Permanent magnet multipole with adjustable strength
First Claim
1. A multipole permanent magnet structure for guiding, focusing and turning charged particle beams, said structure having an adjustable field strength and a substantially constant magnetic field distribution, comprising:
- a first pole piece and a second pole piece, each formed of magnetically-soft material, each pole piece having a pole tip, said pole pieces being spaced-apart to permit a magnetic field to be established between the pole tips, said pole pieces being arranged about a longitudinal axis to provide a cylindrical multipole structure having a central space formed between the pole tips and extending along the longitudinal axis for passage of a charged particle beam through the space;
first and second permanent magnets having high remanent fields and strong coercive forces, said permanent magnets being mounted in close proximity to the rear of said pole pieces and magnetically coupled thereto to thereby establish a magnetic field between said pole tips;
means for moving the permanent magnets with respect to the pole pieces to vary the coupling between the pole pieces and the permanent magnets so that the flux denisity of the magnetic field between the pole tips is correspondingly varied, while the magnetic field distribution between the pole tips is maintained substantially constant.
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Accused Products
Abstract
Two or more magnetically soft pole pieces are symmetrically positioned along a longitudinal axis to provide a magnetic field within a space defined by the pole pieces. Two or more permanent magnets are mounted to an external magnetically-soft cylindrical sleeve which rotates to bring the permanent magnets into closer coupling with the pole pieces and thereby adjustably control the field strength of the magnetic field produced in the space defined by the pole pieces. The permanent magnets are preferably formed of rare earth cobalt (REC) material which has a high remanent magnetic field and a strong coercive force. The pole pieces and the permanent magnets have corresponding cylindrical surfaces which are positionable with respect to each other to vary the coupling therebetween. Auxiliary permanent magnets are provided between the pole pieces to provide additional magnetic flux to the magnetic field without saturating the pole pieces.
104 Citations
9 Claims
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1. A multipole permanent magnet structure for guiding, focusing and turning charged particle beams, said structure having an adjustable field strength and a substantially constant magnetic field distribution, comprising:
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a first pole piece and a second pole piece, each formed of magnetically-soft material, each pole piece having a pole tip, said pole pieces being spaced-apart to permit a magnetic field to be established between the pole tips, said pole pieces being arranged about a longitudinal axis to provide a cylindrical multipole structure having a central space formed between the pole tips and extending along the longitudinal axis for passage of a charged particle beam through the space; first and second permanent magnets having high remanent fields and strong coercive forces, said permanent magnets being mounted in close proximity to the rear of said pole pieces and magnetically coupled thereto to thereby establish a magnetic field between said pole tips; means for moving the permanent magnets with respect to the pole pieces to vary the coupling between the pole pieces and the permanent magnets so that the flux denisity of the magnetic field between the pole tips is correspondingly varied, while the magnetic field distribution between the pole tips is maintained substantially constant. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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Specification