Current Spark Research Articles

Strong Density Gradients in Postdischarges in Argon and Air

High current sparks are created in argon and air using a high-voltage pulse of 16-ns duration. Shadowgraphy is applied to image density fluctuations. Shock waves become visible ~100 ns after the pulse; they expand with a velocity somewhat higher than the speed of sound. The filamentary core of the discharge shows heating that diffuses outward slowly and develops into microturbulences. They remain visible up to 3 ms. In air, the current remains lower than that in argon, and shocks only emerge from the electrodes. No indication of absorption is found; probably gas heating is observed near the electrodes.

An Experimental Study of Spark Anemometry for In-Cylinder Velocity Measurements

It has been demonstrated by previous researchers that an approximate value of the bulk flow velocity through the spark plug gap of a running spark ignition engine may be deduced from the voltage and current wave forms of the spark. The technique has become known as spark anemometry and offers a robust means of velocity sensing for engine combustion chambers and other high temperature environments. This paper describes an experimental study aimed at improving performance of spark anemometry as an engine research tool. Bench tests were conducted using flow provided by a calibrated nozzle apparatus discharging to atmospheric pressure. While earlier studies had relied upon assumptions about the shape of the stretching spark channel to relate the spark voltage to the flow velocity, the actual spark channel shape was documented using high-speed video in the present study. A programmable ignition system was used to generate well-controlled constant current discharges. The spark anemometry apparatus was then tested in a light duty automotive engine. Results from the image analysis of the spark channel shape undertaken in the present study have shown that the spark kernel moves at a velocity of less than that of the freestream gas velocity. A lower velocity threshold exists below, which there is no response from the spark. It is possible to obtain a consistent, nearly linear relationship between the first derivative of the sustaining voltage of a constant current spark and the freestream velocity if the velocity falls within certain limits. The engine tests revealed a great deal of cycle-to-cycle variation in the in-cylinder velocity measurements. Instances where the spark restrikes occur during the cycle must also be recognized in order to avoid false velocity indications.

Increase of energy transfer efficiency in the electromagnetic flux compression technique generating ultra-high magnetic field

Magnetic fields of over 100 T can be generated only through the use of a destructive pulsed magnet. Electro-magnetic flux compression (EMFC) is an efficient method to generate such ultra-high magnetic fields. The EMFC system at Institute for Solid State Physics holds the world record for the highest magnetic field produced in-doors. This system has been used for various sorts of measurements applied to matters under ultrahigh magnetic fields. Recently, we successfully improved the coil system to generate a higher field using less energy injection and more simplified preparation processes. The new system increased the electro-magnetic energy transfer efficiency to at least twice that of the previously employed system. Our new primary coil using a copper current guide has the advantage of shallower high-frequency current skin depth and less contact impedance than previous ones. Therefore the discharge current spark is completely avoided. The improved skin depth resulted in a symmetric implosion of the liner coil with less influence of the feed gap. A high degree of cylindrical liner symmetry was observed during implosion. A fast liner speed of 2.4 km/s was achieved, and 350 T could be generated by 1 MJ and 470 T by 2 MJ.

Measurement of two-dimensional electron density profile in a low current spark using interferometry

We report the measurement of two-dimensional line integrated electron density profiles in a spark plasma by using Michelson interferometer in a single shot. The plasma duration is measured with beam deflection technique. Comparison of duration of plasma and current pulse indicate the existence of after glow region in such pulsed discharges.

Channel One and the Education of American Youths

In 1990, Channel One, the 12-minute commercial news program for schoolchildren, was launched into middle and high schools across the United States. This article analyzes research investigating the alleged benefits of Channel One—the technology, student learning of current events, increased student interest in the news—and the major cost—the advertising. It concludes that outside uses for the technology remain modest. While the program can enhance students' learning of current events and spark their interest in the news, its ability to do so is largely dependent on supplemental activities by teachers. Teachers are constrained in their use by organizational factors and restrictive terms of the Channel One contract. More difficult to assess, due to limited research in this area, are the costs associated with Channel One's advertising to young people in a school setting.

Spectroscopic instrumentation in the 21st Century: excitement at the horizon

Recent developments in technology have suggested a promising future for plasma spectroscopy. New optical technologies, such as volume phase technology and unconventional optical systems, when coupled with new generations of optical detectors promise to provide powerful tools for plasma diagnostics or spectrochemical analysis. Next generation charge injection devices will provide both complete random access of individual detector sites and ‘collective readout,’ a new readout mode. Collective readout will promise faster readout and improved signal to noise ratios. A new generation of pre-amp per pixel array detectors with proper addressing architecture will allow random pixel readout and extreme resistance to blooming. These technological advances will yield new capabilities for not only current and future plasma sources, but also vintage sources such as the microwave-induced plasma, the direct current plasma, direct current arc and the direct current spark. Developments in software data processing techniques including neural networks and other chemometric techniques will allow present and future spectroscopists to extract useful diagnostic and chemical information from the almost overwhelming abundance of analytical data generated by the present and future generations of array detectors.

Dynamic analysis of Eddy currents and forces in the TFTR vacuum vessel due to plasma disruptions

The sudden disappearance of electrical current during a plasma disruption in the Tokamak Fusion Test Reactor (TFTR) induces large transient eddy currents in the surrounding vacuum vessel. These eddy currents interact with the background magnetic fields to produce significant mechanical loads. In this study a detailed model of a representative 36 degree segment of the vessel was chosen for analysis and assumed to have a ten-fold rotational symmetry. The eddy currents and Lorentz forces were calculated using an extended version of the eddy current code SPARK with plasma drivers corresponding to several different stationary and moving plasma disruption scenarios. The forces were then used as input to the structural analysis code NASTRAN to calculate the dynamic mechanical response of the vacuum vessel.

The recovery of high current long gaps in hydrogen and argon

Measurements of the dielectric recovery voltages of high current spark gaps with argon and hydrogen fillings are presented. In addition, values of temperature versus time are given. Improved techniques have enabled temperature profiles to be obtained. Results show that the recovery with argon can be explained completely by temperature, hence gas density effects, but hydrogen recovers more quickly than expected. Possible explanations for the latter observation are discussed.

Determination of temperatures of high current spark channels †

Abstract This paper reviews the experimental methods of determination of temperatures of recovering high current, spark channels in different, stages of the afterglow. Host of the experiments described were performed at atmospheric pressure or pressures sufficiently high that thermal equilibrium among all species is achieved so that the electron, ion and gas temperatures are considered equal. In the early afterglow (within approximately 50 μs after spark initiation) when luminosity of the spark is sufficient, spectroscopic methods are employed to determine channel temperatures. In the intermediate stage of the afterglow (50 μs-500 μs) when luminosity is not sufficient for optical techniques to be employed, measurement, of electrical conductivity or sound or shock-wave velocity can be used to derive the gas temperature. In the late afterglow (1 ms after spark initiation) when the gas has recovered to a neutral state, measurements of reignition voltage together with Poschen's law arc used to derive gas temp...

Temperature determination of a recovering spark channel from conductivity probe measurements†

The temperature of a recovering high current (25 kA) spark channel in the afterglow period from 0·2 ins to 5 ms after spark initiation has been derived from conductivity probe measurements. The model of a weakly ionized gas is used for calculating the conductivity of the recovering plasma. Temperature decay was obtained for an air spark formed between 6·4 mm tungsten electrodes spaced at 5 mm apart at 1 torr pressure at radial distances of 2 cm, 5 cm and 10 cm from the centre of the spark channel. The results are compared with temperature recovery characteristics obtained in similar air spark channels at atmospheric pressure.

Radial recovery of high current spark channels†

Abstract Radial recovery characteristics of high current (40 kA) spark channels in air at atmospheric pressure have been measured using re-ignition voltage technique and pressure probe technique. In the case of re-ignition voltage measurement the temperature was derived by assuming the validity of Paschen's law at the Into recovery period, whereas in the case of pressure probe, measurements of local sound velocity were used to derive the gas temperature. The derived temperature profiles of the spark channel under similar experimental conditions show a uniform temperature profile near the centre of the channel. The boundaries of the spark channels measured by these techniques are not well defined as compared with previous results using the shock-wave Schlieren technique. Discrepancies of results obtained by the present two different sensing techniques are found and are explained as due to the large cooling effects of the re-ignition voltage probes.

Thermal Reignition of a High Current Spark Channel

Reignition measurements of a high current (40KA) spark channel in air at atmospheric pressure during both the early and late post-spark period at different radial distances from the axis of the channel are obtained by simultaneous measurements of current and voltage across a pair of auxiliary probing electrodes. In contrast to previous studies on high current spark channel recovery where reignition measurements are confined to the spark (fast) breakdown regime which occurs at times greater than 1 ms after spark inition, this present work deals primarily with reignition in early delay times as early as 50 µs after the spark initiation where thermal (slow) breakdown occurs. The results of the present study indicate that conductance of the channel increases abruptly during thermal breakdown, and thus the technique of simultaneous measurements of the current and the voltage across the probing electrodes can be used to study recovery during the early post-spark period when thermal breakdown occurs.

Energy levels and classification problems in spectra of highly ionized elements of the fifth period

New Spectra of highly ionized atoms of the fifth period are to be published soon. Selected energy levels obtained with 10 4 A peak current vacuum sparks are presented in Table I.

Explosive Anode Erosion in High Current Sparks

Tree shape optical phenomena erupting from the anode of high density nanosecond spark discharges were studied by means of time resolved photography and identified as explosive erosion jets of electrode material by spectroscopy. The mechanism of the explosive erosion is explained. Thermalization with longer pulse duration is observed.

Fast decision-making spark chambers

A decision-making system of current spark chambers was developed to preselect scattering events. The current signal amplitude of a single chamber appears about 100 nsec after the ignition of the switching spark gap and is a linear function of the coordinate x of the spark position and independent of the coordinate y, orthogonal to x. It is not possible to measure both coordinates simultaneously by one gap. The uncertainty is smaller than ±1% of the useful x-range. Multiple spark events cannot be resolved.

Some Properties of High Current Spark Channels†

ABSTRACT Using discharge peak currents of about 200 kA measurements of voltage drop, expansion rates, etc. were made in spark channels in various gases, but principally in hydrogen, at atmospheric pressure. These data are used to infer discharge temperatures, etc.

A current spark chamber used as a several hundred channel ladder counter

A spark chamber where a current signal is used to measure the position of the spark was developed for the purpose of its use as a several hundred channel ladder counter associated with a magnetic spectrometer. The main characteristics of the chamber were first determined with a β-ray source and with cosmic rays. We studied with special care, the linearity, the resolution of the instrument and the accuracy on the localization of the sparks; we also tried to obtain a counting efficiency as close as possible to 100%. The overall characteristics of the system were then checked on a magnetic spectrometer by studying the scattering of high energy electrons on 9Be.

Cooling of high current spark channels in hydrogen and argon

The considerable importance of gas temperature in the dielectric recovery of high current spark gaps using air as the dielectric has been demonstrated in previous papers. It was obvious however, that some other processes were affecting recovery with some electrode configurations. This paper describes similar experiments with both argon and hydrogen as the dielectric. It is confirmed that other processes might predominate even in the later stages of recovery, and possible effects are briefly discussed. A simple model is used to calculate temperature decay, which gives fair agreement with measured values.

Urement of the Temperature Decay of High Current Spark Channels in Air†

Abstract This paper describes a technique for measuring the temperature decay in a spark gap after the passage of a high current discharge. The discharge current is 187 kA, find temperature measurements in air at atmospheric pressure are given for 6'4 and 16 mm diameter tungsten electrodes and for 16 and 76 mm diameter copper electrodes. The effects of electrode size and material on the temperature are discussed, and it is observed that most of the channel is at a uniform temperature during the recovery period following the discharge. By a comparison of results from temperature measurements and re-ignition voltages, it is concluded that the gas temperature is an important controlling factor in the recovery of high current spark gaps, although other processes are active under certain conditions.

Measurement of Reignition Voltage Characteristics for High Current Spark Gaps in Air†

ABSTRACT This paper describes a technique for the measurement of reignition voltage characteristics of spark gaps after the passage of a high current discharge. The initial discharge current is varied from 100 to 235 kA, and recovery-measurements in air at atmospheric pressure are given for 6 4 and 16 mm diameter tungsten electrodes and for 16, 19 and 76 mm diameter copper electrodes. The effects of gap length, current amplitude and electrode size and material are discussed, and it is observed that electrode size has a powerful influence upon the recovery process Gas temperatures are derived on the assumption that Paschen's law holds during the final recovery period.