Spark Discharge

spark discharge

[′spärk ′dis‚chärj]
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Spark Discharge


one of the types of electric discharge in gases. It usually occurs at near-atmospheric pressures and is accompanied by a characteristic acoustic phenomenon, the “crackling” of the spark. Under natural conditions spark discharge is most frequently observed in the form of lightning.

Spark discharge in the proper sense of the term occurs if the power of the energy source feeding it is insufficient to maintain a stationary arc discharge or a glow discharge. In this case the discharge current increases sharply; simultaneously, the voltage across the discharge gap drops below extinction voltage within a very short time (a few microseconds to several hundred microseconds), thus ending the discharge. Subsequently, the potential difference between electrodes again increases until the firing voltage of spark discharge is attained, and the process repeats itself. In other cases, where the power supplied is sufficiently high, all the phenomena characteristic of spark discharge are also observed, but only as a transient process leading to the establishment of another type of discharge, most frequently arc discharge.

A spark discharge is a bundle of bright filament-like strips (spark channels), which are often strongly branched and disappear or alternate rapidly. The channels are filled with plasma, which in a high-power spark discharge consists of ions not only of the initial gas but also of the electrode material, which is evaporated intensively under the action of the discharge.

The mechanism of formation of spark channels (and consequently, the mechanism of generation of a spark discharge) can be explained by the streamer theory of electric breakdown in gases. According to this theory, under certain conditions streamers will form from the electron avalanches developing in the electric field of the spark gap. The streamers consist of thin, dimly glowing branched channels containing ionized gas atoms and free electrons split from the atoms. As the streamers become elongated, they bridge the discharge gap and develop continuous conductive filaments connecting the electrodes. The subsequent transformation of streamers into spark channels is accompanied by a sharp increase in current and the amount of energy released in the channels. Each channel widens rapidly, and the pressure in it increases abruptly, as a result of which a shock wave is generated at the boundaries of the channel. The aggregate of shock waves at the widening spark channels generates a sound perceived as the crackling of sparks (or thunder in the case of lightning).

The quantities that characterize spark discharge—firing voltage, extinction voltage, maximum current strength, and duration —may vary within wide limits, depending on the parameters of the discharge circuit, the size of the spark gap, the electrode geometry, and gas pressure. As a rule, the firing voltage of a spark gap is rather high. The voltage gradient within a spark falls off from several dozen kilovolts per centimeter at the moment of breakdown to about 100 V/cm a few microseconds later. The maximum current intensity in a high-power spark discharge may be as high as several hundred kiloamperes.

Spark creepage is a special type of discharge, which originates along the interface between the gas and a solid dielectric placed between the electrodes. Regions of spark creepage in which the charges are predominantly of one sign induce charges of opposite sign on the surface of the dielectric, as a result of which the spark channels spread over the surface of the dielectric (Lichtenberg figures). Processes similar to those of spark discharge are also typical of brush discharge.

Spark discharge has found various uses in technology. It is used to initiate explosions and combustion processes and in the measurement of high voltage, in spectroscopic analysis, in switching of electric circuits, and in high-precision metalworking.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
The Study of Biocidal Mechanisms of Spark Discharge Plasma Radiation.
These coupling resistances and capacitances can provide a negative function to control discharge development process effectively, thereby preventing the transition from glow discharge to spark discharge. Under the mediation of the negative feedback mechanism, the rising rate of the discharge current is effectively controlled, which avoids the occurrence of the spark discharge.
In this study, the Electric Spark Discharge Method (ESDM) was used to prepare nano-Ti colloid and using Ti[O.sub.2] for photocatalytic reaction to degrade organic compounds.
Following this pioneering study, significant variations of the ELCAD design have been developed, including solution cathode glow discharge (SCGD) [9, 10], direct current atmospheric pressure glow discharge (DC-APGD) [11, 12], liquid sampling-atmospheric pressure glow discharge (LS-APGD) [13, 14], liquid electrode plasma atomic emission spectroscopy (LEP-AES) [15, 16], alternating current electrolyte atmospheric liquid discharge (AC-EALD) [17, 18], drop spark discharge (DSD) [19, 20], and liquid electrode chip discharge [21, 22].
Among specific topics are formation mechanisms of the red spark discharge of micro-arc oxidation, tribological properties of ceramic tool materials in contact with wood-based materials, the control bearing of pre-tightening force on the guide of a high-speed punch press, technology to reduce noise and vibration in hybrid electric vehicles, and a user-friendly design of a modern forest fire helmet.
In the conventional microwave heating, there is a problem of spark discharge involving conductive inks that contain metallic materials.
Principal electrical sheme of a device shown, can be divided into two section: power block of a condensed spark discharge, and a block of a integration RC circuit.
Therefore it is no possibility to measure an air flow velocity in the volume between electrodes for the risk of spark discharge and essential distortion not only the corona field, but also the air flow field.