High-power Microwave Excited Plasma Discharge Lamp

Abstract

A high-power microwave plasma discharge lamp is disclosed. The lamp includes a ceramic tube filled with gas and closed at one end by a window transparent to the optical radiation output of the lamp. The ceramic tube extends through a cavity resonator excited with microwave energy for exciting a plasma discharge within the lamp.

Description

DESCRIPTION OF THE PRIOR ART

Heretofore, microwave plasma discharge lamps have been employed as sources of ultraviolet light. These lamps have employed quartz envelopes and quartz windows and their power input has been limited to approximately 100 watts. It is desired to substantially increase the power output of such lamps.

SUMMARY OF THE PRESENT INVENTION

The principal object of the present invention is the provision of an improved high-power microwave plasma discharge lamp.

One feature of the present invention is the provision of a ceramic tubular lamp envelope having the output window sealed across one end of the tubular envelope, whereby the power handling capability of the lamp structure is substantially increased.

Another feature of the present invention is the same as the preceding wherein the envelope is disposed within a cavity and the cavity resonator is provided with fluid coolant passageways for directing a stream of fluid coolant onto the envelope of the lamp for cooling same in use.

Another feature of the present invention is the same as any one or more of the preceding features wherein the lamp envelope structure passes through aligned bores in the opposite walls of the cavity resonator, the inside walls of such bores being in good heat exchanging relation relative to the envelope of the lamp via the intermediary of a pair of compressible metallic sleeves to facilitate removal of heat from the lamp in use.

Another feature of the present invention is the same as any one or more of the preceding wherein the output window is connected to the remaining portion of the envelope of the lamp via the intermediary of a metallic demountable gastight flange assembly to facilitate replacement of window members.

Another feature of the present invention is the same as any one or more of the preceding features wherein the output window has enlarged transverse dimensions relative to the transverse dimensions of the central ceramic tubular portion and wherein a reflector is provided internally of the envelope for reflecting optical radiation through the window.

Another feature and advantage of the present invention will become apparent upon a perusal of the following specification taken in connection with the accompanying drawings wherein:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view, partly broken away of a microwave plasma lamp incorporating features of the present invention,

FIG. 2 is a longitudinal sectional view of a lamp envelope incorporating features of the present invention, and

FIG. 3 is an enlarged view of an alternative embodiment of a portion of the structure of FIG. 2 delineated by line 3--3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1, there is shown microwave plasma lamp 1 incorporating features of the present invention. The lamp 1 includes a rectangular microwave cavity resonator 2 having a pair of mutually opposed broad walls 3 and 4 closed about their periphery by narrow sidewalls 5, 6, 7 and 8. The cavity 2 is conveniently formed by bolting together two flanged sections of rectangular waveguide 9 and 11.

A pair of axially aligned bores 12 and 13 pass through the mated flanges 14 and 15, such bores being centrally disposed of the broad walls 3 and 4 of the cavity 2 and directed generally at right angles to the plane of the broad walls 3 and 4. An elongated tubular envelope portion 16 of the lamp 1 extends through the cavity 2 and axially through the aligned bores 12 and 13. The envelope portion 16 of the lamp is more fully described below with regard to FIGS. 2 and 3. A pair of axially adjustable metallic sleeves 17 and 18 are disposed in the bores 12 and 13 intermediate the tubular envelope 16 and the inside wall of the bores 12 and 13. The sleeves are axially adjusted to define an optimum gap length 1 between their inner mutually opposed ends. The sleeves are preferably split into two semicylindrical portions which are pressed into intimate physical contact between the inside wall of bores 12 and 13 and against the outer surface of the tubular envelope to provide a good thermally conductive path between the envelope 16 and the flanges 14 and 15, such flanges being cooled by coolant ducts 19 and 21 passing therethrough.

A second pair of axially aligned bores 22 and 23 pass through the narrow sidewalls 5 and 6 and through the flanges 14 and 15 to provide a fluid coolant passageway for directing a stream of coolant, such as air, onto the tubular envelope portion 16 disposed within the cavity 2 for cooling the lamp envelope in use.

The opposite ends of the rectangular waveguide sections are closed off by narrow end walls 7 and 8. End wall 7 is centrally apertured to accommodate a section of coaxial transmission line 24 having a coupling loop 25 extending into the cavity 2 from the center conductor 26 of the coaxial line 24 for exciting the cavity 2 with microwave energy at a convenient frequency such as 2,450 MHz derived from a microwave source 27, such as a 2.5 kw. C.W. magnetron.

The other narrow end wall 8 is defined by the inner end of an axially slidable nonelectrically contacting double-choke shorting plunger 28 which is axially translatable via a worm shaft 29 and crank 31 for tuning the resonant frequency of the cavity 2 to impedance match the cavity 2 to the microwave source 27.

The microwave energy within the cavity 2 excites a plasma discharge within the envelope 16. Optical radiation emanating from the plasma discharge is passed through a window 32 to a utilization device, not shown. The window 32, as of sapphire or calcium fluoride is sealed over one end of the tubular envelope 16 via a metallic frame structure 33 which includes a demountable gastight flange assembly 34, such as a conventional Conflat flange assembly marketed by Varian Associates of Palo Alto, Calif. In an alternative embodiment, not shown, the window 32 is merely glazed over the end of the ceramic tubular envelope 16 without providing any metallic parts to the envelope 16.

Referring now to FIG. 2, the gastight envelope 16 of the lamp 1 is shown in greater detail. The envelope 16 includes a tubular ceramic central portion 35, as of alumina or beryllia, 0.5 inch diameter, 4 inches long, and having a wall thickness of 0.125 inch. Window frame structure 33 is sealed over one end of the central section 35 via a metallized ceramic-to-metal seal 36. The other end of the central ceramic section 35 is similarly sealed off by a metal cap 37 having a length of tubulation 38 sealed thereto for exhausting and filling the envelope 16 with suitable gas fills. Suitable gas fills includes 20 percent nitrogen, 80 percent argon by volume, at 1.5 mm. Hg at room temperature, introduced after bakeout and evacuation at 500.degree. C. to produce a relatively narrow band of optical radiation in the ultraviolet band of 1,700 A to 1,900 A wavelength. Other suitable gases include krypton, xenon, helium, hydrogen.

Sapphire is a suitable window 33 for optical radiation having a wavelength of 1,600 A and longer, whereas calcium fluoride is suitable as a window material for optical wavelengths falling within the range of 1,600 A to 1,200 A.

Referring now to FIG. 3, there is shown an alternative embodiment of the present invention. In this embodiment, the envelope 16 is essentially the same as that of FIG. 2 except that the output end of the envelope 16 is formed by an outwardly flared metallic window frame structure 41 which is sealed in a gastight manner, as before, over the output end of the central ceramic section 16. The outwardly flared portion 41 is shaped like the reflector of a flashlight and coated on its interior with a reflective coating 42 to reflect optical radiation emanating on the axis of the envelope 16 out through an enlarged window 33' which is sealed in a gastight manner over the open end of the flared reflector 41. The plasma discharge extends axially out of the cavity resonator 2. Optical radiation emanating from this end portion which would otherwise be lost is reflected by reflector 42 out through window 33'.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Claims

I claim:

1. In a high-power microwave excited plasma discharge lamp, means forming a cavity resonator structure having a pair of aligned bores in opposite sides of said cavity structure, means forming an elongated gastight tubular plasma discharge lamp envelope structure extending through said cavity resonator and into said aligned bores, said lamp envelope being filled with a gas capable of emitting optical radiation within a certain range of desired wavelengths upon excitation by microwave energy, means for exciting said cavity resonator with microwave energy to produce a microwave plasma discharge within the gas filled lamp, means forming a gastight window structure sealed over one end of said tubular lamp envelope for passing output optical radiation at the desired wavelength therethrough, and said tubular lamp envelope including a central portion made of ceramic, and a pair of coolant apertures in opposite sidewalls of said cavity, and means for directing a stream of coolant onto said tubular lamp envelope for cooling same in use.

2. The apparatus of claim 1 including means forming a metallic window frame structure for sealing said window over the end of said tubular ceramic lamp envelope.

3. The apparatus of claim 2 wherein said ceramic lamp envelope is made of a material selected from the class of alumina and beryllia.

4. The apparatus of claim 2 wherein said cavity resonator is rectangular having a pair of opposed broad walls closed about their periphery by narrow sidewalls, and wherein said pair of aligned apertures for receiving said lamp envelope are centrally disposed in said pair of broad walls.

5. The apparatus of claim 1 including a pair of fluid coolant passageways disposed in a pair of opposed ones of said narrow sidewalls of said cavity for directing a stream of fluid coolant upon said tubular lamp envelope and through said cavity resonator for cooling said lamp in use.

6. The apparatus of claim 4 wherein one of said narrow sidewalls is movable in a direction generally parallel to the plane of said broad walls for tuning said rectangular cavity resonator.

7. The apparatus of claim 5 wherein said means for exciting said cavity resonator with microwave energy includes a coaxial line communicating with said cavity via an aperture in said narrow sidewall thereof which is opposed to said movable sidewall, and a coupling loop extending from the center conductor of said coaxial line into said cavity resonator.

8. The apparatus of claim 2 wherein said metallic window frame structure includes a demountable gastight flange assembly having a pair of demountable mating flange portions, one of said flange portions being attached to said window, and the other one of said flange portions being attached to said tubular ceramic lamp envelope.

9. The apparatus of claim 2 wherein said window frame structure is disposed externally of said cavity resonator, said window frame structure having enlarged transverse cross-sectional dimensions relative to the transverse cross-sectional dimensions of said tubular lamp envelope portion which is disposed within said cavity resonator, said enlarged window frame structure having an internal surface reflective to the output optical radiation for reflecting same outwardly of the lamp through said window.