Canada’s synchrotron a made-in-Saskatchewan design

By Michael Robin
Research Communications

Les Dallin, accelerator physicist at the Canadian Light Source synchrotron, stands in the heart of the $174-million U of S facility that he helped to design, at the point where the booster ring shoots electrons travelling at nearly the speed of light into the larger storage ring. From the storage ring scientists will pull super-bright light into beamlines, to focus on their experiments.

Photo by Lawrence McMahen

On the evening of December 9th, 2003 a light flashed into a diagnostic beamline hutch at the Canadian Light Source (CLS) – the first light observed from the $174-million synchrotron at the U of S.

“There was a lot of cheering and dancing around in the control room that night,” says Les Dallin, CLS accelerator physicist and commissioning leader.

For Dallin, it was visible proof that the design born on his desktop worked as planned. It was the culmination of a journey that began in Ottawa in 1990, at a meeting of scientists called by Michael Bancroft, professor of chemistry at the University of Western Ontario and long-time synchrotron user.

Dallin, with a U of S PhD in accelerator physics fresh under his belt, heard the discussions about the potential for synchrotron-based research in Canada and the need for a machine in this country. He went back to his desk at the Saskatchewan Accelerator Laboratory (SAL) at the U of S and got to work on a design.

Bancroft, former CLS interim director, says it was primarily the SAL know-how in accelerator physics that tipped the decision to build the facility in Saskatchewan.

“SAL had the expertise to build the synchrotron,” he says. “That’s incredibly important to get the project off the ground. It was a significant advantage.”

Dallin designed the lattice, that is, the arrangement of magnets and hardware for the booster and storage rings that are the heart of the machine. Experts from other synchrotrons offered input, and the user group kept adding to the wish-list.

“What we wanted from a machine kept changing every few years,” Dallin says. “We started with a machine that was 1.5 GeV (giga electron volts) and ended up with 2.9 GeV.”

The CLS is remarkably compact. In the circular concrete hallway that houses the storage ring, massive 3.75-tonne magnets are shoulder-to-shoulder with monitoring devices and ion pumps that maintain vacuum. No space is wasted.

“Nobody’s attempted what we did, with a smaller lattice, a smaller building, a smaller ring,” Dallin says. “Getting the performance for the dollar value was our goal.”

This is a major accomplishment, according to Bancroft. The storage and booster ring have been built on time and on budget.

“What other project in Canada of this type can boast this?” he says. “It’s a tremendous tribute to what these folks have done. I don’t think people realize what they have achieved. It’s remarkable.”

Dallin is quick to point out that success comes from the efforts of many people both in Saskatchewan and around the world.

“The international synchrotron community is a good and open one,” he says. “The spirit of co-operation is great.”

A key innovation in the CLS is the superconducting radio frequency (RF) cavity that “kicks” the electron beam every time it comes around the storage ring to maintain its energy. Chilled to near absolute zero (–269 C), the cavity is simpler, more efficient, and delivers higher voltages than conventional technology.

The idea for using superconducting technology in storage ring cavities came from Cornell University in New York to SAL Director Dennis Skopik, now with the Thomas Jefferson National Accelerator Facility (TJNAF) in Virginia. Skopik was one of the early prime movers in the CLS project.

Skopik, then the CLS acting director, handed the superconducting file to Mark de Jong, who was in an ideal position to evaluate the technology. Recruited from Atomic Energy of Canada’s Chalk River research facility, he helped build RF cavities for particle accelerators at Stanford University and Cornell in the U.S. But while superconducting technology had been in development for more than a decade at major facilities like CERN in Switzerland and TJNAF in the U.S., it had never been used in an accelerator dedicated to producing synchrotron light.

“People were pretty nervous,” de Jong, now CLS project manager, recalls. “But I was very familiar with those designs. I said, ‘You don’t want those room-temperature cavities. I helped design them, and they’re way too complicated.’”

While Dallin knew the physics to write the overall design specifications, it took further collaboration and some special tools to crunch the numbers. Roger Servranckx, an expert in applied mathematics formerly with the U of S, wrote the optics design software Dallin used to design the booster and storage rings.

With the specs in hand, CLS project engineer Dan Lowe and his team could come up with an accurate price tag.

“By the time we applied for funding, we pretty well knew what it would cost,” Dallin says. “This was a tremendous advantage.”

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