It’s time to say goodbye to a beloved assemblage of machinery: In July, the Central Helium Liquefier produced its last batch of liquid helium.
The CHL ran continuously during the Tevatron’s operation from 1983 to 2011. Following 4.5 miles of piping to 24 satellite refrigerators around the Main Ring, liquid helium flowed over the Tevatron’s magnets to keep them at superconducting temperature — about minus 450 degrees Fahrenheit.
“We relied heavily on the CHL to run the Tevatron,” said Jay Theilacker, the Accelerator Division Cryogenics Department head. “And for all those decades it was incredibly reliable.”
In the CHL, helium glided through a series of pipes, gigantic compressors, coldboxes and turbines that cooled it from gas to liquid. When running, the massive compressors shook the entire building, forming waves in coffee cups during meetings.
Thanks to the CHL’s supply of liquid helium, electrical current flowing through the Tevatron’s magnets felt no resistance as it created magnetic fields to steer the Tevatron beam. The CHL also helped rapidly cool quenched magnets, which allowed the Tevatron to resume beam operations.
“It was the lifeblood of the Tevatron,” said Jerry Makara, former CHL head. “When we went down, everybody was waiting for us to get back up.”
The CHL was so vital to the Tevatron’s operation that Fermilab built a second, redundant liquefier in the 1980s. When something in the first liquefier went awry, crews could bring the second liquefier online within 24 hours. These two helium liquefiers remained the world’s largest until recently.
At the heart of the CHL was a crew of dedicated staff that manned it 24/7, working 12-hour shifts. Makara recalls the late Ron Walker, CHL head before him, as the “spirit of the CHL.” The entire CHL crew, both operators and supervisors, emulated Walker’s devotion, including Mike Hentges, Gary Hodge and Bob Kolar. When the CHL was shut down with the Tevatron, some crew members retired, and others moved on to other jobs within the laboratory.
“One thing that was true for all of us after the shutdown: We appreciated getting a good night’s sleep,” Makara said.
The CHL restarted a couple of years ago to test superconducting magnets for first the MICE experiment, based in the UK, and then Mu2e. Makara said the CHL’s reliable reputation cracked — quite literally for one compressor — during this “last hurrah.” Many parts broke, and the number of functional compressors dwindled from four to one.
“Once you shut things down, it’s never quite the same when you start it back up again,” Theilacker said. “We were really on our last legs here.”
So Fermilab decommissioned the CHL, shutting it down for good this time. The CHL building will be gutted, and salvaged equipment will be distributed among divisions. There’s no verdict yet on who will move in next.