Patent ID: 6498348
Filing Date: 2002-12-24
Classification: H01J

Abstract:
Apparatus for acting upon charged particles differently in dependence upon different values of at least one parameter of the particles, said parameter being selected from the group comprising mass, energy, and charged state, of a particle, said apparatus comprising:an array of magnetic poles constructed and arranged to give parameter dependent dispersion of charged particles moving in the magnetic pole array whereby parameter dependent selection of charged particles may be achieved; said array of magnetic poles having a virtual reference surface providing a reference for the arrangement of components of the apparatus, said virtual reference surface passing through said array of magnetic poles with at least one magnetic pole on each side of said reference surface; a beam source constructed and arranged to provide a beam of charged particles in the field of said magnetic pole array, said beam having at any given position across the beam an initial general direction of propagation of the beam and having an elongate cross-section perpendicular to said initial general direction of propagation; said virtual reference surface being a virtual surface selected from the group comprising (I) a surface defined as extending in said direction of elongation of said beam cross-section and also containing said initial direction of propagation of said beam at any position across the beam, and (II) a surface defined as extending in said direction of elongation of said beam cross-section and also parallel to said initial general direction of propagation of the beam at any position across the beam; and resolving structure constructed and arranged to select required particles from said beam by said parameter dependent dispersion; said magnetic poles being elongate poles extending in a direction of elongation which lies in said virtual reference surface and which is transverse to said initial general direction of propagation of said beam; said beam source being constructed and arranged in such a manner that said charged particles of said beam moving in the field of the magnetic pole array have an initial general direction of movement which is selected from the group comprising (I) a direction which is in said reference surface and which is other than said direction of elongation of said magnetic pole array, and (II) a direction which is substantially parallel to said reference surface and which is other than said direction of elongation of said magnetic pole array, said initial direction being selected from the group comprising an initial direction of particles entering into the field of the magnetic pole array, and an initial direction of particles originating in the field of the magnetic pole array; said magnetic poles being constructed and arranged in such a manner that, in a plane perpendicular to said direction of elongation of said array, said magnetic poles have a physical geometry which is constant along said direction of elongation of the array and have a magnetic field distribution which is constant along said direction of elongation of the array, and said magnetic poles being constructed and arranged to give parameter dependent focusing action in a plane perpendicular to said virtual reference surface to give selection of particles by parameter dependent dispersion and focusing of different particles of said beam in dependence upon different values of said parameters.