Observation of induced beam oscillation from actively displaced RF accelerating structures

At high beam currents the alignment of the accelerating structure in a linear collider relative to the lattice quadrupoles and position monitors dominates all other alignment issues. These structure misalignments drive wakefield emittance growth. Consequently, great efforts have been spent at SLAC to align the accelerating structure of the Stanford Linear Collider (SLC). As an accelerator test, remote controlled mechanical movers have been installed on several RF structures to study wakefield effects. Experimental tests of induced beam wakefields and the resulting oscillations downstream generated by these remotely displaced structures have been performed. The observed wakefield and have been compared with a computer model. The results from displacements at the beam´s betatron frequency are particularly exciting as that frequency strongly excites emittance growth. In general, a control mechanism can be made to move the structure at that spatial frequency, thus providing sine and cosine adjustments for cancellation of alignment errors in the accelerator of a future collider. A similar method to control emittance growth by changing the beam trajectory has already been tested and is in daily use