Beam transport systems consisting of two quadrupole triplets

The versatility of charged-particle beam transport systems consisting of two symmetric triplets of magnetic or electrostatic quadrupole lenses is investigated. It is shown that the two-triplet configuration can be operated with a number of different symmetries so that telescopic transfer properties are obtained. As a consequence of the symmetry, the system automatically has unit horizontal and vertical magnification ('unit telescope'). The transfer matrix elements for this system are calculated, and the operation of a typical system is illustrated by plotting rays traced through the system using matrix methods. Results are also presented for the more general cases of (a) unit magnification in one plane and variable magnification in the other ('modified telescope'), and (b) equal but variable magnifications in both planes ('zoom lens'). These characteristics are independent of the shape ofthe initial beam