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Power devices and systems operating in partial vacuum are susceptible to partial discharges, corona, or volume discharges. In this paper, we present an image-analysis technique and its results for optical-emission characterization of a breakdown initiation. The example set for demonstration is breakdown events under a 20-kHz unipolar sinusoidal applied field for a point-to-point electrode geometry at partial vacuum in helium. The voltage and current waveforms along with the light-emission data are collected. The results of the image-analysis technique used to obtain the R/G/B emission characteristics of the breakdown events as a function of time, location, and pressure are presented. The images obtained by a standard 30-ft/s video camera are used for analysis to characterize the progress of the breakdown. Index Terms--High frequency breakdown, optical image analysis, partial vacuum, spectroscopy.

Power devices operating in partial vacuum, such as aerospace systems or space environment are susceptible to partial discharges, corona, or volume discharges due to the partial vacuum conditions. These power systems also operate under frequencies and waveforms quite different from those studied and developed for earthbound power distribution systems. In this paper, we present our studies on the breakdown characteristics of helium and nitrogen gases under positive square-pulsed voltage at frequencies varying from 50 kHz to 200 kHz in partial vacuum, for a point-to-point electrode configuration. It is observed that high frequency breakdown voltage is lower than the dc breakdown voltage under the same experimental conditions and electrode geometry. Also, breakdown voltage versus pressure curves exhibited a Pashcen like behavior. Breakdown voltages of helium and nitrogen as a function of signal frequency are also presented. Index Terms--Helium, nitrogen, electrical breakdown, inhomogeneous field, aerospace power systems, high frequency.

We present two optical system designs using aspherical lenses for beam circularization, collimation, and expansion of semiconductor lasers for possible application in lidar systems. Two different optical lens systems are investigated; namely, two aspherical lens and single aspherical lens systems. Software package programs of ZEMAX and MATLAB to simulate the optical designs are used. The beam reshaping results are presented for one specific laser beam output. OCIS codes: 280.3640, 140.3300, 080.2720, 080.2740, 080.3630.

In this paper, we present two optical system design methods for beam circularization, collimation, and expansion of semiconductor laser output beam for possible application in LIDAR systems. Two different optical mirror systems are investigated: an off-axis hyperbolic/parabolic mirror system and an off-axis parabolic mirror system. Equations specific to these mirror systems are derived and computer package programs such as ZEMAX and MATLAB are used to simulate the optical designs. The beam reshaping results are presented. OCIS codes: 280.3640, 140.5960, 140.3300, 080.2720, 080.2740, 230.4040.

In this paper, we present experimental results of surface flashover characteristics of epoxy resin and epoxy resin cast with powdered [Al.sub.2][O.sub.3] (nano/micro-composite dielectric) samples in partial pressure of nitrogen. The flashover studies are conducted separately using dc and 20 kHz ac signals. The voltage, current, and light emission waveforms are obtained. The optical data is collected by a video camera and a photomultiplier tube (PMT). The nano/micro composite dielectric samples used in the experiments are produced in-house by mixing 1:10 weight ratio of [Al.sub.2][O.sub.3] powder with epoxy resin of known properties. Throughout this study, copper electrodes are used and are placed over the dielectric samples to initiate surface flashover events. The results of surface flashover voltages as a function of pressure are presented. Additionally, optical emission characteristics along with the voltage and current waveform data are also presented. Index Terms--Partial pressure nitrogen, surface flashover, hand/micro composite dielectrics.

Generation of intense electron beams by superposing two discharges, namely, a low-pressure dc glow discharge and a high-current pulsed discharge at pressures and voltages very similar to that of the pseudospark gap devices, has been studied. The small beam diameter, high peak current, and short pulse length are the characteristics of the electron beam generated using this technique. This technique does not require high vacuum facilities, and applications such as microprocessing, X-ray generation, and preionization for high-power lasers are feasible. The electron beam current is in the range of 10-30 A. Microprocessing as drilling tenths of microns diameter holes in different materials such as copper, titanium, and tantalum has been performed. The microstructure of the irradiated materials has been investigated by means of scanning electron microsope (SEM) and atomic force microscope (AFM). Currently, the possibility of processing a matrix of holes is being considered. In this paper, preliminary study regarding the interaction of intense short electron beams with different metallic targets is presented. The electron generator consists of a fast filamentary discharge in low-pressure gases, and the filling gases such as helium, argon, or nitrogen at approximately 0.1 torr pressure are used. Some of the important characteristics of the device for drilling and micromachining are that the targets can be easily changed, and the beam can be deflected by means of a magnetic field. After the initial device characterization, several holes at different experimental conditions were drilled onto the target materials, and the interaction of the beam with these different targets was investigated by means of a scanning electron microscope. Index Terms--Electron beam, material processing.

This work presents experimental results of optical emission from polycrystalline, as well as single crystal diamonds, during the surface flashover events in a vacuum environment. Optical emission spectra were recorded and the source of this luminosity was investigated. Analysis showed that the surface flashover events were associated with relatively high intensity optical emissions. The light emission started much earlier than the voltage collapse, increased very rapidly with the breakdown, and eventually ended after few seconds; much later than the voltage across the surface was recovered. The polycrystalline diamond sample used in the experiments was produced by a microwave plasma CVD (chemical vapor deposition), and the sample surface was polished to optical quality before the experiments. The electrode material was copper, and a dc voltage was applied between the electrodes. Surface flashover voltage characteristics and breakdown voltage waveforms of both samples were determined.

Synthetic thin films such as diamond-like carbon (DLC) and polycrystalline diamond thin films can be used to increase surface flashover voltage of dielectric materials used in HV devices operating in vacuum. This work presents experimental results identifying some surface flashover characteristics of diamond-like carbon (DLC) thin films in space vacuum conditions. The DLC samples used in the experiments are produced by a microwave plasma deposition technique. The electrode material was copper, and a dc voltage was applied between the electrodes. Surface flashover voltage characteristics and the breakdown voltage wave forms of DLC thin film samples were determined. The re-suits showed that DLC thin films may not be suitable materials for HV applications as dielectric materials in vacuum when coated onto semiconductor materials. Additionally, these results were compared with the surface flashover characteristics of polycrystalline diamond thin film and quartz samples.

A segmented hollow cathode has been designed, constructed and operated over a wide pressure range from 1 mbar to 200 mbar to determine optimum operating characteristics for a series of unique applications. The device is designed for use as a plasma source for molecular gas lasers operating in the UV and visible spectra. The cathode consists of 1 mm thick nickel disks and 0.1 mm tungsten foil disk segments stacked alternately, forming a cylindrical geometry on its outer surface and a near-spherical geometry inside. The tungsten foil disk inner diameters vary along the longitudinal axis of the cathode. With this special geometric arrangement one hollow cathode structure is embedded within another. The spacing between the segments (tungsten foil disks) creates one hollow cathode geometry, and the spherical geometry formed by the inner diameter of the segments is a second hollow cavity. This design permits one to operate the device at an expanded pressure range. The device's voltage and current characteristics are studied at different operating pressures and the optimum operating parameters such as pressure, voltage, current, and foil thickness are investigated. Helium, argon or a helium-argon mixture is used as the fill gas throughout the series of experiments.