New compensation of transverse wakefield effects in a linac by displacing accelerating structures

Beams accelerated in the linac of a linear collider experience transverse wakefield effects due to small residual misalignments of the accelerating structure. These wakefields lead to emittance growth. The traditional correction method is to add induced betatron oscillations to the trajectory of the beam to counteract the effects of the unknown actual errors and, thereby, reduce the emittance enlargement. However, practical considerations make this solution operationally difficult. In this note a second correction method is proposed where the positions of the accelerating structures are remotely controlled. By adding position offsets of the RF structure at the spatial frequency of betatron oscillations, direct wakefield reduction can be made. A hardware solution suitable for the SLC is presented which does not move the quadrupoles or position monitors. 6 refs., 2 figs