The first superconducting magnets for the High Luminosity Large Hadron Collider Accelerator Upgrade Project (HL-LHC AUP) have arrived at CERN in Switzerland. The LHC is the world’s highest energy particle collider and discovered the Higgs boson—the key to understanding the origin of particle mass. As noted in the recently released Particle Physics Project Prioritization Panel (P5) report, the HL-LHC AUP project is “proceeding successfully with critical US contributions. This project addresses key questions about the Higgs boson while searching for new particles and phenomena.”

These new superconducting magnets are based on niobium-tin (Nb3Sn) technology, which can produce much stronger magnetic fields to create more focused particle beams that will be used to achieve much higher luminosity. They could extend the capabilities of the LHC, promising discoveries in high energy and particle physics.

“This is a major step forward in the LHC upgrade, and the team at Berkeley has done an outstanding job in delivering these magnets to CERN,” said ATAP Division Director Cameron Geddes. “They promise to push the frontiers of science further and could begin to unlock the secrets of the Higgs boson as a key next step in particle physics.”

The magnets are the first deliverable to CERN as part of the ongoing contribution of the U.S. Accelerator Upgrade Project (US-AUP) to HL-LHC AUP and is a “culmination of many years of work resulting from close collaboration between Berkeley Lab and three other U.S. national laboratories,” says Soren Prestemon, a senior scientist and deputy division director of technology for the Accelerator Technology & Applied Physics (ATAP) Division in Berkeley Lab, who is also the director of the Berkeley Center for Magnet Technology.

The cryo-assembly, which arrived at CERN in late November, houses two 4.5-meter-long quadrupole magnets made from high-performance Nb3Sn superconducting cables installed in a stainless-steel pressure vessel (the whole assembly being called the Cold Mass) that provides alignment for the magnets and a leak-tight helium enclosure. Surrounding this vessel are cryostat shields, piping, and a vacuum chamber.

Four institutions collaborated to design, produce, and test these magnets for US-AUP: Berkeley Lab, Brookhaven National Laboratory (BNL), the National High Magnetic Field Laboratory at Florida State University (FSU), and Fermi National Accelerator Laboratory (Fermilab).

Researchers from ATAP’s Superconducting Magnet Program (SMP) fabricated the superconducting cables and assembled the quadruple magnets. Fermilab and FSU procured and tested the Nb3Sn superconducting strands (used to make the superconducting cables); BNL and Fermilab made the superconducting cables into coils; BNL tested the quadruple magnets; and Fermilab designed and fabricated the Cold Masses and cold-tested the quadrupole magnets.

According to Paolo Ferracin, a senior scientist and deputy program head of SMP, the function of these magnets is to “focus the particle beam just before the collision in the interaction point in the LHC to increase the rate of collisions in the accelerator.”

“This is the first time that Nb3Sn superconducting magnets will be used in an operating accelerator, and the increased collision rates could give researchers a much better chance of seeing rare (or unexpected) processes and particles, like the Higgs boson.”

The magnets will operate at about 11 tesla. Once upgraded with the new magnets, the LHC will generate up to 10 times more collisions in the first 12 years after the upgrade compared with the first ten years of the LHC’s lifetime. According to CERN, the upgrade will produce at least 15 million Higgs bosons per year, compared to around three million from the LHC in 2017.

Because the magnets are assembled at room temperature, they must be cooled down and tested at cryogenic temperatures to ensure their superconductivity. Following cold-testing at Fermilab, which confirmed they met acceptable performance requirements, the magnets were sent from Fermilab to the East Coast for shipment to CERN.

Prestemon says that Inner Triplet (IT) String testing of the cryo-assembly will be conducted at CERN.

“A critical step in the HL-LHC AUP, the IT String test will validate the collective behavior of the different systems.” The IT String test, he adds, includes testing magnet positioning, alignment, interconnection procedures, mechanical and thermal behavior, and operation under static and dynamic conditions.

The SMP team is now in full production mode, completing the remaining Nb3Sn superconducting quadrupole magnets for installation in the Cold Masses, testing, and shipment to CERN.


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