Muon g-2 ring receives first beam

From left: Brian Drendel, Dean Still, Mary Convery, Jim Morgan and Jerry Annala, pictured here inside the Main Control Room, oversaw the modification of old beamlines and construction of new ones to be able to deliver muons to the Muon g-2 ring. Photo: Marty Murphy

On May 23, after seven weeks of commissioning a recently completed addition to the Fermilab accelerator chain, a team of accelerator experts successfully delivered first particle beams to the Muon g-2 storage ring magnet, the centerpiece of the future Muon g-2 experiment. Over the past several years, the beamlines and storage rings that made up the former Antiproton Source have been repurposed for the new role in the Muon Campus.

The arrival of 50-foot-wide ring at Fermilab made a splash in June 2013, when it safely and soundly completed its 3,200-mile trip from Brookhaven National Laboratory.

The achievement of first beam is the initial step in providing the Muon g-2 experiment with a continuous beam of muons. The experiment will use muons — heavy cousins of electrons — to look for theorized but as yet unobserved particles popping in and out of the vacuum.

The group responsible for managing the reconfiguration of the accelerator complex for Muon g-2 — Jerry Annala, Mary Convery, Brian Drendel, Jim Morgan and Dean Still — oversaw the modification of old beamlines and construction of new ones to be able to direct particles to the big ring, which in 2015 moved into its permanent home, a building constructed for the purpose.

Members of the Accelerator Division Muon Department worked with physicists and engineers to create the beamline and Delivery Ring design and began transitioning to construction in 2014. The support departments within the Accelerator Division were tasked with installing the equipment, ably led by Construction Coordinator Consolato Gattuso. In addition to support from lab employees both within and outside of the Accelerator Division, contract electricians and ironworkers contributed an enormous amount of work.

The new particle path is more than a kilometer long and includes several laps around the old antiproton Debuncher Ring to complete the nearly light-speed jaunt from the existing complex to the Muon g-2 storage ring.

The Recycler accelerator fires protons with 8 billion electronvolts of energy down the first set of beamlines toward a target. The protons strike the target, producing showers of other kinds of particles, including muons, which are focused by a lithium lens.

Then these newly produced particles, which travel with an energy of 3 billion electronvolts, continue down a second set of beamlines toward the former Antiproton Source.

The muons are filtered from the rest of their particle companions and travel through a third, brand new beamline to the Muon g-2 storage ring, where scientists will study the particles to uncover new physics.

Incorporating the ring into the accelerator complex meant building a new tunnel enclosure and hundreds of meters of beam transport lines, in addition to rebuilding magnets, magnet stands and targets. A mix of new and repurposed power supplies were used to power the new beamlines, including several specialized pulsed supplies that will need to operate in 100-hertz bursts.

Over the next several months, both before and after the summer shutdown, Fermilab accelerator experts will commission the beamlines, preparing the Muon g-2 experiment for operation.