Ideal pole faces for weak-, strong- and FFAG-focusing particle accelerators and other nuclear instruments
For the weak-, strong- and FFAG-focusing magnets of particle accelerators and other nuclear instruments (particle spectrometers, deflectors, electromagnetic isotope separators, etc.) the concept of ideal pole face is introduced by neglecting saturation, remanence and edge effects. From the analytic expression of the magnetic scalar potential, derived by the author for a general case, the equation of the ideal pole face is deduced and applied to weak-, strong- and FFAG-focusing magnets. For FFAG nuclear instruments with spiral sectors an ideal pole face is derived from a fundamental pole face with cylindrical symmetry, modified to obtain the azimuthal variation of the magnetic guiding field. The actual pole face can be computed from the ideal one if the edge effects are taken into account. General analytic expressions of the equipotential set and potential network, useful for this computation, are deduced.