So long, Cockcroft-Walton

After 40 years operation, Fermilab’s iconic Cockcroft-Walton generators will be decommissioned tomorrow morning. Photo: Reidar Hahn

Fermilab has had many different accelerators in its four-decade history. From the Linac to the Tevatron to the Main Injector, every one of them has been powered by a Cockcroft-Walton generator. That ends tomorrow, when the generators send out their last beam.

“They’ve been a critical part of our experiments,” said Proton Source Department Head Bill Pellico, who is overseeing their decommissioning. “People who work on these things have come to love them, but it’s time to move on and modernize.”

Developed at the University of Cambridge in the early 1930s by John Cockcroft and Ernest Walton to accomplish the first artificial splitting of an atom, Cockcroft-Walton generators became an essential part of particle accelerators and other devices.

However, most particle accelerators today use radio-frequency quadrupole systems that are more efficient than Cockcroft-Walton generators. Fermilab and Los Alamos National Laboratory were, until now, the only two major laboratories in the world still operating them. At the end of the current accelerator complex shutdown, Fermilab’s accelerators will run on RFQ systems.

Pellico said that, while the Cockcroft-Walton generators have been generally reliable over the past 40 years, they will not be up to the task of running Intensity Frontier experiments.

“It’s like an old car,” he said. “After 40 years, maintaining it becomes more and more difficult.” The new RFQ systems will be much smaller and have fewer parts to maintain and replace over their lifetimes.

There is one aspect of the Cockcroft-Walton generators that is irreplaceable: their aesthetic. The generators’ distinctive design inspires wonder in the many tour groups who see them every week.

“They look like something out of science fiction, and people think they’re cool,” Pellico said. The generator seen on the tour will be disconnected but largely remain in place in its room. The other generator, located in a separate enclosure, will likely be removed and preserved.

Pellico said that Los Alamos is watching Fermilab’s conversion to RFQ systems to inform their own planned decommissioning of their Cockcroft Walton generators.

Tomorrow at 11 a.m. in the Linac Gallery, AD will host a ceremonial final shutdown of the Cockcroft-Walton generators. Jim Wendt and Ray Hren, retired Fermilab operators who commissioned and worked on the generators until 2010, will be on hand to shut down the generators for the last time.

“I’ll miss the Cockcroft-Waltons,” operations specialist Pat Karns said. “Hopefully the RFQ will run more stably than the Cockcroft-Waltons and I won’t get as many calls at 2 a.m. when something’s broken.”

Joseph Piergrossi