Triplets pass their pressure test
All the LHC inner triplets have now been repaired and are in position. The first ones have passed their pressure tests with flying colours.
The repaired inner triplet at LHC Point 1, right side (1R). Ranko Ostojic (on the right), who headed the team responsible for repairing the triplets, shows the magnet to Robert Zimmer, President of the University of Chicago and of Fermi Research Alliance, who visited CERN on 20th August.
Three cheers for the triplets! All the LHC inner triplets have now been repaired and are in position in the tunnel. Thanks to the mobilisation of a multidisciplinary team from CERN and Fermilab, assisted by the KEK Laboratory and the Lawrence Berkeley National Laboratory (LBNL), a solution has been found, tested, validated and applied.
At the end of March this year, one of the inner triplets at Point 5 failed to withstand a pressure test. A fault was identified in the supports of two out of the three quadruple magnets that make up the triplets, magnets Q1 and Q3 located at each end of the assembly. Following analysis of the problem, the team led by Ranko Ostojic (AT/MEL) had the idea of reinforcing the support structure of the two magnets concerned with four metal cartridges (see Bulletin 28-29/2007).
The solution was fully validated by the conclusive results of the pressure tests. To ensure that the supports performed optimally, the tests were conducted at a pressure of 2500 kPa, i.e. 25% higher than the nominal, maximum operating pressure of 2000 kPa.
The nine triplets, including one replacement, have been fitted with their cartridges over the summer. Three of them have now been subjected to pressure tests, passing them with flying colours. The cryogenic electrical distribution feedboxes, known as DFBXs, which form part of the triplet assembly, have also been repaired. Only the one triplet that was damaged during the spring test plus one DFBX have been removed from the tunnel. The others have been repaired in situ, which was in fact one of the prerequisites for a solution. Jim Kerby of Fermilab has reason to be well pleased: "This problem is now behind us. All the magnets are in place in the tunnel and the DFBX that was removed is now ready to go back down into the tunnel again."
The pressure tests on the other triplets will continue during the autumn but their success is not in doubt. The team that led this recovery in record time deserves a hearty round of applause!
A new generation of triplets
As part of the developments for the LHC upgrade, the test of the first "Long Racetrack Shell" magnet was successfully completed recently at Brookhaven National Laboratory (BNL). The 3.6-metre Long Racetrack Shell (LRS) magnet, so called because of its shape, is a prototype to prepare the next generation of "inner triplet" quadrupole magnets, which will be put into service for running the LHC at higher luminosity.
Higher luminosity will mean more radiation, and thus a hotter environment, for the inner triplets. The upgraded magnets will also need to run at a higher magnetic field. So the team from Fermilab, Lawrence Berkeley National Laboratory and BNL turned to a different material, Niobium-Tin (Nb3Sn), for the magnet coils. A European project, CARE/NED, is also investigating Nb3Sn conductors for use in LHC magnet upgrades (see Bulletin No. 43-44/2006). The support structure of the Long Racetrack magnet (Photo Courtesy of Paolo Ferracin, LBNL).
The LRS magnet is the first Nb3Sn magnet significantly longer than one metre to be successfully built and tested. BNL fabricated the coils for the LRS, LBNL designed and fabricated the support structure and Fermilab contributed through project management, conductor characterization, insulation development and the insulation of a practice coil. The first LRS magnet was tested the week of 23 July at BNL. The magnet carried 91% of the current scientists expected and reached a coil peak field of 11 Tesla. "The test was very successful," said Fermilab’s Giorgio Ambrosio, who coordinated the activities at the three labs. "The next step is to build the first Long Quadrupole magnet from Nb3Sn."