TRIUMF brown reports 70-4

This report presents some of the techniques used in designing the sector-focused magnet for the TRIUMF cyclotron. An empirical method is given for calculating the magnet pole tip shape required to contain a 500 MeV beam of H- ions. The method is good only for small changes in the shape. In the test case, the generated pole tip had a spiral angle correct to within ±5 deg, and a hill angle correct to ±1 deg. The average field was found to be isochronous to ±70 G. An empirical solution to the problem of finding the field inside the magnet air gap is also given. The magnetic field resulting from a given pole tip contour is calculated at a point on the median surface by finding the perpendicular distance from the point to the edge of the pole and comparing this to an experimentally measured curve of field against distance. Fields generated by this technique have their averages correct to within 70 G and flutter to within 8%. Again, previous knowledge of similar pole tips is assumed. The method and results of calculating the pole edge position tolerances for the latest model magnet are given. The field strengths inside the steel return yoke as obtained from a series of flux measurements are also presented. Finally, it is shown that a simple approximation to the magnetic circuit of the magnet predicts the coil induction required to an accuracy of only 25%.TRIUMFUnreviewedResearche