US3244931A

US3244931A - Electric arc projection lamps

Info

Publication number: US3244931A
Application number: US267666A
Authority: US
Inventors: Vantine Allan D Le; Jerry S Townsend
Original assignee: Thompson Ramo Wooldridge Inc
Current assignee: Northrop Grumman Space and Mission Systems Corp
Priority date: 1963-03-25
Filing date: 1963-03-25
Publication date: 1966-04-05
Anticipated expiration: 1983-04-05

Description

April 1966 A. D. LE VANTINE ETAL 3,244,931

ELECTRIC ARC PROJECTION LAMPS Filed March 25, 1963 3 Sheets-Sheet 1 ALLA N 0. A e VA/vT/Ms JERRY s. TOWNSEND INVENTORS A 77'OR/VE Y April 1966 A. D. LE VANTINE ETAL 3,244,931

ELECTRIC ARC PROJECTION LAMPS Filed March 25, 1963 3 Sheets-Sheet 2 O4 LEG A \2o\ no L/- E6 1 5.7

ALLA/v D. LeVAN7'7NE COQLANT Jamey 5. TOWNSEND INVENTORS April 5, 1966 A. D. LE VANTINE ETAL ELECTRIC ARC PROJECTION LAMPS Filed March 25, 1963 3 Sheets-Sheet 5 ALLA/v D. L e VANT/NE JZERRY 5. TO WA/SEND INVENTORS United States Patent 3,244,931 ELECTRIC ARC PROJECTIQN LAMPS Allan D. Le Vantine, Tarzana, and Jerry S. Townsend,

Los Angeles, Calif., assignors, by mesne assignments,

to Thompson Ramo Wooldridge, Inc., Cleveland, Ohio,

a corporation of Ohio Filed Mar. 25, 1963, Ser. No. 267,666 7 Claims. (Cl. 314-40) The present invention relates to high intensity lamps utilizing electric arc plasma as a radiation source and more particularly to arrangements for relatively positioning the electrodes of such a lamp so that the optical efficiency and light power output are substantially increased.

While the present invention may find application in various systems which require intense illumination of large areas or high intensity collimated light beams, it has particular utility in connection with projection lamps of the type generally utilized in the moving picture industry for projecting images of the film on the cinema screen or, in the case of moving picture production, for the illumination of scenes which are to be photographed. In addition, the present invention finds one particularly advantageous application in the art of simulating solar radiation as is required for laboratory testing of satellites,

aerospace vehicles and the like. One such system to which the present invention has particular application is disclosed in detail in copending patent application of Allan D. Le Vantine, Serial Number 267,702, filed March 25, 1963, entitled Beam Forming Apparatus, and assigned to the same assignee as that of the present application.

Forconvenience, the present invention is hereafter described with reference to the particular embodiments which have been found most suitable for use in systems of the general type disclosed by the above mentioned copending application. It is to be understood, however, that the invention may have broad application wherever large quantities of high intensity radiant energy are required, and its application is not restricted to any particular system or field of .art.

Accordingly, it is an object of the present invention to provide an improved high intensity electric arc lamp.

It is another object of the present invention to provide an improved arc lamp arrangement in which the electrodes are relatively positioned at an angle of departure from colinear alignment substantially largerthan has been practicable in similar prior art apparatus.

An additional object of this invention is to provide an arc lamp arrangement in which the angle between the axes of the positive and negative electrodes of the order of 90 degrees and in which hairpinning of the arc, undercutting of the electrodes, and instability of the arc current amplitude are avoided by provision of magnetic fields adapted to constrain the arc to a desired position.

It is a further object of our invention to provide an electric arc mechanism arranged to provide for more facile and efiicient optical collection of the light emanating from the arc.

A different object of this invention is to provide an electric arc lamp which includes a reflective radiation beam forming structure positioned on the opposite side of the arc fromthe positive electrode and in which the negative electrode is positioned at an angle of about 90 degrees or less relative to the positive electrode so that obstruction of the light paths from the electric arc to the beam forming structure is avoided.

Still another object of this invention is to provide an arc lamp of the type described in which the electrodes have a relatively large angle of departure from colinear alignment and in which stability of the electric arc is assured 3,244,931 Patented Apr. 5, 1966 "ice by partial neutralization of magnetic fields which tend to cause unstable distortions of the arc.

In accordance with the broader aspects of the present invention there is provided a projection arc lamp including first and second electrodes arranged with their ends in close proximity so that, when energized, they may sustain an electric arc for producing high intensity illumination throughout a large, solid angle. Slightly spaced from the ionized gas plasma which sustains the are there is provided a light collecting means for either refiectively or refractively gathering the arc light and at least partially focusing the light rays to form a high intensity output beam. To achieve improved efficiency and to avoid obstruction of the light ray paths it is desirable to position both of the electrodes outside of the solid angle which is defined by the paths of the light rays from the arc to the light collecting means. Preferably, one of the electrodes is positioned generally on the opposite side of the are from the light collecting means and the other electrode is positioned either approximately normal to the first electrode or at an acute angle relative to the first electrode. When the electrodes are disposed so that the angle of departure from colinear alignment is larger than about 45 to 50 degrees, are lamps characteristically exhibit a tendency to instability. That tendency is overcome in accordance with the present invention by an arrangement for at least partially neutralizing the magnetic fields which tend to disrupt the arc current path.

In accordance with a preferred embodiment of the present invention, the electrodes are positioned at a relative angle of the order of degrees. The instability which tends to arise from autornagnetic distortion or stretching of the arc current path is alleviated by provision of a stabilizing means which includes a pair of elongated conductors located in approximately parallel alignment on opposite sides of the electrodes. By this arrangement, current which is passed through the stabilizing conductors generates therearound a magnetic flux which overlaps the self-induced magnetic flux surrounding the arc and the carbon electrodes. When the current through the carbon arc is in a direction generally opposite to the currents through the stabilizing conductors, the stabilizing magnetic fields operate to cancel or at least partially neutralize the self-induced magnetic fields around the arc and the electrodes, thereby preventing automagnetic disruption of the are or at least alleviating the tendency t such disruption.

The novel features we consider characteristic of our invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

FIG. 1 is a perspective view, partially in section, of an electric arc projection lamp embodying improvements in accordance with the present invention;

FIG. 2 is a sectional view, taken along lines IIII of FIG. 1;

FIG. 3 is an electrical diagram useful in explaining the theory and operation of the present invention;

FIG. 4 is .a schematic diagram illustrating the usual relationship of the electrodes in carbon arc lamps;

FIG. 5 is a schematic diagram illustrating the usual tendency to automagnetic disruption of the electric arc;

FIG. 6 is a schematic diagram similar to FIG. 5 but including arc stabilization means in accordance with one form of the present invention;

FIG. 7 is a side view of a preferred form of the are stabilizing device of the apparatus of FIG. 1;

3,12 3 FIG. 8 is an end view of the device illustrated in FIG. 7; and

FIG. 9 is a plan view of the device illustrated in FIG. 7.

To provide a background for better understanding of the improved structural arrangements which comprise the present invention, and for full appreciation of the advantages of such improvements, it is well to consider briefly the mechanisms which have been used heretofore-in high intensity carbon are projection lamps. As shown in FIG. 1, the mechanism for supporting the Usual positive electrode 10 comprises a base plate 16 on which is supported a positive head support member 18 which in turn carries a pair of solid

silver contact blocks

24 and 26 for peripherally engaging the carbon electrode it to provide a low resistance electrical connection through which currents of the order of 160 amperes may be delivered without excessive heat generation or power loss. In conventional projection lamps the positive electrode 10, which is normally a 10 to 16 millimeter diameter carbon rod, is ordinarily consumed at the rate of several inches per hour. T o maintain optimum spacing between the

electrodes

10 and 12 it is necessary to continuously advance both of the electrodes toward the plasma arc region 14. Specifically, the positive carbon it) must be fed toward the are at a considerably higher rate than the negative carbon feed rate. Accordingly, there is conventionally provided a positive carbon feed mechanism or assembly 22 comprising three knurled rollers 48 spaced equi-angular-ly around the electrode lit and tightly engaging the surface thereof. The rollers 48 are conventionally knurled or diagonally grooved so that as the rollers 48 are driven, they not only rotate the carbon electrode but also advance the same toward the plasma are .14.

The drive assembly 22 includes a Worm-follower gear 34 positioned below the support plate 16 and adapted to engage a driving worm-gear (not shown) conventionally actuated by a speed controllable electric motor. The worm-follower gear .34 is coupled by vertical drive shaft 32 to a first bevel gear 36 which meshes with and drives a second bevel gear as. The second bevel gear 36 is affixed to one end of a horizontal drive shaft 38, journaled in the casting portion 40 and adapted to drive a set of spur gears 44 which individually drive the rollers 48 by means of coupling shafts which extend through the roller driving assembly 46. The entire positive electrode drive assembly is spaced from .and insulated from the base plate 16 by an insulating plate which enables appliaction of energizing potential to the positive electrode 1t? and the entire positive drive assembly including the support casting 18 without .the electrode support being shorted or grounded to the base plate 15.

With the exception of the vertical or right ange alignment of the negative electrode 12 (as shown in FIG. 1) the apparatus of FIG. 1 as thus far described is conventional is substantially identical to the drive mechanisms which have been used in various prior art projection lamps. Specifically, the mechanisms thus far described may conveniently be similar to the corresponding mechanisms of one commercially availableapparatus marketed by the Strong Electric Corporation, 87 City Park Avenue, Toledo, Ohio, and designated as their projection equipment type "Strong U.H.'I. In prior art projection lamps such as that referred to above, the radiant energy emitted by the plasma region 14 has a polar intensity pattern which approximates a cardioid of revolution with the maximum intensity occurring in a direction on the opposite side of the plasma from the positive carbon electrode 10; that is, approximately in the direction of the axis 66. To maximize the intensity of the collected light beam, it has been the convention-a1 practice to collect the emitted light by means of a parabolic reflector disposed concentrically about and substantially normal to the axis 66 so that the reflected light beam is projected back across the plasma l4} and around the positive electrode drive i assembly 22 toward the right hand end of the apparatus as illustrated in KG. 1.

Reflective projection of the light back across the arc region and the driving mechanisms has a number of disadvantages. Reflection of the light beam back across the mechanism which supports the positive carbon results in a portion of the output beam being blocked by that mechanism and results in an undesirable heating of the mechanism by the absorbed radiant energy. Further, it will be appreciated that the positive electorde drive assembly 22, which includes a large piurality of moving parts, is subject to deterioration from operation at excessively high temperatures. For that reason it would be very desirable to provide a vertically oriented heat shield or battle surrounding the positive electrode between the plasma region 14 and the electrode support casting 18. Unfortunately, in prior art apparatus where the retlectively collected light beam is projected back across the positive carbon support and drive assembly, it is necessary to restrict the dimensions of any heat baffle which is used to the frontal area of the positive carbon drive mechanism 22 in orderto prevent excessive blockage of the light.

In the apparatus disclosed in the above mentioned copending application of Allan D. Le Vantine, some of the foregoing difficulties are avoided by the use of :a light collecting means 60 positioned substantially normal to the optical axis 66. Preferably the collecting means '60 is operative to gather the light which emanates from the positive electrode and the plasma 14 throughout a solid angle of the order of degrees and to'form a beam which is projected outwardly from the apparatusto the left along the axis 66 as shown in FIG. 1. In a preferred form the light collecting means of the apparatus of the present invention comprises a large plurality of concentrically arranged reflective rings 62 and a centrally mounted lens 64. The structure and operation of such devices are fully disclosed in the above mentioned copending application and therefore are not considered in further detail heiein except to emphasize that the present invention may utilize any one of a number of different light collecting means with the only limiting criteria being that the light collecting means 60 should becapable of collecting light throughout a solid angle of ,theorder of about 140 degrees and should transmit or reflect the collecied light outwardly to the left along the optical axis 66 rather than back across the electrode drive mechanism 22. The transflector 60, as illustrated in FIG. 1, is fully disclosed and claimed in the above mentioned copending application and is not to be considered a limiting feature of the present invention; rather, it is illustrated herein by Way of example as being one component of one type of system in which the hereinafter described features and structures of the present invention are particularly advantageous.

Because the output light beam is projected outwardly to the left in the apparatus of FIG. *1, it is possible and highly advantageous to provide a heat shield baffle 28 formed of copper plate or the like surrounding the active end portion of the positive carbon 10 and extending outwardly from the carbon to the walls (not shown) of the housing which contains the apparatus "illustrated in FIG. 1. Specifically, the heat shield 28 preferably extends to and is heat conductively joined to the base plate 16 and extends upwardly to the top wall of the lamp housing. Likewise the battle 28 extends in both directions tfrom the plane of FIG. 1 to the side walls of the lamp housing. By that battle arrangement the positive carbon feed mechanism is completely shielded from impinging infrared and visible radiation and is protected from deposition of carbon particles, smoke, and the like. Moreover, since the heat shield 28 substantially divides the lamp housing into two completely separate sections, the positive carbon drive mechanism advantageously may be cooledzby a flow of air thereacross,

In prior art projection lamps it has been the general practice to orient the carbon electrodes 12. in end-to-end alignment, for exam-ple as shown in United States Patent Number 639,387, issued December 19, 1899, or alternatively, to position the negative carbon at a relatively small angle of departure from colinear alignment (for example as in the Strong Electric Corporation projection unit noted heretofore). In that projection unit (Strong type U.H.I.), the negative carbon has been positioned at an angle of approximately 45 degrees from the extended axis of the positive carbon. It has heretofore been considered that the angle of the negative carbon is quite critical and most difiicu lties with arc instability, such as hairpinning of the are or rapid fluctuations in the arc current amplitude, have been attributed to improper angulation of the negative carbon.

We have found that utilization of magnetic arc stabilization means such as the arrangements described in further detail hereinafter, is admirably effective to overcome the above-recited difficulties so that when such stabilizing means are used the negative carbon 12 may be positioned at much greater angles relative to the extended longitudinal axis of the positive carbon. That is, by provision of magnetic arc stabilizing means it is possible to increase the angle of departure from colinear alignment to substantially any desired 'angulation of the negative carbon.

In the exemplary apparatus illustrated in FIG. 1 the negative carbon is positioned substantially at right angles to the longitudinal axis of the positive carbon. The negative carbon extends downwardly from the plasma region 14 and through a ceramic bushing 76 which is positioned in an aperture in the base plate 16. As noted heretofore, the negative carbon is required to be slowly advanced toward the plasma region M at a rate determined by the rate of disintegration [or consumption of the active end of the carbon electrode. To that end, there is provided a negative carbon carriage assembly 70 adapted to rigidly support the negative carbon and to advance the same toward the arc region under the control of a variable speed electric drive motor (not shown). The carriage assembly 70 for supporting and driving the negative carbon may be generally conventional and, hence, is shown only in outline form. :For example, carriage mechanism 70 may be generally similar to the negative carbon carriage and drive mechanism which is utilized in the Strong Electric Corporation projection lamp type U.H.I. with the only essential difference being that in accordance with the present invention the negative carbon 12 is supported vertically, i.e., substantially normal to the longitudinal axis 66.

Positioning the negative carbon 12 either normal to the axis 66 of the positive carbon or even at an acute angle relative to the positive carbon 14 is particularly advantageous in that such arrangement completely removes the negative carbon and its carriage 7t) from the solid angle subtended by the light collecting means 69. This means that the (efficiency of the light collecting means 60 is appreciably enhanced and the output light beam has a more uniform intensity over all elemental portions of a plane normal to the beam. Moreover, perpendicular or acute angle orientation of the negative carbon 12 means that the negative carbon carriage 70 may be located beneath the base plate 16 whereby the carriage 70 and its appurtenances are operable at lower temperatures and are completely protected from deposition of the smoke, ashes, and metallic particles which are notoriously associated with carbon arcs. I

The are sustaining ionized gas plasma of a carbon arc lamp is subject to distortion by the magnetic fields generated by the current passing through the arc. Heretofore, this tendency to automagnetic disruption of the arc has placed severe limits on the geometrical configuration of carbon arcs. These limits relate to the angular relationship of the electrodes and the amount of current that 6 can be passed through the arc. The arc current can be made to reach its highest values, without disrupting the arc, if the electrodes (positive and negative) are aligned end to end along a common axis. It the axes of the electrodes are shifted from exact colinearity, distortion of the plasma tends to occur. This distortion lies primarily in the plane defined by the axes of the two electrodes 12 and 14. The greater the angle betwen the axes of the two electrodes, the more severe will be the distortion, until at some large angle of departure from colinear alignment .it becomes impossible to sustain an arc even at impractically low current levels.

Autom'agnetic distortion of the electric arc can best be understood by brief consideration of the electromagnetic effects of the moving charges in the electrodes and in the plasma. To facilitate consideration of the theory there is shown in FIG. 3 a linear conductor 102 with a unidirectional current (1 passing therethrough. The unidirection current q will generate a magnetic field around the conductor 102 as indicated schematically by the magnetic field lines 104. If another charge q having a velocity and direction as indicated by the vector 166 moves through the magnetic field surrounding the conductor Hi2, a torce F will be exerted upon the charge q in a direction mutually perpendicular to its velocity vector 1% and the direction of the magnetic flux lines 104 at that point. This force can be expressed in vector notation as:

where B represents the magnetic flux intensity resulting [from the current q flow-ing in the conductor 102. Now,

referring to FIG. 4, if q v is a component of the plasma which lies to one side of the axis of the electrode 110, and if a current g is passing through electrode 110, a

- force F will act on the incremental plasma element q v resulting in acceleration of the particle q along an outwardly curving path.

FIG. 4 is illustrative of a typical arrangement of the electrodes in carbon a'rc lamps, wherein the positive electrode 1.10 is normally positioned horizontally and the negative electrode 112 is positioned at an angle of departure from colinear alignment of about 45 degrees. In such an arrangement the effect of the force F acting on elemental plasma particles adjacent the end of electrode 112 is to force the charge carrying plasma particles away from the electrodes in a generally outward direction. The effects on the plasma particles adjacent to the active end of the positive electrode 11$ as a result of the magnetic field surrounding electrode 112 are comparable. The ensuing distortion of the arc causes the plasma to assume a hairpin shape until ultimately the arc disrupts and conduction through the electrodes ceases. Because the magnetic fields surrounding the two

electrodes

110 and 112 are of equal magnitude, the distortion exactly bisects the angle formed between the two electrodes and the plasma hairpin, theoretically, will be symmetrically positioned about the bisection line 113. if the current through the are 114 is increased, the hairpin distortion will increase until separation of the two legs of the plasma occurs, resulting in collapse of the arc.

FIG. 5 shows the effect when the angle between the electrodes is, for example, approximately degrees. Because the force F is a function of 5, the maximum current level at which a stable arc can be maintained between the

electrodes

110 and 112 gradually decreases as the angle is increased. Specifically, with the angle of departure from colinear alignment being about 90 degrees, as shown in FIG. 5, at low arc current levels a stable arc 116 will be maintained. At a current level approaching the maximum which can be maintained, the plasma will hairpin as shown at 118, with the electrode current exhibiting a concomitant fluctuation. When the applied current is increased further, the ionized plasma current path is ultimately severed as indicated at 126) so that conduction ceases, necessitating manual reignition which is usually accomplished by moving one of the electrodes toward the other until they contact and the arc is initiated.

In accordance with the present invention, the foregoing difficulties are alleviated by provision of an arc stabilizing means for at least partially neutralizing the self-induced magnetic fields which normally surround the electrodes and the plasma. By neutralizing these magnetic fields, the disruptive forces acting on the plasma particles are appreciably reduced so that for a given negative electrode angle much larger arc currents may be utilized (or alternatively, for a given desired current magnitude the electrode angle may be greatly increased without encountering instability of the are or excessive random fluctuations of the arc current amplitude).

One embodiment of a practical arc stabilizing device or arrangement is illustrated schematically in FIG. 6. The arrangement comprises in combination with a pair of

electrodes

130 and 132, disposed approximately at right angles, a pair of

elongated conductors

134 and 136 which are welded or otherwise conductively affixed to an electrical contact block 138 which engages the electrode 130 at a point preferably a few inches back from its active end. The lower ends of the

conductors

134 and 136 are connected together by a conductive spreader bar 149 which determines the separation between the conductors 134- and 136 and which is preferably welded to those conductors at its respective ends. An inlead cable 142 from the power source (not shown) is connected to feed current to the spreader bar 140 and therethrough to the

conductors

134 and 136. By arranging the arc stabilizing device so that it is substantially symmetrical the current from inlead 142 can be caused to divide equally between the

conductors

134 and 136; thus the

conductors

134 and 136 are effectively connected in parallel with the parallel combination being connected in series with the electric are between the positive inlead 142 and the negative inlead 144. The negative electrode 132 is, of course, connected to the negative inlead 144 in accordance with conventional practice.

The current in the two

conductors

134 and 136 fiows in a direction generally opposite to the current flowing through the

electrodes

130 and 132 and through the plasma arc. The direction of the magnetic fields resulting from the

arc stabilization conductors

134 and 136 is therefore directly opposed to the fields which normally surround the active ends of the

electrodes

130 and 132. Accordingly, the magnetic fields provided by the

arc stabilization conductors

134 and 136 are directly opposed to and tend to neutralize the magnetic fields produced by the arc circuit, per se. By varying the location of conductors 13:4 and 136, the degree of neutralization of the normally present magnetic fields can be controlled. To increase the neutralization effect the

conductors

134 and 136 can be spaced more closely together and, therefore, closer to the

electrodes

130, 132 to thereby increase the degree of magnetic cancellation. Spreading the conductors 134 and 13d farther apart will, of course, decrease the neutralizing effect. By making the

conductors

134 and 136 substantially the same length and formed of the same material, they are arranged to have equal resistances so that when connected in parallel they conduct equal currents.

Now, referring again to FIG. 1 and to FIGS. 7, 8 and 9, there is shown in greater detail another embodiment of an arc stabilization means in accordance with our invention as it is applied to the projection lamp apparatus shown in FIG. 1 and generally described heretofore. As shown in FIG. 1, the

arc stabilization conductors

146 and 148 are positioned on opposite sides of the negative electrode 12 and are formed or bent to generally follow the arc path between the active ends of the electrodes and 12. Preferably the stabilizing

conductors

146 and 148 are formed of a single piece of 4-inch diameter copper tubing having a cross-over portion 149 at the top end which is silver soldered over a distance of about two inches to the top surface of a U-shaped connector 152 which is attached to the upper end of the support casting 18. The U-shaped bracket 152 makes good electrical connection to the solid silver contact blocks 24 and 26 as shown in FIG. 2 and thereby provides a low resistance connection between the cross-over portion 1.49 and the positive carbon 15). The lower portions of the

conductors

146 and 148 extends in generally parallei alignment on either side of the positive carbon support casting 118 toward the rear end of the lamp housing The ends of the tubes are connected to water hoses 16:! to provide for circulation of water or another appropriate coolant fluid through the stabilizing conductors 14d and 148 and through the cross-over portion 149. The coolant flow not only cools the

conductors

146 and 148 but also assists in cooling the U-shaped bracket 152, and, if desired, may be utilized to cool the contact blocks 24 and 26.

At the lower front portion of the

conductors

146 and 148 there is provided a spreader bar 156 which is silver soldered to both of the stabilizer conductors 14 6 and 148 and which has its center point silver soldered to a curved bus bar 162 (FIGS. 7 and 9) which extends fr m the spreader bar 156 and which connects to a terminal 164 of the power source. The terminal 164 is preferably supported in the base plate 16 by means of a ceramic bushing 166 with appropriate connection being made from the power source (not shown) toterminal 164 underneath the base plate.

In some cases of apparatus constructed in accordance with FIGS. 1, 7, 8 and 9 we have found that there is a tendency for the

stabilizer conductors

146 and 148 to deteriorate in the areas closely adjacent to the plasma region 14. Sporadic conduction between the negative electrode 12 and the

conductor tubes

146 and 148, by way of the high temperature plasma, tends to etch, pit and eventually perforate the copper tubing. In extreme cases there may be occasional shifting of the are from the end of the positive carbon 10 to one of the stabilizer conductors so that an arc is supported intermittently be-= tween the negative electrode 12 and one of the stabilizer conductors. To avoid such malfunction and consequent deterioration of the stabilizer conductors they are preferably externally coated or covered with a heat resistant; electrical insulating material 170. As shown in FIGS.- 7 and 8, the insulating sheath 179 extends along the

conductors

146 and 148 from a point closely adjacent to the U-shaped connector 152 down to the region where the stabilizer conductors are adequately spaced from the negative carbon 12. If desired, the stabilizing

conductors

146 and 148 may be insulatively coated or covered along their entire length from the connector 152 to the spreader bar 156. The insulating sheaths 170 not only prohibit arcing from the plasma to the stabilizing conductors but also prevent flame etching of the copper tubing. One; example of a material which has been successfully used for the insulating sheaths 17% is an aluminum oxide sold under the trade name Rokide A, by Norton Company, Worcester, Massachusetts. This material is applied to the.

conductors

146, 148 by a conventional plasma jet spraying technique to form a substantially impervious ceramic, sheath on the conductors.

While the stabilizing means, in accordance with a preferred embodiment of the present invention, has been, disclosed as comprising water-cooled conductive tubing connected in series with the arc energizing circuit, it will be appreciated by those skilled in the art that the specific. structural arrangement disclosed is not essential, and that various other arrangements for providing neutralizing or compensating magnetic fields in the region surrounding the arc path may be utilized without departing from our; invention.

9 While the v present invention hasbeen shown in certain specific' forms only, it will'be obvious tothose skilled in .the art that it is not so limited'but is susceptible ofvarious changes .and modifications without departing from 'the sp'iritand scope thereof.

The embodiments of the-inventionin which anexclusive property or privilege is claimed are de fined'asfollows.

We claim:

1. In an 'arcilatmpz light generating means including'first and second electrodes arranged to sustain an are intermediate the adjacent ends thereof;

lightcollecting means for gathering a substantial portion of the generated light rays to 'form an output beam; 7

said first and second electrodes being positioned substantially outside the solid angle subtended by said collecting means and at an inter-electrode angle such that the magnetic fields gene-rated by currents within the electrodes tend to disrupt the intra-arc current path; and

stabilizingmeans for at least partially neutralizing said magnetic fields, said stabilizing means comprising at least one curved electrical conductor extending generally parallel to and on each side of'the arc supporting end portions of said first and second electrodes and means for causing current to fiow in each of said conductors in a direction opposite to the direction of current flow in said electrodes.

2. In an arc lamp:

light generating means including first and second electrodes arranged to sustain an arc intermediate the adjacent ends thereof;

light collecting means for gathering a substantial portion of the generated light rays to form an output beam;

said first and second electrodes being positioned substantially outside the solid angle subtended by said collecting means and at an inter-electrode angle such that the magnetic fields generated by currents within the electrodes tend to disrupt the intra-arc current path; and

stabilizing means for at least partially neutralizing said magnetic fields, said stabilizing means comprising a pair of elongated electrical conductors extending generally parallel to and on opposite sides of the are supporting end portions of said electrodes, with both said conductors being electrically coupled to said first electrode at a point spaced from the arc supporting end and with the opposite ends of both said conductors being coupled to the same current source so that substantially equal portions of the arc-circuit current are constrained to flow through each of said conductors and in a direction substantially opposite to the current in the are.

3. In an arc lamp:

light generating means including first and second electrodes arranged to sustain an are intermediate the adjacent ends thereof;

stabilizing means for at least partially neutralizing said magnetic fields, said stabilizing means comprising a pair of elongated electrical conductors extending generally parallel to and on opposite sides of the are supporting end portions of said electrodes, with said conductors being connected in electrical parallel and with the parallel combination being connected in In an'ar'c lamp:

lig'htgene'rating means including-first and second elec- "trodes arranged to sustain an are intermediate the adjacent ends thereof;

"light collecting'rneans for gathering 'a substantial portion of the generated light rays'to form an output beam;

said first and second electrodes beingpositioned substantially outside the solid angle subtended by said collecting means and' at an inter-electrode angle such that the magnetic fields generated by currents within the electrodes tend to disrupt the intra-arc current path; and

stabilizing means for at leastpar'tially neutralizing said magnetic fields, said stabilizing means comprising a pair of elongated metallic *members of sufficient rigidity to be substantially self-supporting, with those portions of said conductors which are disposed adjacent the arc being externally coveredby'sheaths of "heat resistant electrical insulating'mat'erial to ensure against transfer of the are from said first electrode toone'of said conductors and means for supplying current ineach of said conductors 'that'flows opposite to the currentflow in said electrodes.

- 5. In an arc lamp:

light generating means including first and second elec- "trodes arranged 'to sustain an arc intermediate 'the adjacent ends thereof;

stabilizing means for at least partially neutralizing said magnetic fields, said stabilizing means comprising a pair of elongated hollow metallic tubes arranged for circulation of a coolant fluid therethrough and extending approximately in parallel adjacency to and on opposite sides of the arc and the proximate end portions of said electrodes, with said metallic tubes being electrically connected in parallel with the parallel combination being connected in series with one of said electrodes in a manner such that substantially equal portions of the current delivered to said are are constrained to pass through each of said metallic tubes in a direction substantially opposite and parallel to the currents Within the electrodes.

6. In a projection lamp apparatus:

electric are means for producing light which emanates therefrom with approximately even intensity over a large solid angle, said means comprising first and second elongated electrodes and source means for applying power to the electrodes so that an electric arc may be maintained therebetween;

light collecting means for receiving the light which emanates within a solid angle of the order of 140 degrees and collirnating said light to form an output beam, with said collecting means having its optical axis positioned substantially in alignment with the central axis of said output beam;

said first and second electrodes being relatively positioned so that the inter-electrode angle is at most about degrees and so that the are supporting end of said first electrode is positioned substantially on said optical axis on the opposite side of the are from said light collecting means; and

stabilizing means to provide dynamically variable compensating magnetic field components in regions adjacent the are for at least partially neutralizing the 'arc-current-generated magnetic fields to thereby assure against arc instabilities which tend to arise from automagnetic distortion of the are, said stabiliz ing means comprising a pair of elongated metallic conductors having approximately equal resistance and extending on opposite sides of and substantially parallel to the adjacent end portions of said electrodes and means for supplying current in each of said conductors that flows opposite to the current flow in said electrodes.

7. Light projecting apparatus comprising:

electric are means including at least first and second elongated carbon electrodes arranged to support an electric-arc plasma between their proximate ends for emitting light of substantially constant intensity throughout a solid angle of at least about 140 degrees;

light collecting means for receiving a substantial portion of said light to form an output beam having a central axis substantially aligned with the optical axis of said collecting means;

said first electrode being positioned approximately in axial alignment with said optical axis on the opposite side of said plasma from said collecting means, said second electrode being positioned substantially outside the solid angle subtended by said collecting means and at angle of the order of 90 degrees relative to said first electrode;

stabilizing means to provide a compensatory magnetic field adjacent said plasma for assuring arc stability by substantially preventing automagnetic distortion of the intra-plasma current path; and

said stabilizing means comprising a pair of elongated hollow metallic tubes arranged for circulation of a coolant fluid therethrough and extending approximately in parallel adjacency to and on opposite sides of the arc and the proximate end portions of said electrodes, with said metallic tubes being electrically connected in parallel with the parallel combination being connected in series with one of said electrodes in a manner such that substantially equal portions of the current delivered to said are are constrained to pass through each of said metallic tubes in a direction substantially opposite and parallel to the currents within the electrodes, both said metallic tubes being sheathed over substantially their entire length with a heat resistant, ceramic electrical insulating material.

References Cited by the Examiner UNITED STATES PATENTS 218,749 8/1879 Jarnin 314-20 X 1,184,824 4/1916 Chillas 313-154 X 2,608,675 8/1952 I Buckingham 314-20 X FOREIGN PATENTS 433,798 11/1911 France.

30 RICHARD M. WOOD, Primary Examiner.

JOSEPH V. TRUHE, Examiner.

Claims

1. IN AN ARC LAMP: LIGHT GENERATING MEANS INCLUDING FIRST AND SECOND ELECTRODES ARRANGED TO SUSTAIN AN ARC INTERMEDIATE THE ADJACENT ENDS THEREOF; LIGHT COLLECTING MEANS FOR GATHERING A SUBSTANTIAL PORTION OF THE GENERATED LIGHT RAYS TO FORM AN OUTPUT BEAM; SAID FIRST AND SECOND ELECTRODES BEING POSITIONED SUBSTANTIALLY OUTSIDE THE SOLID ANGLE SUBTENDED BY SAID COLLECTING MEANS AND AT AN INNER-ELECTRODE ANGLE SUCH THAT THE MAGNETIC FIELDS GENERATED BY CURRENTS WITHIN THE ELECTRODES TEND TO DISRUPT THE INTRA-ARC CURRENT PATH; AND STABILIZING MEANS FOR AT LEAST PARTIALLY NEUTRALIZING SAID MAGNETIC FIELDS, SAID STABILIZING MEANS COMPRISING AT LEAST ONE CURVED ELECTRICAL CONDUCTOR EXTENDING GENERALLY PARALLEL TO AND ON EACH SIDE OF THE ARC SUPPORT-