CERN70: Superconductors accelerate progress

In 2000, I [was asked] if I would consider leading CERN's team in charge of superconducting magnets. It took me approximately one microsecond to say yes! Then started this incredible adventure of building the most complex accelerator in the world, using the most complex technology.
Lucio Rossi

Lucio Rossi began his career in plasma physics and moved into the field of applied superconductivity for accelerators in the early 1990s, heading the INFN-LASA team that had just begun to work on the first prototype superconducting dipole magnet for the LHC. In 2001, he became the leader of CERN's Superconducting Magnets and Cryostats group, which was responsible for developing and launching the industrial production of the superconducting magnets needed for the LHC. From 2010 to 2020, he was the leader of the High-Luminosity LHC project.

"The INFN-LASA team delivered the first LHC prototype magnet to CERN in 1994. This type of magnet has been very successful and that first dipole was used until recently by the CAST experiment - you could still read the words "LHC DIPOLE PROTOTYPE CERN-INFN 1" on it.

A few years later, in 2000, I received a phone call from Lyn Evans, then leader of the LHC project, who asked me if I would consider leading CERN's team in charge of superconducting magnets. It took me approximately one microsecond to say yes! Then started this incredible adventure of building the most complex accelerator in the world, using the most complex technology. We had to produce 300 000 km of superconducting wire for the LHC superconducting dipole and quadrupole magnets and for the several thousand corrector magnets, and to do so we had to collaborate with industry. That was not easy. Moving from our complex superconducting dipole magnet prototypes to industrialisation was a challenge, in particular when it came to getting the level of quality that we wanted from the companies. We had to make compromises, because sometimes best is the enemy of good. It was difficult, but we did it.

Producing the magnets was a real challenge; assembling them and making them work together was yet another one. The difficulty with the LHC is that everything is in series, so if you have a single weak link, the chain breaks. And that's what happened on 19 September 2008. One single electrical connection between two adjacent magnets - out of 10 000 such connections - failed, leading to extensive collateral damage and a one-year delay. I have to assume that the mistake was made by us, the engineers, the designers, because we had thought of a system that was not robust against faulty workmanship.

We learnt from this incident collectively. I think this is the strength of CERN: at that moment, I could feel that CERN was united. Afterwards, the LHC was resurrected stronger than before, and we got the Higgs boson.

When the LHC restarted, in November 2009, it was really a triumphal march. I was very moved to see the LHC restarting, to see the machine working well. We had done a good job. That was a glorious day.

In 2010, we then started to think about the future of CERN, and I proposed the High-Luminosity LHC project. This was an important project for me, as the HL-LHC sort of closed the loop for me personally, so I took on the role of HL-LHC Project Coordinator in 2010. From then on, we flew... but not without some difficulties, as one can expect in such a project, the biggest one probably being COVID-19. We also had some difficulties with the magnets: for the HL-LHC, we decided to build new types of magnets, based on the new niobium-tin superconducting technology, while the LHC's magnets are based on the niobium-titanium technology.

We thought that we would set up the technology on a short magnet, a 1.5-metre-long magnet, and then just extend it to a 7-metre-long magnet. It was like that for the LHC. But we learnt the hard way that it was not so easy with the niobium-tin technology, as the coils are much more fragile; that's why we faced these challenges, in particular with the HL-LHC 11 T magnets. We also learnt from failures, and we now have successful long magnets for the inner triplet quadrupoles, a key element of the HL-LHC, but it took a lot of time. That was a bumpy ride but it was necessary. The HL-LHC will be a real test of the niobium-tin technology, to help make the jump to future colliders.

CERN is here to make things that are truly difficult, to dream what is not yet possible. I'm convinced of this, otherwise it wouldn't be CERN."

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