Strongly Asymmetric Beams at the University of Maryland Electron Ring (UMER)

The standard operation of the University of Maryland electron ring (UMER) employs symmetric strong focusing with magnetic quadrupoles, i. e., a FODO scheme whereby the zero-current betatron phase advances per period in the two transverse planes are equal or nearly so. Asymmetric focusing, on the other hand, employs quadrupoles with different strengths in a FODO cell. Typically, a small focusing asymmetry is implemented in most accelerators to set the operating point (horizontal and vertical zero-current tunes) in order to avoid resonances and/or compensate for edge focusing of bending magnets. Extreme asymmetry, however, is rarely, if at all, used. We review the motivation and theory of beam transport with general focusing asymmetry. We also present preliminary results of an experiment with highly asymmetric focusing of a space-charge dominated electron beam in UMER.