Patent ID: 8723135

Claim:
An ion beam bending magnet having an ion beam inlet, an ion beam outlet and a curved path through the magnet for an ion beam, said curved path having a path length between said beam inlet and said beam outlet, said curved path bending monotonically in an ion beam bending plane and having a curved central beam axis, said magnet being adapted to accommodate and bend along said curved beam path, a ribbon-shaped ion beam having a cross-sectional profile with a major dimension normal to said bending plane; the magnet comprising a ferromagnetic yoke surrounding said curved beam path along said path length, said ferromagnetic yoke defining a uniform cross-sectional internal profile along said path length in respective planes normal to said curved central beam axis, said uniform cross-sectional internal profile being defined in Cartesian (x,y) co-ordinates having an origin at said central beam axis, an x-axis extending in said ion beam bending plane and a y-axis normal to said bending plane; and electrical windings associated with said ferromagnetic yoke, arranged to generate a magnetic bending field within said yoke across said curved path to bend a ribbon-shaped beam of ions having a desired mass/charge ratio along said curved path; wherein said uniform cross-sectional internal profile has sides including four angled sides respectively lying on lines defined by the four equations: a 1 x+b 1 y=a 1 b 1 , 1) a 2 x−b 1 y=a 2 b 1 , 2) a 3 x+b 2 y=−a 3 b 2 , 3) a 4 x−b 2 y=−a 4 b 2 ; 4) where a 1 , a 2 , a 3 , a 4 , b 1 and b 2 are positive numbers, wherein each of said angled sides lying on the lines defined by equations 1) and 4) extends on the respective said line up to y=y′, and each of said angled sides lying on the lines defined by equations 2) and 3) extends on the respective said line down to y=−y″, where both y′ and y″ are positive, y′ is less than or equal to the smaller of a 1 and a 4 , and y″ is less than or equal to the smaller of a 2 and a 3 .