PHASEFIX-correcting the tunes of the SLC arcs

The betatron phase advance tunes are crucial parameters in the SLC (Stanford Linear Collider) arc optics because of the strong cross coupling between the x and y phase spaces, which takes place at rolled achromat boundaries. Phase measurements have been performed with an accuracy of about 0.3 degrees /cell and, initially, substantial deviations from the design (108 degrees ) were observed. Corrections on an achromat-by-achromat basis have been performed to reduce the phase errors within less than 1 degrees /cell. They were done by adjusting a current balance between focusing (F) and defocusing (D) magnets and by changing the horizontal relative displacements of F and D magnets using the XMOV magnet movers or with realignment work.<>