Oscillation data analysis during the LCLS-II commissioning at SLAC

Analyzing the betatron oscillation of a beam is mainly used to find focusing errors in the lattice, like quadrupole errors. The generated trajectory differences can be compared with the design lattice or the current machine lattice where some magnets have been changed for different purposes or accidentally. Each method has different advantages and disadvantages like finding a quadrupole which got turned off by mistake won't be discovered with the current lattice method, while matching quadrupoles errors (which get tuned away from design) are harder to identify with the design lattice comparison. Besides lattice errors BPM (Beam Position Monitor) problems can be found too. Interpreting the data can have many pitfalls, some will be explained.