual working process of electric thrusters based on high-voltage electric fields, the discharge breakdown phenomenon is universal and complex, and such phenomena will have a significant impact on the thruster structure, working state and spacecraft system. In order to study the interpolar discharge breakdown characteristics of ionic liquid electrospray thrusters, a basic electrospray model and test system were constructed, and the change curves of discharge characteristic parameters such as breakdown voltage, threshold current, breakdown voltage frequency and so on in the range of 7×10−3~105 Pa with air pressure and transmitter inner diameter were obtained, and the air pressure range that the electrospray model could work in normally was calibrated. The results show that the breakdown voltage characteristic curve of the electrospray model has typical minimum characteristics, and the minimum values all appear around 80 Pa. Lowering the air pressure below 10−2 Pa can effectively increase the breakdown threshold between the poles and the emission current, thereby obtaining a larger voltage regulation range, and when the air pressure is reduced to 7×10−3 Pa, the breakdown can reach more than 3200 V. The 60-μm inner diameter emitter performed better in the discharge experiment, and the breakdown threshold, emission current and operating area range were better than the slightly larger inner diameter emitter under the same working conditions.

Ion behavior and interelectrode breakdown voltage of a drift tube**Supported by Financial Support from the National Major Scientific Instruments and Equipment Development Special Funds (2011YQ030113), National Recruitment Program of Global Experts (NRPGE), the Hundred Talents Program of Sichuan Province (HTPSP) and the Startup Funding of Sichuan University for Setting up the Research Center of Analytical Instrumentation

We experimentally studied ion behavior and interelectrode breakdown voltage. The ion behavior of a drift tube directly influences the detection of ion intensity, and then influences the detection sensitivity of a system. Interelectrode voltage and pressure directly influence the ion behavior. Gas discharge between electrodes influences the adjustments required for interelectrode voltage. The experimental results show: ion intensity increases exponentially with the increment of voltage between drift electrodes; ion intensity decreases exponentially as pressure increases; with the increment of pressure, the breakdown voltage at first decreases, and then increases; ion injection has a significant influence on breakdown voltage, and this influence depends on the pressure and shapes of the electrodes. We explain the results above through assumptions and by mathematical methods.

Ni–C powder synthesis by a submerged pulsed arc in breakdown mode

Abstract Powders of Ni–C nanoparticles were synthesized using a pulsed arc between Ni electrodes submerged in pure ethanol. The arc was ignited by inter-electrode breakdown. The ethanol was arc treated for 5 min with 1 μs duration pulses, at a repetition rate of ∼1 kHz. The pulse energy was in a range of 0.01–0.05 J. Powder samples were obtained by extracting liquid from the treatment vessel after a pre-determined sedimentation time, or by allowing the liquid to evaporate from the vessel, and collecting the residue. The samples were examined by HRSEM, EDX and XRD. It was found that a powder of Ni–C nanoparticles was produced. The powder consisted of carbon particles and nickel–carbon alloy particles. The latter were also coated by carbon. The carbon concentration in the Ni alloy was approximately triple of the maximum equilibrium solid solubility of carbon in nickel. The production rate of carbon was greater than the erosion rate of the Ni electrodes by factors of 2–6. The ratio of carbon production rate to electrode erosion rate decreased with the discharge energy. The size distribution of the produced particles was narrow. No particles with diameter more than 0.7 μm were observed.

Generation of Electron Beams in the Range of Forevacuum Pressures

This paper presents the results of a study on the generation of electron beams at gas pressures ranging from 0.01 to 0.1 Torr. The fact that this range of pressures is attainable with mechanical pumps only has provoked interest in this problem. To generate an electron beam, use is made of a plasma source based on a hollow-cathode discharge in combination with a plane-parallel acceleration gap. In the given range of pressures, the peculiarities of emission and acceleration of electrons are related to the high probability of ionization of the gas in the acceleration gap and to the formation of an ion flow propagating toward the electron beam. This causes a decrease in discharge operating voltage and also an increase in plasma density in the emission region. Two types of breakdown are observed in the acceleration gap: an interelectrode breakdown and a breakdown in the plasma–electrode system. The designed electron source allows one to obtain beams of cylindrical cross section with currents of up to 1 A and energies of up to 10 keV.

Influences of coal slag on electrical characteristics of a Faraday MHD generator

In order to clarify the influence of coal slag on the electrical characteristics of a large scale Faraday MHD generator, numerical analysis by a new equivalent circuit method is performed. At first, an equivalent circuit for a space element in the Faraday channel and a slag layer element are derived. Next, the numerical results are compared with the experimental ones obtained from the ETL Mark VII. The results are: (1) when the thickness, the conductivity, etc. of the slag are nonuniform, distributions of not only the load voltage, but also the voltage between adjacent electrodes becomes nonuniform, and the latter may cause interelectrode breakdown; (2) when the shortings over several cathodes occur, a typical distribution of the load voltage appears near the shorted region, in which, at first, the load voltage rises a little, then decreases gradually, and finally, recovers rapidly to the normal voltage along the gas flow. By the above short-circuit, the distribution of the voltage between adjacent electrodes is made remarkably nonuniform, and this may lead to another inter-electrode breakdown.

Interelectrode breakdown in MHD ducts

A simple model has been presented for the conduction of current between adjacent electrodes separated by an insulating wall and duct filled with conducting hot gases. Analytical expressions and calculations have been made for plasma initiated and insulator initiated breakdowns for the conditions prevailing in a typical open cycle MHD generator. The relative importance of the two types of breakdowns has also been evaluated.

Rotational electrodynamics of airborne fibers

The dynamic behavior of acicular-shaped aerosol particles subjected to electric fields is discussed, and equations are developed to model the motion of such particles under the influence of rotating and oscillating fields. Effects of gas viscosity, Brownian bombardment, high-Reynolds number motion, and particle conductivity and dimensions are treated. Several different electric field configurations can be applied to align and/or rotate airborne particles of fibrous shape: pulsed d.c., sinusoidal, rotational, and oscillatory. For practical geometries, field intensities are limited to about 10 kV/cm by interelectrode breakdown in air. Rotational frequencies of up to 10 3 rad/s may be imparted to fibers longer than about 1 μm. Deviations from Stokesian behavior become significant only when the product of fiber projected area and rotational frequency exceeds approximately 10 8 μm 2 rad/s. It appears feasible that curled or bent fibers, such as chrysotile asbestos, may be straightened during exposure to field intensities of several kV/cm. The application of rotational electrodynamics to the real-time measurement of airborne fibers is discussed.

Experimental and Theoretical Study of Hall Field Limitations in MHD Generators

Experimental and theoretical results pertaining to the Hall field behavior in combustion-driven MHD generators using clean fuel are presented. MHD generators are subject to Hall field breakdown as a result of electrical-thermal instabilities within the interelectrode plasma region and the interelectrode insulator. Interelectrode breakdown within the insulator typically occurs at a lower threshold voltage than breakdown of the plasma itself. As a result, experiments have been carried out to study the effect on the insulator initiated breakdown threshold of interelectrode insulator cooling. Experiments have also been carried out to study the dependence of the breakdown threshold on the electrode boundary-layer Joule heating, insulator width, and magnetic field. A two-dimensional computer model of the plasma and insulator regions has been developed. Theoretical results based on this model are compared with experimental data. The comparisons indicate both qualitative and quantitative agreement between experiment and theory. 12 references.

Power output of segmented MHD Faraday generators with hall voltage compensation

Hall voltage causes a deterioration of the performance of a segmented MHD Faraday generator, and methods of compensation for this effect are studied. A simple network analogue is developed and used to analyze current flow through the generator and the effect of compensating voltages. Practical segmentation ratios are found to be <0.2. This limit is shown to be well below that required to minimize Hall effects due to electrode length. Smaller segmentation ratios, as used in larger designs therefore, are used mainly to cover inter-electrode breakdown caused by Hall voltages. Hall effect compensation is found to produce a significant increase in generator power only at the expense of a large recirculation of power and internal losses.

Vacuum breakdown induced by ionic bombardment of cathode electrode

Ion bombardment of the cathode in a vacuum diode can induce high-voltage breakdown. The breakdown damage at the cathode consists of a central initiation site caused during the high-voltage collapse and a surrounding dendritic etching caused after the voltage collapse. Energy dispersive analysis of the central region shows that when contaminants are observed they are dielectric. Dielectric particles above 10 μ diameter which are deliberately placed on the cathode cause breakdown during ion bombardment. These particles attain fields comparable to their dielectric strength (MV/cm) in μs times from charging during ion bombardment (0.3 A/cm2). The discharging of these particles is believed to initiate interelectrode breakdown.

FXR discharges at various pressures

The formation period time, current rise time, and photon energy of FXR discharges have been investigated at initial pressures of 5×10−6 to 1×10−2Torr. It has been found that the parameters studied are almost constant between 5×10−6 and 1×10−3Torr. The results obtained indicate that the upper limit of the interelectrode breakdown pressure is about 10−3 Torr when the initial pressure is 10−6 Torr.