MagLab Awarded DOE Grant to Develop New SRF Cavities

The National High Magnetic Field Laboratory (MagLab, CSA CSM) is playing a role in a nationwide effort to make human-scale particle accelerators for a host of applications. And now, with a $1 million grant from the US Department of Energy, scientists at the lab’s Applied Superconductivity Center (ASC) are developing a key component of these slimmed-down accelerators called superconducting radio frequency (SRF) cavities.

Larger machines—like CERN’s Large Hadron Collider—often dominate the science headlines, but high-energy particles are handy for all kinds of research and so there are actually tens of thousands of particle accelerators of different designs, uses and sizes worldwide. “They can be used for everything from zapping cancer cells to curbing pollution to scanning cargo for contraband,” says Lance Cooley, an ASC scientist, CSA board member and professor at the FAMU-FSU College of Engineering, who is leading the SRF 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. “They can be used anywhere you need a catalyst or an X-ray,” Cooley says. He is focused on the problem of designing an SRF cavity that doesn’t require the fancy infrastructure used in large-scale accelerators and doesn’t break the bank.

SRF 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 SRF cavities made out of the stuff fetch as much as a Ferrari, says 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 says.

ASC has worked with niobium-tin for decades, refining superconducting wires and tapes for use in magnets at the MagLab and other facilities. “That’s why we can succeed where other groups might not,” Cooley says. 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 says. “But you’ve got to start somewhere.”