US2609500A - Injector mechanism - Google Patents

Description

Sept. 2, 1952 M. D. MARTIN INJECTOR MECHANISM Filed Oct. 11, 1950 INVEN TOR. MA/PV/N D. MART/N i atenteti Sept. 2

UNITED STATES PATENT OFFICE 2,509,500 mmcron MECHANISM Marvin D. Martin, Berkeley, Calif, assignor to the, United States of America as represented. by the United States Atomic Energy Commission Application October 11, 1950, Serial No. 189,642- 8 Qiaims, (Cl. 2250-27) 1 The sen nv n on r ates enerall t particle accelerators andginmore particular to m r m nts n ie to s or sv h onsaod the like.

The injection of char ed Particles; into particle accelerators and similiar apparatus that constrain ar ed particlest e v rs ubst ntially circular orbits often interferes with the subsequent acceleration of the particles in that the injector mechanism is, of necessity, located in close proximity to the-particle orbit. This is particularly true in synchrotrons which cona n e ted ar icles o r n. tsuo constant radius that therefore approach the-inm han sm endilifitmw w th. rei r n s to pa i e er rs o th hrotron. t e

that the invention isdisclosed and described.

Considering first the magnitude of interference normally resulting from the injector mechanism of a synchrotron, it is noted that maximum. injector efliciency is obtained with the injector mechanism located approximatleyon the circular orbit of the accelerated particles.

In 'a typical synchrotron operatiQn electrons areaccelerated about a constant radius orbit wherein, for example, they. traverse the orbit about 25 times each microsecond and an aceelerating1 cycle lasting 8,000 .rnicrosecends requires 200,000 complete trayersals of the orbit within this time. It, will be appreciated that only the relatively few electrons whichfollow displaced orbits} or orbits. deviating from" normal will complete thev above accelerating cycle. Thus only thesefew electrons constitute, the final accelerated beam and comprise useful output of the. apparatus Numerous synchrotron modifications have in thepast been developed for the purpose oi overcoming the above-noted problems and these modifications have proven more or less advanr tageous with the maximum increase in the output beam being of the order of 50%. While such an increased output is undoubtedly desirable,

the modifications generally relate to magnet modifications or the addition of expansion coils V which not. only add to the complexity. and cost of the acceleration apparatus but also contain inherent limitations which limit further improvement in. the; accelerator efficiency.

The present invention accomplishes. injection without interference with subsequent particle acceleration, in a mannerexplained in detail below and in conformity with. thefollowing objects.

t s. an je o th p es n nven io o pro e a e nd im o ed Wehrmacht-- et. P .net le eee ler wra- It amt e bie of e er se t nvent on to provide an improved inj ctor mechanism {or particle accelerators which does not interfere with particle acceleration.

t is a e bieet i e; s nt m n ion to provide synchrotron injector mechanism ca: p e of r v n a le im i ement thereon.

It is. st a ot object ofthe masco in n tion to provide-an improved injector mechanism r Pa ticle ac e r to a d n lu i n. e e

ati field gu din ac elera ed. articl s. past a d n ec mec an m- It e ano her b e f hemesen i ven: e; *9- P IQ im r ved m th d t n ect:

a icl s t a pa cce er or w ere n e ac eler t on 0 arfiqle no m ded by the injection.

It is a further object oi the present invention l o provide an mproved s n h r in ctor seha sm v a le r s at ie d u ding accelerated particles about the injector.

It is a still further object of the present ine vention to provide an improved synchrotron i;n.

jectormechanism having an integral accelerat ing field further employed to guide accelerated pa i l s, as hei i e rc mp sh d. s. f ll s t f r h n hefol w e;

e c o f nstr qtiqnr a e at onw i il t n er d h n o sider d i lQQDr Jun i with a om any ng; drawin s...

wherein:

F ure 1 is a l n i w t e in to mesh? m srn in section;

F is a e eleva o of he. i ect r l p.

partially broken away and including a simplified representation of an associated electrical sys-l tern; and i Fig. 3 is a plan view 'of a synchrotron chamber showing the injector mechanism inposition.

Referring first to an injector mechanism as shown in Figs. 1 and 2, it will be noted that there;

c or nd. orm dte el etron misthereto.

m ns o h re i:

he m erin h c the a o e s are is provided a filament ll heated by electrical shield l3 and surrounding same is an accelerating electrode I6 which may be formed in the general shape of a square truncated cone with a closed small end or may alternatively comprise a generally U-shaped plate disposed about shield [3 as shown in Fig. 1. Electrode 16 has an elongated aperture I'I therein in general alignment with the aperture l4 in shield I3 and preferably of a greater width to accommodate the passage of a slightly divergent beam of electrons. A second aperture [8 in electrode [6, of the same size as aperture I1, is provided on'the opposite side of filament H and shield [3 from aperture H. In the illustrated embodiment of the invention, strengthening of the tip of electrode [6 may be accomplished by the .use' of braces I9.

filament current supply 3|, electrons are thermally emitted from the surface of filament l l in copious quantities. Filament H and associated conductors 12 are electrostatically shielded by shield member l3 except for one face of filament II which lies adjacent aperture l4 in shield 13. The relatively high positive potential upon accelerating electrode l6 establishes an electrostatic field which, acting through aperture I4 in shield 13', attracts electrons formed at filament ll. Under the influence of this field, electrons at filament II are accelerated through aperture [4 in shield I3'toward electrode I6. and thence through aperture l1 therein. These electrons emerge from the injector mechanism with a ceri tain minimum velocity and a small divergence in secured to electrode l6 across the ends of aper- I tures I1 and [8.

The above-described injector elements may be secured in position by any suitable means such as,"for example, the mounting arrangement illustrated in Fig. 1. As shown, electrode [6 is provided with a flange extending outwardly from the-open; end thereof, and this flange is secured as bysoldering to a plate 2|, which is in turn mounted upon pins 22, as shown. Extending into the synchrotron chamber 23, as shown in Fig. 3,- is an insulating stem 24 having indentations upon the inner end thereof into which pins 22 -mate to provide support for electrode 16. Within insulating stem 24 there is provided a second elongated insulating member 26 through which filament leads I2 pass in rigid relation thereto and upon which is mounted shield member- 83-, as'by clamping means 21. Synchrotron chamber 23 is made vacuum tight about stem 24 and insulating member 26 by any suitable means, not shown, in order that particle acceleration. may be accomplished in a high vacuum.

The elements of the injector are maintained at particular potentials relative to each-other in order that they may accomplish their functions, as briefly stated above and more specifically explained below inthe description of operation. As shown schematically in Fig. -2, a filament current supply 3| is connected between filament leads 12 to provide heating current for filament I I. -Shield I3 is electrically connected to filament ll-tomaintain each at the same potential, and potential supply means '32 is electrically connectedbetween electrode [6 and shield-l3. In the embodiment of the invention illustrated, electrons-are produced at filament II for acceleration and in this instance electrode I6 is maintained at a positive potential with respect to shield l3 and filament II by potential supply means 32 for the purpose of attracting electrons from filament II. It will be appreciated, however, that the relative potentials of the elements of the injector are determined by the type of particles to be accelerated, and also the type of source employed may be varied in order to produce the desired'type of particles.

Considering now the operation of the invention, attention is first directed to the fact'that the inje'ctor' mechanism contemplates ejection of charged particles into a chamber or other envelope wherein these particles are more or less separately operated upon. For convenience of illustration, the following explanation i with ref erence to synchrotron operation wherein electrons expelled from the injector mechanism are constrained to travel constant radius orbits with increasing velocities. With filament H energized byheating current through conductors [2 from direction. Because of this small but unavoidable divergence in direction, these emerging electrons actually follow slightly diiferent orbits which each have the same radii but which have the centers thereof slightl'ydisplaced. For the sake of simplicity, it is desirable to consider the electrons emerging from the injector mechanism as comprising a plurality of beams, as illustrated in Fig.

3. As may be seen from Fig. 3, upon completion of one revolution within the synchrotron, the dis- I placed electron beams converge upon the injector mechanism and in the-absence of preventative measures wouldin the great majority impinge it Will be appreciated that the equipotential linesbetween electrode [6 and shield l3 lie generally parallel thereto except in the vicinity of apertures'in these elements. Immediately adjacent aperture l8 in electrode I6, the equipotential lines are bowed toward the aperture and in fact equipotential lines directly adjacent electrode I6. are materially expanded into a bubble which protrudes through aperture [8 exterior to electrode [6 much in the manner illustrated by dashed lines 36 in Fig. 1. This field configuration extends outwardly from the back of the injector mecha-' nism and directly affects the orbits of electron beams accelerated in synchrotron chamber 23. As previously noted, the electron beams from the injector mechanism'travel orbits of constant radius which are, however, slightly displaced from one another as a result of a small divergenc in the direction of the electrons leaving the injector mechanism. This divergence is greatly magnified in Figs. 1 and 3, in order to more clearly illustrate the phenomenon. As will be seen from Fig. 3. the beams generally converge in the vicinity of the injector mechanism and it i thi portion of the orbits that is depicted by lines 31 in Fig. 1.

.As the electron beams approachthe bubblelike electrostatic field protruding from the back of main slightly deflected toward the center of their orbit. This deflection or repelling action is'suflicient to guide a large portion of the electrons 4 around the injector mechanism and these electrons then continue to revolve about the synchrotron chamber without subsequent interference by the in ector mechanism. As -will be seen' from The present invention overcomes this" 1.,isomeview. electronslapnroach the hacker back of the injector mechanism when aperture i8 is made, the same size as aperture i1 and is exactly aligned'therewith.

Typical operation of a synchrotron includes electron injection for a period of two microseconds, in the course of which some'fifty revolutions are made by electrons in the synchrotron. Total acceleration may last 8,000 microseconds in which time some 200,000 revolutions are made and with a conventional injector a large percent of the electrons impinge upon the back of the injector mechanism; however, with the present injector the synchrotron output is multiplied some fifteen or more times over that possible with conventional apparatus.

The above description of the invention is referenced to only one type of particle accelerator and is disclosed in terms of but a Single embodiment; all of which is in no-wise to be taken as limiting but only as one illustration of the invention. As it will be apparent to those skilled in the art that numerous modifications and variations are possible within the spirit and scope of the invention, no limitations are to be taken from the above description but instead attention is directed to the following claims for a precise definition of the novelty contained in the invention.

What is claimed is:

1. Particle accelerator injector mechanism comprising an electron emissive filament, a shield about said filament electrically connected to said filament and having an aperture therein for the passage of electrons therethrough, and an accelerating electrode adapted to be maintained at a positive potential with respect to said shield and filament and encompassing said shield and filament, said accelerating electrode having a first aperture therein aligned with the aperture in said shield and a second aperture situated on the opposite side of said shield and filament and aligned with said first aperture.

2. Synchrotron injector mechanism comprising an electron emissive filament, electrostatic shielding means including first and second electrodes surrounding said filament and defining an electron path therethrough from said filament, said first and second electrodes being disposed in part in front and in back respectively of said filament,

and potential supply means connected between said filament and first and second electrodes to maintain said first electrode at a positive potential with respect to said second electrode and filament for attracting electrons from the front of said filament and repelling electrons from the back of said filament.

3. Synchrotron injector mechanism adapted to be disposed within a synchrotron chamber and comprising an electron emissive filament, an electrostatic shield about said filament and electrically connected thereto, said shield having an aperture therein adjacent one face of said filament for the passage of electrons from said filament therethrough, and accelerating electrode structure about said shield at a distance therefrom, said accelerating electrode having a first aperture therein in alignment with said shield aperture and adapted to be maintained at a positive potential with respect to said shield and filament whereby electrons emitted fromsaidfilament are ulged-xthroughsaid :shield aperture and -,Said:first accelerating electrode aperture into said synchroe tron chamber, and said accelerating eleetrqflea having .:a second aperture therein on theopposite sideof said filament and shield andaligned With.-

said first aperture wherebythe positive potential;

of. said accelerating potential. 'isgmodified. in they vicinitylof said second aperture to repel electrons,

approaching said injecto'rmechanism- 4. Synchrotron injector mechanism comprising; a source of electrons, first apertured-electrode;

means, power-supply means havinga positiv er'tere minal connected to said first electrode and a negative terminal connected to said source of electrons to establish an electrostatic field for attracting electrons from one side of said source, and second electrode means connected to the negative terminal of said power supply to establish a further electrostatic field exterior to the opposite side of said source of a polarity to repel electrons.

5. A synchrotron injector mechanism including an electron source disposed within a toroidal synchrotron chamber, an apertured electrostatic shield about said source and electrically connected thereto, and an accelerating electrode structure disposed about said shield to be maintained at a positive potential relative thereto whereby electrons are attracted from said source, said accelerating electrode having a first aperture therein in alignment with the aperture in said shield whereby electrons are accelerated therethrough into said synchrotron chamber, and said accelerating electrode having a second aperture in the opposite side thereof from said first aperture and in substantial alignment therewith to thereby form a relatively negative electrostatic field configuration about said second aperture exterior to said accelerating electrode from said electrostatic shield for repelling electrons approaching said injector mechanism.

6. In combination with an electron source having an apertured electrostatic shield thereabout, the improvement comprising accelerating electrode structure disposed exterior to said shield and having first and second apertures therein,

said apertures being in substantial alignment said electrostatic shield and the first aperture in said accelerating electrode structure and electrons are repelled from said accelerating structure in the vicinity of the second aperture therein by virtue of the relatively negative potential upon said electrostatic shield.

7. Injector mechanism for apparatus accelerating electrons along a constant radius orbit comprising an electron source, an apertured electrostatic shield about said electron source, electron accelerating means adjacent and exterior to said electrostatic shield for removing electrons from said source and urging said electrons into the orbit of said apparatus, and electrostatic field producing means for establishing an electron repelling electrostatic field exterior to said ion source and shield on the opposite side thereof from the removal of electrons whereby the orbits of said electrons in said apparatus are deformed to pass said injector mechanism.

8. An improved injector mechanism adapted 1" for disposition within an evacuated chamber and comprising an electron source, first and second electrodes disposed about said electron source,

saidflrst electrode being exposed to said electron source and to said chamber to define an electron path therebetween and said second electrode bes electrons are repelled irom 'the oppos'ite-si de of said mechanism from-said electronpathf 5 p REFERENCES CITED The following references are of recordin thefile of this patent: l

10 UNITED STATES PATEN'VI'S' Number Name Date H 2,335,014 Kerst Nov. 23,1943 V 2,497,891 Kerst Feb. 21,1950

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