A mark of some of the world’s most powerful particle accelerators, past and present, is the underground loop through which scientists accelerate subatomic particles to investigate the many mysteries of the universe. Crucial to keeping particle accelerators alive are the cooling systems that prevent damage from overheating. In Fermilab’s case some of those cooling systems make up the iconic double loop that adorns the grounds.
The two loops, which trace the tunnels of the Main Injector and the former Tevatron, are a system of man-made water trenches. Before the Tevatron shut down in 2011, engineers would pump water from the trenches, called cooling ponds, into service buildings. The service buildings would then direct the water through heat exchangers, transferring heat from the Tevatron low-conductivity water cooling system. But when the Tevatron shut down, so did the cooling system.
“You can’t beat the efficiency of water cooling,” said Kent Collins, the deputy head of the Facility Engineering Services Section. “The cooling ponds did a phenomenal job for as long as we ran, but now they’re just like any other pond.”
During Tevatron operations, as many as 30 service buildings, divided into six operational sectors, directed the cooling water. Near-term plans call for one sector to remain operational for post-Tevatron operations. Service buildings will help cool accelerator components that will send beam to external beamline experiments such as Seaquest and MTest experiments.
The Main Injector ponds will also remain active, providing cooling for beamlines to the laboratory’s neutrino programs, such as NOvA.
As for the other cooling pond sectors—they now host beavers and are slowly eroding. Once 7 feet deep when constructed in the 1970s, most are now 1 to 2 feet deep. Yet their story may not be over, said the Accelerator Division’s Maurice Ball, whose group is looking at ways the lab could revive some of the ponds.
“The way that the ponds operated for the Tevatron was through a domino drainage effect from one sector to the next, but that may not work for future projects that may use these ponds,” Ball said. “The Accelerator Division is working with Facilities Engineering to figure out how we could reconfigure existing pond infrastructure at minimal cost to maintain a more efficient pond circulation for possible future projects.” The projects include Mu2e, Muon g-2 and work under consideration at CDF and DZero.
Recommissioning the shallow ponds for short-term needs may be reasonable, but the longer the mechanical systems are inactive, the greater the restoration cost will be, Collins warned. Without increasing the ponds’ depth, the heat load they will be able to manage will also be limited.
“For any project with an extended run, the ponds will require renovation,” Collins said. “Our near term plan will leave the piping and other infrastructure in place and use the dried ponds as vegetated drainage swales. Future projects will determine when reviving ponds is cost-effective compared to alternative cooling sources.”