INCREASED STABILITY REQUIREMENTS FOR SEEDED BEAMS AT LCLS

Running the Linac Coherent Light Source (LCLS) with self-seeded photon beams requires better electron beam stability, especially in energy, to reduce the otherwise huge intensity variations of around 100%. Code was written to identify and quantify the different jittersources. Some improvements are being addressed, especially the stability of the modulator high voltage of a few critical RF stations. Special setups like running the beam off crest in the last part of the linac can also be used to reduce the energy jitter. Even a slight dependence on the transverse position was observed. The intensity jitterdistribution of a seeded beam is still more contained with peaks up too twice the average intensity, compared to the jitterdistribution of a SASE beam going through a monochromator, which can have damaging spikes up to 5 times the average intensity.