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 Melbourne. As part of this program, a detailed field mapping of the fringe field region of the Melbourne magnetic quadrupole lenses has been conducted (G.R. Moloney, D.N. Jamieson and G.J.F. Legge, Nucl. Instr. and Meth. B 54 (1991) 24). The field mapping technique measures the radial magnetic field component, Br over the three cylindrical coordinates, r, α and z. We have also conducted a program of modifying the pole tip termination of the lenses to reduce the duodecapole field components. Complete magnetic field measurements for the modified lens pole tips 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 presents an Ion Optical analysis of the effects of the fringe field components on the beam optics of the Melbourne Microprobe systems. The optical effects are calculated with a new computer code developed at Melbourne. Standard numerical ray tracing is performed utilising Runge-Kutta techniques.