Electric Field and Heat at the CAT-SG Coatings Interface Under Fast Rise Pulses

During the formation of thunderclouds, simultaneous macrophysical and microphysical processes cause the separation of charges inside the cloud, forming the electrical structure of storm clouds. As a result of that, the electric field at the ground level can change significantly. Irregularities on the surfaces of grounded structures can provide conditions for corona discharges that generate ions and form a space charge layer at ground level.In this work, we investigate the features of corona point discharges from grounded conductive rods installed in three different sites. In all of them, we measured current along the grounded rod under high background electric field conditions or during its fast changes caused by lightning strikes. The current signals reveal pulses with a fast rise time (tens of nanoseconds) and slow decay (hundreds of nanoseconds), with polarity compatible with the background electric field. Comparing laboratory experiments with the results in the field, we observed that positive discharges required a lower electric field threshold than negative discharges. Their pulse frequency is also equivalent to one-tenth of the pulse frequency of negative discharges, for a similar electric field level.In one of the sites, one current sensor coupled to a grounded rod, 1.5 m above a roof, was installed in a site located at an altitude of 2525 m, near a ski-station. We observed a large number of events, and we were able to correlate the frequency of the pulses with the electric field, as well as evaluate the effect of the wind on the discharges. In the other two sites, the rods were placed near the ground and on the roof of a conventional building. Pulses were registered on some occasions when there was lightning activity nearby, either before or after lightning events. Previous works on this topic correlate the electric field with the average current flow, and on this work, we evaluate the pulse frequency and electric field. This investigation is relevant for understanding the production of corona and space charges from high structures.

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Resolution in photoelectron microscopy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100086593 ◽

1991 ◽

Vol 49 ◽

pp. 458-459

Author(s):

G. F. Rempfer

Keyword(s):

Electron Microscopy ◽

Electric Field ◽

Ultraviolet Light ◽

Uniform Field ◽

Virtual Image ◽

Lens System ◽

Photoemission Electron Microscopy ◽

Planar Electrode ◽

Electron Lens ◽

Photoemission Electron

In photoelectron microscopy (PEM), also called photoemission electron microscopy (PEEM), the image is formed by electrons which have been liberated from the specimen by ultraviolet light. The electrons are accelerated by an electric field before being imaged by an electron lens system. The specimen is supported on a planar electrode (or the electrode itself may be the specimen), and the accelerating field is applied between the specimen, which serves as the cathode, and an anode. The accelerating field is essentially uniform except for microfields near the surface of the specimen and a diverging field near the anode aperture. The uniform field forms a virtual image of the specimen (virtual specimen) at unit lateral magnification, approximately twice as far from the anode as is the specimen. The diverging field at the anode aperture in turn forms a virtual image of the virtual specimen at magnification 2/3, at a distance from the anode of 4/3 the specimen distance. This demagnified virtual image is the object for the objective stage of the lens system.

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Field-assisted ionization theory for microscopists

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100171833 ◽

1994 ◽

Vol 52 ◽

pp. 820-821

Author(s):

Patrick P. Camus

Keyword(s):

Electric Field ◽

Electron Tunneling ◽

Ionization Probability ◽

Critical Distance ◽

Tunneling Probability ◽

Field Ionization ◽

Radius Of Curvature ◽

Field Evaporation ◽

A Value ◽

Ion Emission

The theory of field ion emission is the study of electron tunneling probability enhanced by the application of a high electric field. At subnanometer distances and kilovolt potentials, the probability of tunneling of electrons increases markedly. Field ionization of gas atoms produce atomic resolution images of the surface of the specimen, while field evaporation of surface atoms sections the specimen. Details of emission theory may be found in monographs.Field ionization (FI) is the phenomena whereby an electric field assists in the ionization of gas atoms via tunneling. The tunneling probability is a maximum at a critical distance above the surface,xc, Fig. 1. Energy is required to ionize the gas atom at xc, I, but at a value reduced by the appliedelectric field, xcFe, while energy is recovered by placing the electron in the specimen, φ. The highest ionization probability occurs for those regions on the specimen that have the highest local electric field. Those atoms which protrude from the average surfacehave the smallest radius of curvature, the highest field and therefore produce the highest ionizationprobability and brightest spots on the imaging screen, Fig. 2. This technique is called field ion microscopy (FIM).

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