Beam-based alignment technique for the SLC linac

It is pointed out that misalignments of quadrupole magnets and beam position monitors (BPMs) in the linac of the SLAC (Stanford Linear Accelerator Center) Linear Collider (SLC) cause the electron and positron beams to be steered off-center in the disk-loaded waveguide accelerator structures. Off-center beams produce wakefields which limit the SLC performance at high beam intensities by causing emittance growth. A general method is presented for simultaneously determining quadrupole magnet and BPM offsets using beam trajectory measurements. Results from the application of the method to the SLC linac are described. The alignment precision achieved is approximately 100 mu m, which is significantly better than that obtained using optical surveying techniques.<
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