Two magnet asymmetric doubly achromatic beam deflection system

摘要

The beam deflection system includes two dipole magnets for deflecting a charged particle beam in a deflection plane. The first magnet bends the beam in a path having a radius &rgr;.sub.1 and a deflection angle &thgr;. sub.1 greater than 180°. The first magnet has an effective exit edge at an angle (90°-&eegr;.sub.1) with respect to the beam path. The second magnet further bends the beam in a path having a radius &rgr;. sub.2 and a deflection angle &thgr;.sub.2 where 225°≦(. theta..sub.1 +&thgr;.sub.2)≦280°. The effective entry edge of the second magnet is at an angle of (90°- &eegr;.sub.2) to the beam path. In the usual practical case the effective interior edges of the two magnets are roughly parallel, that is, &eegr;. sub.1 ≃ -&eegr;.sub.2 and the doubly achromatic properties are obtained to first order when the angles satisfy the following formula: ##EQU1## and when the distance D between the effective edges of the two magnets is set so that the dipoles produce equal beam dispersion in the drift distance between them. For the case of 270° total bend with &rgr;.sub.2 =. rho..sub.1 this occurs at a distance D, given by ##EQU2##