Astigmatic Magnetic Analyzer

Abstract

A fringe field double focusing magnetic spectrograph is described which was designed to achieve a resolution of the order of 103, a solid angle of the order of 10−2, and an energy range capability from about 0.5E0 to 2.5E0, where E0 is the energy of the design point. The analyzer can be used as a spectrometer with still larger solid angle near 1.44E0. The system corresponds to a prism astigmatic-lens combination which takes a point object into line images for each energy represented. At the design point, the y image distance equals the object distance, and the z image distance is at infinity. At other energies, the z image distance has various large magnitudes. A ``bootstrap'' procedure is used to generate the entrance and exit faces with the aid of a ray tracing instrument. Approximate methods are used to allow for fringe field effects so as to shape the actual pole pieces to achieve the desired effective faces. A numerical method of optimizing the horizontal focal properties is presented. The initially observed performance of the system approximately fulfills the design objectives.