A new generation of magnets for accelerators, MRIs

Giorgio Apollinari, head of the Technical Division, wrote this column.

Giorgio Apollinari

In March 2011, I wrote about the collaboration we began with CERN for the development of high-field niobium-tin (Nb3Sn) dipole magnets. Today, after less than 15 months, I am happy to report on the success the 11-Tesla project has achieved in this short period, and the potential of this technology beyond particle physics.

To my knowledge, the project set a record for turning an idea for a collared Nb3Sn superconducting magnet into a working, accelerator-quality magnet with an acceptable aperture and strong magnetic field in less than 20 months. Exceeding the 10-Tesla barrier with the relatively new niobium-tin technology instead of the more common but less powerful niobium-titanium technology clearly shows that, in my opinion, the Nb3Sn technology is ready for applications in accelerators and beyond.

The 11-Tesla project originated from a proposal made by CERN’s Lucio Rossi in September 2010. To increase the number of collisions produced by the Large Hadron Collider, he suggested replacing a few 8-Tesla dipole magnets in the LHC tunnel with shorter, stronger, 11-Tesla magnets in order to create enough space to install additional collimators. The only way to achieve this goal is to use the relatively new Nb3Sn technology.

Rossi’s proposal aligned well with the goals of Fermilab’s High-Field Magnet R&D program, which aims to develop collared magnets with fields in excess of 10 Tesla for use in future machines such as the Muon Collider. The two laboratories quickly established a collaborative effort.

The technical team started its work in late 2010. Fermilab and CERN manufactured coils and other parts for the first 2-meter-long, collared Nb3Sn dipole magnet, which was completed this spring. The testing of this model in our facilities started a few weeks ago. Although it is the first magnet that we’ve made for this specific program, it almost could be installed in the LHC as is. Further tests will determine the detailed magnetic field quality and transient field performances of this magnet.

In the last couple of weeks, we achieved an electrical current of up to 11.2 kiloamps, only 5 percent below the goal of 11.8 kA for the 14-TeV LHC. According to our latest measurements, the current creates magnetic fields of approximately 10.4 Tesla. The test, performed at a temperature of 1.9 Kelvin in the Fermilab Vertical Magnet Test Facility, continues as we aim to understand the ultimate field that this magnet can achieve.

The great news is that the Nb3Sn technology will have applications beyond particle physics as well. I expect that in a few decades, thanks to our efforts today, hospitals will rely on Nb3Sn-equipped MRI systems, which will provide more detailed images due to the higher magnetic fields achieved by these magnets, leading to improved medical diagnoses. The Illinois Accelerator Research Center, under construction across the street from the Technical Division, will act as the proper bridge to bring this exciting particle accelerator technology to society.