The Use of the Magnetic Angle Changer in Atomic and Molecular Physics

The magnetic angle changer (MAC) is a system of solenoids that produces a localized and shaped magnetic field, which can change the direction of an electron beam in a controlled way. When it is used in conjunction with a conventional electron spectrometer employing hemispherical deflector analyzers, it can extend the angular range of the spectrometer. In particular, it enables the spectrometer to view the complete back-scattering hemisphere up to and including scattering angles of 180 degrees. The principles of operation of the MAC are described, and practical examples of it are presented. The use of the MAC is described in measurements of differential cross sections in elastic and inelastic electron scattering in atoms and molecules, including the observation of resonance structures in these cross sections. Applications of the MAC to coincidence measurements of electron impact excitation and ionization and to photoelectron studies are also described. Comparisons of experimental measurements with theoretical predictions are presented where applicable.