Observation and analysis of static deflections from transverse long-range wakefields in the SLC

Abstract

In the SLC main linac a train of three bunches is accelerated. The leading positron bunch is followed by two bunches of electrons. When the positron bunch passes off-axis through the RF structures, it excites dipole modes in the structures, for example long-range transverse wakefields which deflect the subsequent electron bunches. Although the magnitude of the deflections is small one can infer the deflections by measuring the trajectory difference while changing the spacing between the positron and electron bunches. Knowing the positron trajectory the misalignments of the accelerating RF structures with respect to the BPM's can be calculated. We present measurements from the SLC linac and discuss the data analysis and errors.