Big advance towards the LHC upgrade

The LHC is currently the world’s most powerful accelerator. With its technical achievements it has already set world records. However, big science looks very far ahead in time and is already preparing already for the LHC’s magnet upgrade, which should involve a 10-fold increase of the collision rates toward the end of the next decade. The new magnet technology involves the use of an advanced superconducting material that has just started to show its potential.


The first Long Quadrupole Shell (LQS01) model during assembly at Fermilab.

The first important step in the qualification of the new technology for use in the LHC was achieved at the beginning of December when the US LHC Accelerator Research Program (LARP) – a consortium of Brookhaven National Laboratory, Fermilab, Lawrence Berkeley National Laboratory and the SLAC National Accelerator Laboratory founded by US Department Of Energy (DOE) in 2003 – successfully tested the first long focussing magnet that makes use of niobium tin (Nb3Sn).

“Niobium tin can be superconducting at a magnetic field more than twice as strong as that tolerated by niobium titanium, the material that we presently use in the LHC magnets”, explains Lucio Rossi, head of the Magnets, Superconductors, and Cryostats group in CERN's TE Department. “This is just the first step towards a new generation of magnets for high energy colliders but I am confident that all the efforts put in by the DOE in supporting the R&D in this field – which started as early as 1998 with visionary long-term R&D on niobium tin superconducting cables – will soon pay off”.

The collaboration between CERN and LARP began in 2005 when it was agreed to start testing the potential of niobium tin. The goal was set of reaching, before the end of 2009, a gradient, or rate of increase in field strength, of 200 tesla per metre (200 T/m) in a four-metre-long superconducting quadrupole magnet with a 90-millimetre bore for housing the beam-pipe. This goal was met by LARP on 4 December. The superconducting coils of the model magnet performed well, as did the mechanical structure that supports the coils against large forces generated by high magnetic fields and electrical currents. The prototype’s ability to withstand quenches, i.e. sudden loss of superconductivity with resulting heating, was also excellent.

The design luminosity of the LHC is already a big challenge for both the machine and the experiments. Magnets located near the collision points and detectors’ inner parts have to withstand high radiation levels and extremely high temperatures. CERN is already pursuing a first upgrade of the LHC quadrupole magnets located near collision points (the so-called inner triplets). This first phase is based on niobium technology and aims at increasing the LHC luminosity of a factor 2-3 above the nominal 1034, probably the ultimate step for this technology.  The new magnet technology, based on niobium tin superconductor, could help to achieve a luminosity in the range 5 to 10 times the nominal one, which will mean even more multiple collisions for each bunch crossing and therefore a higher complexity in resolving the results of the interactions. “ATLAS and CMS will have to upgrade  their  detectors to cope with the challenge that this represents”, confirms Sergio Bertolucci, Director for Research and Computing. “On the other hand, the increase in integrated luminosity will allow experiments  to extend their reach in discovering new phenomena. Presently, we are discussing the best way to optimize the collected luminosity, while  reducing the effect of the associated background”.

Although the successful test of the magnet prototype was a major milestone, it is only one of several steps needed to fully qualify the new technology for use in the LHC. The next goal is further increasing the aperture of the quadrupole, which will result in a higher peak field. This will be done first in a short quadrupole model and then in a long magnet prototype to explore the technology limits.


by CERN Bulletin