Cranking it up to 11: a new superconducting magnet

Fermilab’s Technical Specialist Marty Whitson installs the 11-Tesla niobium-tin dipole magnet inside a bolted skin. Photo: Fermilab

Like the famous volume controls in This Is Spinal Tap, a new magnet developed by CERN and Fermilab goes to 11. But unlike the dubiously labeled amplifier, the magnet doesn’t just say it goes to 11, it really does. 11.7, in fact.

Pushing past 11 Tesla is a goal that both laboratories have been working on since they combined forces three years ago to develop stronger magnets for the LHC upgrade. It’s a remarkable achievement for the accelerator community.

“There were many happy e-mails going around,” said 11-Tesla Project Leader Mikko Karppinen, of CERN.

For more than 10 years, Fermilab has been working to develop accelerator magnets with high fields using niobium-tin superconductor. In March, the High-Field Magnet Group announced a new milestone: In collaboration with the High-Luminosity LHC project at CERN, the group developed a niobium-tin magnet that broke the 11-Tesla barrier.

The first practice coil for the 11-Tesla niobium-tin dipole—wound, reacted and impregnated with epoxy at CERN—is used to validate the technology transfer from Fermilab. Photo: CERN

“When we heard about the need at CERN to develop these 11-Tesla magnets, we offered our help here,” said Fermilab’s Alexander Zlobin, head of the High-Field Magnet Program. “For us this was a good opportunity to implement niobium-tin technology in a real machine.”

11 Tesla isn’t an arbitrarily chosen value. The LHC is planning to use shorter magnets to make room in its tunnel for new instruments that will help narrow the particle beam, protecting the LHC ring from beam losses. But if the magnets must be shorter, they must also be stronger to compensate. The LHC currently uses niobium-titanium magnets at their maximum of 8.33 Tesla. The niobium-tin magnets will kick it up a few notches.

“Anywhere that we install new equipment, we can use this kind of magnet to make space available,” Karppinen said. “It’s a good first step on a path to having niobium-tin technology for accelerators in general.”

For Fermilab and laboratories across the United States, the push for better magnets for accelerators has been steadily increasing.

“The goal is to develop new technologies for present and future accelerators, and the new technology now is niobium-tin as a baseline technology for the next generation of accelerators,” Zlobin said.

The 11-Tesla project teams achieved their success on a 1-meter-long, single-aperture magnet at Fermilab. Photo: Fermilab

Niobium-tin is a brittle and difficult-to-manage superconductor, so researchers have been working on methods to withstand the large forces and large temperature changes it will be subjected to in accelerator magnets as they help bend and focus particle beams.

The 11-Tesla project teams achieved their success on a 1-meter-long, single-aperture magnet (see photo; credit: Fermilab) developed at Fermilab. Over the next few years, the teams will work to develop a 5.5-meter magnet—the size required for the LHC upgrade—with accelerator-quality fields and that can also accommodate LHC’s piping and connections.

“We see needs and possibilities to improve and really demonstrate all the capabilities of these magnets, which are higher than what we have now,” said Zlobin, who pointed out that his group hasn’t popped any champagne bottles so far. “We will celebrate when we satisfy ourselves with the magnet performance. Now we have to work hard.”