Hughes Aircraft Company

Hughes Electronics Corporation

Hughes Aircraft

Robert W Schumacher

Dan M Goebel

Jesse N Matossian

Robin J Harvey

Joseph Santoru

Robert L Poeschel

Julius Hyman, Jr

David M Pepper

Hayden E Gallagher

Frans G Krajenbrink

Simon K Nieh

A high dose rate, high impedance plasma ion implantation method and apparatus to apply high voltage pulses to a target cathode within an ionization chamber to both sustain a plasma in the gas surrounding the target, and to implant ions from the plasma into the target during at least a portion of each pulse. Operating at voltages in excess of 50 kV that are too high for the reliable formation of a conventional glow discharge, the plasma is instead sustained through a beam-plasma instability interaction between secondary electrons emitted from the target and a background pulsed plasma. The voltage pulses are at least about 50 kV, and preferably 100 kV or more. Pulse durations are preferably less than 8 microseconds, with a frequency in the 50-1,000 Hz range. The preferred gas pressure range is 1.times.10.sup.-4 -1.times.10.sup.-3 Torr; auxiliary electrodes can be used at the lower pressures to provide sufficient seed electrons for initiating a plasma, which is sustained by the beam-plasma instability interaction.

High impedance plasma ion implantation apparatus

Plasma-cathode electron gun structures capable of operation in low-pressure, e.g., &lt;5.times.10.sup.-3 Torr, ionizable gas environments are disclosed. They utilize a thermionic emitter within an enclosure with a partially transparent electrode defining a plasma face. Spaced anodes are disposed adjacent the electrode to extract an electron beam from the plasma face. A magnetic system forms an inward directed field, and a portion of the plasma electrons are directed through this field to enhance ionization efficiency.

High-current, low-pressure plasma-cathode electron gun

Wear-resistant titanium nitride coatings onto cast iron and other carbon-containing materials is enhanced by means of a new surface preparation and deposition process. The conventional pre-deposition surface cleaning by Ar.sup.+ ion bombardment is replaced by a hydrogen-ion bombardment process which cleans the substrate surface by chemical reaction with minimal sputtering and simultaneously removes graphite present on the cast iron surface. Removal of the graphite significantly improves the wear resistance of titanium nitride, since the presence of graphite causes initiation of wear at those sites. Hydrogen ion bombardment or electron bombardment may be used to heat the substrate to a chosen temperature. Finally, titanium nitride is deposited by reactive sputtering with simultaneous bombardment of high-flux Ar.sup.+ ions from an independently generated dense plasma. The resulting titanium nitride coating on cast iron evidences superior wear properties and adhesion compared to conventional reactive evaporation deposition techniques for titanium nitride.

Surface preparation and deposition method for titanium nitride onto

An object (30) is plasma processed by placing an electrically conducting grid (34) over all or a portion of the surface (32) of the object (30) so that the grid (34) generally follows the contours of the surface (32) but is displaced outwardly from the surface (32). Ions or electrons from a plasma surrounding the object (30) are accelerated into the surface (32) of the object (30) using as a processing driving force an electrical potential applied to the electrically conducting grid (34). The use of a contoured conducting grid (34) allows plasma processing of large, electrically nonconducting objects and objects having sharp surface features or recesses.

Surface potential control in plasma processing of materials

High impedance plasma ion implantation method and apparatus

A diverging magnetic field is established between the cathode and control electrode of a hollow cathode plasma switch to expand the plasma at a passageway through the control electrode, thus significantly increasing the switch's current handling capability. Preferred ranges of magnetic field strength, gas pressure, spacing between the hollow cathode and control electrode, and the mesh aperture size for the control grid are described.

Hollow cathode plasma switch with magnetic field

A hollow cathode capable of self-heating by back ion bombardment to a thermionic emission temperature axially discharges therefrom an ionized plasma of an ambient gas such as xenon. Electrons are axially or radially extractable from the plasma by an anode. A voltage is applied to a keeper electrode disposed between the cathode and anode to sustain plasma discharge of the gas between the cathode and keeper electrode. A control electrode is disposed between the keeper electrode and the anode. Application of a positive voltage (relative to the cathode) to the control electrode causes the plasma discharge to extend from the cathode to the anode, thus closing the switch. Application of a negative control electrode voltage, or simply returning the control electrode to cathode potential, causes the plasma discharge to retract back to the area of the keeper electrode, thereby opening the switch.

Plasma switch with hollow, thermionic cathode

A plasma switch employs a cold cathode which yields secondary electrons to sustain a plasma within the switch. The cathode is provided with a series of perturbations which increase the effective cathode surface area exposed to the plasma and increase the average effective path lengths of secondary electrons emitted from the cathode and the probability of such electrons having ionizing collisions with gas molecules within the switch. The interior cathode surface is provided with a coating formed from chromium or a chromium mixture. Chromium combines a high rate of secondary electron emission with low sputtering and other advantageous properties for plasma switch operation. Various types of chromium-plated perturbations are described.

Plasma switch with chrome, perturbated cold cathode

A plasma wave tube and associated operating method are described in which a pair of cold-cathode electron beam generators discharge counterpropagating electron beams into an ionizable gas, preferably hydrogen or a noble gas, within a waveguide housing. A voltage within the approximate range of 4-20 kV relative to the waveguide housing is applied to the cathodes to produce electron beams with current densities of at least about 1 amp/cm.sup.2. The beams form a plasma within the gas and couple with the plasma to produce electron plasma waves, which are non-linearly coupled to radiate electromagnetic energy in the microwave to mm-wave region. A magnetic field is established within the waveguide between the cathodes to confine the plasma, and to control the beam discharge impedance. The gas pressure is held within the approximate range of 1-100 mTorr, preferably about 10-30 mTorr, to damp plasma instabilities and sustain the beam voltages, while the magnetic field is within the approximate range of 100-500 Gauss. A very rapid frequency slewing or chirping is achieved with a relatively high magnetic field that reduces the discharge impedance to the lower end of the permissible range. Frequency-stabilized operation is achieved with a lower magnetic field that increases the discharge impedance so that the beam current changes very slowly with time.

Plasma wave tube and method

A plasma wave tube is described in which a pair of counterpropagating electron beams are injected into a waveguide housing in which a plasma is formed, prefeferably by an array of fine wire anodes. The electron beams couple with the plasma to produce electron plasma waves, which radiate electromagnetic energy for beam voltages and currents above established threshold levels. A rapid control over output frequency is achieved by controlling the plasma discharge current, while the output power can be controlled by controlling the voltage and/or current levels of the electron beams.

Plasma wave tube

A high-power microwave/mm-wave oscillator is filled with an ionizable gas at a pressure of about 1-20 mTorr, into which an electron beam is injected at a high current density of at least about 1 amp/cm.sup.2, but typically 50-100 A/cm.sup.2. A plasma is formed which inhibits space-charge blowup of the beam, thereby eliminating the prior requirement of a magnet system to control the beam. The system functions as a slow-wave tube to produce narrow-band microwaves for a gas pressure of about 1-5 mTorr, and as a plasma wave tube to produce broadband microwave/mm-wave radiation for a gas pressure of about 10-20 mTorr. A new high output, hollow-cathode-plasma electron gun is employed in which a metal oxide layer is formed on the inner surface to enhance the secondary electron yield; a cathode, grid, and extraction anode have respective sets of multiple apertures which are mutually aligned to yield a high perveance beam; the cathode, grid, and anode are curved to geometrically focus the beam, and a beam with a circular cross-section is generated.

Plasma-assisted high-power microwave generator

An improved Wire-Ion-Plasma Electron-gun (WIP E-gun) is disclosed, having a very rapid electron beam current interruption capability. An auxiliary grid is employed to provide a potential barrier to the reservoir of plasma ions in the ionization chamber, thereby containing these ions in the chamber after the wire anode is turned 'OFF'. The E-gun current fall time is reduced to the time required for the plasma potential to fall in the ionization chamber after the wire anode is turned 'OFF'. The WIP E-gun current fall time is reduced, from greater than fifteen microseconds for devices not employing the invention, to less than two microseconds.

Wire-ion-plasma electron gun employing auxiliary grid

A cold-cathode, plasma discharge modulator switch is disclosed. A crossed-field discharge plasma supplied charge carriers for the switch. A dc magnetic field is employed to provide a highly localized cusp magnetic field near the cathode, so that gas ionization occurs primarily in the cathode-source grid gap. The region between the cathode and anode is filled with a relatively low pressure gas. A highly transparent control grid with small apertures is closely spaced from the anode. The switch is closed through application of positive potential (relative to the plasma) to the control grid, and opened through application of negative potential relative to the plasma to the control grid. The application of negative potential to the control grid creates an ion sheath around the control grid which permits plasma cut-off to the anode region provided the sheath size is larger than the control grid aperture radius. Upon plasma cut-off, the switch current is interrupted as the remaining plasma in the control grid-anode gap decays. Low pressure operation insures that ionization cannot sustain the plasma in the narrow, isolated control grid-anode gap.

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Woodland Hills, CA, United States of America

Robert W Schumacher