US3072786A

US3072786A - Beam splitter

Info

Publication number: US3072786A
Authority: US
Publication date: 1963-01-08
Anticipated expiration: 1980-01-08

Description

Jan. 8, 1963 w. B. JONES ETAL 3,072,786

BEAM SPLITTER Filed Jan. 3, 1961 2 Sheets-Sheet 1 COOLANT SUPPLY VACUUM /2/ j 4/ c'g/ i 44 43 32 HIGH VOLTAGE SUPPLY 7/ INVENTORS WILLIAM B. JONES BY PETER F MCWALTERS ATTQRWEY Jan. 8, 1963 w. B. JONES ETAL 3,072,786

BEAM SPLITTER 2 Sheets-Sheet 2 Filed Jan. 3, 1961 HIGH VOLTAGE SUPPLY INVENTORS WILLIAM B. JONES BY PETER F MCWALTERS ATTORNEY Stts 3,072,786 Patented Jan. 8, 1963 Free Commission Filed Jan. 3, 1961, Ser. No. 80,511 Claims. (Cl. 250-419) The present invention relates to charged particle accelerators and more particularly to an apparatus for dividing the particle bearn from an accelerator into two separate beams for the bombardment of more than one target.

Charged particle accelerators, such as the cyclotron or the linear accelerator, are generally designed to provide as much beam current as is possible. In use, the full beam of the accelerator is frequently delivered to a target and the accelerator is therefore operated at its full capability. However in many accelerator operations, the full beam current will greatly exceed the desired beam strength.

Where a bubble chamber is used to detect the beam, for example, only a small fraction of the full beam may be amployed to avoid instant saturation of the chamber. A similar requirement is present with other forms of counting equipment. To provide for these situations, it has heretofore been necessary to diminish the accelerator beam by using a restricted collimator or by reducing the beam injected into the particle accelerator by the source. Such operaitons are ineflicient in that the accelerator is eifectively operating below its maximum output. Considering the large monetary investment in such particle I accelertaors and the operating expense necessary for maintaining the machine, it is obvious that means are needed for utilizing the full output of the accelerator irrespective of the requirements of a particular bombardment.

The present invention provides a means for dividing a particle beam into two separate parts for simultaneous utilization at two targets thereby providing for more efli cient use of the accelerator. The two portions of the beam need not necessarily be equal in magnitude, thus a small portion of the original beam may be used for bombarding a target where the above discussed requirements are present while the major portion of the beam may be used for bombarding another target which is not so restricted.

In the invention the beam is divided into two sections by a thin plate disposed somewhat like a knife edge in the beam. A pair of deflection plates are disposed on each side of the central plate in parallel relationship therewith so that each of the divided beam sections passes between the central plate and a different one of the deflection plates. A potential diiference is established between the cnetral plate and each of the deflection plates to separate the two beam sections so that they may be directed individually toward separate utilization areas.

It is therefore an object of the present invention to provide for more productive use of charged particle accelerators.

It is a further object of the present invention to provide a means for conducting separate simultaneous bombardments at a charged particle accelerator.

It is yet another object of this invention to provide a paratus for dividing a charged particle beam into two separated beams for simultaneously making two separate bombardments.

It is another object of the invention to provide a means for delivering selected proportions of a charged particle beam to separate targets.

It is a further object of the invention to provide a means which is readily attachable to existing charged particle accelerators and which divides the beam thereof for bombarding more than one target.

It is still another object of the invention to provide opposed electrical fields Within a charged particle bearrrfor imparting opposite lateral drifts to two portions thereof.

The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following specification taken in conjunction with the accompanying drawing, in which:

FIGURE 1 is a longitudinal section view of a first embodiment of the invention with certain elements thereof shown in schematic form.

FIGURE 2 is an enlarged cross section view of the apparatus of FIGURE 1 taken at line 2-2 thereof,

FIGURE 3 is a longitudinal section view of the invention, taken along line 33 of FIGURE 1,

FIGURE 4 is a view schematically showing a cyclotron and two dilferent forms of target typically used there-- with and showing the use of the invention therewith to provide for the simultaneous bombardment of both targets, and

FIGURE 5 is a longitudinal section view showing a second embodiment of the invention.

Referring now to FIGURES 1 to 3 in conjunction, there is shown a cylindrical beam tube 11 of Lucite or other insulative material which tube is mountable at the beam outlet of an accelerator in alignment with the beam 12 thereof. The tube 11 is made vacuum tight by closing the ends with thin radiation transparent windows which are mounted in first and second

circular end plates

13 and 14 secured coaxially against the beam entrance and exit; ends of the tube respectively. A vacuum tight juncture is formed by the inclusion of O-rings 16 between the

end plates

13 and 14 and tube 11. Circular beam openings 17 are provided in each of the

end plates

13 and 14 which openings are offset downwardly from the axis of tube 11. First and second

circular foil windows

18 and 19 close the openings 17 to complete the vacuum enclosure. As shown in FIGURE 1 in particular, a vacuum pump 21 is communicated with the interior of the tube 11 to remove the atmosphere therefrom and thus to avoid deterioration of the beam within the tube. In many instances the beam splitter can be coupled to the accelerator vacuum system, or may be disposed within the accelerator, thereby making one or both of the above described

windows

18 and 19 unnecessary.

In this embodiment of the invention there is included a movable Faraday cup 22 which may be extended to in tercept the beam 12 just after it passes through the first window 18. A rod 23 extends laterally through a sliding seal 24 in the wall of the beam tube 11 and supports the cup 22 to permit external control of the cup' end plate openings 17 so that the beam 12 is divided into' two portions. Since a thin section of the beam 12 strikes and is dissipated on the center plate 26, the plate is constructed with as small a cross section as possible to avoid excessive beam loss. To support the plate 26, a pair of spaced center plate holders 27 extend upwardly from a bar 28 which is secured along the upper edge ofthe center plate 26. Each holder 27 comprises an electrically c nductive hollow shaft extending axially through a seal 29 which seals are mounted in the tube wall above the center plate 26. The seals 29 provide a vacuum seal between the holder 27 and the tube 11 while permitting the holders to be retracted upwardly when it is desired to remove center plate 26 from the beam. A stop collar 3% is secured coaxially on the holder 27 by a set screw and abuts against the outer surface of the seal 29 to maintain the holder 27 in a selected fixed position.

Cooling water is forced through a first of the holders 27 and along a passage 31 in bar 28 for removing heat generated by the portion of the beam 12 which strikes center plate 26, the coolant being removed through the second of the holders. To provide for the coolant circulation, water fitting 32 is coupled to the outer end of each holder 27 for connection with a suitable cooling water source 33 as shown in FIGURE 1. Since a high voltage supply is connected to the holders 27, the piping 34 to the cooling water supply must be of insulative material at least in part.

To provide electric fields acting to separate the beam 12 on opposite sides of center plate 26, rectangular

outer plates

36 and 37 are disposed within tube 11 one on each side of the center plate 26 and in parallel spaced apart relationship therewith. The first and

second plates

36 and 37 are made of carbon for improved heat characteristics.

To support

plates

36 and 37, backing strips 38 and 39 are secured against the upper outer surface of

plates

36 and 37 respectively which portions of the plates are thick to provide for the attachment of the strips. A first and second

plate support shaft

41 and 42 respectively extend through opposite points on the wall of tube 11 and are attached to backing strips 38 and 39 respectively near the forward ends thereof.

Shafts

41 and 42 are formed of electrically conductive material to provide for grounding of

plates

36 and 37 as will hereinafter be described. The

shafts

41 and 42 extend through fittings 43 mounted in the tube wall which fittings support the shafts and provide a vacuum seal. A stop collar 44 is clamped on each

shaft

41 and 42 and abuts against the fittings 43 to prevent inward motion of the shafts.

The

shafts

41 and 42 are connected to electrical ground and a high voltage supply 46 is connected to one of the center plate holders 27. In the usual case where the ion beam 12 is composed of positively charged particles, supply 46 will be of a type providing a positive potential to the center plate 26 relative to the

grounded side plates

36 and 37.

Considering now the operation of the invention, assume that a voltage in the order of 60 kilovolts is applied to the center plate 26, that the tube 11 is evacuated, and that a beam of charged particles is directed through the first window 18 parallel with the axis of tube 11. Provided the particles in the beam have a positive charge, the positive potential on the center plate 26 repels the particles away from the center plate 26 toward the

outer plates

36 and 37. Thus, the portions of the particle beam on opposite sides of the center plate 26 are impelled in opposite lateral directions. At the time the two beam portions leave the electrostatic field between the plates and pass through the second window 19, an angular divergence between the two beam segments has been created. With increasing distance from the beam splitter the space between the two beam portions increases, allowing the two portions to be treated as two separate beams and to be utilized in differing ways. By small lateral shifts of the position of the beam splitter the size ratios of the beam portions may be varied to meet the requirement of different situations.

In one embodiment of the invention for use with a high energy accelerator, the

plates

26, 36 and 37 are 18 inches long and the spacing between the central plate and an outer plate is 0.5 inch. .A positive potential in the 4 order of 30 to 50 kilovolts is applied to the central plate relative to the outer plates for deflecting a one microampere alpha particle beam having an energy of 48 mev. In usage, less than 30 percent of the beam is lost from striking the central plate.

Referring now to FIGURE 4 a typical positioning of the beam splitter on an accelerator is illustrated. The accelerator may, for example, be a cyclotron 51 and it may be desired to irradiate two physically separated targets such as a secondary particle producing target 52 and a scattering chamber 53. In the absence of the beam splitter, the cyclotron beam will be emitted along a linear trajectory 54. The beam splitter is disposed in alignment with trajectory 54, preferably adjacent the accelerator beam exit windows. The splitter will then function, as hereinbefore discussed, to divide the accelerator beam into two

separate beams

56 and 57 which are divergent in a direction away from the accelerator. Thus the separation of

beams

56 and 57 will increase with distance from the accelerator 51. Generally, the drift space between the beam splitter and the

targets

52 and 53 will be evacuated to avoid deterioration of the beam. If greater separation of the

beams

56 and 57 is desired, a beam turning magnet 58 may be situated outwardly from the accelerator in the path of at least one of the beams.

To adjust the relative strengths of the

beams

56 and 57, the beam splitter is mounted by means which allow movement of the device in a direction normal to the charged plates therein. Such means, for example, may comprise a stationary base plate 59 having the beam splitter tube 11 fastened to the upper surface thereof by a pair of clamps 61. Clamps 61 extend around the upper side of tube 11, one near each end thereof, and each is provided with longitudinally slitted arms at both sides of the tube. Bolts 62 are transpierced through the slotted arms of clamps 61 and engaged in the base plate 59. Thus by loosening bolts 62 small lateral adjustments of the position of tube 11 may be made.

Variations of the foregoing structure may be made to provide for a physically more compact splitter structure. Referring now to FIGURE 5, for example, a modified electrode structure for the beam splitter is shown which provides for a greater degree of divergence between the beam portions by allowing a closer spacing between the electrodes. As modifed, the

outer electrodes

36 and 37 are each of arcuate configuration and curve away from the axis of the incoming beam 12 in opposite lateral directions. The modified center electrode 26 is formed with two

sections

71 and 72 which are joined at the end nearest the incoming beam 12 and which diverge from the axis of the beam 12 with curvatures corresponding to that of the outer electrodes 36' and 37 respectively.

Sections

71 and 72 in conjunction with

outer electrodes

36 and 37 respectively thus define a pair of diverging beam channels '73.

As in the former instance, a high voltage supply 46 is connected between the center electrode 26 and the two outer electrodes 36' and 37, the center electrode having a potential relative to the outer electrodes which is of like sign with the charge of particles in beam 12. The electrode structure of FIGURE 5 may be mounted within vacuum and support structure similar to that shown and described in conjunction with FIGURES 1 to 3.

Since the electrodes 36', 37 and 26' follow the curvature of the diverging particle beams, such elements may be more closely spaced than in the embodiment of FIG- URES 1 to 3, providing a more intense electric field and producing greater divergence of the two portions of the particle beam. As a further variation, the

electrodes

36, 37' and 26 may be made from some flexible material so that the curvature of the beam channels 73 may be adjusted.

Thus it will be apparent to those skilled in the art that numerous variations and modifications may be made within the spirit and scope of the invention and thus it is not intended to limit the invention except as defined in the following claims:

What is claimed is:

1. A device for splitting a charged particle beam into two separate beams, comprising a vacuum enclosure having a first thin window at a first end and having a second thin window at the opposite end, a pair of long fiat parallel outer electrodes disposed within said enclosure one on each side of an axis extending between said windows and in parallel relationship therewith, a long thin flat center electrode disposed between said outer electrodes in spaced apart parallel relationship therewith, means for adjusting the spacing of each of said outer electrodes from said center electrode, means for retracting said center electrode from between said outer electrodes, and a voltage source connected between said center electrode and each of said outer electrodes for applying a potential therebetween.

2. In a charged particle beam splitter, the combination comprising a long inner electrode having opposite convex faces which converge at a first end and increasingly diverge towards the opposite end, a pair of long outer electrodes each having the same curvature as one of said faces of said inner electrode and each being disposed adjacent one of said faces of said inner electrode and spaced therefrom to form two curved divergent beam channels, and a power supply connected between said inner electrode and said outer electrodes and applying a potential to said inner electrode relative to said outer electrodes which is of similar sign to said charged particles.

3. Apparatus for dividing a charged particle beam into two divergent beams comprising, in combination a center electrode having long opposite flat surfaces which converge at a first end of said center electrode and which increasingly diverge toward the opposite end of said center electrode, a pair of long outer electrodes disposed one along each of said opposite surfaces of said center electrode in spaced apart relationship therewith, said outer electrodes having fiat surfaces facing said opposite surfaces of said center electrode which flat surfaces have curvatures similar to that of said center electrode surfaces to form two diverging beam channels, a voltage source applying a potential to said center electrode relative to said outer electrodes which is of similar sign to the charge of said particles, and means forming a vacuum envelope around said electrodes.

4. In apparatus for dividing a high energy ion beam into two divergent beams, the combination comprising a pair of spaced apart outer electrodes forming a long channel into which said charged particle beam may be directed, a long center electrode disposed between said outer electrodes and dividing said channel into two separate beam passages, means for varying the spacing of said center electrode from said outer electrodes for varying the relative widths of said two beam passages, a vacuum enclosure surrounding said electrodes and having thin high energy ion beam transparent windows at each end of said electrodes, and a voltage source connected between said center electrode and each of said outer electrodes for creating oppositely directed electric fields on each side of said center electrode.

5. Apparatus for dividing a high energy ion beam into two separate beams comprising, in combination a vacuum enclosure having charged particle transparent windows at opposite ends, a pair of long spaced apart outer electrodes one on each side of an axis extending between said opposite ends of said enclosure and forming a beam channel therebetween, a center electrode disposed between said outer electrodes in alignment with said axis, said center electrode having a thin edge adjacent one of said ends of said enclosure for dividing an incoming ion beam into two sub-beams, means for retracting said cen-' ter electrode from between said outer electrodes, and a voltage source coupled between said center electrode and said outer electrodes.

References Cited in the file of this patent UNITED STATES PATENTS 2,035,623 Sukumlyn Mar. 31, 1936 2,090,636 Olskevsky Aug. 24, 1937 2,214,019 Gray Sept. 10, 1940 2,336,895 Shelton et al Dec. 14, 1943 2,574,655 Panofsky et al. Nov. 13, 1951 2,757,301 Jones et a1. July 31, 1956 2,921,228 Farnsworth Jan. 12, 1960

Claims

1. A DEVICE FOR SPLITTING A CHARGED PARTICLE BEAM INTO TWO SEPARATE BEAMS, COMPRISING A VACUUM ENCLOSURE HAVING A FIRST THIN WINDOW AT A FIRST END AND HAVING A SECOND THIN WINDOW AT THE OPPOSITE END, A PAIR OF LONG FLAT PARALLEL OUTER ELECTRODES DISPOSED WITHIN SAID ENCLOSURE ONE ON EACH SIDE OF AN AXIS EXTENDING BETWEEN SAID WINDOWS AND IN PARALLEL RELATIONSHIP THEREWITH, A LONG THIN FLAT CENTER ELECTRODE DISPOSED BETWEEN SAID OUTER ELECTRODES IN SPACED APART PARALLEL RELATIONSHIP THEREWITH, MEANS FOR ADJUSTING THE SPACING OF EACH OF SAID OUTER ELECTRODES FROM SAID CENTER ELECTRODE, MEANS FOR RETRACTING SAID CENTER ELECTRODE FROM BETWEEN SAID OUTER ELECTRODES, AND A VOLTAGE SOURCE CONNECTED BETWEEN SAID CENTER ELECTRODE AND EACH OF SAID OUTER ELECTRODES FOR APPLYING A POTENTIAL THEREBETWEEN.