US3394217A

US3394217A - Method and apparatus for controlling plural electron beams

Info

Publication number: US3394217A
Application number: US463190A
Authority: US
Inventors: Fisk Robert Walter
Original assignee: Air Reduction Co Inc
Current assignee: Airco Inc
Priority date: 1965-06-11
Filing date: 1965-06-11
Publication date: 1968-07-23
Anticipated expiration: 1985-07-23
Also published as: NL6608065A; LU51261A1; DE1565881B2; DE1565881A1; AT278187B; DK117649B; SE346196B; BE681839A; CH452731A; GB1141594A; NO117547B

Description

July 23, 196s R. w. FISK 3,394,217

METHOD AND APPARATUS FOR CQNTEOLLING PLURAL ELECTRON BEAMS Filed June 11, 1965 ,w mm QMJW'E Patented July 23, 1968 3,394,217 METHOD AND APPARATUS FOR CONTROLLING PLURAI. ELECTRON BEAR/IS Robert Walter Fisk, Sunnyvale, Calif., assigner, by mesne assignments, to Air Reduction Company, Incorporated,

a corporation of New York Filed June 11, 1965, Ser. No. 463,190 9 Claims. (Cl. 13-31) ABSTRACT F THE DISCLSURE A method and apparatus for electron beam bombardment heating is disclosed which includes means for generating at least two independent generally parallel electron beams, means for generating separate transverse magnetic fields in the path of each electron beam for deflecting the beams in a first direction, and means for generating a common transverse magnetic field in the path of at least two of the electron beams which has lines of fiux perpendicular to the lines of ux of the separate magnetic fields.

The present invention relates generally to high vacuum electron beam methods and apparatus and more particularly to a method of and apparatus for magnetically controlling the impact pattern of a plurality of beams of electrons in a high vacuum electron beam apparatus.

Normally in electron beam apparatus, where a target material conned within a Crucible is heated by bombardment with a beam of electrons, the beam is directed or guided by magnetic fields onto a selected area of the material. In prior art electron beam apparatus, the directing or guiding of a plurality of adjacent electron beams has been difficult. In such situations, it was normally necessary to provide means for separately controlling each of the individual beams of electrons in order to produce the desired heating effects.

Accordingly, it is an object of the present invention to provide a new and improved apparatus for magnetically guiding a plurality of electron beams.

It is another object of the present invention to provide a method and apparatus for controllably directing the path of travel of a plurality of electron beams so as to attain a desired bombardment pattern on the target material.

It is still another object of the present invention to provide a method of and apparatus for controlling the bombardment pattern of two or more adjacent electron beams by employing differently oriented magnetic fields for deecting the electron beams.

Other objects and advantages of the present invention will become readily apparent from the following detailed description and accompanying drawings wherein:

FIGURE 1 is a schematic view of an apparatus in ac cordance with the present invention;

FIGURE 2 is a sectional view taken along line 2-2 of FIGURE l; and

FIGURE 3 is a sectional view taken along line 3-3 of FIGURE 1.

Generally, a method in accordance with the present invention includes injecting two or more adjacent and generally parallel electron beams through a first magnetic field having lines of fiux extending generally perpendicular to the paths of the beams, to thereby deflect the beams in a predetermined direction. The deflected electron beams are then passed through a second magnetic eld having lines of magnetic flux extending generally perpendicular to the path of the beams and the direction of the rst magnetic field. The first and second magnetic fields are of selectively controllable flux density, whereby the electron beams are directed onto a predetermined area on the target material.

For purposes of description, the method is described hereinafter with respect to an apparatus for practicing the method.

Referring to the drawings, an apparatus in accordance with the present invention includes an evacuated electron gun chamber 10 which contains a pair of electron beam sources 14 adapted for supplying adjacent and generally parallel, high density, ribbon-shaped electron beams. The electron beam sources may be of the conventional variety of self-accelerated source, including a cathode, focusing electrode, and accelerating anode. The beams are directed through a pair of

corresponding slits

18 and 20 into a focusing or concentrating magnetic field provided by a suitably energized axial coil 21 disposed adjacent the

slits

18 and 20. The axial coil 21 establishes a magnetic field which extends generally parallel to the initial direction of travel of the electron beams emanating from the slits 18 and 2t) thereby causing concentration or focusing of each of the electron beams. The concentrated beams are then directed through a pair of

corresponding slits

22 and 23, disposed at the opposite end of the axial coil 21. The slits open into a conventional high vacuum electron beam furnace enclosure 24 which contains a Crucible 25 on which the material to be heated (the target material 26) is disposed. High vacuum pump means 28 is coupled to the enclosure 24 for maintaining a predetermined pressure within the enclosure 24, usually about 0.1 to 5 microns of mercury.

The beams are directed into the enclosure 24 at a preselected angle, with respect to the target material. For the sake of convenience, the beams are shown entering the enclosure 24 generally parallel to the surface of the target material 26, which in the illustrated embodiment is in a horizontal direction. The horizontally directed beams are directed onto a predetermined region of the target material by mutually perpendicular magnetic fields disposed successively in the path of the electron beam. The first field is employed to guide the beams in one direction along the surface of the target material, hereinafter referred to as the lateral direction, and the second field guides the beam along the surface in a direction perpendicular to the former direction, hereinafter referred to as the transverse direction.

As shown particularly in FIGURE 2, the lateral magnetic field is generated adjacent the

slits

22 and 23 by a lateral electromagnetic means 30. The lateral electromagnetic means 30 includes a first pair of magnetic

core multiturn coils

32 and 34, having cores preferably fabricated of'mild steel, adjacent the ends of the upper slit 22, and a second pair .of similar

magnetic core coils

36 and 38 adjacent the ends of the lower slit 23. The coils in each of the pairs are magnetically oriented in opposed relationship with respect to each other and are generally similar in physical structure. Thus, the coils in each pair have like magnetic poles facing in the same direction.

The

coils

32 and 34 of the first pair are magnetically coupled at their upper ends by a bar 4i) of relatively high permeability material such as mild steel, and are similarly coupled at their lower ends by a bar 42 of relatively high permeability material, which is generally similar to the bar 40. The tops of the

coils

36 and 38 of the second pair are also magnetically coupled by the bar 42. The lower ends of the

coils

36 and 38 of the second pair are magnetically coupled by a bar 44 which is generally similar to the bars 4t) and 42. As may be seen the magnetic flux generated by the

opposed coils

32 and 34 is supplied through the

bars

40 and 42 in opposite directions. Since magnetic lines of flux are closed paths, the magnetic lines of flux generated by the

opposed coils

32 and 34 must necessarily pass across the slit 22 as they emanate from one end of their respective coils and return to the other end. Thus, when current is supplied to the

coils

32 and 34, a magnetic field is established across the slit 22 having generally vertical lines of magnetic fiux 50, as shown. In this fashion, a magnetic field of a desired intensity, dependent upon the amount of energization supplied by the sources 46 and 48, and having lines of force oriented generally perpendicularly with respect to the direction of travel of the electron 'beams may be established within the slit 22. Likewise, the

coils

36 and 38 are coupled to suitable sources of current 52 and 53 generally similar to the sources 46 and 48, and upon energization provide a similar magnetic field of controllable flux density, extending vertically across the slit 23.

The lateral magnetic fields established across the

slits

22 and 23 may be conveniently varied in intensity by merely changing the total amount of current supplied to the pair of coils, disposed at opposite ends of each of the slits. Since a change in the magnetic iiux density changes the lateral deflection of electrons passing thro-ugh the

slits

22 and 23, a means is provided for effecting separate control of the deflection of the respective electron beams passing through the

slits

22 and 23. Accordingly, the beams of electrons passing through the

slits

22 and 23 may be deflected differing amounts with respect to each other or they may both ybe defiected similar amounts depending upon the amounts of current supplied to the associated pairs of coils. Alternatively, the current supplied to each of the respective opposed coils comprising each of the pairs of coils may be varied in amount, so as to delieet electron beams passing through different regions of the

slits

22 and 23 by differing amounts.

A plurality of cooling coils (not shown) are disposed adjacent the outer edges of the

bars

40, 42 and 44 in order to limit the amount of heat which may be generated therein as a result of heat emanating from the furnace and from the electron beams.

After the electron beams have passed through the lateral ,magnetic field established across the

slits

22 and 23 they are directed into a transverse magnetic field. The transverse magnetic field serves to curve the horizontally directed electron beams through an angle of between approximately 45 to 120 such that the electron beams impinge onto the target material 26.

`Referring particularly to FIGURE 3 of the drawings, the transverse magnetic field is establlshed by a transverse electromagnetic means 54. The means 54 generally includes an upper horizontally disposed iron core coil 5'8 and a lower horizontally disposed iron core coil 62. These coils are generally cylindrical in form, and contain a sufficient number of turns to establish a magnetic field, which curves the electron beams passing therethrough through an angle of approximately 90. The coils are each respectively connected to suitable sources 63 and 64 of direct current so that the current `respectively supplied to each can be readily adjusted.

The

coils

58 and 62 are coupled =by a side plate 66 which interconnects the respective end portions at one end of the

coils

58 and 62 and another side plate 70 which interconnects the respective ends of the

coils

58 and 62 at their opposite ends. The side plates 66 and 70 are generally similar in structure. Preferably the side plates 66 and 70 are fabricated of a ferro-magnetic material such as mild steel, and thus function to magnetically couple the

coils

58 and 62. In this connection the

coils

58 and 62 are disposed in opposed relationship such that like magnetic poles face in the same direction. Thus, when the

coils

58 and 62 are supplied with current the magnetic flux emanating from the respective ends of the coils passes through each side plate in opposite directions. Since the lines of magnetic fiux form closed paths, the flux lines pass into the space 74, defined by the

coils

58 and 62 and the side plates 66 and 70, and then return to the opposite ends of their respective coils through the opposite side Cil plate. Thus, when the coil-s 58 and 62 are supplied with current a relatively intense transverse magnetic field is established within the space 74 having lines of magnetic fiux 78 as shown in FIGURE 3.

In this connection it is advantageous to establish the magnetic ux such that the beams of electrons may be directed into regions of maximum fiux concentration, thereby imparting a maximum amount of deflection to the electron beams. It is thus desirable to fabricate each of the side plates -in :a generally triangular form, as shown in FIGURE l, oriented such that its base generally faces in the direction of the

slits

22 and 23. Since magnetic fiux follows the path of least resistance most of t-he flux passing through the side plates reaches the wider center portion before passing across the space 74. The beams of electrons are generally directed into the central region of the space 74, wher-e most of the flux is present, thereby receiving a maximum amount of deflection such that they impinge on the target material 26. The ux density within the space 74 may be readily adjusted as desired by appropriately adjusting the amounts of current respectively supplied to the

coils

58 and 62, thereby directing each of the beams onto predetermined regions of the target material 26 or alternatively focusing the beam to impinge onto a common region on the surface of the target material 26.

Thus, it can be seen that as the beams of electrons pass out :through the

slits

22 and 23 land through the lateral magnetic yfield produced by the means 22 they are laterally deflected to a desired extent by this field and directed into the space 74. The beams of electrons -are then directed through the transverse magnetic field whereby the beams are deflected transversely to the desired extent from their initial trajectory. Through appropriate adjustment of the aforementioned lateral and transverse magnetic fields it is possible to cause the beams of electrons to impinge on predetermined regions on the surface of the target material, thereby defining a predetermined impact palttern.

In certain instances it may be desirable to generate a cyclically repetitive impact pattern. This may be conviently achieved by suitably programming the coils comprising the lateral magnetic means 30 or the transverse electromagnetic mean-s S4 so as to establish a cyclically varying magnetic field. Such a field will deflect the beams of electrons pass-ing therethrough so as to provide a cyclically repetitive impact pattern.

While the above method and apparatus has been described Iwith reference to two beams of electrons, more than two beams may be readily employed if desired.

Various changes `and modifi-cations may be made in the above-described method and appartus without departing from the spirit or scope of the present invent-ion.

Various features of the invention are set forth in the following claims.

I claim:

1. An electron beam bombardment heating apparatus comprising, an evacuated enclosure adapted to receive a target material to be heated, means in said enclosure for generating at least two independent electron beams, the initial paths of the electron beams being generally parallel to one another, means for generating a separate transverse magnetic field in the path of each electron beam, each of said separate magnetic fields being controllable for defiecting the respective electron beams in a rst di` reetion, and means for generating a common transverse magnetic field in the path of at least two of the electron beams, said common magnetic field having lines of fiux perpendicular to the lines of flux of said separate magnetic elds for deflecting the electron beams in a second direction generally perpendicular to the rst direction.

2. An electron beam lbombardment heating apparatus generating at least two independent electron beams, the comprising, an evacuated enclosure adapted to receive a target material to be heated, means in said enclosure for initial paths of the electron beams being generally parallel to one another, electromagnetic means for genenating yan independent transverse magnetic field in the path of each electron beam, each of said electromagnetic means including a pair of spaced apart magnetically opposed coils, means for magnetically coupling said coils, and means for controllably supplying current to said coil-s for deflecting the electron beam in a first direction, and means for generating `a common transverse magnetic field in the path of at least two of the electron beams, said common magnetic field having lines of flux perpendicular tto the lines of flux of said independent magnetic fields for defiecting the electron beams in a second direction generally perpendicular to the first direction.

3. An electron beam bombardment heating apparatus comprising, an evacuated enclosure adapted to receive a target material to be heated, means in said enclosure for generating at least two independent electron beams, the initial paths of the electron beams being generally parallel to one another, first electromagnetic means for generating an independent transverse magnetic field in the path of each electron beam, each of said first electromagnetic means including a pair of magnetically opposed coils, means for magnetically coupling said coils, and means for controllably supplying current to said coils for defiecting of the electron beam in a first direction, and second electromagnetic means for generating a common transverse magnetic field in the path of the electron beams, said second electromagnetic means including a pair of magnetically opposed coils, means for magnetically coupling said coils, and means for controllably supplying current to said coils, said common magnetic field having lines of fiux perpendicular to the lines of flux of said independent magnetic fields for defiecting the electron beams in a second direction generally perpendicular to the first direction.

4. An electron beam bombardment heating apparatus comprising, an evacuated enclosure adapted to receive a target material to be heated, means in said enclosure for generating at least two independent electron beams, the initial paths of the electron beams being generally parallel to one another, first electromagnetic means for generating an independent transverse magnetic field in the path of each electron beam, each of said first electromagnetic means including a pair of magnetically opposed coils, means constructed of high permeability material connecting like poles of said coils and defining an opening through which the electron beam passes, and means for controllably supplying current to said coils for defiecting of the electron beam in a first direction, means for generating a common transverse magnetic field in the path of all the electron beams, said common magnetic field having lines of flux perpendicular to the lines of flux of said independent magentic fields for defiecting the electron beams in a second direction generally perpendicular to the first direction.

5. An electron beam bombardment heating apparatus comprising, an evacuated enclosure adapted to receive a target material to be heated, means in said enclosure for generating at least two independent electron beams, the initial paths of the electron beams being generally parallel to one another, first electromagnetic means for generating an independent transverse magnetic field in the path of each electron beam, each of said first electromagnetic means including a pair of spaced apart magnetically opposed coils having like poles facing the same direction, means constructed of high permeability material connecting like poles of said coils and defining an opening through which the electron beam passes, and means for controllably supplying current to said coils for defiecting the electron beam in a first direction, and second electromagnetic means for generating a common transverse magnetic field in the path of all the electron beams, said second electromagnetic means including a pair of spaced apart magnetically opposed coils having like poles facing in the same direction, means constructed of high permeability material connecting like poles of said coils, and defining an opening through which the electron beams pass, and means for controllably supplying current to said coils, said common magnetic field having lines of fiux perpendicular to the lines of flux of said independent magentic fields for defiecting the electron beams in a second direction generally perpendicular to the first direction.

6. An electron beam bombardment heating apparatus comprising, an evacuated enclosure adapted to receive a target material to be heated, means in said enclosure for generating two independent ribbon shaped electron beams, the initial paths of the electron beams being generally parallel to one anothr, first electromagnetic means for generating an independent transverse magnetic field in the path of each electron beam, each of said first electromagnetie means including a pair of spaced apart magnetically opposed coils having like poles facing in the same direction, a bar of high permeability material connecting like poles of said coils and defining an opening through which the electron beam passes, and means for controllably supplying current to said coils for deflecting the electron beam in a first direction, and second electromagnetic means for generating a common transverse magnetic field in the path of both electron beams, said second electromagnetic means including a pair of spaced apart magnetically opposed co-ils having like poles facing in the same direction, a triangular shaped plate member constructed of high permeability material connecting like poles of said coils and defining an opening through which the electron beams pass, and means for controllably supplying current to said coils, said common magnetic field having lines of fiux perpendicular to the lines of fiux of said independent magnetic fields for deiiecting the electron beams in a second direction generally perpendicular to the first direction.

7. An electron beam bombardment heating apparatus comprising, an evacuated enclosure adapted to receive a target material to be heated, means in said enclosure for generating two independent ribbon electron beams, the initial paths of the electron beams being generally parallel to one another, first electromagnetic means for generating a common axial magnetic field extending generally parallel to the initial path of both electron beams, second electromagnetic means for generating an independent transverse magnetic field in the path of each electron beam, each of said second electromagnetic means including a pair of spaced apart magentically opposed coils having like poles facing in the same direction, means for magnetically coupling said coils, and means for controllably supplying current to said coils for defiecting the electron beam in a first direction, and third electromagnetic means for generating a common transverse magnetic field in the path of both electron beams, said third electromagnetic means including a pair of spaced apart magnetically opposed coils having like poles facing in the same direction, means for magnetically coupling said coils, and means for controllably supplying current to said coils, said common magnetic field having lines of flux perpendicular to the lines of fiux of said independent magnetic fields for defiecting the electron beams in a second direction generally perpendicular to the first direction.

8. A method for controllably heating a target material in a high vacuum electron beam apparatus comprising the steps of generating at least two adjacent and generally parallel electron beams, passing each of the electron beams through a separate lateral magnetic field having lines of flux extending generally perpendicular to the paths of the beams, controlling the strength of each of the lateral magnetic field for controllably deflecting each beam in a first direction, passing said defiected beams through a transverse magnetic field having lines of fiux extending generally perpendicular to both the path of the cams and the direction of the lateral magnetic field, and controlling the strength of the transverse magnetic eld for controllably detlecting the electron beams in a second direction perpendicular to the rst direction.

9. A method or controllably heating a target material in a high vacuum electron beam apparatus comprising the steps of generating at least two adjacent and generally parallel electron beams, passing each of said electron beams through independent lateral magnetic fields having lines of flux extending generally perpendicular to the path of the beams, controlling the strength of each of said lateral magnetic elds thereby separately deecting said beams in a first direction, thereafter passing said electron beams through a relatively int-ense transverse magnetic eld including a region of maximum flux concentration having lines of magnetic ux extending perpendicular to both the path of the beams and the direction of the lateral magnetic eld, and controlling the strength of said traverse magnetic eld, thereby directing said beams of electrons onto predetermined areas on the target material.

References Cited UNITED STATES PATENTS 3,046,936 7/ 1962 Simons.

FOREIGN PATENTS 1,374,335 8/1964 France.

950,672 2/1964 Great Britain.

ROBERT K. SCHAEFER, Primary Examiner.

5 M. GINSBURG, Assistant Examiner.

UNITED STATES rPATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,394,217 July 23, 1963 Robert Walter Fisk It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 19, "pair" should read pairs Column 4, line 25, "beam" should read beams Column 4, line 73, cancel "generating at least two independent electron beams, the" and insert the same after "for" in line 75, same column 4. Column 6, line 14, "anothr" should read another Column 8, line 2, "traverse" Should read transverse Signed and sealed this 23rd day of December 1969.

(SEAL) Attest:

Edward M. Fletcher, Jr. WILLIAM E. SCHUYLER, JR.

l Attesting Officer Commissioner of Patents