US3736453A - Arc control in compact arc lamps - Google Patents

Abstract

Arc stabilization resulting in greater steadiness, and increased power input resulting in increased and brighter light output in compact arc lamps are made possible by the use of magnetic fields or of equivalent mechanical motion to control the location of the attachment point of the arc to the anode. In one embodiment, magnets disposed within the anode and particularly, within a novel toroidal shaped anode are utilized to rotate the arc foot around a larger area of the tip. In another embodiment, magnets external to the lamp are utilized to the same effect. In yet another embodiment, mechanical movement of the anode causes the same effects. This allows increased power handling capability by tungsten-tipped anodes. For thin copper anodes, an improved cooling circuit allows the area of high efficiency heat exchange to coincide with the larger area of the anode subjected to arc attachment. Additionally, an axial gas circulating arrangement for the cathode can be pumped toward the flue of the toroidal anode to contribute to the cooling of both electrodes and the axial laminar jet of cooling gas around the arc stream is used to stabilize the arc, to increase the power input and the brightness of the lamp, and to increase the light output of the lamp.

Description

United States Patent 1191 Miller et al. 1 May 29, 1973 [54] ARC CONTROL IN COMPACT ARC Primary Examiner-Nathan Kaufman LAMPS Attorney-Lindenberg, Freilich & Wasserman [75] Inventors: Charles G. Miller, Los Angeles;

Ralph E. Bartera, La Canada, both [57] 1 ABSTRACT of Calif. Arc stabilization resulting in greater steadiness, and increased ower in ut resultin in increased and [73] Asslgnee Camomm 5 of Technology brighter ligiit output in compact arc lamps are made Pasadena Cahf' possible by the use of magnetic fields or of equivalent [22] Filed: Jan. 22,1971 mechanical motion to control the location of the attachment oint of the arc to the anode. In one em- [211 Appl' bodimentfinagnets disposed within the anode and particularly, within a novel toroidal shaped anode are [52] U.S. Cl. ..313/146, 313/60, 313/182 u ilized to rotate he are foot aro n a l rg r area of [51] Int. Cl ..H0lj 1/02 the tip. In another embodiment, magnets external to [58] Field of Search ..313/182, 153, 155, th amp ar utilized to the a f t- I y another 313/161, 12, 30, 24, 35, 36, 39, 184, 146, embodiment, mechanical movement of the anode 11, 326, 149, 152, 40, 332, 60 causes the same effects. This allows increased power handling capability by tungsten-tipped anodes. For [56] References Cit d thin copper anodes, an improved cooling circuit allows the area of high efficiency heat exchange to coin- UNITED STATES PATENTS cide with the larger area of the anode subjected to arc 3,229,145 l/1966 Jensen ..313/146 attachment Additimlanyr axial? circulating 3 1 769 3l 9 7 Schmidtlein 313 35 X rangement for the cathode can be pumped toward the 3,366,814 1/1968 Sileo ..313/35 x flue 0f the toroidal anode to contribute to the cooling 3,384,772 5/1968 Rabinowitz ..313 153 x f th electrodes and the axial laminar jet of cooling 3,412,275 11/1968 Thorret ..3l3/30 X gas around the arc stream is used to stabilize the arc, 3,452,236 6/1969 Beese X to increase the power input and the brightness of the 3,488,546 1/1970 Paquette ..313/146 l d to increase the light output of the lamp. 3,529,209 9/1970 Lienhard et a1. ..3l3/l46 X OUTLET Patented May 29, 1973 3,736,453

4 Sheets-Shoot 1 1 53 4a COOLANT J- comm ourusr X flaw 20 26 24 56 Q17 FIG. 2

INVENTORS F| G I CHARLES G. MlLLER RALPH E. BARTERA BY W MI ATTORNEYS Patented May 29, 1973 4 Sheets-Sheet 2 Fl G. 6

FIG. 8

I'MEnToRs CHARLES s. MILLER HIYQALPH BARTERA Wm, $441 F I G. T

ATTORNEYS Patented May 29, 1973 4 Sheets-Sheet 5 FIG. l4

' .mvwons CHARLES G'.'Ml'l,-LER RALPH E. BARTERA BY:

Patented May 29, 1973 3,736,453

4 Sheets-Shut 4 INVENTORS CHARLES G. MILLER RALPH E. BARTERA FIG. l3 BY ATTORNEYS ARC CONTROL IN COMPACT ARC LAMPS ORIGIN OF THE INVENTION The invention described herein was made in the performance of work under a NASA contract and is subject to the provisions of Section 305 of the National Aeronautics and Space Act of 1958, Public Lay 85-568 (72 Stat. 435; 42 USC 2457).

BACKGROUND OF THE INVENTION 1. Field of the Invention:

The present invention relates to arc lamps and more particularly, to improvements in compact-arc lamps.

2. Description of the Prior Art:

Light sources with a continuum luminous output, and with a spectral distribution and brightness approaching or surpassing that of the sun are needed. One of the best present sources of such light is a direct current electric arc in pressurized Xenon gas. However, the brightness, power handling capacity and useful lifetime of these lamps are not enough for many present needs. Present lamps operate with an electrical cathode and anode spaced in line across a s mall gap. These small separations raise the maximum brightness of the very useful light-emitting volume just off the cathode tip and increase the utilizable light efficiency of the lamp. An extreme heat load is applied to the anode due to the electron an ion bombardment along the arc stream direction impinging upon the anode tip, and due to the flow of hot gas, flowing along the axial line joining the anode and cathode.

Such lamps operate with a fireball about 30 mils in diameter, disposed just above the apex of the cathode. The lamp is usually mounted in a collecting reflector and focussed with respect to the location of the fireball. After many hours of operation, the fireball erodes the cathode tip. Since the fireball locates itself adjacent to, and just off the actual cathode tip after erosion of the tip, the fireball location moves from the previously selected focus point of the collecting reflector, and defocussing results.

The are contacts the a node in a small hot spot which, while substantially larger than the fireball, imposes a considerable heat load on a relatively small area. Anodes in present lamps fail under the sustained and severe concentrated heat load impinging always on the same spot. In the case of a copper anode, failure is generally due to creep of the metal; in the case of a tungsten-tipped anode, it is generally due to recrystallization of the tungsten metal plug.

In Ser. No. 888,362, filed Dec. 23 1969, a lamp having a substantially increased power handling ability is disclosed. In that lamp, the limitation set by the powerhandling capacity of a single anode is circumvented by arranging a plurality of anodes axially around a common cathode. By sequentially firing the anodes with increased power and shortened duty cycle, each anode could handle its normal design maximum as a long time average load. Thus, the energy inputs and power capability of the multi-anode lamp is given by the normal ratings multiplied by the number of anodes, resulting in a substantial increase in power rating of the lamp. Multi-anode lamps require careful alignment of the elements and elaborate cooling circuits which add considerably to the cost of manufacturing each lamp.

SUMMARY OF THE INVENTION The present invention relates to several methods designed to stabilize the operation of arc lamps, and to increase the power handling capacity and light output of these lamps. It allows a single-anode lamp to function as efficiently, in terms of power-handling capacity, as the complete multi-anode lamp just described. In one aspect of the invention, magnetic field means are used to control the location of the arc attachment points on the electrodes. Furthermore, the magnetic field may be used to move the attachment points of the arc on the anode in a predetermined manner that will greatly improve the usefulness and output of a lamp. In order to take full advantage of this capability, yet another aspect of the invention relates to an improved internal cooling circuit designed to provide increased cooling efficiency to a larger and selected area of the anode tip. In a further embodiment of the invention, magnetic control means preferably disposed within the cooling circuit apparatus, are utilized to rotate the arc attachment points around the larger cooled area of the anode tip.

These and many other attendant advantages of the invention will become apparent as the invention becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view, partly in section, of an arc lamp, according to the invention including one type of magnetic means for moving the arc attachment points, in which the magnetic means is internal to the lamp;

FIG. 2 is a view of the anode tip illustrating the rotation of the arc attachment point;

FIG. 3 is a partial sectional view of a further anode construction illustrating reciprocating motion of the arc attachment point;

FIG. 4 is a sectional view taken along the line 4-4 of FIG 3;

FIG. 5 is a view of a magnetic means external to the lamp for moving or rotating the arc attachment point;

FIG. 6 is a partial view of an arc lamp partly in section illustrating a first embodiment mechanical movement of the anode;

FIG. 7 is a partial view of an arc lamp partly in section illustrating a second embodiment of mechanical movement of the anode;

FIG. 8 is a partial view of an arc lamp partly in section illustrating mechanical rotation of a magnet within the anode to control are attachment;

FIG. 9 is a sectional view of an arc lamp anode according to the invention, incorporating a novel cooling design;

FIG. 10 is a sectional view of an alternate structure for the cooling circuit design of the anode, which incorporates a support means for the anode tip;

FIG. 11 is a sectional view taken along the line 11-11 of FIG. 10, looking toward the cathode;

FIG. 12 is a perspective view of an electromagnet, a set of which is to be incorporated in the cooling head insert of the anode of FIGS. 9 and 10;

FIG. 13 is a sectional view of a novel toroidal anode and gas cooled cathode in accordance with the invention; and

FIG. 14 is a sectional view of a convective gas recirculation system incorporating the toroidal anode of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, a first embodiment of a high intensity arc lamp, according to the invention generally includes an envelope 10, a cathode 12 axially spaced a discharge gap 13 away from the tip 52 of an anode 14. The envelope is formed of a transparent material, suitably quartz, and contains a discharge gas 11 under pressure.

In one suitable type of lamp construction, flange 18 is attached to the envelope adjacent each open end thereof. Lamp ends 22 and 24 having a plurality of apertures adjacent the outer periphery are attached to the lamp envelope 10 by means of a plurality of bolts 26 extending through the apertures and through correspondingly located holes in flange 18 and are secured by means of nuts 28. A circular groove which receives an end O-ring 20 is formed on the inner surface of each end 22, 24 and the grooves receives each end surface of the envelope. When the bolt 26 and nuts 28 are secured, the O-rings 20 form a gas-tight seal between the ends 22, 24 and the envelope 10.

In another suitable type of lamp construction, the 0- rings 20 may be dispensed with, and metal-glass seals used to join end caps to the glass envelope serving the same function as 22 and 24.

Obviously, only the window portion of the lamp need be transparent, while the other portions of the envelope may be constructed of higher structural strength material, such as metal or ceramic. The lamp housing may contain an integral, internal, prealigned reflector, and a transparent window portion disposed transverse to the axis of the electrodes. The cathode may be supported within a narrowed neck portion while the anode may be supported by means of straps attached to the side wall of the envelope. A suitable construction for such a lamp is disclosed in my copending application, Ser. No. 841,278, filed July 14, 1969, and the improvements cited in the present application are suitable for incorporation into a sealed-beam configuration lamp.

In the particular type of lamp shown in FIG. 1, gas inlet tube 30 penetrates through lamp end 22 into the interior 32 of the envelope 10. A cathode support 34 is attached to the lamp end 20. The cathode 12 is in the form of a cylinder, suitably manufactured from a high temperature metal, such as tungsten, and terminates in a conical tip 36. A hollow cap 37 is attached to the exterior of lamp end 22 and receives a flow of coolant through the coolant inlet tube 39, and discharges the coolant via coolant outlet tube 40. If greater heat removal capacity is required or desired, the cathode 12 may be hollow and water circulated through the support '34 and cathode 12. Electrical connection to the anode 14 and cathode 12 are provided by electrical leads, 56, 58 connected to the respective lamp ends 22, 24 and to a DC. source, not shown.

The cathode 12 is spaced a discharge gap 13 from the tip 52 of the anode 14. The anode may be provided with an internal coolant passageway 38 by disposing an insert 44 within the hollow anode 14 to form an annular coolant passageway 38 which communicates with coolant inlet 48 and coolant outlet 53.

Sufficient operating gas which may be any of the gases chosen from the class comprising neon, argon, krypton, xenon or their mixtures is introduced into the evacuated and moisture-free interior of the envelope 10 through the gas inlet tube 30, which is then closed. Typical internal pressures are about 30-60 psig when non-operating, at ambient temperature, which increases to about -180 psig when in operation.

During operation, water or other coolant fluid is circulated through both hollow electrodes. Typically, the cathodes and anodes are about three-fourths inch in diameter, and are separated by a discharge gap of about one-half inch. On application of an electrical power input, to the anode and cathode, a negative ion or electron stream and a positive ion arc stream are established between the anode 14 and cathode l2 and the arc contacts the anode at a localized area of the anode tip 52.

In the embodiment illustrated in FIG. 1, the point of attachment of the arc to anode tip 52 is delocalized and the heat loading spread over a larger area of the tip. A plurality of electromagnets 60 are embedded within insert 44, as illustrated, The electromagnets comprise a bar 59 of soft magnetizable material surrounded by a coil 61.

The electromagnets 60 are positioned to apply an outwardly directed radial magnetic field, transverse to the axial line joining the anode 14 and cathode 12. When the three electromagnets 60, disposed in a symmetrical pattern, are connected by lead lines 62 to a three-phase power supply 70, a rotating transverse magnetic field is developed. The rotating transverse magnetic field will rotate the arc attachment point in a circular pattern 54 as indicated in FIG. 2.

Experience indicates that magnetic fields of -130 gauss are sufficient to cause the desired movement of the arc. Larger fields are believed to be undesirable and may cause unwanted effect on the cathodes spot or fireball. The speed of rotation of the magnetic field should be so chosen that it is matched to the diffusivity of heat in the tip 52 of the anode. If the rotational speed of the anode attachments spot is too slow, a quasistationary heat flow will be experienced by the metal at the anode attachment point and the instantaneous heat transfer rate may exceed the capacity of the coolant system. A diffusion time of about 10 milliseconds is believed sufficient to dissipate the heat and this will permit rotational speeds of at least about 50 revolutions per second.

FIGS. 3 and 4 illustrate the coolant passageway in one of the most advanced and most satisfactory of present day anode constructions. The coolant passageway 50 is formed between the walls 49 of the anode 14 and an ovoid cross-section insert 45. The insert 45 is attached to the walls of the anode 14 by brazing along the lines a-a and b-b where the ovoid insert contacts the circular cross-section of the anode interior. The bottom end of the insert 45 terminates in a rounded arcuately shaped member 47 forming the coolant flow passageway 50. Coolant enters from behind the insert 45 and can only leave via the passageway in front of the insert as shown in FIG. 3. The passageway 50 which is the maximum flow constriction extends unidirectionally at right angles to the flow direction from inlet to outlet under the tip 51 of the anode insert. The greatest velocity occurs at the point 55 which is just above an imaginary equatorial line on the anode tip. This equatorial line is the one whose extension runs on the outside of the anode, directly opposite the brazing lines a-a and b-b. The greatest heat transfer capability of the coolant is concentrated in this region.

In the embodiment of this invention illustrated in FIGS. 3 and 4, a moving transverse magnetic field is applied to the region of the tip 52 of the anode 14 such that the point of attachment of the arc is moved, and oscillates back and forth along the imaginary equatorial line described. To accomplish this effect, one or a number of the electromagnets 60 are located at or partially imbedded within the sides of insert 45 as shown in FIG. 4. The electromagnets 60. comprise bars 59 of the soft, magnetizable iron surrounded by coils 61. The lead wires 62 extend along the insert 45 and through the lamp end 24, and are connected to an AC power source, not shown. On energizing the AC source, a varying magnetic field is created which will cause the anode attachment points to oscillate along the anode tip 52 in the desirable fashion along the aforementioned equatorial line.

An alternate arrangement for producing oscillatory movements of the anode arc attachment points illustrated in FIG. 5 comprises a plurality of external electromagnets 60 placed adjacent to or in the vicinity of the surface of the envelope 10. The electromagnets includes a bar 59 of soft magnetizable iron surrounded by coils 62. The lead wires 62 are connected to an AC source, not shown.

The external electromagnets 60 may comprise a pair of electromagnets disposed to apply a reciprocating transverse magnetic field to the tip 52 of the anode 14 in the case of an anode containing an ovoid insert such that the arc attachment point moves along the equatorial line as described. The external magnets may also comprise three or more electromagnets disposed in a symmetrical pattern around the envelope such that when connected to a polyphase power supply, a rotating magnetic field is applied across an extended area of the anode tip 52.

With arrangements such as those described above, it is possible to appreciably increase the heat transferred to the anode, since the heat load applied to the anode tip by the arc attachment points moves in an oscillating line, (FIGS. 3-4), or concentric line 54 as illustrated in FIG. 2, and does not apply a sustained heat load to any one point. The increased allowable heat loading of the anode makes possible greater lamp brightness by allowing an increased power input. In general, the main factor which limits the power handling ability of a lamp is the ability to remove heat from the anode attachment point.

It is to be realized that the use of magnetic means to move the anode attachment foot, while convenient and effective, is not the only way in which heat load may be spread over an extended area of an anode according to this invention.

The results of this invention can also be accomplished by providing relative motion between the arc foot and the anode surface to spread the heat load. This relative motion can be accomplished as illustrated in FIGS. 6-8, using mechanical motion of the anode. FIG. 6 illustrated revolving the anode by means of an external motor drive and 0 ring housing 70 exposing an extended path length to are attachment. The housing 70 is attached to a'metallic end cap 72. The end cap 72 has a recess for receiving an 0-ring 74 for forming a gas tight seal between the envelope l0 and end cap 72. The end cap is secured to the envelope by means of a clamp, not shown.

An alternate arrangement illustrated in FIG. 7 utilizes a metal bellows 81 to attach the anode to the end cap 83. Mechanical motion may be applied to the bellows by a harmonic drive comprising a distortion-gear and diaphragm. Alternately, the anode may be driven by means of a shaft 85 attached to the anode insert 87 and to a linking rod 89 at fulcrum 91. The other end of linking rod 91 is attached to a rotating cam 93.

Yet another mechanical device to accomplish the spreading of the anode attachment foot over an extended area is illustrated in FIG. 8. A small bar magnet 95 disposed near the end of the anode is rotated mechanically during operation, either by positive mechanical drive such as the rotation of shaft 97 or by directing the cooling water onto the pivoted, balanced magnet, so that the rotating transverse magnetic field effectively moves the arc foot.

These are all improvements in operation compared to the normal stationary or non-oscillatory motion of the arc foot in which the heat input is concentrated steadily into one single point on the anode exterior surface. Furthermore, the improvement mentioned can be accomplished even in existing lamps by the use of the magnetic means shown in FIG. 5, thus allowing an appreciable improvement in the operation of lamps which are already in production and general use.

Although the description above has shown how to improve the operation of a lamp by an appreciable factor, one may realize a yet further improvement in the operation of the lamp by the use of the anode construction illustrated in FIGS. 9 and 10, in which the line of contactof the sweeping arc foot with the anode end hecomes a complete circle near the end of the anode tip, and the contact retraces the circle continuously in one direction. By the use of a specially shaped insert 86, the circular pattern 54 of the attachment of the arc foot to the anode tip 52 shown in FIG. 2 is directly adjacent to the high velocity narrowest annular channel 88 for the cooling water which is the locus of best heat transfer points for the anode tip 52.

Referring now to FIG. 9, the anode 14 comprises a hollow metal tube 80 terminating in a rounded bottom tip portion 82, and having a closed top member 84. A specially shaped insert 86 is positioned within the rounded bottom 82 of the anode tube 80 to form an annular shaped flow constriction 88. An axial inlet bore is provided in the insert 86. The lower end of the bore 90 is rounded at 92. The fluid output from the bore 90 impinges against a flow diverter 94, which is attached to the inner surface of the center of the anode tip 82. The flow diverter 94 is in the form of a concave pyramid having an outside surface formed by a revolution of two tangential arcs around their common axis.

The insert 86 is supported within the anode tube 80 by means of a central coolant inlet tube 96, which is secured within the bore 90. The coolant inlet tube 96 is further secured and sealed in an aperture provided within the top 84 of the anode 80. A coolant outlet tube 98 also penetrates the top 84 of the anode l4 and communicates with the annular space l00surrounding the coolant inlet tube 96.

Incoming coolant delivered to coolant inlet tube 96 impinges on flow diverter 94 and is uniformly dispersed in all directions and enters the narrowed construction 88 defined between the outer surface of the insert 86 and the inner surface of the anode tip 82. Thus, uniform maximum flow restriction, with accompanying highest velocity of fluid flow, occurs on an interior circle which coincides with the exterior line of arc attachment points 54, illustrated in FIG. 2.

As the fluid flows past the insert 86, it enters the annular space 100 and leaves the anode through coolant outlet tube 98. Satisfactory cooling can also be effected without the flow diverter 94. The water stagnation area formed in the absence of the diverter 94 is immaterial, since the arc attachment points traverse a circular path removed from the center of the anode tip 82.

A plurality of spaced bores 102 extend from the upper surface 104 of the insert 86 into the body of the insert. The bores 102 are provided to receive the poles 106 of the U-shaped magnet structure 108 illustrated in FIG. 12. The poles 106 are joined by a U-shaped member 110. The U-shaped member includes a pair of legs 112, having one end joined to the poles 106 and an outer end joined to a cross-bar member 114. The member 114 is surrounded by a coil 116. A different style electromagnet is shown as 60 in FIG. I, but the principle of operation is the same.

The poles 106 of the U-shaped magnet 108 are inserted into the bores 102 such that the north and south poles 106 alternate. The displacement provided by the legs 106 permit placement of the cross member 114 in an equilatorial triangular configuration surrounding the inlet tube 96. These poles, shown in FIG. 11, fit into the bores 102 illustrated in FIGS. 9 and 10. The magnetic axis of each magnet will be displaced 120 from the next adjacent magnetic axis. The ends of the wires constituting the coils 116 pass through the tube 96 and extend from the magnets 108 through the top 84 of the anode 14 to a source of three-phase alternating current (not shown). It is also possible to decrease the number of leads needed to pass through the top 84 by grounding the appropriate wire from each pair.

On actuation of the source of three-phase alternating current, a rotating magnetic field is created which causes rotation of the anode attachment point. The close proximity of the magnet poles 106 to the anode arc attachment points allows the desired rotational force to be created with a very small amount of magnetic force. Altemately, the insert 86 may be solid and three magnet structures may be disposed external to the lamp to achieve the desired rotational effects in the manner shown in FIG. 5.

It has not heretofore been possible to utilize extremely thin-walled shells for the anode structures since considerable pressure is exerted on the anode tip during operation by the hot gas inside the envelope 10. Some remedies that have been developed by the present inventors involve balancing the gas pressure inside the envelope of an operating lamp by an increased hydrostatic pressure of the cooling fluid inside the anode, using either manual control or feedback methods and the use of special copper alloys having high resistance to creep deformation. Those alloys that have been found satisfactory and usable are combinations of copper with zirconium, chromium, silver or other minor additives. A combination of oxygen-free, high conductivity copper with 0.15 percent zirconium is particularly well suited, and leads to a much improved anode cap. A further, and very effective remedy that has been developed by the present inventors consists of providing a substantial reinforcement of the anode tip by reducing the unsupported span of the anode tip.

In general, the effectiveness of a liquid cooling system could be increased, and consequently the power input and power handling capability could be increased if the wall of the anode shell, in particular, the wall of the anode tip could be made thinner. The mode of failure of the anode in a lamp that has a higher power input than it can handle is that the anode tip collapses inwardly under operating conditions and closes off the coolant passage. This happens for the normal construction of anodes as generally used in lamps. Failure happens at a higher input power level for lamps with the anode construction shown in FIG. 3, at a yet higher level for system incorporating balanced hydrostatic pressure, and still a higher level for those anodes adding the feature of special copper alloys having high resistance to creep deformation.

The embodiment of the invention illustrated in FIGS. 10 and 11 provides substantial reinforcement of the anode tip by reducing the length of unsupported span of the desirably thin anode tip, and increases yet further the power handling capacity of the anode for any of the improved versions already described. Referring now to FIG. 10, a thin support rod 120 is positioned under the anode tip to provide increased support. The rod 120 is anchored to some suitable structure. One satisfactory method is to form a bend 122 in the rod such that the upper end 124 can be attached to the inner wall 126 of the coolant inlet tube 96.

FIGS. 10 and 11 illustrate the axial position of the support rod 120 in relation to the relative disposition of the magnet poles 106 and the axes of the magnets 108. The reinforcement provided by rod 120 substantially stiffens the anode cap under operating conditions.

This makes possible the use of an anode end cap of lesser thickness. 1

A greater heat transfer to the anode tip is then realizable, because of its greater thinness, and a higher lamp operating gas pressure is then permissible because of the shorter, unsupported span. Either or both of these factors permit increased electrical power inputs to the lamp, and a further gain in luminosity and brightness.

In some circumstances, notably for very narrow diameter anodes, it may be inconvenient to incorporate the magnet structures in the coolant inserts. Moreover, the use of a configuration utilizing a central anode diverter 44 as illustrated in FIG. 1, or a central coolant tube 96 as illustrated in FIG. 9, is not optimally compatible with the use of coaxial gas circulation to give more effective heat exchange between the hot arc gas and the anode member. Another suitable and efficient structure for an arc lamp is illustrated in FIG. 13. The anode 14 is in the form of a toroidal tube 200 which provides a structure which simplifies the magnetic means used to cause movement of the arc and is particularly suitable for use with axial gas cooling of the electrodes. The toroidal anode can receive a circular magnetic coil which when excited by a DC source produces a magnetic field which interacts with the longitudinal arc current to rotate the arc in a circular path.

Referring to FIG. 13, the anode 14 is comprised of an outer circular tube 202 joined to the anode end 204 and to a semi-toroidal rounded bottom 206. An inner tube 208 is also joined to the bottom 206. The inner tube forms a gas flue 210 which may be closed by anode end 204, extend through the anode end 204 or 9 extend transversely through the tubes 208, 216 and 202 as will be subsequently described.

An inner annular chamber 212 is formed bebetween outer tube 200 and inner tube 208. An encapsulated coil winding 214 is attached to the lower end of a tubular insert 216 which is received within annular chamber 212 and supported by anode end 204. The coil winding 214 is surrounded by a toroidal shaped encapsulation or covering 218 and the disposition of insert 216 is adjusted such that a restricted passage 220 is provided between encapsulation 218 and the opposed inner surface of bottom 206. The insert 216 divides chamber 212 into two passageways on each side of restricted passage 220.

One or more coolant inlets 222 are disposed about the perimeter of outer cylinder 202 and are suitably connected to a supply of coolant under pressure, not shown. A plurality of coolant outlets 224 are provided in end member 204 surrounding the flue 210.

The anode 14 is axially supported within one end of a quartz envelope 10 by forming glass-to-metal seals between the envelope 10 and insert 216, coolant outlet tubes 224, inner tube 208, and coolant inlet tube 222. A cathode 12 is similarly axially supported within the other end of the envelope 10 by forming glass-to-metal seals between the envelope 10 and the cathode 12.

When the coil 214 is energized by a DC source, not shown, suitably electrically connected to the coil 214 by means of an electrical wire 233 attached to tubular insert 216, the winding of solenoid coil 214 produces magnetic field lines as indicated by the wavy arrows adjacent the tip 240 of the anode 14. Negative ions leaving the vicinity of tip 36 of the cathode 12 will travel generally toward the anode tip 240 as indicated by the broken lines emanating from cathode tip 36. In the absence of provision for rotating the arc attachment point, the arc discharge would be localized and unmoving imposing a tremendous heat load on an area which is approximately four square mm. However, the aforementioned magnetic field produced by coil 214 interacts with the arc discharge to produce a circular rotation of the arc attachment point in much the same manner as illustrated in FIGS. 9 and 10.

However, the circulation of the arc is produced in a much more efficient and convenient manner, and the use of DC is often more convenient than the use of polyphase AC, or even single-phase AC. The advantage of the circular rotation of the arc attachment point in this embodiment is similar to that described for the earlier structures described, in that it is possible to appreciably increase the heat transferred to the anode, since the heatload applied to the anode tip by the arc attachment points moves in an extended line, and does not apply a sustained heatload to any one point. It is to be understood that one or more of the features previously described as improvements in the anode structures, namely, balancing the gas pressure inside the envelope of an operating lamp by an increased hydrostatic pressure of the cooling fluid inside the anode, using either manual control or feedback methods, and the use of special copper alloys having high resistance to creep deformation, and the use of a reinforcement of the anode tip by the use of reinforcing struts may be applied to the structures shown in FIG. 13, as well as to the structures shown in FIGS. 1, 3, 5, 6, 7, 8, 9 and 10.

In particular, the reinforcing struts shown for FIG. 13 may consist of a plurality of copper bridges 243 between the shell 206 and the encapsulated coil winding 218. When suitably located, these can materially assist in heat transfer from the momentary arc foot attachment point to the cooling fluid, and also serve as a positive location device for the member 218 with relation to the whole anode structure shell 200.

A normal or non-gas-flow-coolant type of cathode 12 comprising a cylindrical portion 245 terminating in a conical tip 36 is suitable for use with the toroidal anode type described in FIG. 13 or any of the other previously described embodiments whether internally water cooled, support cooled or uncooled. However, the cathode 12 illustrated in FIG. 13 is particularly suitable for use when provision is made for recirculating the gas from exit 236 of the flue 210.

The cathode 12 may be provided with a slightly truncated conical tip 36. The cathode tip 36 is surrounded by a suitably shaped shell 230 forming an axial gas coolant passage 232 terminating in an annular opening nozzle 234 adjacent tip 36. The exit 236 is connected to the passage 232 by recirculating conduit 255. The conduit is sealed to the envelope 10 at 257. Since convection currents may not be sufficient to provide the desired cooling, a pump 238 may be provided within the recycle circuit to increase gas flow. When gas is pumped through passage 232 it flows past tip 36 and into flue 210 and contributes to cooling the cathode l2 and spreading the heatload on anode 14, since the unionized, hot, flowing gas will contact a large area of anode l4, notably much of flue 210 and much of the outside wall 202, instead of impinging mainly on the arc foot area. The peak heat transfer of the anode is still mainly concentrated at some point on the omnidirectional cooling path of the coolant as it flows past restriction 220, which is the locus of the arc discharge anode foot locations.

A further embodiment of an arc lamp incorporating a convection driven recycling system to cool'the toroidal anode is illustrated in FIG. 14. In this embodiment the flue 210 formed by the inner tube 208 is closed by the end member 204. A recycle conduit 260 sealingly penetrates the lamp envelope 10 below the tip 36 of the cathode 12 and sealingly penetrates the envelope 10 below the anode end 204. The conduit is transversely disposed within the coolant chamber 212 also penetrating outer tube 202, insert 216 and inner tube 208. The inlet end 262 of the recycle conduit communicates with the flue 210.

When the lamp is in operation the hot anode gases will rise into flue 210, enter inlet 262 and are cooled as they travel through the portion of the conduit 260 submerged in the coolant chamber 212. The cooled discharge gas will flow by convection through the conduit into outlet 264 back into the envelope 10. The recycled discharge gas will rise by convection and cool the cathode tip 36 and anode tip 240. Altemately the recycle conduit 260 may terminate after penetrating the wall of outer tube 202. The cooled discharge gas will flow by convection within the envelope toward the cathode 12 and will cool the cathode tip 36 and anode tip 240 as it rejoins the gas discharge stream flowing toward the flue 210.

It is to be understood that although particular embodiments of the invention have been described and illustrated herein, it is recognized that modifications and variations may readily occur to those skilled in the art and, consequently, it is intended that the claims he interpreted to cover such modifications and equivalents.

What is claimed is:

l. A high-intensity arc lamp comprising in combination:

a sealed envelope for containing a discharge gas at greater than atmospheric pressure;

a cathode having a tip extending into the envelope;

an anode disposed within said envelope parallel to a line through the axis of said cathode, defining an axial line, and having a tip which is spaced from the tip of the cathode a fixed distance in a direction parallel to said axial line;

electric discharge means connected to the anode and cathode for forming an arc discharge between said tips; and

are translation means associated with said anode for selectively moving the attachment point of the are at the anode tip across an extended area of the anode tip and in a direction which is substantially perpendicular to said axial line.

2. An arc lamp according to claim 1 in which said arc translation means includes mechanical drive means attached to said anode for moving said anode in a pattern transverse to said axial line, so that as said anode is moved different points on the tip thereof are aligned with said axial line.

3. An arc lamp according to claim 1 in which said arc translation means includes magnetic means for applying a selectively varying magnetic field transverse to said axial line and in the vicinity of said anode tip for moving said arc attachment point in a pattern across the anode tip.

4. An arc lamp according to claim 3 in which said magnetic means comprises at least one electromagnet disposed external to said envelope.

5. An arc lamp according to claim 3 in which said magnetic means comprises at least one electromagnet disposed in the interior of said anode.

6. An arc lamp according to claim 3 in which the magnetic means includes a plurality of electromagnets and a polyphase power supply connected to said electromagnets.

7. An arc lamp according to claim 6 in which a plurality of said electromagnets are disposed in a symmetrical pattern and said polyphase power supply develops a rotating transverse magnetic field for rotating the attachment point in a circular pattern around the tip of the anode, said circular pattern being in a plane which is substantially perpendicular to said axial line and centered about said axial line.

8. An arc lamp according to claim 3 in which said anode is hollow and contains an axially disposed insert forming an annular restricted coolant flow path across said anode tip.

9. An arc lamp according to claim 8 in which said hollow anode includes a coolant inlet and coolant outlet, said insert includes a central passage communicating with said inlet and includes an enlarged shaped portion spaced from said passage forming a narrowed, annular flow constriction and said coolant outlet communicates with said constriction.

10. A high-intensity arc lamp comprising in combination:

a sealed envelope for containing a discharge gas at greater than atmospheric pressure;

a cathode having a tip extending into the envelope;

an anode disposed within said envelope parallel to a line through the axis of said cathode and having a tip which is fixedly spaced from the tip of the cathode in a direction parallel to said axial line;

electric discharge means connected to the anode and cathode for forming an arc discharge between said tips; and

are translation means associated with said anode for selectively moving the attachment point of the are at the anode tip across an extended area of the anode tip, said are translation means including magnetic means for applying a selectively varying magnetic field transverse to said axial line and in the vicinity of said anode tip for moving said are attachment point in a pattern across the anode tip, said anode being hollow and containing an axially disposed insert forming an annular restricted coolant flow path across said anode tip, said hollow anode including a coolant inlet and coolant outlet, said insert includes a central passage communicating with said inlet and includes an enlarged shaped portion spaced from said passage forming a narrowed, annular flow constriction and said coolant outlet communicates with said constriction, said insert further including a plurality of symmetrically disposed recesses, an electromagnet forming part of said magnetic means is at least partially received in each of said recesses and polyphase power supply means are connected to said electromagnets for developing a rotating transverse magnetic field for rotating the arc attachment point in a circular pattern substantially coinciding with said annular flow constriction.

11. An arc lamp according to claim 10 further including flow diverter means disposed on the inside surface of the anode tip facing said central passage.

12. An arc lamp according to claim 10 further including anode tip support means extending between the inside surface of the anode tip and said insert.

13. An arc lamp according to claim 8 in which said hollow anode comprises an outer shell and an inner shell joined at their lower ends by a semi-toroidal tip and said insert comprises a toroidal member disposed in said tip, said member containing said magnetic means which apply said magnetic field so that the arc point attachment is moved in a circular pattern across the anodes semi-toroidal tip.

14. An arc lamp according to claim 13 further including a tubular member concentrically disposed between said shells supporting said insert and dividing said hollow anode into a coolant inlet chamber and a coolant outlet chamber.

15. An arc lamp according to claim 13 further including discharge gas recirculating means connected to the flue space within said inner shell and to said envelope below said cathode tip.

16. An arc lamp according to claim 15 in which said recirculating means includes a pump.

17. An arc lamp according to claim 15 in which said cathode is surrounded by an outer shell spaced from said cathode to form an axial gas coolant passage and said recirculating means communicates with the outer shell of the cathode.

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Claims (17)

1. A high-intensity arc lamp comprising in combination: a sealed envelope for containing a discharge gas at greater than atmospheric pressure; a cathode having a tip extending into the envelope; an anode disposed within said envelope parallel to a line through the axis of said cathode, defining an axial line, and having a tip which is spaced from the tip of the cathode a fixed distance in a direction parallel to said axial line; electric discharge means connected to the anode and cathode for forming an arc discharge between said tips; and arc translation means associated with said anode for selectively moving the attachment point of the arc at the anode tip across an extended area of the anode tip and in a direction which is substantially perpendicular to said axial line.

2. An arc lamp according to claim 1 in which said arc translation means includes mechanical drive means attached to said anode for moving said anode in a pattern transverse to said axial line, so that as said anode is moved different points on the tip thereof are aligned with said axial line.

3. An arc lamp according to claim 1 in which said arc translation means includes magnetic means for applying a selectively varying magnetic field transverse to said axial line and in the vicinity of said anode tip for moving said arc attachment point in a pattern across the anode tip.

4. An arc lamp according to claim 3 in which said magnetic means comprises at least one electromagnet disposed external to said envelope.

5. An arc lamp according to claim 3 in which said magnetic means comprises at least one electromagnet disposed in the interior of said anode.

6. An arc lamp according to claim 3 in which the magnetic means includes a plurality of electromagnets and a polyphase power supply connected to said electromagnets.

7. An arc lamp according to claim 6 in which a plurality of said electromagnets are disposed in a symmetrical pattern and said polyphase power supply develops a rotating transverse magnetic field for rotating the attachment point in a circular pattern around the tip of the anode, said circular pattern being in a plane which is substantially perpendicular to said axial line and centered about said axial line.

8. An arc lamp according to claim 3 in which said anode is hollow and contains an axially disposed insert forming an annular restricted coolant flow path across said anode tip.

9. An arc lamp according to claim 8 in which said hollow anode includes a coolant inlet and coolant outlet, said insert includes a central passage communicating with said inlet and includes an enlarged shaped portion spaced from said passage forming a narrowed, annular flow constriction and said coolant outlet communicates with said constriction.

10. A high-intensity arc lamp comprising in combination: a sealed envelope for containing a discharge gas at greater than atmospheric pressure; a cathode having a tip extending into the envelope; an anode disposed within said envelope parallel to a line through the axis of said cathode and having a tip which is fixedly spaced from the tip of the cathode in a direction parallel to said axial line; electric discharge means connected to the anode and cathode for forming an arc discharge between said tips; and arc translation means associated with said anode for selectively moving the attachment point of the arc at the anode tip across an extended area of the anode tip, said arc translation means incLuding magnetic means for applying a selectively varying magnetic field transverse to said axial line and in the vicinity of said anode tip for moving said arc attachment point in a pattern across the anode tip, said anode being hollow and containing an axially disposed insert forming an annular restricted coolant flow path across said anode tip, said hollow anode including a coolant inlet and coolant outlet, said insert includes a central passage communicating with said inlet and includes an enlarged shaped portion spaced from said passage forming a narrowed, annular flow constriction and said coolant outlet communicates with said constriction, said insert further including a plurality of symmetrically disposed recesses, an electromagnet forming part of said magnetic means is at least partially received in each of said recesses and polyphase power supply means are connected to said electromagnets for developing a rotating transverse magnetic field for rotating the arc attachment point in a circular pattern substantially coinciding with said annular flow constriction.

11. An arc lamp according to claim 10 further including flow diverter means disposed on the inside surface of the anode tip facing said central passage.

12. An arc lamp according to claim 10 further including anode tip support means extending between the inside surface of the anode tip and said insert.

13. An arc lamp according to claim 8 in which said hollow anode comprises an outer shell and an inner shell joined at their lower ends by a semi-toroidal tip and said insert comprises a toroidal member disposed in said tip, said member containing said magnetic means which apply said magnetic field so that the arc point attachment is moved in a circular pattern across the anode''s semi-toroidal tip.

14. An arc lamp according to claim 13 further including a tubular member concentrically disposed between said shells supporting said insert and dividing said hollow anode into a coolant inlet chamber and a coolant outlet chamber.

15. An arc lamp according to claim 13 further including discharge gas recirculating means connected to the flue space within said inner shell and to said envelope below said cathode tip.

16. An arc lamp according to claim 15 in which said recirculating means includes a pump.

17. An arc lamp according to claim 15 in which said cathode is surrounded by an outer shell spaced from said cathode to form an axial gas coolant passage and said recirculating means communicates with the outer shell of the cathode.

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