For the first time since April 2023, electrons are circulating in the booster accelerator, bringing the Advanced Photon Source (APS) one step closer to fully returning to life.

The booster is a racetrack-shaped ring of electromagnets, roughly 1,200 feet in circumference, that serves as the last destination of the APS electron beam before it is injected into the storage ring. The booster’s job is to accelerate those electrons from 425 MeV (and eventually 450 MeV) to 6 GeV, which it accomplishes in about half a second before sending them to the storage ring to create ultrabright X-ray beams.

While the booster did not undergo a full upgrade like the storage ring, its timing system is entirely new, according to Lisa Berkland, chief of operations for the Main Control Room. The new technology is called the Injector Extraction Timing System (IETS), and it’s needed because the new storage ring operates at a different radiofrequency than the booster.

With this new timing system, the booster RF frequency is ramped over the course of the booster cycle, and the booster is synchronized with the storage ring at the moment of beam injection so that the correct storage ring “bucket” is filled. The accelerator team successfully tested the IETS in April before shutting off the electron beam for the storage ring removal and installation period.

Recently, the team held an internal readiness review for the booster, and on Feb. 12, they successfully injected electrons back into it. While this is an important accomplishment, Berkland said, it’s also a crucial part of a larger goal: operating the new APS storage ring for the first time.

“Without the booster there’s no storage ring,” Berkland said.