Correction of dispersion and the betatron functions in the CEBAF accelerator

Abstract

During the commissioning of the CEBAF accelerator, correction of dispersion and momentum compaction, and, to a lesser extent, transverse transfer matrices were essential for robust operation. With changing machine conditions, repeated correction was found necessary. To speed the .diagnostic process we developed a method which allows one to rapidly track the machine optics. The method is based on measuring the propagation of 30 He modulated betatron oscillations downstream of a point of.perturbation.. Compared to the usual methods of dispersion or difference orbit measurement, synchronous * detection of the beam displacement, as measured by beam position monitors, offers rs significantly improved speed and accuracy of the measurements. The beam optics of the accelerator was altered to decrease lattice sensitivity at critical points and to simplify control of the betatron function match. The calculation. of the Courant-Snyder invariant from signals of each pair of nearby beam position monitors has allowed one to perform on-lie measurement and correctionof the lattice properties.

Diagnostics For Recirculating And Energy Recovered Linacs

“…A more quantitative system was developed based on 30 Hz toggling of the 60 Hz tune-up beam [22]. For difference orbits, the beam is toggled between two states with two sets (one for each transverse direction) of air-core magnets, and for dispersion the beam is toggled in two energy states.…”