Patent Grant
8829462
This application is a national stage application of International Application No. PCT/GB2011/051879, filed Oct. 4, 2011, which claims priority to GB 1016917.5, filed Oct. 7, 2010, the disclosures of which are expressly incorporated herein by reference.
This invention relates to an improved multipole magnet, and more specifically, although not exclusively, to an improved multipole magnet that includes permanent magnets and is suitable for deflecting, focusing or otherwise altering the characteristics of a beam of charged particles.
Multipole magnets consist of a plurality of magnetic poles and, among other things, are used to deflect, focus or otherwise alter the characteristics of beams of charged particles in particle accelerators. Multipole magnets may be used to change the overall direction of a beam, focus or defocus a beam, or correct aberrations in a beam. The suitability of a multipole magnet for performing these tasks is determined largely by the number of magnetic poles present. Quadrupole magnets having four magnetic poles, for example, are particularly suitable for focusing and defocusing a beam of charged particles. In modern particle accelerator beamlines, hundreds of multipole magnets may be employed along a single beamline. In proposed future beamlines, thousands of multipole magnets are likely to be required for a single beamline.
The magnets used in multipole magnet arrangements may be electromagnets, consisting of a current carrying wire coiled around a ferromagnetic pole, or permanent magnets, which are inherently magnetized.
Electromagnets typically require an expensive power supply and may also require cooling means to remove the heat produced by the current carrying coils. The cooling means may comprise, for example, a plumbing system capable of circulating a coolant, or an airflow system for circulating cooled air. Any cooling system will incur additional set-up and running costs associated with each multipole magnet and will also require sufficient space around the multipole magnets in which to operate.
In contrast, permanent magnet multipole magnets do not require a power supply or a cooling system. An example of a permanent magnet multipole magnet is described in US-A-2002/0158736 (Gottschalk S. C.). The Gottschalk multipole magnet includes a plurality of ferromagnetic poles and one or more permanent magnets that are moveable relative to the poles to produce a variable magnetic field between the poles.
It is an object of the present invention to provide an improved multipole magnet that includes permanent magnets and is advantageous over the multipole magnets of the prior art.
In accordance with a first aspect of the present invention, there is provided a multipole magnet for deflecting a beam of charged particles, comprising:
In a preferable embodiment, the magnetisation direction of each permanent magnet is orientated in the pole plane at an angle of less than or equal to 135° relative to the pole axis of the associated pole. In a further or alternative preferable embodiment, the magnetisation direction of each permanent magnet is orientated in the pole plane at an angle of 75° relative to the pole axis of the associated pole. In another alternative preferable embodiment, the magnetisation direction of each permanent magnet is orientated in the pole plane at an angle of at least 90° relative to the pole axis of the associated pole. In another alternative embodiment, the magnetisation direction of each permanent magnet is orientated in the pole plane at an angle of 120° relative to the pole axis of the associated pole.
In any of the above described embodiments, the multipole magnet is capable of producing a high quality magnetic field that does not require a power supply or cooling system, and which can be constructed within a minimal volume. Thus, the multipole magnet is particularly suited for use in beamlines where space is particularly restricted (e.g. in a shielded enclosure, such as a tunnel) or where the reduction in heat dissipation into the surrounding space is a constraint. Given that no power supply is required, large numbers of these multipole magnets can be operated at a considerably lower cost compared with a similar number of electromagnetic multipole magnets.
In preferable embodiments, at least one of the plurality of permanent magnets and the plurality of ferromagnetic flux conducting members is moveable in the pole plane relative to the plurality of ferromagnetic poles so as to vary the strength of the magnetic field in the beamline space. This preferable feature provides the multipole magnet with adjustability whereby the magnetic flux density in the beamline space is controlled by controlling the displacement of the at least one of the plurality of permanent magnets and the plurality of ferromagnetic flux conducting members.
Preferably, each ferromagnetic flux conducting member is in a spaced arrangement from an associated ferromagnetic pole, and only the plurality of permanent magnets are moveable in the pole plane relative to the ferromagnetic poles.
In an alternative preferable embodiment, each permanent magnet is moveable in the pole plane together with an associated ferromagnetic flux conducting member relative to an associated ferromagnetic pole such that substantially no relative movement between each permanent magnet and its associated ferromagnetic flux conducting member is permitted. Further preferably, the at least one of the plurality of permanent magnets and the plurality of ferromagnetic flux conducting members are moveable along the pole plane along a path orientated at an angle of 45° relative to the pole axis of the associated pole.
In one preferable embodiment, the magnetisation direction of each permanent magnet is orientated in the pole plane at an angle that is greater than 45° and less than 135° relative to the pole axis of the associated pole, and each of the plurality of permanent magnets is associated with one of the plurality of poles; and
In accordance with a second aspect of the present invention, there is provided a multipole magnet for deflecting a beam of charged particles, comprising:
The multipole magnet is therefore capable of producing a high quality, adjustable magnetic field that does not require an external power supply or cooling system, and which can be constructed within a minimal volume. Thus, the multipole magnet is particularly suited to use in beamlines where space is particularly restricted (e.g. in a shielded enclosure, such as a tunnel) or where the reduction in heat dissipation into the surrounding space is a constraint. Given that no power supply is required, large numbers of these multipole magnets can be operated at a considerably lower cost compared with a similar number of electromagnetic multipole magnets.
Preferably, each ferromagnetic flux conducting member is in a spaced arrangement from an associated ferromagnetic pole, and only the plurality of permanent magnets are moveable in the pole plane relative to the ferromagnetic poles.
In an alternative preferable embodiment, each permanent magnet is moveable in the pole plane together with an associated ferromagnetic flux conducting member relative to an associated ferromagnetic pole such that substantially no relative movement between each permanent magnet and its associated ferromagnetic flux conducting member is permitted.
In a particularly preferable embodiment, the multipole magnet comprises an even number of ferromagnetic poles, each pole being arranged to diametrically oppose another of the poles in the pole plane along a pole axis. Preferably, the at least one of the plurality of permanent magnets and the plurality of ferromagnetic flux conducting members are moveable along the pole plane along a path orientated at an angle of 45° relative to the pole axis of the associated pole.
In a preferable embodiment, each of the plurality of permanent magnets has a magnetisation direction, and each permanent magnet has at least one of the plurality of poles associated with it, where the magnetisation direction of each permanent magnet is orientated in the pole plane at an angle of at least 45° relative to the pole axis of the associated pole.
In a preferable embodiment, the magnetisation direction of each permanent magnet is orientated in the pole plane at an angle of less than or equal to 135° relative to the pole axis of the associated pole. In a further or alternative preferable embodiment, the magnetisation direction of each permanent magnet is orientated in the pole plane at an angle of 75° relative to the pole axis of the associated pole. In another alternative preferable embodiment, the magnetisation direction of each permanent magnet is orientated in the pole plane at an angle of at least 90° relative to the pole axis of the associated pole. In another alternative embodiment, the magnetisation direction of each permanent magnet is orientated in the pole plane at an angle of 120° relative to the pole axis of the associated pole.
In any of the above described embodiments, the multipole magnet is capable of producing a high quality magnetic field that does not require a power supply or cooling system, and which can be constructed within a minimal volume. Thus, the multipole magnet is particularly suited for use in beamlines where space is particularly restricted (e.g. in a shielded enclosure, such as a tunnel) or where the reduction in heat dissipation into the surrounding space is a constraint. Given that no power supply is required, large numbers of these multipole magnets can be operated at a considerably lower cost compared with a similar number of electromagnetic multipole magnets.
In one preferable embodiment, the magnetisation direction of each permanent magnet is orientated in the pole plane at an angle that is greater than 45° and less than 135° relative to the pole axis of the associated pole, and each of the plurality of permanent magnets is associated with one of the plurality of poles; and
As the permanent magnet moves away from the poles, less magnetic flux goes through the poles and into the beamline space. Proximity of the permanent magnets to flux conducting members provides short circuits that act to reduce the magnetic flux density in the beamline space. Therefore, flux conducting members may be moved closer to the permanent magnets in order to create a short circuit and reduce the magnetic field strength in the beamline space. Relative movement of the permanent magnets and flux conducting members may create air gaps which also serve to reduce the magnetic flux density in the beamline space.
In one preferable embodiment, at least some of the ferromagnetic flux conducting members comprise a cap associated with at least one of the permanent magnets to channel magnetic flux therefrom.
In a further or alternative preferable embodiment, at least some of the ferromagnetic flux conducting members comprise a discontinuous shell surrounding the poles and permanent magnets.
In some preferable embodiments, the sum of ferromagnetic poles and ferromagnetic flux conducting members is greater than the number of permanent magnets.
In a further or alternative preferable embodiment, the multipole magnet is a quadrupole magnet comprising four ferromagnetic poles and two permanent magnets, wherein each of the two permanent magnets is associated with two of the poles to supply magnetomotive force thereto.
Embodiments of the invention are further described hereinafter with reference to the accompanying drawings, in which:
Whilst the present invention relates generally to multipole magnets having any number of poles, it is described hereinafter in relation to quadrupole magnets i.e. magnets having four poles. However, the skilled reader will appreciate that the invention is not limited to quadrupole magnets. Embodiments of the invention may be envisaged as other multipole magnets, such as dipole, sextupole and octupole.
A cross sectional view of a four pole quadrupole magnet 10 according to an embodiment of the present invention is shown in
In the pole plane, the poles 12a and 12c are arranged diametrically opposite one another along a first pole axis 100ac, while the poles 12b and 12d are arranged opposite one another along a second pole axis 100bd, where the first pole axis 100ac is orthogonal to the second pole axis 100bd in the pole plane. Within the pole plane, the four poles 12a,b,c,d define a beamline space therebetween, centered about the point of intersection 200 of the first and second pole axes 100ac,bd. In operation, a beam of charged particles, such as electrons or positrons, travels substantially orthogonally to the pole plane through the beamline space i.e. substantially parallel to the z-axis.
A moveable permanent magnet 14ab is disposed between the two pole roots 13a and 13b and a substantially identical moveable permanent magnet 14cd is disposed between the two pole roots 13c and 13d. In an alternative embodiment, each of the permanent magnets 14ab and 14cd may each be made up of two or more separate permanent magnets that may be moveable independently of one another. Furthermore, other permanent magnets may be arranged in other locations about the multipole magnet 10. Thus, the number of permanent magnets may or may not equal the number of poles.
A ferromagnetic flux conducting member 16ab is disposed radially outward of the poles 12a and 12b relative to the point of intersection 200. Similarly, a ferromagnetic flux conducting member 16cd is disposed radially outward of the poles 12c and 12d relative to the point of intersection 200. The ferromagnetic flux conducting members 16ab and 16cd are ferromagnetic “caps” and are described in further detail below. In an alternative embodiment, the flux conducting members 16ab and 16cd may each be made up of two separate cap components.
In the embodiment shown in
The permanent magnet 14ab is arranged across the quadrants 10a and 10b to supply a magnetomotive force to the ferromagnetic poles 12a and 12b (via the pole roots 13a and 13b respectively) to produce a magnetic field that extends along the pole plane into the beamline space , thereby being capable of deflecting, focusing or otherwise altering one or more characteristics of a beam of charged particles passing therethrough. The poles 12a and 12b are shaped to provide the required spatial variation of magnetic flux density across the beamline space. In alternative embodiments of the present invention, the pole shape may be somewhat different to the pole 12a of
The ferromagnetic cap 16ab is spaced apart from the pole root 13a such that the cap 16ab and the pole root 13a are not in contact with one another. The cap 16ab is arranged to channel the magnetic flux produced by the permanent magnet 14ab and is, itself, not a pole. The purpose of the cap 16ab is to direct the magnetic flux produced by the permanent magnet 14ab to reduce the magnetic field strength in the beamline space. The closer the cap 16ab is to the permanent magnet 14ab, the weaker the magnetic field strength in the beamline space.
The permanent magnet 14ab is moveable within the pole plane along direction 18ab (which is parallel to the y-axis and orientated at 45° relative to the pole axis 100ac) so as to vary the relative distance between the permanent magnet 14ab and the poles 12a and 12b and pole roots 13a and 13b, and the permanent magnet 14ab and the cap 16ab. The permanent magnet 14ab is moveable from a first position where a first surface (substantially parallel to the y-axis) of the permanent magnet 14ab contacts a surface of each of the pole roots 13a and 13b (as shown in
Movement of the permanent magnet 14ab along direction 18ab varies the magnitude of magnetic flux in the cap 16ab, the pole roots 13a and 13b and the poles 12a and 12b which ultimately varies the magnetic flux across the beamline space. Therefore, the magnetic field strength within the beamline space can be adjusted by movement of the permanent magnet 14ab along direction 18ab. The profile of the gradient of magnetic field strength with respect to displacement of the permanent magnet 14ab along direction 18ab is found to depend on the arrangement and geometry of each of the poles 12a and 12b, the pole roots 13a and 13b, the permanent magnet 14ab and the cap 16ab.
In a substantially equal manner, the permanent magnet 14cd is moveable relative to the cap 16cd, the pole roots 13c and 13d and the pole 12c and 12d to vary the magnitude of magnetic flux across the beamline space. In the embodiment shown in
The quadrants 10a and 10b form a first magnetic circuit of magnetic flux while the quadrants 10c and 10d form a second magnetic circuit of magnetic flux. Due to the pairing of quadrant 10a with quadrant 10b, and the pairing of quadrant 10c with 10d, the quadrupole magnet 10 extends along the y-axis in the pole plane to a greater extent than it extends along the x-axis in the pole plane. Therefore, the quadrupole magnet 10 of
Further embodiments of the invention are described hereinafter with reference to
In any of the embodiments shown in
Further preferable embodiments of the invention are shown in
In
In the embodiments of
Movement of the bridge portions, with or without the permanent magnets, creates an air gap which has the effect of reducing the strength of the magnetic field in the beamline space.
Preferably, the permanent magnet and/or the flux conducting members is/are moveable relative to the pole and pole root (although the pole root may also be moveable). In particularly preferable embodiments, the flux conducting member (e.g. bridge) and permanent magnet are moveable together, such that no relative movement is permitted therebetween. Preferably, the direction of movement of the flux conducting member and permanent magnet along the pole plane is at 45° relative to the pole axis (i.e. parallel to the y-axis in the embodiments shown in
Permanently magnetic materials are generally known to be mechanically poor under tension. Therefore, to improve the mechanical strength of the permanent magnets of the present invention, one or more steel plates may be attached by glue or any other suitable attachment means to the permanent magnets. This minimizes the risk of the permanent magnets being structurally damaged as they are mechanically moved relative to the poles. The attachment means may additionally or alternatively include straps wrapped around the steel plates and the permanent magnets.
Throughout the description and claims of this specification, the word “ferromagnetic” and variations thereof are synonymous with the terms “magnetically soft” and “magnetically permeable” and refer to reasonably high permeability of at least 10μo, where μo is the permeability of free space. For the purpose of the present invention, one suitable ferromagnetic material is steel, however other suitable ferromagnetic materials may also be used.
Throughout the description and claims of this specification, the terms “magnetic field strength” and “field amplitude” and variations of these terms are substantially equivalent to the magnetic flux density for the purpose of the present application, whatever its spatial distribution.
Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to”, and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.
Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.
The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1016917.5 | Oct 2010 | GB | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/GB2011/051879 | 10/4/2011 | WO | 00 | 4/4/2013 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2012/046036 | 4/12/2012 | WO | A |
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| Number | Date | Country | |
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| 20130207760 A1 | Aug 2013 | US |
