ANALYSIS OF THE FRINGE-FIELD REGION OF MAGNETIC QUADRUPOLE LENSES - FIELD-MEASUREMENTS AND ION-OPTICAL CALCULATIONS

An investigation into the minimisation of the duodecapole fringe field components of magnetic quadrupole lenses has been conducted at Melbou rne. As part of this program, a detailed field mapping of the fringe f ield region of the Melbourne magnetic quadrupole lenses has been condu cted (G.R. Moloney, D.N. Jamieson and G.J.F. Legge, Nucl. Instr. and M eth. B 54 (1991) 24). The field mapping technique measures the radial magnetic field component, B, over the three cylindrical coordinates, r , alpha and z. We have also conducted a program of modifying the pole tip termination of the lenses Co reduce the duodecapole field componen ts. Complete magnetic field measurements for the modified lens pole ti ps have been presented previously (G.R. Moloney, D.N. Jamieson and G.J .F. Legge, Nucl. Instr. and Meth. B 77 (1993) 35-38). This paper prese nts an ion Optical analysis of the effects of the fringe field compone nts on the beam optics of the Melbourne Microprobe systems. The optica l effects are calculated with a new computer code developed at Melbour ne. Standard numerical ray tracing is performed utilising Runge-Kutta techniques. (C) 1997 Elsevier Science B.V.