EMITTANCE CONTROL FOR DIFFERENT FACET BEAM SETUPS IN THE SLAC LINAC

The linac beam at SLAC requires different setups for different users at the FACET (Facility for Advanced aCcelerator Experimental Tests) area, like highly compressed, intense bunches, or lower charge, long bunches. These require typically a lengthy tuning effort since with an energy-time correlation (or "chirp") the bunch transverse wakefield kicks can be compensated with dispersive trajectory oscillations and vice versa. Lowering the charge or changing the bunch length will destroy this delicate balance. Besides the typical steering to minimize BPMs (Beam Position Monitors) with correctors, we applied different techniques to try to localize beam disturbances like dispersion with phase changes, RF-kicks and RF quadrupole fields turning a klystron off and on, or varying the phase, and finally wakefield kicks with different beam intensities. It is also important to quantify BPM to quadrupole offsets with "bowtie" plots and that the correctors give the expected kicks with orbit response matrix measurements.