Development and Testing of Tools for ORM Measurements and Quadrupole Centering

Abstract

In preparation for the commissioning of Linac2 (formerly referred to as the {PIP-II} linac) at Fermilab, we are developing high-level applications that automate Orbit Response Matrix (ORM) measurement and beam-based localization of quadrupole magnetic centers. Both procedures are designed to run in a low-amplitude mode compatible with otherwise regular operation. The ORM is measured by exciting multiple dipole correctors simultaneously at low amplitude, each at a distinct frequency, and applying a Discrete Fourier Transform to the recorded BPM signals to extract per-element transfer function with quantified noise. One application of the measured ORM is to predict the corrector coefficients that form local orbit perturbations (bumps). To center the trajectory in a quadrupole, such a bump is created around it, the quadrupole current is oscillated, and the responses of the downstream BPMs are recorded and analyzed. Repeating this at several beam positions inside the quadrupole -- each set by the bump -- the dependence of the BPM signal on beam position provides information about the quadrupole center. The applications are being tested at the Fermilab 400\,MeV Linac during regular production runs, and the lessons learned are fed back into their improvement.