US2814728A

US2814728A - Ion beam collimator

Info

Publication number: US2814728A
Application number: US523134A
Authority: US
Inventors: Jr Alexander S Langsdorf
Original assignee: Individual
Current assignee: Individual
Priority date: 1955-07-19
Filing date: 1955-07-19
Publication date: 1957-11-26
Anticipated expiration: 1974-11-26

Description

Nov. 26, 1957 A. S. LANGSDORF, JR

ION BEAM COLLIMATOR 3 Sheets-Sheet 2 Filed July 19, 1955 INVENTOR.

(/zz forrz e Nov. 26, 1 7 A. s. LANGSb ORF, JR 2,814,728

ION BEAM COLLIMATOR Filed July 19, 1955 3 Sheets-Sheet 3 -"i VIIIIIIIII'III I) 4mm", m

United Stat ION BEAR I COLLIMATOR Alexander S.-Langsd0rt, In, Roselle, Ill., assignor tothe- United States of America as represented by the United States Atomic Energy Commission Application July 19, 1955, Serial No. 523,134

13 Claims. (Cl. 250-495) This inventionrelates generally to devices for defining beams of high energy and in particular to a device-for shaping a high energy beam produced in aparticle accelerator preparatory to the bombardment of a target undergoing studies related to the compositio'n'of matter.

Many methods have been employed in the study of atomic structure of elements utilizing artificial disintegration of said elements. Most of the methods utilize the s atentO erated and impressed across an accelerator tube, said tube apparatus having collimating or beam-defining members,"

for shaping the ion beam-to-thedesired size; Thetdisadvantage of using presently available apparatus lies'in the short life of the beam-defining members. 'These beam-forming members, because of the ever increasing potentials used in modern particle accelerators, do not last long because ofthe erosion brought'about by the bombardment of the members by the particles in the -ion beam. The bombardment of the forming-members isof sufi'icient intensity to raise the temperature of themembers to such an extent that the materials comprising-the members wear away after short-periods of use; Another disadvantage of the hereto existing beam-forming apparatus is the length of time required for adjustingth'e beam source-to project a beam so that the beam would pass centrally between the beam-forming. members. .Oneof the methods used at the-presenttime requires'theinsertion of a luminescent target into the apparatusrto intercept the shaped beam passing therethrough andlviewing the result through an optical opening; This :is time-consuming and interrupts the beam whenever'it has to be realigned during operation; Visual observation of the shaped'beam is not conclusive as' to theparallelism of the beam with the axis of the tube and requires haphazard adjustments to direct the beam uponthe distant target.

The main object of this invention is to provide means' including collimating means for forming an ion-beam generated by a particle accelerator,- said collimatingi means beingjadequately cooled to prevent disintegration thereof due to high temperatures caused by beam interception.

Another object of the inventionis to provide means for 2,814,723 Patented Nov. 26, 1957 forming an ion beam generated by aparticle' accelerator, said means having rotatably' adjustable means therein so that the movement of the adjustable means is linearly related to the movement of the collimating means.

A further object of this invention is to provide an apparatus for defining the shape of a particle" beam, generated by a particle accelerator, in an evacuated accelerator tube without the loss of existing vacuum.

Still another object is to provide'a' beam-forming device, adapted to cooperate with other means for aligning the beam within the accelerator tube without total interception of the beam and to indicate the amount of p'artial beam interception by the collimating means.

Other objects and advantages of this invention Will-become apparent and will be better understood by reference to the following description in conjunction with the accompanying drawing comprising several'figu'res, wherein:

Fig. 1 is a schematic representation of a beam-forming apparatus shown in its relationship to a high energy beam source and means for controlling said beam source;

Fig. 2' is an end view of the beam-forming apparatus partially in cross section, taken along the 1ine2-'-2 of Fig. 3, to expose to view channels'used for conducting a cooling medium;

Fig. 3 is a side view of thebeam forming-apparatus;

Fig. 4 is a partial enlarged cross-sectional viewof Fig. 2. taken along the line 44'to show the construction and relationship of a beam-forming unit in the apparatus;

Fig. 5 is a plan view of one'of a first pair'of retainer walls;

Fig. dis a cross-sectional view of- Fig. 5 taken along the line 6-6;

Fig. 7 is a cross-sectional view of the retainer wall taken along the line 77 of Fig. 5;

Fig. 8 is a plan view of one of a second pair of retainer walls;

Fig. 9'is a side View of a mounting blockhaving'frust'oconical cavities therein;

Fig. 10 is a cross-sectional view of the mounting block taken along the line 1010 of Fig. 9;

Fig. 11 is a cross-sectional view of the beam-forming apparatus taken along the line 1-111 of Fig. 3;

Fig. 12 is a cross section of a beam formin'g niember taken along the line 12-12 of Fig. 13; v

m Fig. 13 is an end View of the beam fo'rmin'g' member of Fig. 12 showing the eccentric mounting of a cam;

Fig. 14 is a cross-sectional View taken alongthe line 1414 of Fig. 13;

Fig. 15 is a partial cross-sectional view of a beam-forming member taken along-theline 15-15'of Fig. 14;

Fig. 16' is an end view of a modified form of a cam; and

Fig; 17 is a cross-sectional view taken along the line 17-17 of Fig. 16.

In accordance with the teachings ofthis invention there is provided an apparatus for shaping 'a beam produced by a beam-producing source. The apparatus comprises a mounting block having a central opening through which the beam is projected, means for rotatably supporting two pairs of beam-forming members including hollow slit cams, the beam-forming members being'insulated; from each other and the block and extendinginto the-opening, said members being adjustable and cooperatively-positioned to define the beam passing between the slit cams, the supporting means and the beam-formingmembers-being cooperatively adapted to receive a medium for cooling internally the slit cams. The slit cams have individual means connected thereto for indicating the amount of charge collected thereon due to beam interception to asconnected between evacuated beam tubes 102-.and-103 3 wherein the beam tube 102 has its other extremity connected to a high energy beam source 104 and the beam tube 103 has its other extremity coupled to a target 105. The illustration in Fig. 1 of the beamforming apparatus 101 shows a top view of only one pair of slit cams 106- and 107 (for shaping the beam in the horizontal plane) in order to simplify the discussion on the shaping of the beam produced by the highly evacuated beam source 104. These cams, because of their function, are called horizontal cams. The cam 106 is connected to a preamplifier 108 and the cam 107 is connected to a preamplifier 109. Each of the preamplifiers 108 and 109 is connected to a difference amplifier 111. The output of the difference amplifier 111 is fed into a control circuit 112 which is connected to the high energy beam source 104. A pair of instruments 113 and 114, such as vacuum tube voltmeters, are connected between the outputs of the preamplifiers 108 and 109, respectively, and ground. The high energy beam source 104 may be any one of the well known particle accelerators, such as a Van de Graaif generator, which has means associated therewith for evacuating the chamber proper and the beam tubes 102 and 103 communicating therewith to provide a suitable path for accelerating the particles. by the high energy beam source 104 and directed through the tube 102. The beam is then shaped by the pair of

horizontal slit cams

106 and 107, and allowed to be directed to the target 105. The amount of current generated by the bombardment of the target 105 is measured by indicating means 115 which is connected thereto. The beam-forming apparatus 101 also possesses a pair of vertical slit cams (not shown), similar in construction to the horizontal slit cams, which define the projected beam in the vertical plane. Observation of the voltmeters 113 and 114 enables an operator to determine whether the

cams

106 and 107 bear identical spatial relationship to the projected beam in the tube 102. The voltage developed on the

slit cams

106 and 107 is amplified by the preamplifiers 108 and 109, respectively, and fed into the amplifier 111, the output of said amplifier being used to operate the control circuit 112 which controls the beam output of the high energy beam source 104. The slit cams are initially adjusted to define the size of the beam and to pass the beam therethrough coaxially with the beam tubes. During operation, if the beam deviates from its preset direction, the control circuit 112 will respond to the charges built up on the abnormally intercepting cams and will exert control on the beam source 104 to realign the beam. Since the slit cams in the beam-forming apparatus 101 are in the path of the beam of particles generated by the beam source 104, they become hot and would not last long if a cooling medium furnished by a source 115 were not provided. The cooling medium is circulated internally within the slit cams as will be described in reference to Fig. 4.

Fig. 2 discloses an end view of a beam-forming apparatus 101, partially in cross section, comprising a rectangular mounting block 201 made of metal, preferably brass, having mounted on each of its sides individual retainer walls 202205, said retainer walls being made of insulating material, such as plastic, preferably Lucite. The function of the retainer Walls is to support beamforming units as will be described hereinafter. Each of the retainer Walls has a pair of parallel main channels 207 therein for admitting a cooling medium. Each of the retainer walls is mounted on one side of the mounting block 201 and overlaps an adjacent retainer wall in such a manner as to connect serially the L-shaped main channels 207. To prevent the escape of the cooling medium out of the channels 207, the joints between the adjacent forming walls, such as the joint 206 between the

retainer walls

203 and 204, are sealed by means of rings 208. The mounting block 201 has a longitudinal bore 209 running therethrough, said bore being utilized for passing a stream or a beam of high energy particles. The retainer The beam is initially formed 4 walls 202205 are used for supporting beam-forming units 211214, respectively. The external portion of each beam-forming unit, such as 212, visible in Fig. 2 comprises a retainer knob 216, a retainer knob pin 217, a dial plate 219, and an adjusting gear 220. The beamforming unit 212 may be rotatably adjusted by direct application of torque to the retainer knob 216 and its associated pin 217. The beam-forming unit 212 may also be adjusted by remote application of torque through suitable means to the gear 220, if desirable, therefore allowing adjustments to be made during operation without exposing operating personnel to radiation hazards. The dial 219 is calibrated to indicate the position of the internal portion of the beam-forming unit 212 with respect to the axis passing through the bore 209.

Referring to Fig. 3, the retainer walls 202205 are mounted on the mounting block 201 by screws 301. Mounted on the retainer wall 204 is a pair of fittings 302 and 303, said fittings being secured thereto by screws 304. A pair of O ring seals 306 prevent leakage in the joints formed between the fittings 302 and 303 and the wall 204. The fittings have tapped openings 305 which are adapted to engage pipes or hoses carrying a circulating cooling medium.

An enlarged cross-sectional view of the beam-forming unit 212 is shown in Fig. 4 wherein said unit comprises a member 401 having a frusto-conical shape adapted to seat in a similarly shaped cavity in the mounting block 201 and a cylindrical end adapted to seat in the retainer Wall 203. The member 401 has a bore 402 running longitudinally therethrough and a barrier 403 subdividing the bore into two semi-cylindrical spaces 402a and 402b. The barrier 403 is supported within the bore 402 by contact with the Walls of the bore and also by a plug 404 (Figs. 12 and 14) which is soldered to the member 401. The frusto-conical end of the member 401 terminates in a slit cam 405 which is soldered to said end. The frustoconical portion of the member 401 is seated within a frusto-conical cavity 406 in the mounting block 201, but is insulated therefrom by an insulating insert 407. The slit cam 405 extends entirely across the bore 209 but is off-center thereto. Loss of vacuum in the bore 209 is prevented by utilization of 0 ring seals 408 which are disposed between the retainer wall 203 and the mounting block 201 and the member 401 and the retainer wall 203. The seals 408 are located in peripheral grooves 408a in the cylindrical portion of the member 401. The external portion of the member 401 has a pair of dowel pins 409 mounted therein which pins engage the body of the gear 220. The gear 220 is made an integral part of the member 401 by means of a screw 215 which serves to maintain the pin engagement. The retainer knob 216 as well as the dial plate 219 are mounted on the adjusting gear 220 by screws 410. The member 401, which is made preferably of metal such as brass, has a pair of transverse openings 411 and 412; the opening 411 communicating by way of a groove 40812 and a channel 413 with the main channel 207a and the opening 412 communicating by way of a groove 400a and a channel 413a with the main channel 207b. The communication of the main channel 207a with the channel 413 which terminates in the groove 408b is more clearly indicated in Fig. 7. The grooves 40% and 408a enable the member 401 to be rotated and still maintain communication between the bore 402 and the main channels. The barrier 403 is used to direct the flow of the cooling medium to the extremity of the slit cam 405. This is readily seen by observing that if a cooling medium is forced from the main channel 207a, through the channel 413, and the opening 411, the cooling medium will then be directed through the semi-cylindrical space 402a, into the interior of the slit earn 405 and then through the semi-cylindrical space 402b, the opening 412, and through the channel 413a into the main channel 207 b. The beam-forming unit 212 and its associated cam 405 may be rotated by applying torque to the retainer pin 217 and the retainer knob 216, as was previously indicated. The beam-forming units, such as 212 and 214, are arranged in pairs and are adapted to cooperate together to shape the beam passing between their individually associated slit cams. As seen in Fig. 3, the centers of the

units

212 and 214 are contained in one plane, but they are in ofl-center relationship in the transverse plane, as shown in Fig. 2, so as to straddle the bore 209. The cooperation of the units in each pair is more readily seen in Fig. 11 which is a cross-sectional view taken along the line 11-11 of Fig. 3.

. Fig. 5 discloses one of the retainer walls, such as 203, with the various channels therein. Since these channels, such as 207a, 207b, 413 and 413a, are not exposed to view, they are shown by appropriate designation. In addition to the aforementioned channels, there are additional channels 501 and 502 (hidden from view). The disposition of the

channels

501 and 502 within the retainer wall 204 is more clearly indicated in Figs. 6, 7 and 8. The

channels

501 and 502 are used for testing the seal existing between the rotatable beam-forming unit and the rest of the apparatus 101. The seal may be tested by applying a gas under pressure and detecting the escape of gas in several places such as in the bore 209, the area adjacent the gear 220 and the channels 207 by means of a suitable gas detector.

The disposition of the frusto-conical cavities in the mounting block 201 is indicated in Figs. 9 and 10 wherein one of the cavities 406a is located opposite, in oif-center relationship, to the cavity 406]; (hidden lines), the axes of said cavities being displaced from each other by ap proximately the diameter of the bore 209. Similarly, another pair of off-center located frusto-conical cavities 406a and 406d (hidden lines) are seen in a plane transverse to the plane containing the first pair of cavities. The cavities 4060 and 406d connect commonly with the bore 209.

The construction of the member 401 is shown in Fig. 12.

Fig. 13 indicates that the slit cam 405, which is cylindrical in the end view, is mounted eccentrically with respect to the axis of the member 401. Similarly, Figs. 14 and 15 further reveal additional structural details.

The cooperation of the various beam-forming units 211214 can be realized from the inspection of Fig. 11 wherein two beam-forming

units

212 and 214 are shown. The slit cams 405 associated with said beam-forming units shape the beam in the horizontal plane. The separation between the slit cams 405 can be adjusted by rotating either one or both of beam-forming

units

212 and 214. As indicated before, rotation of the beam-forming unit 212 can be obtained by application of torque to the retainer knob 216, the gear 220, or the retainer knob pin 217. As the beam-forming units 211214 are rotated, the slit cams 405 individually associated with said units will intercept more or less of a certain portion of the beam passing through the bore 209. The amount of current picked up by each slit cam can be determined by means of the voltmeters, such as 113 and 114, which may be connected by suitable means to the retainer knob 216. As a result of the indications on said voltmeters, it is possible to observe whether the beam is projected properly by the beam source. If the particle beam traversing the bore 209 is not projected properly, one of the voltmeters will give a greater reading than the other voltmeter thereby indicating that the control circuit controlling the operation of the beam source has to be adjusted. It is to be understood that the discussion hereinbefore related to only one pair of beam-forming

units

212 and 214 and that another pair of beam-forming

units

211 and 213 cooperate in a similar manner to shape the beam in the vertical plane. As a result of the cooperation of these two pairs of beam-forming units, the beam traversing through the bore 209 may be defined to have a square or a rectangular cross-sectional area.

As discussed previously in relation to Figs. 13 and 15, the slit cam 405 is cylindrical in cross section and eccentrically mounted on the member 401. Rotation of the member 401 will cause the slit cam 405 to travel along an eccentric orbit. Since the rotation of the member 401 bears no linear relationship to the variation of separation between the cooperating slit cams 405, it is diflicult to calibrate the dial plate 219 so that it will indicate correctly the dimensions of the closure occurring between the slit cams 405. In order to have the opening between the slit cams 405 vary linearly with the angular rotation of the dial plate 219, a preferred type of a slit cam is shown in Fig. 16 and Fig. 17. A partial cross-sectional view of the member 401a is shown having mounted thereon a mounting insert 17a which is used for supporting a linear-type slit cam 17b. The shape of the cam 1711 can be accurately determined from the parametric formulae 0=tan tit-ct =0 sec at where (9, r) are the angle and radial coordinates of a spiral. Eliminating the parameter or, the result is 0= 2- 1 cos 2 Y a r The use of such a cam facilitates the calibration of the dial plates 219.

While there has been described What is at present considered to be the preferred embodiment of the invention, it will be understood that various modifications may be made herein and it is intended in the appended caims to cover all such modifications as found within the true spirit 'and scope of the invention.

What is claimed is:

1. An apparatus for defining a beam generated by 'a high energy particle accelerator in an evacuated tube, comprising a body including an opening therethrough coupled to the tube and oriented to pass the beam through the opening, a plurality of cavities in the body grouped around the periphery of the opening and communicating therewith, adjustable collimating means, means for rotatably supporting the collimating means in the cavities and electrically insulating the collimating means from the body and from each other, said collimating means including internally cooled hollow beam-intercepting bosses extending into the opening to define a slit whose width is variable by rotation of the collimating means, the sides of the slit being parallel to the axis of the collimating means, and a source of cooling medium, said supporting means connected to the source for channeling the cooling medium through the collimating means into the interiors of the bosses, whereby the heat developed on the bosses due to partial beam interception is adequately removed.

2. The apparatus as claimed in claim 1, the adjustable collimating means comprising two pairs of members, the members of each pair being disposed approximately opposite each other about the periphery of the opening, said pairs being disposed quadrantly with respect to each other about the opening, said members terminating in eccentrically mounted slit cams extending through the opening, the members in the pair including their associated slit cams being mounted in off-center relationship to the axis of the opening and adapted to bracket the opening between the slit cams, and means for actuating the members to define the beam passing between the slit cams.

3. The apparatus as claimed in claim 2, the slit cams being cylindrical elements afiixed eccentrically to the members, whereby the rotation of the members will vary the spacing between each pair of elements.

4. The apparatus claimed in claim 2, the slit cams being spiral shaped elements afiixed to the members, the crosssectional shape of the elements being determined by the formula where and r are the angle and radial coordinates of the spiral shape and a is a constant, whereby angular rotation of eachpairof members bears a linear relationship to the spacing between their individually associated: elements.

5. An apparatus for shaping a beam comprising, in combination, a high energy particle accelerator having an evacuated output beam tube for projecting energy beam therethrough, means being interposedly coupled with the tube and having a central opening therein for passing the beam therethrough, a pair of means inopposed relation extending into the opening for collimating the beam passing therebetween, means for introducing a coolant into the collimating means to dissipate heat generated thereon due to beam interception; means connected to the collimating means to indicate the-amount of beam interception by the collimating means, means for detecting a difference in the beam current intercepted by the pair of collimating means, and means responsive to the detecting means to align the beam.

6. A beam-forming device for shaping anenergy beam comprising, a body having a central opening running therethrough for admitting the beam, a pair of opposed collimating means including hollow elements extending into the opening to define the beam passing therebetween, insulating means for rotatably supporting the collimating means and electrically isolating the collimating means from the body and from each other, said collimating means being responsive to angular rotation to define the beam between the hollow elements, means for indicating the amount of beam interception by each collimating means, means for detecting a ditference in the amount of beam interception by the pair of collimating means, and means responsive to the detecting means to align the beam, the insulating means and the collimating means cooperatively engaged to provide an ingress and egress to a cooling medium introduced into the hollow elements, whereby the heat generated by the portions of the beam intercepted by the hollow elements can be removed.

7. A beam-forming device for shaping an energy beam comprising, a body having a central opening therethrough for admitting the beam, a pair of opposed collimating means including hollow elements extending into the opening to define the beam passing therebetween, insulating means for rotatably supporting the collimating means and electrically isolating the collimating means from the body and from each other, the collimating means responsive to angular rotation to define an aperture between the elements for passing the beam therebetween, means connected to each collimating means to indicate the amount of energy intercepted from the beam, means for detecting a difference in the amount of energy intercepted from the beam by the pair of collimating means, means responsive to the detecting means to align the beam, and means in the insulating means and the collimating means cooperatively engaged to provide an ingress and egress to a cooling medium introduced into the hollow elements, whereby the heat generated by the portions ofthe beam interrupted by the hollow elements is removed.

8. An apparatus for shaping an energy beam comprising, a body having a central opening therein for admitting the beam, a pair of opposed rotatably adjustable means disposed about the body and extending into the opening to form an aperture for passing the beam therethrough, said aperture means being electrically insulated from the body and from each other, means associated with the aperture means to indicate the amount of beam interception by each said aperture means, means for detecting a difference in the amount of beam interception by the pair of aperturemeans, and means responsive to thedetecting means to align the beam.

"9. An apparatus for shapingan energy beamcomprising abody having a central boretherein' foradmitting'the beam, and a pair of means rotatably dispo'sed in the'opening to form an opening for shaping the beam passing therethrough, said pair of i means 1 being electrically insulated from each-"other-and from the body to store up the energy receivedfrom the interceptedportions of the beam, and means to determine unequal interception of the beam by each of said' means.

10. An apparatus for shaping an energy beam comprising a bodyhaving a central opening therein for admitting the 1368111,:3. pairof f-rusto-conical cavities in the body oppositely disposed in off-center relationship about said opening and communicating therewith, and a pair of frust'o-coni'calmembers'hermetically seated in said cavities and extending into the opening to define a slit therebetween for the passage of the beam; said members electrically insulated iromeach other and from the body to support an'energy charge developed thereon by the interceptedportions of the beannand'me'ans to measure the charge on'the members.

llxAn apparatustor shaping anenergy beam comprising a body having acentral opening therein for admitting thebeam, a plurality of frustowonical cavities in the bodyoppositely disposed in off-center relationship aboutsaid openingand' communicating "therewith, a plurality' of frusto-coni'cal members hermetically seated in said cavities and extending into the opening to define an aperture"thereb'etween for the passage of the beam, the size of the beam being controlled by rotatable actuation of the members, said members electrically insulated from each other and the body to support an energy charge developed thereon by the intercepted portions of the beam, means to indicate the amount of beam interception by each member, and means responsive to the indicating means to direct the beam through the opening to cause equal interception of the beam by all members.

12. A beam-forming apparatus for shaping an energy beam comprising a body having an opening therethrough for the passage of the beam, two pairs of hollow beamintercepting members, each member being mounted within the body opposite to its mate in oft-center relational about the opening, each member including a hollow cuplike boss extending into the opening, rotation of a member causing the axis of its boss to move in parallel relation With respect to the axis of its mating boss, this parallel relation of mating bosses causing the sides of a slit of variable size to be defined by the sides of the mating bosses and to be disposed normally to the slit defined by the other pair of mated bosses, and means for rotatably supporting the members, said last means channeling a cooling medium through the bosses to remove heat generated by the intercepted beam.

13. The apparatus of claim 12, the hollow cup-like bosses being shaped to linearly relate angular rotation of the hollow beamintercepting members to variation in slit size and positioned to cause a full range variation to slit size by a rotation of the hollow beam-intercepting members.

References Cited in the file of this patent UNITED STATES PATENTS 2,455,676 Hillier Dec. 7, 1948 2,520,813 Rudenberg Aug. 29, 1950 2,674,698 Danforth et al Apr. 6, 1954