GB1463001A - Achromatic magnetic beam deflection system - Google Patents

Abstract

1463001 X-ray tubes VARIAN ASSOCIATES 16 Jan 1974 [22 Jan 1973] 2037/74 Heading H1D A method for achromatic magnetic deflection about a magnetic median plane of symmetry of a beam of non-monoenergetic beam of charged particles along a central axis defined by a particle of momentum P 0 in a bending plane between entrance and exit planes, comprises subjecting the beam to a series of magnetic forces so that particles of momentum P 0 which are initially radially displaced from and parallel to the orbital axis in the bending plane are focussed to first and second cross-overs of the central axis, and to zero slope relative to the axis at the m.m.p. of s.; particles of momentum P 0 which are initially on and angularly divergent from the central axis in the bending plane are focussed to a cross-over of the central axis at said m.m.p. of s.; beam particles of momentum P 0 and initially displaced from and parallel to the central axis in the transverse plane are focussed to a cross-over of the central axis at said m.m.p. of s.; beam particles of momentum P 0 initially on and angularly divergent from the central axis in the transverse plane are focussed to a cross-over of the central axis at the exit plane and to zero slope at the m.m.p. of s.; and particles of momentum differing from P 0 and having trajectories initially coincident with the central axis are achromatically focussed to the central axis at the exit plane. The respective trajectories C x , S x , C y , S y and d x are shown in Fig. 1, as are three bending electromagnets 12, 13, 14 and collimator 17 which may be ahead of a linear accelerator (not shown), drift lengths l 1 -l 4 , shunt 10 of soft iron, target 19 and an X-ray transparent portion of vacuum envelope 22 defining a window of an X-ray therapy machine. Shunt 10 has tunnel portions (23) (Fig. 2, not shown) and coil halves (24), (24<SP>1</SP>) are about coil spacer structure (26), (26<SP>1</SP>) closed by magnetically permeable side return plates (27). Momentum defining slot (36) at the m.m.p. of s. may shave the momentum distribution tails (Fig. 6, not shown) and positioning at that plane allows X-rays emitted from the analyser to be easily shielded from the treatment zone. Only one vane of the analyser need be provided and the analyser may be between adjacent magnets. Fringing effects of the magnets are discussed with reference to Figs. 8 and 9 (not shown). The bending angle may be 270 degrees, and the second magnet 13 may be split into two magnets with an intervening drift space. A detailed mathematical analysis is included, and dimensions exemplified.