US3506871A - Electron beam gun having elongated tensioned emitter - Google Patents

Description

C. DA. HUNT April 14, 1970 ELECTRON BEAM GUN HAVING ELONGATED TENSIONED EMITTER Filed May 29. 1967 ('fiar/ss 0Z1 Ham Mam, 116%, $91, 5&1, fa:

United States Patent U.S. Cl. 313278 Claims ABSTRACT OF THE DISCLOSURE An electron beam gun is described having an elongated emitter supported under tension by supports resiliently biased outwardly against contact elements on the respective ends of the emitter.

This invention relates to electron beam guns such as are used in high vacuum electron beam furnaces. More particularly, the invention relates to an electron beam gun utilizing an elongated electron emitter and having improved means for supporting the emitter and conducting heating current thereto.

Electron beam furnaces have been used for some time in the vacuum processing of various materials. Such furnaces are utilized, for example, in the melting and casting of metallic ores to obtain relatively pure metals or alloys. Such furnaces are also used in the melting of materials other than metals, such as ceramics and plastics, and are frequently used to produce vapors of metals and other materials for deposition upon a substrate.

Electron beam furnaces utilize one or more electron beam guns for producing high energy electron beams. These beams are then directed in some manner to a target for heating the same. Electron beam guns generally comprise a heated electron source or emitter for emitting the electrons, and suitable means for generating a magnetic field for accelerating and focusing the electrons into a beam. The interior of the furnace is usually evacuated to a high degree and the electron beam gun is disposed at a convenient location within the vacuum chamber.

The emitters of electron beam guns usually require replacement from time to time. This is due, at least in part, to the fact that emitters pit and corrode and become contaminated as a result of the condensation thereon of volatile substances emanating from the heated target. Naturally, it is possible to replace the emitter by replacing the entire gun. This, however, becomes inconvenient and necessitates a rather expensive item for replacement purposes. Thus, it is desirable that the emitter alone be replaceable as an individual item.

One type of electron beam gun, which has been found highly advantageous for many electron beam furnace applications, utilizes a thin elongated emitter, preferably of tungsten. Because of its thinness, such an emitter is flexible and it is usually necessary that it be supported under sufiicient tension to hold it taut. Because of the thinness of the emitter, however, it is easily pulled apart. The necessity for supporting the emitter with proper tension to hold it taut but to avoid pulling the emitter apart, while at the same time affording suflicient electrical conact to supply heating current to the emitter, adds considerable complication to devising a simple and expedient way of replacing the emitter.

It is an object of this invention to provide an improved electron beam gun such as may be used in an electron beam furnace.

Another object of the invention is to provide an elec tron beam gun utilizing an elongated emitter and having improved means for supporting the emitter and conducting heating current thereto.

3,506,871 Patented Apr. 14, 1970 Still another object of the invention is to provide an electron beam gun utilizing an elongated emitter which is easily replaced.

Other objects of the invention and the various advantages thereof will become apparent to those skilled in the art from the following detailed description taken in connection with the accompanying drawings wherein:

FIGURE 1 is a side elevational view of an electron beam gun constructed in accordance with the invention;

FIGURE 2 is a partial section top view of the electron beam gun of FIGURE 1, taken along the line 22 of FIGURE 1;

FIGURE 3 is a sectional view taken along the line 33 of FIGURE 2; and

FIGURE 4 is a fragmentary view, partially in section, of a further embodiment of the invention.

Very generally, the invention comprises an electron beam gun including at least one elongated emitter 11 for producing electrons, and means for supporting the emitter and conducting heating current thereto. The supporting means comprises a pair of resilient electrically conductive members 12 and 13 disposed, respectively, at opposite ends of the emitter. The supporting means further comprise a pair of contact elements 14 and 16 secured, respectively, to opposite ends of the emitter and having shaped surfaces 14a and 16a thereon mating with corresponding surfaces on the conductive members to provide electrical contact therebetween. The resilient conductive members are biased away from each other against the contact elements to apply tension on the emitter and to support same. The emitter may thereby be readily removed and replaced by manually relieving the bias on the conductive members.

Referring now more particularly to the preferred embodiment of the invention illustrated, it may be seen that the electron beam gun of the invention utilizes two parallel emitters 11 and 21. It is to be understood, however, that only one emitter may be utilized, and further, that more than two emitters may be utilized, depending upon the particular gun characteristics desired.

The emitters 11 and 21 are each comprised of a thin tungsten Wire of approximately 0.080 inch diameter supported parallel with each other in a manner more fully explained subsequently. As may be seen from FIGURE 1, each of the tungsten emitters is machined with opposite flattened surfaces 15, one of which is disposed toward the desired beam direction, to a thickness of approximately 0.040 inch over a length which corresponds to the width of the ribbon beam it is desired to produce. Heating current is conducted through the emitters, as subsequently explained, and causes emission of free electrons by the heated tungsten emitters in accordance with known phenomena. The emitters are each positioned with one of the flattened surfaces aligned to face the desired beam direction to present maximum surface area in that direction. The reduction in emitter cross section also maximizes current density for greater heating in the desired region of emission. Where a less precise beam is acceptable, however, the flattened surfaces may be unnecessary and a round cross section emitter will suflice. Moreover, wire diameters other than that specified may be satisfactory.

A focusing electrode 17, which is maintained at a negative potential, is disposed immediately behind and alongside each of the emitters 11 and 21 in order to direct the electrons emitted thereby into a beam. The focusing electrode 17 is provided with a pair of recesses or grooves 18 and 19 in which the emitters 11 and 21 are disposed, respectively. Each of the recesses 18 and 19 is shaped to form an individual electron beam of the electrons emitted from the associated emitter. In the particular apparatus shown, the focusing electrode 17 is designed to direct the two separate electron beams to converge into a composite electron beam at a predetermined location. This location may be at or near the surface of a target to be heated or may be in a magnetic field for deflecting the beam in a desired manner.

Suitable accelerating electrodes or anodes (not shown), maintained at a positive potential, are positioned to accelerate the beams of electrons emanating from the emitters. The anodes may comprise screens or grids which produce accelerating fields but which permit the beams to pass therethrough. Alternatively, the target itself may comprise an accelerating anode.

The focusing electrode 17 has a downwardly extending appendage 27 for supporting the focusing electrode. The appendage 27 is secured to a mounting plate 28 by means of mounting bolts 29 passed through suitable opening in the mounting plate and threaded into the appendage 27. Further holes, not shown, may be provided in the mounting plate 28 to facilitate securing the mounting plate to a suitable mounting bracket, also not shown, in the electron beam furnace. Thus, the electron beam gun, depending upon the orientation and position of the unillustrated mounting bracket, may be disposed to direct the beam to almost any position in the electron beam furnace.

Opposite ends of the support plate 28 are each provided with a downward extending arm 31 and 33, respectively. The arms 31 and 33 are preferably made integral with the support plate 28 and are staggered in relation to the center thereof such that the left and right halves of the support plate, as viewed in FIGURES 1 and 2, are identical, and so that the inner edges of the arms are in alignment.

The downwardly extending arms 31 and 33 provide support for a pair of spacer blocks 34 and 36, to which the means which support the emitter are attached. The spacer block 34 and 36 are attached to the arms 31 and 33, respectively, by mounting bolts 37 and 38. The bolts 37 are secured by suitable nuts 39 and the bolts 38 are secured by suitable nuts 41. The bolts 37 and 38 pass through the respective spacer blocks 34 and 36 toward one edge thereof such that the spacer blocks extend beyond the aligned edges of the arms 31 and 33 to be aligned with each other and approximately centered with respect to the support plate 28.

Turning now to the means by which the emitters 11 and 21 are supported, four conductive members in the form of leaf springs 12, 13, 22 and 23 are secured to the spacer blocks 34 and 36 on the arms 31 and 33. The leaf springs 12 and 23 are secured to the spacer blocks 34 and 36, respectively, by the same pairs of bolts 37 and 38, respectively, which secure the spacer blocks to the arms 31 and 33. The leaf springs 22 and 13 are secured to the spacer blocks by additional pairs of bolts 42 and 43, respectively. The nuts for bolts 43 are indicated at 44. The nuts for the bolts 42 are not visible in the drawings. All four of the leaf springs 12, 13, 22 and 23 extend from the spacer blocks 34 and 33 on opposite sides of the focusing electrode 17 and terminate near the ends of the emitters 11 and 21.

The leaf springs 12, 13, 22 and 23 are made of elec trically conductive material in order to conduct heating current to the emitters-supported thereby, explained subsequently. This heating current is conducted to the leaf springs by a plurality of electrical connectors 46 and conductive cables 47 connected thereto. The electrical connectors are bolted in contact with the corresponding leaf springs by means of the same bolts which secure the leaf springs against the spacer blocks 34 and 36. Each of the electrical connectors is provided with a socket 48 in which one end of the cable associated therewith is received.

- The ends of the leaf springs 12, 13, 22 and 23 nearest the focussing electrode 17 are provided with recesses therein. in FIGURE 1, the recesses 49 and 51 for the leaf springs 12 and 13, respectively, may be easily seen. These recesses are formed in the leaf springs, such as by hot stamping, and each recess comprises a pair of intersecting planar surfaces. Thus, each recess has a V-shaped cross section. A slot 52 is provided in the end of each of the leaf springs. These slots extend past the apex or intersection line of the planar surfaces comprising the recesses and are of a size suflicient to permit the emitter associated therewith to pass through the slot to the opposite side of the leaf spring.

A cylindrical contact element is secured to each end of each of the emitters 11 and 21. In the drawings, the contact elements 14 and 16 for the emitter 11 are shown, as is one of the contact elements 24 for the emitter 21. All the contact elements are electrically conductive and are provided with suitable holes therein through which the associated emitter passes. The contact elements are secured to the emitter by suitable means such as a shrink fit, welding, soldering, etc. The contact elements have curved surfaces 14a and 16a which mate with the corresponding recesses in the ends of the leaf springs 12, 13, 22 0nd 23. Thus, as seen in FIGURE 1, the contact element 14 having surface 14a mates in the recess 49 and the contact element 16 having surface 16a mates in the recess 51. Alternatively, a construction may be used wherein the surfaces 14a and 16a-of the elements have V-shaped protrusions which mate with the corresponding recess. In either case, good contact exists between each leaf spring and the contact element in engagement therewith. As may be seen in FIGURE 1, the center line of the emitters is preferably on a radius of the curved surface of the contact elements. Moreover, in accordance with the preferred embodiment illustrated, the contact elements are secured to the emitters so that the flat portions of the emitters are parallel with the V of the recesses 49 and 51. Thus, the orientation of the mating surfaces on the contact elements and those on the leaf springs facilitates positive alignment of each of the flat portions 15 with respect to the rest of the electron beam gun.

Although the illustrated embodiment utilizes cylindrical contact elements which mate with V-shaped recesses, this configuration is not critical so long as the selected configuration provides the desired positive alignment of the emitter in respect to the remainder of the gun. For example, where the contact elements are cylindrical in shape as shown, the recesses may be formed to have corresponding cylindrical surfaces. The basic consideration is to provide a mating configuration which establishes satisfactory electrical contact between the emitter and the conductive springs, which provides sufficient support for the emitter as explained in detail subsequently, and which facilitates alignment of the flat area of the emitters with respect to the rest of the gun.

A plurality of guard straps 53 are provided, one at each end of the emitters 11 and 21. The guard straps are attached to the respective electrical connectors 46 on the opposite sides thereof from the respective leaf springs 12, 13, and 22 and 23. The guard straps 53 are preferably of conductive material and are provided with holes 54 therein near the ends of the guard straps close to the emitters such that the ends of the emitters projecting beyond the contact elements extend through the holes 54. This insures that the emitter will not fall and short to ground in the event it breaks. I

The emitters, being thin tungsten wires, are easily flexed or bent. This fact makes it important that the emitters be maintained under a slightly taut condition to insure that the spacing between the emitters and thefoscusing electrode is constant for a constant electron beam configuration. In order to accomplish this, the leaf springs are biased outwardly of each other in an amount which applies tension On each of the emitterswhich issufficient to maintain the emitter taut but which is belowthe yield point of the emitter material at operating temperatures. Thus, the emitter will not be damaged or pulled apart due to excessive tension. The particular configuration of the invention enables the proper tension to be readily achieved by balancing spring bias while at the same time provides adequate electrical contact for conducting heating current through the emitter. Satisfactory results have been achieved in apparatus of the illustrated type using tensions in the range of 220 to 400 grams at operating tem peratures of 2200 C. to 2300 C.

As previously mentioned, normal electron beam furnace operation generally necessitates occasional replacement of the emitters of electron beam guns. A particular advantage of the invention exists in this respect, since a simple manual pressure on the leaf springs supporting the emitter will relieve the outward bias of the leaf springs sufficiently to permit removal of the emitter. Thus, for example, in removing the emitter 11, the leaf springs 12 13 may be manually urged toward each other enough to permit the contact members 14 and 16 to be lifted out of their corresponding recesses 49 and 51. In the embodiment shown, it is necessary to press the guard straps 53 outwardly so that the ends of the emitter 11 are removed from the holes 54. For installing a new emitter 11, one end of the emitter may first be inserted into the hole 54 in the left-hand one of the guard straps 53 (in FIG- URE 1), and the portion of the emitter on the opposite side of the adjacent contact element 14 from the guard strap may be placed into the slot 52. The leaf springs 12 and 13 may then be urged toward each other to permit insertion of the contact element 16 at the opposite end of the emitter 11 in its associated recess 51. The emitter will fall into the slot 52 in the leaf spring 13 when the contact element is positioned in the recess 51. The opposite end of the emitter may be inserted in the adjacent hole 54 in the right-hand guard strap 53 (FIG- URE 1). When the manual compression on the springs is released, the bias of the spring will position the emitter and support it as above described.

The ease of replacement of the emitters, the excellent electrical contact which is established, and the proper tension and support which is placed upon the emitters by the invention affords a considerable advantage in that the emitters alone may be replaced, without the necessity of replacing the electron 'beam gun. Complex supports, brackets, and clamping devices are not utilized, obviating the necessity for more complex procedures and operations if an emitter alone is to be replaced. Finally, the relative simplicity of the arrangement over more complex clamping devices renders the cost aspects of electron beam guns constructed in accordance with the invention attractive.

FIGURE 4 illustrates another embodiment of the invention. Elements in FIGURE 4 having design and function similar to that of elements in the embodiment illustrated in FIGURES 1 through 3 have been given identical numbers. Thus, as may be seen in FIGURE 4, the emitter 11, having flats 15, is supported in a recess or groove 18 in a focusing electrode 17. The focusing electrode is, in turn, mounted on a supporting plate 28 by suitable bolts 29. The supporting plate 28 includes a pair of perpendicularly extending arms, one of which is shown at 31. Bolts 37 having nuts 39 thereon secure a spacer block 34 on the arm 31.

The bolts 37 also serve to support a connector element 61 having a socket 62 in which an electrical current conducting cable 63 is secured. A leaf spring 64 is secured between the connector element 61 and the spacer b ock 34 by the bolt 37. A further leaf spring 66, which extends generally parallel with the leaf spring 64, is secured against the connector element on the opposite side thereof from the leaf spring 64 by the bolts 37. A contact element 67 is suitably secured to the upper portion of the leaf spring 64 and is spaced from the upper end of the connector element 61. The leaf spring 66, at its upper end, is free to move with respect to the contact element 67. A similar arrangement (not shown) is supported by the supporting plate 28 at the opposite end of the emitter.

The ends of the emitter 11 are each formed into the shape of a book 69 for supporting the emitter 0n the contact element 67 and the corresponding contact element at the other end (not shown), and for providing electrical contact therebetween. A groove 71 is provided in the surface of the contact element 67 opposite the emitter 11. The top of the groove 71 communicates with the opposite side of the contact element over a curved shoulder 72 which corresponds to the inner curvature of the hook 69. The contact element 67 with the groove 71 thereby constitutes a shaped catch for receiving the hook 69. The hook 69 mates in the slot 71, passing over the shoulder 72. The springs 64 and 66 are biased to place a tension on the emitter 11 suflicient to hold the emitter taut but not sufliciently strong to break the emitter. This construction, as was the case in the previous embodiment, supports the emitter in the desired manner while affording adequate electrical contact. To provide further insurance of adequate electrical contact between the electrical connector 62 and the hook portion 69 of the emitter 11, the upper end of the spring 66 is provided with right-angle flange 73. This flange extends over the end of the contact element 67 and the resilience of the spring 66 biases the spring against the hook portion 69 to gently urge same against the contact element 67. This also helps prevent the hook portion from becoming dislodged.

The flat portions 15 of the emitter 11 are aligned properly with respect to the remainder of the electron beam gun by making the groove 71, and the corresponding groove at the other end of the emitter, not shown, lie generally in a plane which is perpendicular to the flat portions. The hook 69, and the corresponding unillustrated hook at the opposite end of the emitter 11, also lie in such a plane.

When it is desired to replace the emitter 11 in the embodiment of FIGURE 4, the tension, produced by the bias of springs 64 and 66 and the corresponding springs on the opposite end of the emitter, not shown, is manually relieved. At the same time, the upper end of the spring 66 is manually urged outwardly of the groove 71 to permit removal of the hook portion 69 therefrom. A similar manual operation is performed at the opposite end of the emitter 11, not shown. The procedure may be reversed when a new emitter is installed.

Although slightly more complex than the embodiment of FIGURES 1 through 3, it will be appreciated that the embodiment illustrated in FIGURE 4 follows the basic principles of the previous embodiment and affords similar advantages. Thus, manual replacement of the emitter is facilitated while maintaining proper electrical contact, mechanical support, and emitter flat alignment.

It may therefore be seen that the invention provides an improved electron beam gun utilizing an elongated emitter or filament which is manually replaceable. The construction of the gun is simple and supports the elongated emitter for proper positioning and electrical contact. Various other modifications and embodiments of the invention in addition to those shown and described herein will be apparent to those skilled in the art from the foregoing discussion, and such other embodiments, and modifications thereof, are intended to fall within the scope of the appended claims.

What is claimed is:

1. An electron beam gun comprising, a generally elongated flexible emitter, a pair of electrically conductive contact elements secured to said emitter adjacent respective ends thereof, each of said contact elements having a mateable surface thereon, a fixed support, a pair of resilient electrically conductive elongated members secured to said support and projecting outwardly therefrom in generally mutually parallel relation, each of said elongated members having a mateable surface thereon near the outer end of said elongated member, engaging the mateable surface on a respective one of said contact elements, said elongated members being biased away from one another an amount suflicient to maintain said emitter taut but which is below the yield point of said emitter at operating temperatures, said elongated members being manually displaceable toward each other to disengage said mateable surfaces to facilitate mounting and demounting of said emitter, and means for conducting an electrical current to said elongated members to produce current flow through said emitter.

2. An electron beam gun in accordance with claim 1 wherein said emitter has at least one substantially flat surface thereon, and wherein said mateable surfaces on said contact elements and said mateable surfaces on said elongated members are oriented to position said flat surface in a predetermined alignment in said electron beam gun.

3. An electron beam gun in accordance with claim 1 wherein the mateable surface on each of said contact elements is a curved surface, wherein said emitter is secured to said contact elements to extend from said curved surfaces, wherein each of said elongated members includes a recess shaped to mate with said curved surface on a respective one of said contact elements, and wherein a slot is provided in each of said elongated members to accommodate said emitter.

4. An electron beam gun in accordance with claim 3 wherein said emitter has a flat surface thereon, and wherein said contact elements are secured to said emitter so that said fiat surface of said emitter will have a predetermined orientation with respect to said electron beam gun.

5. An electron beam gun in accordance with claim 1 wherein said elongated members each' comprises a pair of substantially parallel leaf springs and a shaped catch supported therebetween at one end thereof, wherein each of said contact elements comprises a hook shaped to fit over and engage said shaped catch, and wherein one of said leaf springs is shaped to fit over said hook to resiliently urge same against said shaped catch.

References Cited 20 JOHN w. HUCKERT, Primary Examiner A. J. JAMES, Assistant Examiner us. 01. X.R. 313-271, 27s

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