US3636395A

US3636395A - Light source

Info

Publication number: US3636395A
Application number: US12655A
Authority: US
Inventors: Nathan M Banes Jr; James H Bottcher
Original assignee: Sperry Rand Corp
Current assignee: Sperry Corp
Priority date: 1970-02-19
Filing date: 1970-02-19
Publication date: 1972-01-18
Anticipated expiration: 1989-01-18

Abstract

A compact, short arc, high-pressure, xenon-filled light source provides high-intensity radiation with reliability and tolerance of severe environments. Specially shaped thoriated tungsten electrodes are fixed in opposed relation to nickel support blocks welded within a composite, uniform diameter, cylindrical envelope portion formed of a tube of alumina ceramic sealed to nickeliron-cobalt alloy sleeves.

Description

I United States Patent 1151 3,636,395 Banes, Jr. et al. 1 Jan. 18, 1972 [54] LIGHT SOURCE 3,136,915 6/1964 Jaatinen ..313 231 [72] Inventors: Nathan M. Banes, Jr.; James H. Bottcher, 3346351 10/1967 Llenhind "man/32 both ofoainesviue Fla. 3,378,713 4/1968 Ludw1g ..313/32 3,289,027 1111966 Jones ..3l3/231 [73] Assignee: Sperry Rand Corporation 3,480,829 11/1969 Van Omum ..315/1 1 1 22 F1 d: F h. 19 1970 l I e e Primary Examiner-Herman Karl Saalbach [21] App]. No.: 12,655 Assistant Examiner-C. Baraff Anome S. C. Yeaton [52] U.S.Cl ..3l3/8,3l3/l08,3l3/ll2,

3131184, 313/217, 313 249 [571 ABSTRACT [51] Int. Cl. ..H0lj6l/98 A com pact, short arc, high pressure, xenon-filled light source [58] held of Search 13/25 l provides high-intensity radiation with reliability and tolerance 313/221 8 of severe environments. Specially shaped thoriated tungsten electrodes are fixed in opposed relation to nickel support [56] References cued blocks welded within a composite, uniform diameter, cylindrin- STATES PATENTS cal envelope portion formed of a tube of alumina ceramic sealed to nickel-iron-cobalt alloy sleeves. 3,054,921 9/1962 Lye ..313/32 3,256,383 6/1966 Sasorov ..3 1 3/32 8 Claims, 1 Drawing Figure I90 90 18a H0 360 20a) 2/ INVENTORS NATHAN M Ell/V55 JR JAMES H. BOTTCHEI? BY ATTORNEY PATENTEU JAN 1 8 I972 LIGHT SOURCE BACKGROUND OF THE INVENTION 1. Field of the Invention The invention pertains to high-intensity sources of optical radiation in the ultraviolet, visible, or infrared regions and more particularly relates to such light sources in which electrical power is converted into high-intensity light in an electrical current discharge between closely spaced electrodes within an ionized gas maintained at high pressure.

2. Description of the Prior Art Short arc, high-pressure light sources have been available in the past in which an electrical discharge in an ionized noble gas is employed as a light source. Light sources of this type have conventionally been constructed using bulbous quartz envelopes in which electrode structures have been mounted by using expensive combinations of graded quartz-to-glass and glass-to-metal sealing techniques. Assembly of the light source requires highly skilled glass workers to form graded seals reliable enough to withstand the high internal gas pressure needed for efficient operation of the light source, a pressure on the order of 30 atmospheres. Problems with reliability and reproducible performance are often encountered. A high degree of human craftsmanship is needed to build such light sources, but even with highly skilled personnel, precise reproducibility is not achieved. Lack of reproducibility is especially observed in relatively high failure rates under severe environmental stress.

SUMMARY OF THE INVENTION The present invention is a compact, short arc, high-pressure, xenon-filled, high-intensity electrical discharge light source avoiding the disadvantages of prior art short are light sources. Use of brazed and welded components in the construction of the electrodes and of the pressure envelope for the light source makes it possible greatly to increase the internal operating gas pressure, resulting in an increase in efficiency of light generation, better arc stability, and high reproducibility in manufacture. A uniform diameter tubular envelope is formed of an alumina ceramic brazed at its ends to nickeliron-cobalt sleeves. The pressure envelope is completed by electrode-supporting nickel cylinders welded within the nickel-iron'cobalt sleeves and supporting shaped electrodes of thoriated tungsten. The shaped electrodes are additionally spring supported to afford immunity from the effects of shock or vibration. The electrode-supporting nickel cylinders and the enlarged portions of the electrodes serve to reduce the volume occupied by gas within the light source, to protect the seals between the alumina ceramic and the nickel-iron-cobalt sleeves from direct thermal radiation, and also to provide long heat paths for the protection of the seals and for the improved regulation of the operating temperature of the conical arc electrode tips.

BRIEF DESCRIPTION OF THE DRAWING The invention will be described in detail with reference to the sole FIGURE, which is a longitudinal cross-sectional view of the short are light source of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the sole FIGURE, there is illustrated a novel short are, high-pressure, high-intensity light source comprising a uniform diameter composite envelope unit 1, an anode assembly 2, and a cathode assembly 3, sealed together in order cooperatively to provide a complete high-pressure envelope.

Envelope unit 1 comprises a cylindrical tube of translucent or transparent alumina ceramic or other suitable material. The material of cylinder 10 may be any suitable alumina ceramic, including a material manufactured by the Coors Porcelain Company comprising a 99.9 percent alumina of polycrystalline structure. Transparent sapphire may be used.

The parallel ends 9 and 9a of cylinder 10 are provided in a conventional way with a metal surface readily bonded to the alumina by well-known means. The envelope unit 1 is completed by tubular cylinders 11 and 11a, which are respectively sealed at 9 and 9a by brazing with pure silver. The material of metal-to-ceramic seal forming cylinders 11, 11a, may be any of several available nickel-iron-cobalt alloys suitable for the purpose. As seen in the FIGURE, the inner and outer diameters of the tubular ceramic cylinder 10 and of the tubular nickel-iron-cobalt alloy cylinders 11, Ila sealed thereto atjunctions 9 and 9a respectively match each other.

The anode assembly 2 and the cathode assembly 3 of the novel light source are affixed within the composite envelope unit 1 in substantially mirror image relation about the plane A-A, which plane is located in the center of the arc discharge to be generated within the light source. For example, the anode assembly 2 and the cathode assembly 3 are provided with conically tipped electrode elements 12 and 12a substantially equally spaced on either side of the plane A-A.

Referring now to the anode assembly 2, the conically tipped electrode unit 12 is comprised of a cone 13 supported on a solid cylinder 14 whose diameter is small relative to the inner diameter of the composite envelope unit 1 and is also equal to the diameter of the base of cone l3. Anode element 12 is composed of a known 2 percent thoriated tungsten material and is centrally attached at the circular flat face 15 of a solid cylinder 16 having almost the same external diameter as the internal diameter of composite envelope unit 1. Support cylinder 16 extends from the face 15 past the junction 9 in envelope unit 1 to face 17. From face 17, a smaller cylinder or rod 18 projects axially.

The end 19 of the composite envelope unit 1 is closed by a shaped cylindrical block 20 made of nickel and having two primary functions; one function is to support the rod 18 and thus to support cylinder 16 and electrode 12 in fixed relation along the longitudinal axis of the light source structure. For example, cylinder 18 may be affixed within a bore 21 in the face 22 of block 20 by brazing with a conventional brazing alloy such as the 92 percent gold, 8 percent palladium alloy. The second significant function performed by cylindrical block 20 is to complete the pressure envelope at end 19 of the structure. For this purpose, a portion of cylindrical block 20 has a diameter substantially equal to the inner diameter of nickel-iron-cobalt alloy sleeve 11. The nickel block 20 is thus readily fastened within alloy sleeve 11 by using any suitable welding process to form an annular weldment 23 sealing the interface between block 20 and sleeve 11 at end 19.

Anode assembly 2 is further supported in fixed relation to the composite envelope unit 1 by a toroidal spring element 25 located in an annular groove 26 adjacent surface 15 of surface electrode 16, spring element 25 being comprised of a wire coil made of known tungsten-rhenium alloy. The coiled spring 25 is coiled within a groove 26 in support 16 to form a toroid. The inner portion of coiled spring 25 contacts the valley of groove 26, while the outer portion of spring 25 presses firmly against the inner wall 27 of the ceramic sleeve 10. The toroidal spring 25 is designed as to stiffness and other properties such as to aid in the support of the interior portion of anode assembly 2, and more especially to aid in mechanically stabilizing the anode assembly so that the conical electrode 12 may remain in fixed relation to its cooperating conical electrode 12a under conditions of shock and vibration.

Anode assembly 2 is supplied with an axial nickel rod 30 sealed by brazing at surface 31 using, for example, a 92 percent gold, 8 percent palladium brazing alloy, within an axial bore in cylindrical block 20. Rod 30 extends axially beyond the end 19 sufficiently to serve as an electrical terminal. For example, a nickel anode lead 33 may be fastened to the surface of rod 30, as by spot welding.

Referring now to the cathode assembly 3 opposite anode assembly 2, the conically tipped electrode unit 12a is composed of a cone 13a supported on a solid cylinder 14a whose diameter is small relative to the inner diameter of the composite envelope unit 1 and is also equal to the diameter of the base cone 13a. Cathode element 120 is composed of 2 percent thoriated tungsten and is axially or centrally attached at the circular face 15a of a solid support cylinder 16a having almost the same external diameter as the internal diameter of composite envelope unit 1. Cylinder 16a extends from the face 15a past junction or seal 9a of envelope unit 1 to the face 170.

From face 17a, a smaller cylinder 18a projects centrally. The end 19a of the composite envelope unit 1 is closed by a shaped cylindrical block 20a of nickel and having two primary functions: one function is to support rod 18a and thus to support cylinder 16a and electrode 12a in fixed relation along the longitudinal axis of the structure. For example, cylinder 18a may be affixed within a bore in the face 22a of block 20a by brazing with a conventional brazing alloy such as a 92 percent gold, 8 percent palladium alloy. The second significant function performed by block 20a is to complete the pressure envelope at end 19a of the light source. For this purpose, a portion of the cylindrical block 20a has a diameter substantially equal to the inner diameter of nickel-iron-cobalt alloy sleeve 11a. Block 11a is thus readily fastened with alloy sleeve 2011 by using any suitable welding process to form an annular weldment 23a sealing the interface between block 20a and sleeve 11a at end 19a.

Cathode assembly 3 is further supported in fixed relation to the composite envelope unit 1 by a spring element 251: located in an annular groove 26a adjacent surface 15a of electrode support 16a, spring element 25a being comprised. of a wire coil made of a known tungsten-rhenium alloy. As seen by comparing the cross-sectional view of support 16a and spring 25a with the analogous parts of support 16, the coiled spring 25a is coiled within a groove 26:: to form a toroid; the inner portion of coiled spring 25a contacts the valley of groove 26a, while the outer portion of spring 25a presses firmly against the inner wall 27 of the ceramic sleeve 10. The spring 25a is designed as to stiffness and other properties such as to aid in the support of the interior portion of cathode assembly 3, and more especially further to aid in mechanically stabilizing the cathode assembly 3 so that the conical electrode 12a may remain in fixed relation to its counterpart electrode 12 under conditions of shock and vibration.

The shapes and dimensions of the cooperating electrodes 12 and 1211 are dictated by several considerations. The temperature of the tips of electrode cones 13, 13a must be as high as possible without melting the thoriated tungsten material of which they are composed. This selection results in a relatively higher temperature for the gas plasma in the volume of the arc and therefore, an increase in light output. Furthermore, it is desirable to step the

support cylinder

16 and 16a diameters to a large diameter to protect seals 9, 9a from direct radiation, to provide a substantial heat sink path, and also to reduce the total gas volume within the structure. With reduced gas volume, the arc temperature builds up rapidly and the smaller gas volume produces a desirable higher gas pressure. Also, as a consequence of the reduced volume, convection currents which would otherwise be relatively free to build up and to cool the arc plasma are minimized.

The cathode assembly 3 departs from being a mirror image form of anode assembly 2 in thatcathode assembly 3 provides means for an external electrical connection, as does assembly 2, but cathode assembly 3 particularly provides means for filling the light source interior with an appropriate noble gas. Such means concerns modifications in the cylindrical block 20a whereby passageways are provided for flow of gas relative to the interior of the light source.

The clearance space coupled past face 22a of cylindrical block 20a is dually coupled to a radial bore 36, 36a extending diametrically across block 20a. An axial bore 37 extends at least from bore 36, 36a to the exterior of cylindrical block 2011. A portion of axial bore 37 is further enlarged to support a copper tube 38 sealed therewithin. Copper tube 38 is brazed to the nickel cylindrical block 20a by the gold-palladium alloy used in other brazed joints of the structure. When the interior of the light source is filled with a suitable gas, the end 39 of tube 38 is pinched off in a manner commonly used in the vacuum tube art, thus completing the envelope of the structure. A nickel cathode lead 33a may be conveniently affixed to the surface of tube 38. q

The light source is constructed in a manner affording predictable performance, good reliability, and tolerance of severe environments through the use of construction techniques employing simultaneous forming of brazed joints. Parts of the structure involving fabrication of metal-to-ceramic seals 9 and 9a which must be assembled under conditions not compatible with the brazing operations are formed separately by noncritical processes. Seals 9 and 9a are readily formed, for example, by reliable automatic machines. The units of the structure are designed for final welding at points remote from the metal-toceramic seals 9, 9a. Graded glass or quartz seals are entirely avoided.

For example, the anode parts including the thoriated tungsten electrode 12, electrode support 16, and rod 18, the cylindrical end block 20, and the anode terminal rod 30 are finished and then brazed together to form a composite structure using the aforementioned gold-palladium alloy in a furnace operated for about one-half an hour at substantially l,240 C. The corresponding parts of cathode assembly '3 are similarly made unitary. The composite envelope unit 1 is formed using established seal fabrication techniques by brazing ends of the nickel-iron-cobalt cylinders 11, lla with pure silver at the ends 9, 9a of ceramic cylinder 10 at 960 C. using a conventional procedure.

Now, the respective cathode; and anode assemblies 2 and 3 are slid within envelope assembly after springs 25, 2511 are put in place, and a helium arc weld is made at locations 23 and 23a substantially to complete the structure. The helium arc welding method permits rapid operation with only local heat paths in nickel-ironcobalt tubes 11, 1 la. The structure is sub jected to baking for about 2 hours at 400 to 500 C. to remove all contaminants within its interior. The consequent maintenance of the purity of the gas to be put in the lamp interior has been demonstrated to add to the intensity of the light output.

After returning to room temperature, the light source is evacuated and is then coupled via copper tube 38 to a highpressure container of pure xenon gas, the container being equipped with a calibrated pressure gage, and the lamp is filled with xenon to a pressure level. of substantially 27 atmospheres. Copper tube 38 is then pinched off and the light source is ready to be operated. The brazed construction of the light source makes it possible to increase the internal gas pressure from the prior art level of l7 atmospheres, permitting a corresponding increase in output light level and better arc stability. The increased cold" gas pressure from the prior 17 atmospheres to substantially 27 atmospheres permits a great increase in the hot" or operating pressure within the lamp, and is largely responsible for the increase of about 15 percent in light output in the inventive lamp, for example, from the prior art 2.6 watts per steradian to 3.0 watts per steradian.

In operation, the arc discharge in the light source may be started in conventional fashion, for example, by the initial application to leads 33, 33a of a relatively high-voltage starting pulse on the order of 15,000 volts. Once the xenon gas is ionized, the arc discharge is readily maintained by a much lower voltage of the order of 30 volts, for example. Other applicable means of starting short arc lamps are known to the art.

The novel source provides a light output 10 to 20 percent greater than prior art lamps such as those which, for example, have customarily used graded-seal quartz envelopes. Higher light intensities result from the use of the improved pressure envelope, improved electrode construction, a relatively small volume of gas, and high-temperature bake-out permitting maximum internal cleanliness and thus also ensuring reproducibility and long life.

In addition to achieving a major performance improvement over previous light source designs, the invention presents a design much more suited to mass production, in that many manual steps in manufacture are eliminated. For example, the manufacture of graded seals required in the prior art quartz lamp is avoided and the lamp interior is easily filled with an accurately known amount of xenon gas, whereas the prior art quartz lamp must be filled by introducing into the cooled lamp a quantity of zenon cooled to liquid form because the quartz envelope cannot be tipped off at high pressure.

The uniform diameter of the light source envelope facilitates packaging in shipment and within equipment in which the light source is employed. Of major significance is the configuration of the nickel cylinders and the shaped electrodes such that gas volume is reduced, the alumina-to-metal seals are protected by long heat conduction paths and from direct thermal radiation, and the temperatures of the electrode cones are appropriately regulated.

While the invention has been described in its preferred embodiment, it is to be understood that the words that have been used are words of description rather than limitation and that changes within the purview of the appended claims may be made without departing from the true scope and spirit of the invention in its broader aspects.

We claim:

1. A gas-filled electrical light source comprising:

a substantially uniform diameter tube of ceramic material transparent to light generated by said light source and having first and second ends,

first and second substantially circular metal tubes respectively permanently bonded in hermetically sealed abutting relation to said ceramic tube at said respective first and second ends of said ceramic tube,

first and second electrode support means permanently bonded within said respective first and second metal tubes at ends thereof remote from said first and second ends of said ceramic tube for completing an envelope adapted to contain gas under pressure,

first and second electrode means fixedly supported within said gas envelope by said respective electrode support means and mutually aligned in cooperative light-generating relation for radiation of light through a central portion of said ceramic tube,

said electrode support means having circumferential grooves adjacent said electrodes, and

spring means mounted within said grooves contacting said ceramic tube for resiliently supporting said electrodes within said ceramic tube.

2. Apparatus as described in claim I wherein:

said first and second electrode support means each comprise at, least first and second successive collinear portions of respective small and large diameters for regulation of heat flow along said electrode support means from said electrode means, and

said first and second electrode means are supported directly from said respective large diameter portions.

3. Apparatus as described in claim 2 wherein:

said electrode means are substantially smaller in diameter than said large diameter portions of said electrode support means.

4. Apparatus as described in claim 3 wherein said portions of larger diameter of said electrode support means and said electrode means are so constructed and arranged within said gas envelope that said permanently sealed first and second ends of said ceramic tube are shielded from direct radiation of light generated by said electrode means.

5. Apparatus as described in claim 3 wherein each said electrode means is provided with a conical end comprising thoriated tungsten.

6. Apparatus as described in claim 5 wherein:

said gas envelope contains a noble gas, and

said electrode support means and said electrode means occugy a majority portion of the interior of said electrical lrg source, a mrnonty portion of said rntenor being occupied by said noble gas for providing high operating gas pressure.

7. Apparatus as described in claim 5 wherein:

said ceramic material is comprised of polycrystalline alumina, and

said metal tubes are comprised of an iron-nickel-cobalt alloy adapted to permanent hermetic scaling to polycrystalline alumina.

8. Apparatus as described in claim 7 wherein:

said electrode support means are comprised of nickel, and

said spring means are comprised of a tungsten-rhenium alloy.

Claims

2. Apparatus as described in claim 1 wherein: said first and second electrode support means each comprise at least first and second successive collinear portions of respective small and large diameters for regulation of heat flow along said electrode support means from said electrode means, and said first and second electrode means are supported directly from said respective large diameter portions.
3. Apparatus as described in claim 2 wherein: said electrode means are substantially smaller in diameter than said large diameter portions of said electrode support means.
4. Apparatus as described in claim 3 wherein said portions of larger diameter of said electrode support means and said electrode means are so constructed and arranged within said gas envelope that said permanently sealed first and second ends of said ceramic tube are shielded from direct radiation of light generated by said electrode means.
5. Apparatus as described in claim 3 wherein each said electrode means is provided with a conical end comprising thoriated tungsten.
6. Apparatus as described in claim 5 wherein: said gas envelope contains a noble gas, and said electrode support means and said electrode means occupy a majority portion of the interior of said electrical light source, a minority portion of said interior being occupied by said noble gas for providing high operating gas pressure.
7. Apparatus as described in claim 5 wherein: said ceramic material is comprised of polycrystalline alumina, and said metal tubes are comprised of an iron-nickel-cobalt alloy adapted to permanent hermetic sealing to polycrystalline alumina.
8. Apparatus as described in claim 7 wherein: said electrode support means are comprised of nickel, and said spring means are comprised of a tungsten-rhenium alloy.