The Antiproton Source is a unique accelerator in the U.S. as a storage ring for antiprotons, and has many features not found in other accelerators at Fermilab. Among these is a host of beam diagnostic equipment, many of which have very small apertures for the antiproton beam to get through.
Antiprotons are very hard to make, collect, and store so each one is precious and expensive.
Small apertures are the places where the beam is most likely to scrape against the walls of the vacuum chamber, and any beam that scrapes is lost. To make it easier to adjust the accelerators in the Source to preserve antiprotons and prevent beam losses, most of the small aperture devices were mounted on remotely controlled motorized stands to allow them to be repositioned without anyone entering the Source. Using beam loss monitors, the effect of small adjustments to the aperture positions can be studied and optimized quickly. Moving quadrapole and dipole magnets changes the shape and timing of the orbit of the antiprotons. There isn't much room in many places in the Accumulator to put even small trim magnets, so one of the experiments performed in the Source was to rotate the large horizontally bending dipole magnets by very small amounts to give them the effect of tiny vertical bending dipole magnets as well as horizontal dipoles.