$1 Million Grant Will Advance Compact Particle Accelerators

Contact: Lance Cooley

TALLAHASSEE, Fla. — When you think "particle accelerator," you think big. CERN’s Large Hadron Collider (LHC), for example, spans two countries, features a tunnel more than 16 miles (27 km) long, employs thousands of scientists and requires a budget of $1 billion a year.

This copper RF cavity, about 1 foot (30 cm) long, would be for a small-scale particle accelerator about 3 feet in length (about 1 meter).

Image credit: DSM South / Bailey Tool

Turns out, particle accelerators need not be so massive. In fact, proton-smashing technologies initially developed to reveal the mysteries of the universe are being down-scaled to solve less lofty, but no less important, problems related to environment, health and safety.

The National MagLab is playing a role in a nationwide effort to make human-scale particle accelerators for a host of applications. With a $1 million grant from the U.S. Department of Energy, scientists at the lab's Applied Superconductivity Center (ASC) are developing a key component of these slimmed-down accelerators called radio frequency (RF) cavities.

While big boys (like Europe's LHC, the retired Tevatron at FermiLab outside Chicago and the SLAC National Accelerator Laboratory in California) have grabbed the science headlines with flashy discoveries of top quarks and Higgs Bosons, there are actually tens of thousands of particle accelerators of different designs, uses and sizes worldwide. That’s because high-energy particles are handy for all kinds of things.

"They can be used for everything from zapping cancer cells to curbing pollution to scanning cargo for contraband," said Lance Cooley, an ASC scientist and professor at the FAMU-FSU College of Engineering who is leading the RF cavity research.

Whether made of protons photons, electrons or ions, beams generated by accelerators can break up unwanted molecules like coal flue gases or bacteria; catalyze processes helpful in industry and manufacturing; and identify nefarious stowaways hidden in shipping containers. The list of potential applications could be as long as SLAC's nearly 2-mile linear accelerator.

"They can be used anywhere you need a catalyst or an X-ray," Cooley said.

Cooley is focused on the problem of designing an RF cavity that doesn't require the fancy infrastructure used in large-scale accelerators and doesn't break the bank.

RF cavities boost the speed of particles as they pass through them; in the LHC, for example, 16 cavities work to build up the particles’ velocity to close to the speed of light. When radio waves of just the right frequency are funneled into the cavities, they bounce around inside, creating oscillating electric and magnetic fields that, when timed just right, propel the particles forward. It's similar to what happens inside microwave ovens, but with much higher energy and, of course, a different objective. To minimize any loss of energy, the cavities are made of superconducting materials, which carry electricity with perfect efficiency.

The superconducting material most often chosen to make these cavities is niobium. But it's an expensive element, and RF cavities made out of the stuff fetch as much as a Ferrari, said Cooley, making it impractical for most applications.

That's where the expertise of Cooley and his ASC colleagues comes in. Their contribution is finding a way to coat a cavity fashioned of less expensive copper with a superconducting layer of niobium-tin (Nb₃Sn).

"For me it's the logical approach to an affordable, industrial accelerator cavity," Cooley said.

ASC has worked with niobium-tin for decades, refining superconducting wires and tapes for use in magnets at the National MagLab and other facilities.

"That's why we can succeed where other groups might not," Cooley said.

A microphotograph of niobium-tin film on top of bronze, the type Cooley and his colleagues hope to achieve inside an RF cavity.

Image credit: Peter Lee/National MagLab

But down-sizing complex technologies to a size both portable and affordable is a massive challenge that requires solving lots of engineering problems.

Traditional, "low-temperature" superconductors only perform at extremely cold temperatures that require the use of liquid helium, which complicates the engineering of a small-scale machine. Part of the project's challenge lies in engineering a material that can perform at slightly warmer (in relative terms) temperatures that can take advantage of advances in cryogenic cooling technologies. Niobium-tin offers that potential.

"You still need liquid helium," Cooley said. "But you've got to start somewhere."

Cooley's collaborators on the project are ASC Associate Director Peter Lee; Professor Choong-un Kim of the University of Texas–Arlington; and John Buttles, CEO of DMS-South / Bailey Tool, LLC.

Text: Kristen Coyne