High-voltage Spark Research Articles

One-step electrochemical synthesis and visible-light photocatalytic activities of bismuth titanate coatings: Effect of voltage

Nanostructured Bi12TiO20 coatings with superior photocatalytic property were controllably fabricated on bismuth substrates by one-step electrochemical method in the alkali electrolytes. It was found that the high voltage spark, which initiated the transformation of Bi2O3 precursor generated at low voltage to sillenite type Bi12TiO20, dominated the formation of bismuth titanate coating. Varying the deposition voltage can effectively tailor the crystallinity, morphology and optical property of the coatings. Bi12TiO20 coating consisting of spherical particles of ca. 30nm in size and micropores of ca. 100nm in diameter was obtained at voltage 80V, exhibiting enhanced visible spectrum absorption and higher photocatalytic ability compared to pure TiO2 films prepared with similar electrochemical method.

Study of free air ball formation in Ag–8Au–3Pd alloy wire bonding

An innovative Ag–8Au–3Pd alloy wire has been developed as an alternative to the traditional gold wire bonding. This paper focused on the free air ball (FAB) formation of 0.7mil Ag–8Au–3Pd alloy wire, which was vital for the yield of the subsequent bonding process. During electric flame-off (EFO) process, the wire tail was melted by a high voltage spark, and then the FAB was shaped by the effects of surface tension and gravity. The EFO current was the key factor to influence the Ag–8Au–3Pd alloy FAB size and morphology due to the energy input via arc discharging. The defects including off-center and ripple appeared on the Ag–8Au–3Pd alloy FABs were discussed by cooling and solidification. It is suggested that low EFO current will effectively avoid FAB defects. The contaminants on the Ag–8Au–3Pd alloy FAB surface were analyzed by Auger electron spectroscopy (AES). Under the protection of the shielding gas, oxidation and sulfuration have been effectively prevented.

Development of N+ in P pixel sensors for a high-luminosity large hadron collider

Hamamatsu Photonics K. K. is developing an N+ in a p planar pixel sensor with high radiation tolerance for the high-luminosity large hadron collider (HL-LHC). The N+ in the p planar pixel sensor is a candidate for the HL-LHC and offers the advantages of high radiation tolerance at a reasonable price compared with the N+ in an n planar sensor, the three-dimensional sensor, and the diamond sensor. However, the N+ in the p planar pixel sensor still presents some problems that need to be solved, such as its slim edge and the danger of sparks between the sensor and readout integrated circuit. We are now attempting to solve these problems with wafer-level processes, which is important for mass production. To date, we have obtained a 250-μm edge with an applied bias voltage of 1000V. To protect against high-voltage sparks from the edge, we suggest some possible designs for the N+ edge.

Spectroscopic characterization of lithium combustion

ABSTRACTIn this work, the exothermic reaction of the chemical energy storage material for stranded renewable energy, lithium is analyzed in carbon dioxide (CO2) and air. Spectroscopic techniques were used to characterize the reaction of bulk lithium pellets of up to 1 g weight. In comparison, power plant applicable combustion of atomized lithium spray was analyzed.Electrical high voltage spark was used to overcome to activation energy of the combustion for the experiments with bulk lithium. The lithium spray was successfully ignited by pre-heating the reaction gases (air and CO2).Radiation temperature of the bulk lithium during reaction in air was calculated to 2260 K. The observed green and red emission of the lithium combustion could be demonstrated in the spectral analysis.In CO2 atmosphere the reaction products were found to be lithium carbonate with little lithium oxide. Beside, lithium carbide could be detected in the reaction product of the combustion of bulk lithium. The gaseous reaction product carbon monoxide (CO), which could be further converted with hydrogen from renewable sources to valuable methanol or gasoline, was detected online by gas analysis.

Quench Detection and Protection for High Temperature Superconducting Transformers by Using the Active Power Method

AC high temperature superconducting (HTS) coils have been developed for transformers, motors and so on. Quench detection and protection system are essential for safety operations of the AC HTS facilities. The balance voltage method is universally used for the quench detection and protection, however especially for AC operations, the method has risks in terms of high voltage sparks. Because the method needs a voltage tap soldered to a midpoint of the coil winding and the AC HTS facilities generally operate at high voltages and therefore high voltage sparks may occur at the midpoint with no insulation. We have proposed the active power method for the quench detection and protection. The method requires no voltage tap on the midpoint of the coil winding and therefore it has in-built effectiveness for the AC HTS facilities. In this paper, we show that the method can detect the quench in an HTS transformer and moreover our proposed quench protection circuits which consist of thyristors are simple and useful for the AC HTS facilities.

Non-destructive Detection of Normal Transitions in High Temperature Superconducting Coil

High temperature superconducting (HTS) coils require reliable quench monitoring systems for safety operations. Also, locating of normal transition areas is important for developing reliable HTS coils. Resistive voltage measurement method is universally used for the quench detection and the location. The method needs many voltage taps soldered to superconducting windings and therefore insulations of superconducting wires have to be removed for the soldering and then it has high risks in terms of high voltage sparks. In this paper, the authors present a new detection method of normal transitions by using capacitor taps which can detect normal transitions regardless of the insulations (by no destruction) and has no risks about the high voltage sparks. In this method, two electro-conductive sheets are attached on a surface of a superconducting coil and are connected with an outside capacitor. Then two capacitors are created on the surface of the superconducting coil by sand iching the insulation between each electro-conductive sheet and the superconducting wire. The normal transitions can be detected as a voltage of the outside capacitor by voltage dividing with the three capacitors. A demonstration test was carried out for a Bi2223 coil and the quench detection and the location were successfully achieved.

Laser Spark Ignition in lean burn CNG Engine

The CNG Engines play a dominant role in transportation and energy production. The CNG engine is an environment-friendly engine, which causes drastic reduction in emission to the environment by using CNG as a fuel in IC engine. Spark plugs work by sending small; high-voltage electrical sparks across a gap between two metal electrodes Spark plugs can ignite leaner fuel mixtures, but only by increasing spark energy. Unfortunately spark plug cannot ignite leaner air-fuel mixture for long time it produce exhaust emission as well as reduce the efficiency of engine. ON the other hand, Laser ignition system of engines represents a more and more realistic alternative to traditional spark plug or high-frequency ignition approaches. Its ability to ignite extremely lean mixtures of fuel and air allows one to efficiently reduce the NOX concentrations in the exhaust gases, which are associated with potential long-lived ignition components. In this project, an overview of the laser parameters necessary to ignite the most common lean burn air-fuel mixtures for CNG engines is presented. Furthermore, a novel approach for multipoint laser ignition is discussed as a viable path for speeding up the long combustion durations of lean mixtures. Finally, an innovative approach to compact, robust, and relatively cheap laser ignition is described, which involves miniature laser systems. The passively Q-switched laser head is ideally mounted on each cylinder, while the optical pump should be located far away. Ignition energies in the range of slightly more than 1mj per pulse are realized with the involvement of perfect optical focusing.

Research of an electromagnetically actuated spark gap switch

As an important part of pulsed power systems, high-voltage and high-current triggered spark gap switch and its trigger system are expected to achieve a compact structure. In this paper, a high-voltage, high-current, and compact electromagnetically actuated spark gap switch is put forward, and it can be applied as a part of an intense electron-beam accelerator (IEBA). A 24 V DC power supply is used to trigger the switch. The characteristics of the switch were measured for N2 when the gas pressure is 0.10-0.30 MPa. The experimental results showed that the voltage/pressure (V/p) curve of the switch was linear relationship. The operating ranges of the switch were 21%-96%, 21%-95%, 21%-95%, 19%-95%, 17%-95%, and 16%-96% of the switch's self-breakdown voltage when the gas pressures were 0.10, 0.14, 0.18, 0.22, 0.26, and 0.30 MPa, respectively. The switch and its trigger system worked steadily and reliably with a peak voltage of 30 kV, a peak current of 60 kA in the IEBA when the pressure of N2 in the switch was 0.30 MPa.

A simple high-voltage high current spark gap with subnanosecond jitter triggered by femtosecond laser filamentation

We describe a simple, sturdy, and reliable spark gap operating with air at atmospheric pressure and able to switch currents in excess of 10 kA with sub-nanosecond jitter. The spark gap is remotely triggered by a femtosecond laser filament.

Deflagration to detonation transition and detonation structure in diethyl ether mist/aluminum dust/air mixtures

Although diethyl ether (DEE) is an excellent compression-ignition fuel, it is extremely flammable and presents a serious fire and explosion hazard. Therefore, before widespread use of DEE as an energy carrier, its safety-related issues must first be addressed. In this study, experiments of transition from deflagration to detonation (DDT) and detonation structure in DEE mist/air and DEE mist/aluminum dust/air mixtures are carried out in a horizontal tube of inner diameter 19.9cm and length 32.4m. The mixtures are initiated by a high-voltage electric spark and the histories of pressure wave are recorded by 17 Kistler pressure transducers in the axial direction along the tube to study the DDT process. To study the detonation structure, 4 cross-sections are chosen during the self-sustained propagation phase of the detonation where, 8 pressure transducers are arranged with the same interval angle of 45° on the same tube circumference to obtain the pressure profiles. The experimental results indicate that, deflagration cannot successfully transmit to detonation in DEE mist/air mixtures when DEE concentrations are 164 and 229g/m3. Deflagration is observed to continuous accelerate and the onset detonation occurs at distance of 17.15m as DEE concentration is increased up to 295g/m3, in which a double-headed spinning detonation structure is observed. Among the 5 different mixture composition of DEE mist/aluminum dust/air, DDT phenomenon is only observed in the mixtures of DEE mist (367g/m3)/aluminum dust (184g/m3)/air and DEE mist (314g/m3)/aluminum dust (230g/m3)/air, the run-up distances of DDT are 19.25 and 15.05m, respectively. A single-headed spinning detonation structure is observed in DEE mist (314g/m3)/aluminum dust (230g/m3)/air mixture.

High-Voltage Spark Gap in a Regime of Subnanosecond Switching

This paper describes an investigation of a high-voltage spark gap in the conditions of subnanosecond switching. The high-voltage pulsed generator “Sinus” is used to charge a coaxial line loaded to a high-pressure spark gap. Typical charging time for the coaxial line is in a range from 1 to 2 ns, maximum charging voltage is up to 250 kV, and a range of pressures for the gap is from 2 to 9 MPa. The theoretical models of the switching process on subnanosecond time scale are examined. A general equation for temporal behavior of the gap voltage, which is applicable for the avalanche model and the Rompe-Weitzel model has been obtained. It is revealed that the approach based on the avalanche model offers a possibility to describe the switching process only at extremely high overvoltages. The Rompe-Weitzel model demonstrates a good agreement with the experimental data both for the conditions of static breakdown and for the regime of a high overvolted gap. Comparison of experimental and calculated voltage waveforms has made it possible to estimate an empirical constant in the Rompe-Weitzel model (the price of ionization). This constant is varied from 420 to 920 eV, depending on the initial electric field in the gap.

Nuclear Radiation-Induced Atmospheric Air Breakdown in a Spark Gap

We have investigated the effect of pre-ionization by a radioactive -ray source on the atmospheric air breakdown conditions in a high-voltage spark gap. A standoff millimeter-wave (mmW) system was used to monitor the breakdown properties. A decrease in breakdown threshold was observed with an increase of radiation dose. We attribute this to a space charge-controlled electron diffusion process in a cloud of radiation-induced ion species of both polarities. The space charge-dependent diffusion coefficient was determined from the measurement data. In addition, we found that the breakdown process shows random spikes with Poisson-like statistical feature. These findings portend the feasibility of remote detection of nuclear radiation using high-power mmWs.

Behavior of a Spark Gap Pulser at High Repetition Rate

Operation of a unique pulser system using a miniaturized spark gap geometry is described in this article. The important features of the pulser system are its high power handling capability accompanied by ultrashort pulses with pulsewidths of a few nanoseconds (ns), rise times of a few hundred picoseconds (ps) and very high pulse repetition rates (PRR) exceeding 1 MHz. Although the gaseous breakdown at large gap sizes has long been well established, the breakdown in microgaps has still not been suciently explored. The switching action of a spark gap employing discharges in microgaps or microplasma discharges, unlike commonly used high-voltage and high-current spark gap discharges, has been explored for high repetition rates. Considerable attention has been focused on important properties of and insights into the discharge channel gap, the voltage recovery process and the post spark discharge period for stable and ecient performance of the pulser system. In parallel, a theoretical analysis has been carried out using a PSpice simulation for optimization of several circuit parameters to drive the pulser system. Theoretical calculations of the system eciency and PRR are thoroughly studied and presented through this simulation.

An Experimental Investigation of Flammability Limits and Autoignition Temperatures of Petrofuels and Biofuels in a Tubular Burner

A set of experiments to determine the flammability limits of pure and binary blends of fuels was carried out in a combustion tube operated at atmospheric pressure. The lowest and highest volumetric fraction of vapor fuels that allowed flame propagation when the air/fuel mixture was submitted to a high voltage spark with energy higher than the minimum ignition energy defined the lower and upper flammability limit, respectively. The obtained experimental results for liquefied petroleum gas (LPG), acetone, ethylic alcohol, gasoline, diesel, and bioethanol are in close agreement with results reported in the literature. Diagrams of flammability limits of mixtures of gasoline/bioethanol and diesel/biodiesel were found within the range of composition of standard commercial blends of these fuels available for market in Brazil. The autoignition temperature and the influence of temperature on flammability limits of pure ethanol and a commercial mixture with 4% of biodiesel and 96% of diesel were experimentally determined.

Measurement of effective blast energy for direct initiation of spherical gaseous detonations from high-voltage spark discharge

In this study, effective energy from spark discharge for direct blast initiation of spherical gaseous detonations is investigated. In the experiment, direct initiation of detonation is achieved via a spark discharge from a high-voltage and low-inductance capacitor bank and the spark energy is estimated from the analysis of the current output. To determine the blast wave energy from the powerful spark, the time-of-arrival of the blast wave in air is measured at different radii using a piezoelectric pressure transducer. Good agreement is found in the scaled blast trajectories, i.e., scaled time c o·t/R o where c o is the ambient sound speed, as a function of blast radius R s/R o between the numerical simulation of a spherical blast wave from a point energy source and the experimental results where the explosion length scale R o is computed using the equivalent spark energy from the first 1/4 current discharge cycle. Alternatively, by fitting the experimental trajectories data, the blast energy estimated from the numerical simulation appears also in good agreement with that obtained experimentally using the 1/4 cycle criterion. Using the 1/4 cycle of spark discharge for the effective energy, direct initiation experiments of spherical gaseous detonations are carried out to determine the critical initiation energy in C2H2–2.5O2 mixtures with 70 and 0% argon dilution. The experimental results obtained from the 1/4 cycle of spark discharge agree well with the prediction from two initiation models, namely, the Lee’s surface energy model and a simplified work done model. The main source of discrepancy in the comparison can be explained by the uncertainty of cell size measurement which is needed for both the semi-empirical models.

Fluxes of Charged Particles From Plasma of Nanosecond Vacuum Spark

Fluxes of ions and electrons from plasma of a nanosecond high-voltage vacuum spark have been studied. Differences in the determination of the plasma expansion velocities by the probe method, the method of recording the flux of particles, and the Thomson spectrometer have been established. It has been shown that the spectrum of explosive emission electrons includes a high-energy part with energies higher than the discharge voltage. It has been assumed that the plasma stream contains high-energy electrons formed by intensive plasma oscillations.

Carbon Nanoparticle Generation, Collection, and Characterization Using a Spark Generator and a Thermophoretic Deposition Cell

Nanoparticles can form during nuclear accidents as well as during normal nuclear reactor operations and can be both radioactive and nonradioactive. It is important to understand particle size characteristics, transport properties, and deposition in order to better predict the behaviors of, and effects due to, these particles in a reactor. Fission products can deposit (adsorb/absorb) on the graphite dust in the core [an amount of carbon dust is present in the Pebble Bed Modular Reactor (PBMR) because of graphite sphere abrasion] and can also be carried by the helium flow (together with some dust). Generating nanoparticles of desired shape, size, and purity for experimental purposes is difficult, and hence, there is a need for new and refined synthesis techniques. Nanoparticle generation using high-voltage electric sparks has become a technique of interest for a wide range of conducting materials, and particles with sizes ranging from a few nanometers up to microns have been generated in this manner in an aerosol state. Our purpose in this paper is to report on the generation, collection, and characterization of carbon nanoparticles. We have used a spark generator and a thermophoretic deposition cell, as well as environmental scanning electron microscopy, transmission electron microscopy, and scanning mobility particle spectrometry. We have explored a number of experimental conditions, and we find that one can generate and effectively collect test particles with a variety of different useful characteristics. We also discuss some computational fluid dynamics simulations of particle deposition in the thermophoretic deposition cell.

Resonance analysis of a solid state controlled Tesla transformer

A Tesla transformer is a source that can generate high voltage with high frequency. It is also known a resonance system becomes two air cored coils. Classic Tesla transformer system consists of a high voltage generator which is usually a Neon Sign Transformer (NST), high voltage capacitor and spark gap electrodes. This paper presents mathematical analysis of the equivalent circuit, measure/calculation of its parameters, reasons of resonance, examine of resonance frequencies and a simple solid state driver with a low voltage in the primary side for a Tesla transformer.

Transportable high-energy high-power generator

High-power applications sometimes require a transportable, simple, and robust gigawatt pulsed power generator, and an analysis of various possible approaches shows that one based on a twin exploding wire array is extremely advantageous. A generator based on this technology and used with a high-energy capacitor bank has recently been developed at Loughborough University. An H-configuration circuit is used, with one pair of diagonally opposite arms each comprising a high-voltage ballast inductor and the other pair exploding wire arrays capable of generating voltages up to 300 kV. The two center points of the H configuration provide the output to the load, which is coupled through a high-voltage self-breakdown spark gap, with the entire autonomous source being housed in a metallic container. Experimentally, a load resistance of a few tens of Ohms is provided with an impulse of more than 300 kV, having a rise time of about 140 ns and a peak power of over 1.7 GW. Details of the experimental arrangement and typical results are presented and diagnostic measurements of the current and voltage output are shown to compare well with theoretical predictions based on detailed numerical modeling. Finally, the next stage toward developing a more powerful and energetic transportable source is outlined.

A picosecond-jitter electron-beam-triggered high-voltage gas spark gap

Modes of precision triggering of a high-pressure nitrogen spark gap at voltages in the range from some tens of kilovolts up to one hundred of kilovolts have been investigated. The spark gap was triggered by a high-current electron beam. Experimentally, a total jitter no more than 25 ps relative to the leading edge of the beam-accelerating voltage pulse was attained. The time for which the spark gap was in the induced conduction state corresponds to the duration of the triggering beam current.