Improved CLIC performances using the beam response for correcting alignment errors

It has been demonstrated that in the Compact Linear collider (CLIC) alignment errors of the order of 10 microns r.m.s. can be tolerated on the main linac components, in particular on pick-ups. These results imply the application of trajectory-correction processes involving several correctors and beam-position monitors, of the "dispersion-free" or "wake-free" types. The disturbing effects to be corrected have so far been simulated by gradient variation of the lattice quadrupole chains. Recently the idea of a direct evaluation of these effects was suggested. In particular, one can measure the response of the trajectory when the beam intensity is modulated. By incorporating into the above-mentioned algorithms the measured trajectory differences in order to minimize them, better performances are achieved than when these undesirable effects are simulated. The results presented show a gain of a factor of two on the vertical emittance blow-up.