CA1037555A - Focusing magnet - Google Patents
Focusing magnetInfo
- Publication number
- CA1037555A CA1037555A CA204,402A CA204402A CA1037555A CA 1037555 A CA1037555 A CA 1037555A CA 204402 A CA204402 A CA 204402A CA 1037555 A CA1037555 A CA 1037555A
- Authority
- CA
- Canada
- Prior art keywords
- magnet
- pole
- aperture
- plane
- pole pieces
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F7/00—Magnets
- H01F7/06—Electromagnets; Actuators including electromagnets
- H01F7/20—Electromagnets; Actuators including electromagnets without armatures
- H01F7/202—Electromagnets for high magnetic field strength
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- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Particle Accelerators (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
An electromagnet pole piece structure having four or more pole pieces with the surface of each piece being a modified hyperboloid in the vicinity of the central magnetic focusing gap to improve field linearity, reduce variations in effective length at various angles and radii and minimize field distortions resulting from fringe effects at entrance and exit.
An electromagnet pole piece structure having four or more pole pieces with the surface of each piece being a modified hyperboloid in the vicinity of the central magnetic focusing gap to improve field linearity, reduce variations in effective length at various angles and radii and minimize field distortions resulting from fringe effects at entrance and exit.
Description
BACKGROUND OF INVENTION
It has long been known that charged particles such as electrons are affected by magnetic fields and the principle of strong focusing enunciated in 10 U.S. Patent No. 2,736,799 issued to Nicholas Christofilos provided a way of focusing an electron beam, for example by magnetic fields. This principle has been widely employed and a variety of focusing magnets structur~3s have been developed for use with particle accelerators and transport systems therefor. One conventional magnet structure comprises a quadrupole with four pole pieces disposed in quadrature and generally having curved facing - surfaces to define an aperture through which a charged particle beam is passed for magnetic focusing.
Following relatively early developments of strong focusing magnet structures, the state of the art has remained relatively unchanged for some 20 period of time, at least as regards medium and lower energy accelerator transport systems. Conventional quadrupole designs for a strong focusing of charged particle beams, for example, have the disadvantage o establishing non-linear field gradients in the magnet aperture and also differing field gradients in different directions transverse to a beam axis. Such structures , also suffer from the defect of varying e~ffective magnet lengths at various ` angles and radii in the aperture plane.
` It is also recognized that conventional magnet structures embody undesirable fringe effects resulting in field dis~tortions on opposite sides of the main focusing volume. The foregoing results in a useful diameter for `' 30 strong focusing of onl~r about 60 to 65% of the full field aperture diameter which is then only about 36 to 42% of the full aperture cross sectional area.
Inasmuch as very precise magnetic field relationships are often required for -~
~ , .
' ` `.'.'~' '~
. .:
37~;~;5 strong focusing, the useful ~ocusing area may be considered as that portion of the magnetic field area having no more than one-half to one percent field variation from a true quadrupole field.
It is also noted that undesirable end effects and fringe effects require added magnet length so that length to aperture ratios of less than 2:1 are almost never employed.
SUMMARY OF INVENTION
. ~
Thus, in accordance with the present teachings, a multiple pole magnet structure is provided which comprises a ~`~ 10 plurality of an even number greater than 2 of magnet pole pieceshaving magnet c~ils coupled thereto. The pole pieces are equally `1 spaced apart about an axis of a magnet aperture and each has a tip surface which has a surface of revolution configuration facing the tip surface of an opposite pole piece with the axis of revolution of the pairs of facing tip surfaces being coincident.
In accordanGe with a preferred e~bodiment, a quadrupole magnet structure is provided which comprises four>orthogonally -`~ disposed magnet poles having magnet coils coupled thereto and having the pole pieces thereof spaced apart to define a magnet aperture. The pole pieces each have a substantially hyperboloidal configuration.
The present invention provides an improved quadrupole t magnet pole structure in which the pole configuration is a surface of revolution such as a hyperboloid which becomes flatter as the apertuxe increases. A preferred embodiment of the invention has a configuration providing a slowly increasing air - gap or apertuxe with a constantly changing correction such that ~ -XY = Ka2 , wherein Y and X are the ordinate and abscissa, respectivel~, of a coordinate system centered at the center of the air gap or aperture with the pole piece oriented at 45 to .. ~ ,, .
~J - 2 -;.' ' ~,~37S55 :~
the system and "a" is the radius of the air gap to the innermost point of the pole pieces. The constant K in the foregoing relationship provides for slight deviations as may be required for different applications and conditions. This condition is maintained at least until the air gap or aperture and therefor the field-length product in the axea becomes small as compared to the rest of the magnet. The foregoing condition is obtained by the provision of magnet pole pieces having a sur~ace of ;~ --.i - .
revolution-~uch as a~hyperboloid configuration.
DESCRIPTION OF FIGVRES
~, The present invention is illustrated as to a preferred ` -embodiment thereof in the accompanying drawings wherein:
Figure 1 is a schematic illustration of quadrupole magnet pole pieces in a central plane normal to a center line through the magnet aperture and containing certain notations helpful in defining relationships in the description of the present invention;
Figure 2 is a graph of magnetic field versus magnet aperture radius for conventional quadrupole magnet pole pieces;
Figure 3 is a schematic end elevational view of the ' four magnet pole pieces formed in accordance with the present j invention;
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... . . .
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Figure 4 is a partial longitudinal sectional view of a quadrupole magnet in accordance with the present invention and taken in the plane 4-4 of Figure 3;
Figure 5 is a schematic plan view of a single pole piece of a magnet in accordance with the present invention and Figures 5A to 5F are schematic sectional views taken in the planes A-~ to F-F of Figure 5 and illustrating pole piece curvatures at successive planes displaced from,,the center of the pole piece;
Figure 6 is a front elevational view of a focusing magnet in accord-ance with the present invention;
Figure 7 is a graph of quadrupole magnet field strength versus ideal for a quadrupole magnet of the present invention at curve A and a conventional quadrupole ~nagnet at curve B; and Figure 8 is a graph in polar co-ordinates illustrating the aperture ~ , , area of a .1 percent variation of field strength from ideal field strength of "~ , a quadrupole magnet for a magnet of the present invention as shown at curve A and conventional quadrupole magnets as sbLown at curves B and C. '~
.. . .
' DESCRIPTION OF PREFERRED EMBODIMENT ``
~`, A preferred emb(odiment of the present invention as described herein 20 is a quadrupole magnet; however, the invention is equally applicable to other ~` magnets such as six pole and eight pole magnets. , ' Before considering the details of the present invention it is noted ~`
that a quadrupole magnet is conventionally comprised as a structure having ,' ~ -four orthogonally disposed magnet poles with the pole tips spaced apart to define a magnet aperture, Magnet coils are wound about the pole pieces .,~ . .
which have the bases thereof connected together as by an iron ring or the ; ' like to provide a flux path. In discussing quadrupole magnets it is convenient ;
to employ certain conventions and certain of these are illustrated in Figure I "'-, of the drawings. Magnet pole pieces ll, 12, 13 and 14 are illustrated with ' ' ~' 30 respect to a rectangular co-ordinate system in X and Y lying in a plane normal to and transverse of a Z axis extending through a magnet aperture , ~, defined by the pole pieces. The total magnet aperture is norrnally taken as - 3 - ~;
I~ :
~ )3'75~
a circle having a radius "al~ extending from the Z axis to the closest point of the pole t;ps. Angular measurements are normally considered as being taken from the X axis and are designated ~ with the pole piece lZ, for example, being oriented at ~ = 4S. Aperture radius is designated r with ~;
pole piece width in the plane X-~ being denominated d. Conventionally pole tips in a quadrupole magnet are formed with a curvature R in the X-Y or aperture plane.
It i9 desired, particularly for strong focusing, that a quadrupole magnet should have a field strength H which varies linearly with radius r ~ -10 in the magnet aperture. In Figure 2 there is illustrated a plot of H versus r for an ideal quadrupoleO In Figure 2 there is also illustrated variations in the H versus r relation for conventional quadrupoles at H = zero and ;~ H = 45, It will be seen that the field strength versus radius varies from ideal in accordance with the direction chosen from the Z axis and for many ' applications this variation is at least disadvantageous, if not intolerable.
~; Again taking the example of strong focusing, it is necessarv that the magnet field strength be precisely the same about the circumference of each radius `~, in the magnet aperture and it is common to consider the useful aperture as ; ~
;` being the area in the X-Y plane having a maximum variation of field strength ` ;~ -20 frorn ideal field strength of less than .01 percent to D 05 percent.
A further problem in the field of quadrupole magnets employed, for ; -example, in strong focusing, is the fringing effects of the magnetic field on opposite sides of a central X-Y plane.
Referring now to Figures 3 and 4, there will be seen to be schemati-cally illustrated the improved quadrupole magnet in accordance with the ~ -:~ ; -. .
present invention and particularly with regard to the pole tips thereof. Pole tips 21, 22, 23 and 24 are mounted in ~quadrature and each is formed with identical curvatures, aq further described below. In Figure 4 there are schematically illustrated magnet coils 26 and 27 about ~he pole pieces 21 and s 3023 for inducing a magnetic flu~ therein. There is also illustrated in Figure ;' 4 end plates 31 and 32 having central apertures 33 and 34, respectively, and ~ disposed on opposite sides of the magnet pole pieces. These end plates may ;~
.. ', .
- 4~
,: ., . : . , . : :: . . . .:
. : :: .. ... . ,.. , :.: . , :
r~ S ~ii S
or may not be employed depending upon the application of the magnet. The general composition of the quadrupole magnet of the present invention is con~rentional; however, the present invention provides a particular pole tip configuration for a quadrupole magnet significantly differing from prior art magnets to produce the advantageous results of the present invention.
Referring now to Figure 5 and Figures 5A to 5F, there will be seen to be schematically illustrated a single pole piece 22, for example, having the configuration of the present invention. In Figures 5A to 5F there are illustrated the curvatures of the pole piece at successive parallel planes . . .
10 based outwardly from the center of the pole piece. It is not attempted in these Figures to precisely identify the curvature other than to generally indicate the pole piece configuration. In accordance with the present invention each of the pole pieces shall have the configuration o a surEace of revolution and preferably that of a hyperboloid. Employing the conventions identified above in connection with Figure 1, the pole piece curvature is defined as XY = Ka . This i9 the equation of a hyperboloid with a small correction K
and will be seen to provide curvature in all directions. It will, of course, be appreciated that only the pole tip is formed with this curvature. The r emainder of the pole piece has sides upon which a coil may be wound or ;~
~0 disposed for inducing the flux in the magnet. These sides may be straight for medium power magnets, stepped for low power magnets or tapered for ~
high power magnets. The pole pieces of this invention preferably have a - -., ... ~ .
substantially hyperboloid configuration and the constan$ K provides for slight variations from a true hyperboloid.
. . .~ .
l~tl Figures 7 and 8 there are illustrated field measurements taken with a quadrupole magnet of the present invention as compared to a conven-.: . .:
tional quadrupole magnet. Curve B of Figure 7 shows the variation in field `
strength compared to theoretically proper field strength for a quadrupole magnet of conventional design and it-will be seen that a substantially zero ;
30 variation exists only over about half of the aperture radius. The curve B is seen to depart rather radically from ideal at increasing radius. Curve A, representing a quadrupole magnet having the pole piece configuration of the . ~'' . ' :. . . . . .
~L~375SS
present invention on the other hand, has a substantially zero field gradient variation from ideal over about three-quarters of the radius of the aperture ~ s aI~d has ~H ~ about ~ 01 for the complete aperture. This will be seen to be a very marked improvement over the prior art and is particularly impc~rtant in focusing magnets for electron beams and the like.
. Figure 8 illustrates at Curves B and C field strength variations for -two conventional quadrupole magnets while Curve A represents the area of .: .
.` .1% variation of field strength over ideal strength for a quadrupole magnet .~ -; . .
. of the present invention. Assuming, for example, as stated above, that the useful aperture is limited to .1 ~HH for a charged particle beam focusing `~
:.~ : - .
magnet, it will then be noted from Figure 8 that the present magnet provides ;.~
for utili~:ation of an entire magnet aperture while conventional magnets are ;.
:, :: ~.:.
~ severely limited in this respectO
It is also noted that the present invention provides a marked decrease ;~
.; . .. :. . - .: ~
in length-to-aperture ratio. Conventionally it is necessary to employ a substantial magnet length along the Z axis and in practice length-to-aperture : .
~' ratios of 2:1 are about the minimum useable. The present invention, on the other hand, provides for a pole length-to-aperture ratio of almost 1:1 to ;~ ~
thereby reduce the size and cost of a magnet formed in accordance with the ` ~ ;.
'''I . ~ ~ ~ .
-~ ~ 20 present inventionO
' ~lthough the present invention has been described with respect to a -~
'1 quadrupole magnet, it may also be employed with magnets having a larger .
number of poles. For.a BiX pole magnet a sixty degree hyperboloid is .
~ employed, and :for an.~eight p~le magnet~a ~forty-five degree hyperboloid is~
-~ employed.. ~ -It-will be apparent to those skilled in the art that modifications- .
and val:iations~of the invention are possible. and thus it is not ~intended-to mit the invention to the precise terms of description nor details of `~ illustrationO '~ `
3 :~
:~' :.~. ~:
.:~ 30 3 . ~ ~ ~
~, ;" . ~
,,, ~ :
- 6 ~
A;1 :.
It has long been known that charged particles such as electrons are affected by magnetic fields and the principle of strong focusing enunciated in 10 U.S. Patent No. 2,736,799 issued to Nicholas Christofilos provided a way of focusing an electron beam, for example by magnetic fields. This principle has been widely employed and a variety of focusing magnets structur~3s have been developed for use with particle accelerators and transport systems therefor. One conventional magnet structure comprises a quadrupole with four pole pieces disposed in quadrature and generally having curved facing - surfaces to define an aperture through which a charged particle beam is passed for magnetic focusing.
Following relatively early developments of strong focusing magnet structures, the state of the art has remained relatively unchanged for some 20 period of time, at least as regards medium and lower energy accelerator transport systems. Conventional quadrupole designs for a strong focusing of charged particle beams, for example, have the disadvantage o establishing non-linear field gradients in the magnet aperture and also differing field gradients in different directions transverse to a beam axis. Such structures , also suffer from the defect of varying e~ffective magnet lengths at various ` angles and radii in the aperture plane.
` It is also recognized that conventional magnet structures embody undesirable fringe effects resulting in field dis~tortions on opposite sides of the main focusing volume. The foregoing results in a useful diameter for `' 30 strong focusing of onl~r about 60 to 65% of the full field aperture diameter which is then only about 36 to 42% of the full aperture cross sectional area.
Inasmuch as very precise magnetic field relationships are often required for -~
~ , .
' ` `.'.'~' '~
. .:
37~;~;5 strong focusing, the useful ~ocusing area may be considered as that portion of the magnetic field area having no more than one-half to one percent field variation from a true quadrupole field.
It is also noted that undesirable end effects and fringe effects require added magnet length so that length to aperture ratios of less than 2:1 are almost never employed.
SUMMARY OF INVENTION
. ~
Thus, in accordance with the present teachings, a multiple pole magnet structure is provided which comprises a ~`~ 10 plurality of an even number greater than 2 of magnet pole pieceshaving magnet c~ils coupled thereto. The pole pieces are equally `1 spaced apart about an axis of a magnet aperture and each has a tip surface which has a surface of revolution configuration facing the tip surface of an opposite pole piece with the axis of revolution of the pairs of facing tip surfaces being coincident.
In accordanGe with a preferred e~bodiment, a quadrupole magnet structure is provided which comprises four>orthogonally -`~ disposed magnet poles having magnet coils coupled thereto and having the pole pieces thereof spaced apart to define a magnet aperture. The pole pieces each have a substantially hyperboloidal configuration.
The present invention provides an improved quadrupole t magnet pole structure in which the pole configuration is a surface of revolution such as a hyperboloid which becomes flatter as the apertuxe increases. A preferred embodiment of the invention has a configuration providing a slowly increasing air - gap or apertuxe with a constantly changing correction such that ~ -XY = Ka2 , wherein Y and X are the ordinate and abscissa, respectivel~, of a coordinate system centered at the center of the air gap or aperture with the pole piece oriented at 45 to .. ~ ,, .
~J - 2 -;.' ' ~,~37S55 :~
the system and "a" is the radius of the air gap to the innermost point of the pole pieces. The constant K in the foregoing relationship provides for slight deviations as may be required for different applications and conditions. This condition is maintained at least until the air gap or aperture and therefor the field-length product in the axea becomes small as compared to the rest of the magnet. The foregoing condition is obtained by the provision of magnet pole pieces having a sur~ace of ;~ --.i - .
revolution-~uch as a~hyperboloid configuration.
DESCRIPTION OF FIGVRES
~, The present invention is illustrated as to a preferred ` -embodiment thereof in the accompanying drawings wherein:
Figure 1 is a schematic illustration of quadrupole magnet pole pieces in a central plane normal to a center line through the magnet aperture and containing certain notations helpful in defining relationships in the description of the present invention;
Figure 2 is a graph of magnetic field versus magnet aperture radius for conventional quadrupole magnet pole pieces;
Figure 3 is a schematic end elevational view of the ' four magnet pole pieces formed in accordance with the present j invention;
~,1 ,' .,.'. ' ~' ':~ ' :':' .
-~ - 2ai-:: .
... . . .
7~iSS
Figure 4 is a partial longitudinal sectional view of a quadrupole magnet in accordance with the present invention and taken in the plane 4-4 of Figure 3;
Figure 5 is a schematic plan view of a single pole piece of a magnet in accordance with the present invention and Figures 5A to 5F are schematic sectional views taken in the planes A-~ to F-F of Figure 5 and illustrating pole piece curvatures at successive planes displaced from,,the center of the pole piece;
Figure 6 is a front elevational view of a focusing magnet in accord-ance with the present invention;
Figure 7 is a graph of quadrupole magnet field strength versus ideal for a quadrupole magnet of the present invention at curve A and a conventional quadrupole ~nagnet at curve B; and Figure 8 is a graph in polar co-ordinates illustrating the aperture ~ , , area of a .1 percent variation of field strength from ideal field strength of "~ , a quadrupole magnet for a magnet of the present invention as shown at curve A and conventional quadrupole magnets as sbLown at curves B and C. '~
.. . .
' DESCRIPTION OF PREFERRED EMBODIMENT ``
~`, A preferred emb(odiment of the present invention as described herein 20 is a quadrupole magnet; however, the invention is equally applicable to other ~` magnets such as six pole and eight pole magnets. , ' Before considering the details of the present invention it is noted ~`
that a quadrupole magnet is conventionally comprised as a structure having ,' ~ -four orthogonally disposed magnet poles with the pole tips spaced apart to define a magnet aperture, Magnet coils are wound about the pole pieces .,~ . .
which have the bases thereof connected together as by an iron ring or the ; ' like to provide a flux path. In discussing quadrupole magnets it is convenient ;
to employ certain conventions and certain of these are illustrated in Figure I "'-, of the drawings. Magnet pole pieces ll, 12, 13 and 14 are illustrated with ' ' ~' 30 respect to a rectangular co-ordinate system in X and Y lying in a plane normal to and transverse of a Z axis extending through a magnet aperture , ~, defined by the pole pieces. The total magnet aperture is norrnally taken as - 3 - ~;
I~ :
~ )3'75~
a circle having a radius "al~ extending from the Z axis to the closest point of the pole t;ps. Angular measurements are normally considered as being taken from the X axis and are designated ~ with the pole piece lZ, for example, being oriented at ~ = 4S. Aperture radius is designated r with ~;
pole piece width in the plane X-~ being denominated d. Conventionally pole tips in a quadrupole magnet are formed with a curvature R in the X-Y or aperture plane.
It i9 desired, particularly for strong focusing, that a quadrupole magnet should have a field strength H which varies linearly with radius r ~ -10 in the magnet aperture. In Figure 2 there is illustrated a plot of H versus r for an ideal quadrupoleO In Figure 2 there is also illustrated variations in the H versus r relation for conventional quadrupoles at H = zero and ;~ H = 45, It will be seen that the field strength versus radius varies from ideal in accordance with the direction chosen from the Z axis and for many ' applications this variation is at least disadvantageous, if not intolerable.
~; Again taking the example of strong focusing, it is necessarv that the magnet field strength be precisely the same about the circumference of each radius `~, in the magnet aperture and it is common to consider the useful aperture as ; ~
;` being the area in the X-Y plane having a maximum variation of field strength ` ;~ -20 frorn ideal field strength of less than .01 percent to D 05 percent.
A further problem in the field of quadrupole magnets employed, for ; -example, in strong focusing, is the fringing effects of the magnetic field on opposite sides of a central X-Y plane.
Referring now to Figures 3 and 4, there will be seen to be schemati-cally illustrated the improved quadrupole magnet in accordance with the ~ -:~ ; -. .
present invention and particularly with regard to the pole tips thereof. Pole tips 21, 22, 23 and 24 are mounted in ~quadrature and each is formed with identical curvatures, aq further described below. In Figure 4 there are schematically illustrated magnet coils 26 and 27 about ~he pole pieces 21 and s 3023 for inducing a magnetic flu~ therein. There is also illustrated in Figure ;' 4 end plates 31 and 32 having central apertures 33 and 34, respectively, and ~ disposed on opposite sides of the magnet pole pieces. These end plates may ;~
.. ', .
- 4~
,: ., . : . , . : :: . . . .:
. : :: .. ... . ,.. , :.: . , :
r~ S ~ii S
or may not be employed depending upon the application of the magnet. The general composition of the quadrupole magnet of the present invention is con~rentional; however, the present invention provides a particular pole tip configuration for a quadrupole magnet significantly differing from prior art magnets to produce the advantageous results of the present invention.
Referring now to Figure 5 and Figures 5A to 5F, there will be seen to be schematically illustrated a single pole piece 22, for example, having the configuration of the present invention. In Figures 5A to 5F there are illustrated the curvatures of the pole piece at successive parallel planes . . .
10 based outwardly from the center of the pole piece. It is not attempted in these Figures to precisely identify the curvature other than to generally indicate the pole piece configuration. In accordance with the present invention each of the pole pieces shall have the configuration o a surEace of revolution and preferably that of a hyperboloid. Employing the conventions identified above in connection with Figure 1, the pole piece curvature is defined as XY = Ka . This i9 the equation of a hyperboloid with a small correction K
and will be seen to provide curvature in all directions. It will, of course, be appreciated that only the pole tip is formed with this curvature. The r emainder of the pole piece has sides upon which a coil may be wound or ;~
~0 disposed for inducing the flux in the magnet. These sides may be straight for medium power magnets, stepped for low power magnets or tapered for ~
high power magnets. The pole pieces of this invention preferably have a - -., ... ~ .
substantially hyperboloid configuration and the constan$ K provides for slight variations from a true hyperboloid.
. . .~ .
l~tl Figures 7 and 8 there are illustrated field measurements taken with a quadrupole magnet of the present invention as compared to a conven-.: . .:
tional quadrupole magnet. Curve B of Figure 7 shows the variation in field `
strength compared to theoretically proper field strength for a quadrupole magnet of conventional design and it-will be seen that a substantially zero ;
30 variation exists only over about half of the aperture radius. The curve B is seen to depart rather radically from ideal at increasing radius. Curve A, representing a quadrupole magnet having the pole piece configuration of the . ~'' . ' :. . . . . .
~L~375SS
present invention on the other hand, has a substantially zero field gradient variation from ideal over about three-quarters of the radius of the aperture ~ s aI~d has ~H ~ about ~ 01 for the complete aperture. This will be seen to be a very marked improvement over the prior art and is particularly impc~rtant in focusing magnets for electron beams and the like.
. Figure 8 illustrates at Curves B and C field strength variations for -two conventional quadrupole magnets while Curve A represents the area of .: .
.` .1% variation of field strength over ideal strength for a quadrupole magnet .~ -; . .
. of the present invention. Assuming, for example, as stated above, that the useful aperture is limited to .1 ~HH for a charged particle beam focusing `~
:.~ : - .
magnet, it will then be noted from Figure 8 that the present magnet provides ;.~
for utili~:ation of an entire magnet aperture while conventional magnets are ;.
:, :: ~.:.
~ severely limited in this respectO
It is also noted that the present invention provides a marked decrease ;~
.; . .. :. . - .: ~
in length-to-aperture ratio. Conventionally it is necessary to employ a substantial magnet length along the Z axis and in practice length-to-aperture : .
~' ratios of 2:1 are about the minimum useable. The present invention, on the other hand, provides for a pole length-to-aperture ratio of almost 1:1 to ;~ ~
thereby reduce the size and cost of a magnet formed in accordance with the ` ~ ;.
'''I . ~ ~ ~ .
-~ ~ 20 present inventionO
' ~lthough the present invention has been described with respect to a -~
'1 quadrupole magnet, it may also be employed with magnets having a larger .
number of poles. For.a BiX pole magnet a sixty degree hyperboloid is .
~ employed, and :for an.~eight p~le magnet~a ~forty-five degree hyperboloid is~
-~ employed.. ~ -It-will be apparent to those skilled in the art that modifications- .
and val:iations~of the invention are possible. and thus it is not ~intended-to mit the invention to the precise terms of description nor details of `~ illustrationO '~ `
3 :~
:~' :.~. ~:
.:~ 30 3 . ~ ~ ~
~, ;" . ~
,,, ~ :
- 6 ~
A;1 :.
Claims (5)
1. A multiple pole magnet structure comprising a plurality of an even number greater than two of magnet pole pieces having magnet coils coupled thereto, said pole pieces being equally spaced apart about an axis of a magnet aperture and each having a tip surface which has a surface of revolution configuration facing the tip surface of an opposite pole piece with the axes of revolution of the pairs of facing tip surfaces being coincident.
2. A magnet structure according to Claim 1, wherein the surfaces of the tips of the pole pieces each have a substantially hyperboloidal configuration.
3. The magnet structure of Claim 1 or 2 further defined by said pole tips being spaced from a central axis normal to an aperture plane having co-ordinate XY axes in such plane and the curvature of each of said pole tips being defined by the relation-ship XY = K?2 where "a" is the radial distance from said central axis to the pole tip and K is a correction constant of small value providing minor deviation from a true hyperboloid configuration.
4. A quadrupole magnet structure comprising four orthogonally disposed magnet poles having magnet coils coupled thereto and having the pole pieces thereof spaced apart to define a magnet aperture, said pole pieces each having a substantially hyperboloidal configuration.
5. A magnet structure according to Claim 4, wherein the tip surface of each of said pole pieces is spaced from a central axis normal to the aperture plane and intersects the aperture plane and a parallel plane to define a line which, for each such plane, is defined relative to XY co-ordinate axes in the plane by the relationship XY=K?2 where "a" is the radial distance in that plane from the central axis to the closest point on the tip surface of the pole piece, and K is a correction constant of small value to provide at most a minor deviation from a true hyperboloidal configuration.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US00378013A US3831121A (en) | 1973-07-10 | 1973-07-10 | Focusing magnet |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1037555A true CA1037555A (en) | 1978-08-29 |
Family
ID=23491380
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA204,402A Expired CA1037555A (en) | 1973-07-10 | 1974-07-09 | Focusing magnet |
Country Status (4)
| Country | Link |
|---|---|
| US (1) | US3831121A (en) |
| CA (1) | CA1037555A (en) |
| CH (1) | CH579816A5 (en) |
| GB (1) | GB1461521A (en) |
Families Citing this family (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4381490A (en) * | 1981-11-05 | 1983-04-26 | Peters Harry E | Magnetic state selector |
| DE3321117A1 (en) * | 1983-06-10 | 1984-12-13 | Siemens AG, 1000 Berlin und 8000 München | MAGNETIC MULTIPOLE N-TERM ORDER |
| US4560905A (en) * | 1984-04-16 | 1985-12-24 | The United States Of America As Represented By The United States Department Of Energy | Electrostatic quadrupole focused particle accelerating assembly with laminar flow beam |
| US4673794A (en) * | 1985-05-10 | 1987-06-16 | National Research Institute For Metals | Electron beam welding method |
| US4849705A (en) * | 1985-09-21 | 1989-07-18 | Sumitomo Heavy Industries, Ltd. | Method of incidence of charged particles into a magnetic resonance type accelerator and a magnetic resonance type accelerator in which this method of incidence is employed |
| US4962309A (en) * | 1989-08-21 | 1990-10-09 | Rockwell International Corporation | Magnetic optics adaptive technique |
| US5401973A (en) * | 1992-12-04 | 1995-03-28 | Atomic Energy Of Canada Limited | Industrial material processing electron linear accelerator |
| US5783941A (en) * | 1995-02-01 | 1998-07-21 | The Babcock & Wilcox Company | Technique for magnetic alignment of an octant for fusion toroidal magnet |
| US6573817B2 (en) | 2001-03-30 | 2003-06-03 | Sti Optronics, Inc. | Variable-strength multipole beamline magnet |
| US6822246B2 (en) * | 2002-03-27 | 2004-11-23 | Kla-Tencor Technologies Corporation | Ribbon electron beam for inspection system |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2882396A (en) * | 1953-10-30 | 1959-04-14 | Ernest D Courant | High energy particle accelerator |
| CH393535A (en) * | 1961-09-26 | 1965-06-15 | Trueb Taeuber & Co Ag | Magnet arrangement for generating magnetic fields of variable field strength with constant geometric configuration |
| US3393385A (en) * | 1966-08-24 | 1968-07-16 | Atomic Energy Commission Usa | Quadrupole magnet with reduced field distortion |
| US3388359A (en) * | 1967-01-31 | 1968-06-11 | Atomic Energy Commission Usa | Particle beam focussing magnet with a septum wall |
-
1973
- 1973-07-10 US US00378013A patent/US3831121A/en not_active Expired - Lifetime
-
1974
- 1974-07-09 CA CA204,402A patent/CA1037555A/en not_active Expired
- 1974-07-10 GB GB3057974A patent/GB1461521A/en not_active Expired
- 1974-07-10 CH CH953074A patent/CH579816A5/xx not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| US3831121A (en) | 1974-08-20 |
| GB1461521A (en) | 1977-01-13 |
| CH579816A5 (en) | 1976-09-15 |
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