Beam-based BPM alignment

An operational, beam-based, null-measurement, control room procedure designed to steer the closed orbit through the effective (no steer) center of every quadrupole is described. Performance of the procedure is simulated using UAL (Unified Accelerator Libraries). Matching SNS hardware availability, quadrupole strengths are assumed to be trimmable, but only in families, not individually. The accuracy of the procedure is unaffected by geometric and/or electrical misalignment of BPM's (beam position monitors) but calibration of their misalignments is a byproduct of the procedure. Some of the many possible failure mechanisms have been modeled, and have been found not to invalidate the procedure.