GB949171A - Apparatus for bending beams of charged particles - Google Patents

Abstract

949,171. Particle accelerators. VARIAN ASSOCIATES. March 7, 1960 [May 9, 1959], No. 8066/60. Heading H1D A beam bending and scanning assembly for use with a particle accelerator producing a beam of charged particles of different energies consists of a beam bending magnet 22, Fig. 1, with polepieces on opposite sides of the beam and so arranged that particles of greater energy are forced to travel over longer paths than particles of lesser energy, particles of all energies being deflected through the same angle. As shown, the output surface 29 of the bending magnet is inclined to the axis of the beam. The input surface 28 is also inclined to compensate, by the focusing action of the fringe field at this surface, for the defocusing action of the fringe field at the output surface. Both surfaces 28 and 29 may be formed by the plane surfaces of rotatable semi-cylindrical inserts in the polepieces so that the inclinations of these surfaces can be adjusted. The inserts for the input surface can be adjusted simultaneously or separately or interchangeable inserts may be used. The entire bending magnet may be tilted. The scanning magnet 38 which is claimed independently in Specification 949,172 has concave and convex pole faces 41, 44 shaped to set up a flux density gradient across the gap so that particles of different energies, on opposite sides of the beam, are scanned through the same angle. The pole faces may be hyperbolic, semi-cylindrical or V-shaped in horizontal cross-section or curved in a vertical direction. The beam 11 emerging from a linear accelerator 12 passes into an evacuated chamber 13 comprising a horizontal tube 14 with a downwardly extending branch 15 which merges into the flared scanner section 16. A window 19 is also provided at the end of an extension of the tube 14. Portions of the chamber 13 subject to particle bombardment are lined with liquid-cooled aluminium. The chamber 13 is mounted for rotation in a rotatable coupling 18. A quadrupole focusing magnet 21 is mounted on the tube 14. The focusing magnet 21 and the deflecting and scanning magnets 22, 38 are mounted in a housing 49 which is also mounted for rotation in the coupling 18. The housing 49 may be an evacuated chamber with a flared end, thus eliminating the need for chamber 13. Triangular or sawtooth waveforms may be applied to the scanning magnet to produce a zig-zag pattern or a pattern of parallel lines across a package 48 which is moved beneath the scanning beam. In a modification, Fig. 8, the scanning is effected by oscillatory mechanical movement of the beam bending magnet 95. The magnet yoke 96 is rotated in ball bearing sleeves 97 about the axis of the beam 11 and movement is imparted to the yoke by means of a motor driven flywheel 101 connected to the yoke through a rod 98 pivoted at 99 and 101. The beam particles may be electrons or protons.