Electrostatic Screen Research Articles

Field electron emission properties from aligned carbon nanotube bundles of different density

AbstractDetails are given of an experimental study of the field emission characteristics of well‐aligned carbon nanotube films. The films were prepared in a catalyst‐assisted process using bias‐enhanced microwave plasma chemical vapour deposition. They consist of bundles of carbon nanotubes, the density of which may be controlled by changing the thickness of the pre‐deposited catalyst film. The transparent anode technique was used to measure the field emission properties of the carbon nanotube films and it was found that films having a low density of bundles have better field emission properties. The findings are explained by the electrostatic screen effect. Copyright © 2004 John Wiley & Sons, Ltd.

Electron energy distribution function and plasma potential in a planar inductive argon discharge without electrostatic screen

Studies on electron heating are done during the power coupling change in the discharge mode transition (E–H mode transition) in a planar inductive argon discharge without electrostatic screen (Faraday shield). The electron energy distribution function (EEDF) evolution is measured by the alternating current superposition method with a radio frequency (rf) compensated Langmuir probe. The trend of its integrals, electron density and effective electron temperature, and especially the plasma potential against rf power are presented. It is demonstrated that the plasma potential is governed primarily by the high-energy electron tail in a plasma with bi-Maxwellian EEDF. The interdependence of the EEDF and the plasma potential is discussed. The experimental results show that the plasma potential against rf power reflects a change in the relative contribution of capacitive power coupling to electron heating.

Global Stability of a Shielded Dual-Spin Satellite

Sufficient conditions for the global stabilities of equilibrium positions of a dual-spin satellite equipped with a cylindrical electrostatic screen normal to the circular equatorial orbital plane system under the action of moments induced by the gravitational and Lorentz forces are obtained by Liapunov's direct method. The problem is then studied with respect to all variables, including the angular velocity of the rotor. The instabilities of the problem are solved by the first approximation theorem. Furthermore, sufficient conditions for the global stability of rotation with arbitrary angular velocity for an axisymmetric dual-spin satellite equipped with an electrostatic screen are presented by applying Liapunov's direct method.

Kinetics of partly diffusion-controlled reactions. Part 23.—The case of ionic reactions

Diffusion-controlled reactions have been investigated for many years, and have been modelled for the case where Brownian particles move in a medium of hard spheres. We here present models based upon liquid physics concepts and known interaction potentials for cases where the transport phenomenon is due to a random walk hampered by the electrostatic potential and screen effect.

Precipitation of Charged Dust Particles on Electrostatic Screen

The purpose of this paper is to present collection performance dependence upon the parameters of channeled electrodes in a twostage precipitator. The practical channeled electrostatic screens are classified into two types and the respective theoretical collection efficiency equations are obtained by employing idealized models. It is shown that In normal operating conditions the most effective particle collection mechanism in the device is electrostatic precipitation rather than the Inertlal separation. It is also pointed out that the channeled electrode, in comparison with the plate-type, should be a narrow width. An empirical efficiency equation is recommended and the agreement between experimental data and empirical equation is within 6%.

Present state of development of a gas-pressurised lapped-polythene cable for E.H.V. transmission

Polythene tape in association with sulphur hexafluoride under pressure is an attractive dielectric for underground transmission cables because it has low dielectric loss, low relative permittivity and high thermal conductivity. Unfortunately, polythene tape has a high coefficient of thermal expansion, and care is consequently needed in the design of the conductor electrostatic screen to achieve adequate electric strength. Because of the low thermal conductivity of sulphur hexafluoride between layers of tape, good contact needs to be obtained by controlling the interfacial pressure in the dielectric wall to achieve good heat transfer. It has been demonstrated by work on models and 650 mm2 275 kV cable that this type of cable is technically feasible

Electrostatic screening in a theta-pinch coil

The theoretical and practical considerations involved in the design and construction of a resistive electrostatic screen, as used in certain theta-pinch experiments, are presented. The spatial and temporal variation of the total electric field within the shield is analysed, and a generalized time constant is derived which describes the screening properties of such shields with good accuracy over a wide range of parameters.

Dilute solution properties of nylon 66 dissolved in 2,2,3,3‐tetrafluoropropanol

AbstractLight‐scattering and viscosity measurements have been made on dilute solutions of nylon 66 dissolved in 2,2,3,3‐tetrafluoropropanol. The polyelectrolyte behavior of polyamides in carefully distilled solvent is due to traces of water in the solvent. If care is taken to exclude water, 2,2,3,3‐tetrafluoropropanol is a nonionic solvent for nylon 66. The polyelectrolyte effects of nylon 66 in the wet solvent can be repressed by the addition of sodium trifluoroacetate. The action of the sodium trifluoroacetate is to immobilize the water molecules in solution rather than to act as an electrostatic screen. Molecular weights estimated from the light‐scattering data and the relation between intrinsic viscosity and second virial coefficient are identical with the results based on measurements in the solvent system formic acid–water–sodium formate.

A Comparison of Thin Tape and Wire Windings for Lumped-Parameter, Wide-Band, High-Frequency Transformers

This paper considers the problem of optimum design of the impedance matching, lumped-parameter, wide-band transformer model with all transmission zeros at infinity. The spiral-tape-winding transformer is compared with the wire-winding transformer with an electrostatic screen, and it is shown that the former has no advantage over the latter except (perhaps) at quite low impedance levels. The low-pass-filter model of the transformer is considered in more detail than is customary, and it is shown that the HF performance of any lumped-parameter wideband transformer may be extended in proportion to the number of branches selected for the ladder network model of the transformer; building out the transformer-coupling network to include additional inductors and capacitors thus extends the frequency response. For a given network model and a given low-end cutoff frequency, it is shown that the high-end cutoff frequency is a function of the peripheral distance around the winding, the mean impedance level of the source and load, and the turns ratio. From this relation it is shown that the most favorable turns ratio is unity and that the most favorable impedance levels are low ones.

A new 132,000-volt cable joint

This paper describes what is believed to be a new form of high-voltage joint. The main novelties in the joint are that the metallic union of the conductors is insulated by wrapping on a single sheet of wide, impregnated paper by machine. The ends of the cable insulation are cut into a series of steps, or a taper, and knives on the machine cut the wide sheet of paper exactly to fit the steps or taper as the wide paper is being applied, until a smooth cylinder is built up to the original diameter of cable insulation. At this moment, the knives are removed, and at each end of the wide piece of paper, strips of tinfoil which have previously been cemented to the paper appear, and these strips gradually taper inward so that as the wide paper is applied, a flaring cone of metal is formed in the body of the insulation itself. This metallic cone acts as an electrostatic screen to control the longitudinal and radial stresses. It is formed automatically without any attention on the part of the splicer in the field, and it insures that all the insulation under stress is solid laminate paper insulation of the highest quality and breakdown strength, especially in the regions where the diameter is enlarged from that of the cable sheath to that of the joint sleeve. Test results are given.

A New 132,000-Volt Cable Joint

This paper describes what is believed to be a new form of high-voltage joint. The main novelties in the joint are that the metallic union of the conductors is insulated by wrapping on a single sheet of wide, impregnated paper by machine. The ends of the cable insulation are cut into a series of steps, or a taper, and knives on the machine cut the wide sheet of paper exactly to fit the steps or taper as the wide paper is being applied, until a smooth cylinder is built up to the original diameter of cable insulation. At this moment, the knives are removed, and at each end of the wide piece of paper, strips of tinfoil which have previously been cemented to the paper appear, and these strips gradually taper inward so that as the wide paper is applied, a flaring cone of metal is formed in the body of the insulation itself. This metallic cone acts as an electrostatic screen to control the longitudinal and radial stresses. It is formed automatically without any attention on the part of the splicer in the field, and it insures that all the insulation under stress is solid laminate paper insulation of the highest quality and breakdown strength, especially in the regions where the diameter is enlarged from that of the cable sheath to that of the joint sleeve. Test results are given.