Control of transverse motion caused by chromatic aberration and misalignments in linear accelerators

Corkscrew beam motion is caused by chromatic aberration and misalignment of a focusing system. To minimize chromatic aberration, we have developed a time-independent steering algorithm that minimizes the observed corkscrew-amplitude averaged over the beam pulse. The steering algorithm can be done quickly and is not sensitive to the alignment, calibration and spacing of the beam position monitors. The steering algorithm can also be used even if the corkscrew motion caused by a given misaligned magnet is fully developed, i.e., the relative phase advance is greater than 2π. In this paper, we will discuss corkscrew motion, the optimal dynamic alignment procedure, its corkscrew reduction factor, and the effects of beam position monitors' spacing.