Space Charge

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Space charge

The net electric charge within a given volume. If both positive and negative charges are present, the space charge represents the excess of the total positive charge diffused through the volume in question over the total negative charge.

Space Charge

an electric charge dispersed in a volume. A space charge determines the spatial distribution of electric potential and electric field intensity. In order for a space charge to arise, the concentrations of positive and negative charge carriers, such as ions and electrons in a plasma, must not be equal. The density of a space charge ρ = eΣZini, where ni, is the concentration, Zi, the charge of type i carriers, and e the charge of an electron.

Since the formation of a statically balanced three-dimensional system of free charges is impossible, the appearance of a space charge is usually connected with the passage of an electric current. Space charges arise near electrodes when a current flows through electrolytes and at the junction of two semiconductors with differing (electron or hole) conductivities. They also arise in processes of electron and ion emission in a vacuum and in electrical discharge in gases. A difference in the diffusion coefficient D of charge carriers with different signs promotes the formation of a space charge.

When electrons move in a vacuum with zero initial velocity, the current density at the cathode varies according to the three-halves power law through the effect of the space charge. The solution of the analogous problem for positive ions in a gas depends on the character of the motion of the ions. The fields generated by space charges determine many important properties of gas discharge (development of the discharge over time, formation of streamers) and of the phenomena in plasma (plasma oscillations and waves) and semiconductors. Since ρ is the algebraic sum of charges of different signs, the charges of the space charge can partially or completely compensate one another. Examples are a plasma with nearly equal electron and ion concentrations and the region near the cathode in an arc discharge, where as a result of such compensation the potential drop near the cathode is small and practically independent of the current.

Space Charge

in atmospheric electricity, a measure of the electric charge of the atmosphere, numerically equal to the difference between the number of positive and negative charges of all particles in a given volume. The value of the space charge is characterized by its density—the excess charge per unit volume.

The space charge results from the separation of oppositely charged particles in space (for example, in fog, clouds, and precipitation), when particles are torn away from the earth (for example, during dust storms) or from water (when the surface of a body of water is strongly agitated), in snowstorms, in volcanic eruptions, near high-voltage lines, and during the operation of automobile and aviation engines.

The value of the space charge varies with time as a function of the weather. In good weather, the density of the space charge at the earth’s surface is about ±(1–5) × 10−12 coulomb η m–3, and in storm clouds it may reach ±3 × 10–8 coulomb η m–3. In areas of good weather, the density of the space charge at the ground changes during both a day and a year and decreases exponentially with altitude; at altitudes greater than 10 km, it is less than 0.01 of its value at the earth’s surface. A space charge of up to 5 × 10–10 coulomb · m–3 builds up at the earth’s surface under the influence of the earth’s electric field. As a whole, the atmosphere has a positive space charge of about 3 × 105 coulombs.

REFERENCES

Tverskoi, P. N. Atmosfernoe elektrichestvo. Leningrad, 1949.
Chalmers, J. A. Atmosfernoe elektrichestvo. Leningrad, 1974. (Translated from English.)
Imianitov, I. M., E. V. Chubarina, and Ia. M. Shvarts. Elektrichestvo oblakov. Leningrad, 1971.

I. M. IMIANITOV

space charge

[′spās ‚chärj]
(electricity)
The net electric charge within a given volume.
(geophysics)
In atmospheric electricity, space charge refers to a preponderance of either negative or positive ions within any given portion of the atmosphere.
References in periodicals archive ?
Equation (17) is the dispersion relation for space charge and betatron waves with ES approximation.
Soula, "Transfer of electrical space charge from corona between ground and thundercloud: Measurements and modeling," Journal of Geophysical Research, vol.
The space charge solver fully integrates with Opera-3d's Modeler and Post-Processor, giving access to Opera's full range of model creation and results analysis tools.
As discussed above, success of these cyclotrons depends largely on control of beam "blowup" from space charge. The difficulty of the problem can be gauged using the benchmark of generalized perveance, given in (2), to compare space-charge effects to existing machines.
Palmieri, "Effect of nanoparticle size on space charge behavior of EVA/TiO2 nanocomposites," in Proceedings of the Annual Report Conference on Electrical Insulation and Dielectric Phenomena (CEIDP '11), pp.
While studying the time evolution of the space charge in the interaction space, the electron cloud initially forms in the area near the emission points assumed on the cathode and then expands until it fills the whole interaction space (Fig.
The method to determine the space charge formation in the sample due to the DBD effect is similar to one given in [21, 22].
At very high temperatures, ionic charge migration can occur, which is often observed as the so-called space charge peaks.
A thermionic converter consists of a hot electrode which thermionically emits electrons over a space charge barrier to a cooler electrode, producing a useful power output.
Above the electric field of 3 kV x [mm.sup.-1], the nonlinear behaviour appears, which is caused by the space charge limited currents (SCLC) (Carbone et al., 2005).
It may also be affected by practical problems such as producing the desired beam intensity or maintaining the beam intensity along the path, without excessive divergence due to its own space charge. Other applications may be adversely affected by unwanted charged particle motion effects, for example, multipaction in high-power high-frequency applications, where the desired electrical power of a device leads to problems like sparking.
This work describes beams in accelerators and other devices with negligible to strong space charge effects.

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