On the journey to 15 tesla

Emanuela Barzi

Alexander Zlobin

A year ago, in response to the P5 and HEPAP Accelerator R&D subpanel recommendations, the Office of High Energy Physics at DOE created a National Magnet Development Program (MDP) to integrate accelerator magnet R&D in the United States and coordinate it with the international effort.

Three U.S. labs — Fermilab, Berkeley Lab and the Florida State University/High Magnetic Field Laboratory — got together as a collaboration, and through extensive meetings and discussions converged on a U.S. MDP plan in June 2016.

The work was organized around four goals and several driving questions. It includes four directions – niobium-tin magnets, high-temperature superconducting magnets, magnet technology, and superconductor procurement and R&D. The first collaboration meeting was held in Napa, California, in the second week of February. Participants included representatives of the three collaborating labs, other potential program members, industry representatives as well as colleagues from CERN and KEK.

A Technical Advisory Committee (TAC) was also invited to familiarize themselves with the program and its key people. The TAC includes representatives from Brookhaven Lab, CERN, Fermilab, KEK and MIT and is led by Andy Lankford from the University of California, Irvine.

During this first meeting, which lasted two-and-a-half days, collaborators presented and discussed the status and plans for the four directions. They reached consensus on the strategic and technological importance of the 15- to 16-tesla niobium-tin dipole magnets needed for future very high-energy proton-proton colliders, such as the Future Circular Collider in Europe and Super Proton-Proton Collider in China.

Fermilab had started the development of such high-field accelerator magnets a few years ago, on the heels of the successful 11-tesla dipole program. This is a formidable challenge for niobium-tin accelerator magnets, whose record field of 13.8 T by Berkeley Lab has been sitting unsurpassed for about 10 years now. Surpassing the 14-T brick wall is currently considered worldwide a crucial goal and an inherent demonstration of innovation.

The Fermilab so-called 15-T Dipole Demonstrator was not only integrated into the MDP working plan but has also become a centerpiece of the program for the next two to three years. The field level of 15 T expected to be reached in this magnet is almost four times greater than the magnet strength in the Tevatron and two times greater than that in the Large Hadron Collider. Magnets at this field level require niobium-tin superconductor, an advanced material that has yet to be used in any existing accelerator. This is now possible thanks to the extensive studies and progress made on niobium-tin by Fermilab and other labs in collaboration with industry in the last 20 years.

Magnets based on the niobium-tin technology have been developed, studied and optimized along with the progress of the superconductor in the United States and Europe. Fermilab provided key contributions in the development and demonstration of this technology, including, for instance ,10- to 11-T dipoles for a Very Large Hadron Collider, interaction region quadrupoles for a VLHC and the LHC luminosity upgrades, and most recently an 11-T dipole for the LHC collimation system upgrade.

The importance of this work was emphasized in several meetings, both at the U.S. collaboration meeting in Napa and in other International venues. CERN’s Davide Tommasini, the leader of FCC magnet R&D, highlighted the importance of the Fermilab 15-T dipole to strengthen the 2018 FCC Design Report, which calls for a demonstration of very similar magnets. Andy Lankford, the TAC and HEPAP chair, also underlined this global endeavor in his closing of the meeting.

Unfortunately, this important work is performed in a difficult budget climate, which was not lost on the HEPAP Accelerator R&D subpanel, one of whose recommendations in 2015 was to “significantly increase funding for superconducting accelerator magnet R&D.” Nevertheless, in the past two or three years, funding was significantly reduced. However, with millions of dollars invested in time by the U.S. in this technology, which is now at the forefront of accelerator technology, we should preserve U.S. leadership in this field. With the help of our MDP collaborators and CERN partners, a Dipole Demonstrator will be built and tested as planned in 2018.

Emanuela Barzi is the principal investigator of Fermilab Magnet Superconductor R&D and an adjunct professor at Ohio State University. Alexander Zlobin is the head of the Fermilab High-Field Magnet Program. Both are APS fellows.