On 13 July, an inner triplet assembly of quadrupole magnets successfully completed a pressure test in the LHC tunnel, after installation of metal cartridges to reinforce internal support structures that broke in an assembly during an earlier pressure test in March. The triplet, which included three quadrupole magnets and the associated cryogenic and power distribution box (DFBX), met all test specifications at the requisite pressure of 25 atm for one hour.
The triplets will focus particle beams prior to particle collisions at the four interaction regions in the LHC. The pressure test is designed to verify the accelerator components in conditions that will occur during LHC operations. To withstand the asymmetrical forces generated, the Q1 and Q3 magnets at either end of the triplet assembly had each been fitted with a set of four metal cartridges to limit movement of the magnets inside their cryostats. The cartridges have a compound design consisting of an aluminium-alloy tube and an Invar rod to allow them to function over a broad range of temperatures.
To address design flaws that emerged during the March pressure test, a team from CERN, Fermilab, KEK and the Lawrence Berkeley National Laboratory also made changes to the DFBXs and the attachment of the triplet to the tunnel floor. These changes passed the test on 13 July.
Fermilab, in collaboration with CERN and KEK, supplied eight sets of triplets – one for either side of each of the interaction regions, plus one spare set. About half of the quadrupole magnets were repaired by the end of July, with the remaining repairs estimated to take six weeks to complete. This will be followed by the installation of assemblies and interconnections between quadrupole magnets, DFBXs and the rest of the accelerator. The inner triplets will then become part of the different sectors of the LHC and will be tested as part of the pressure tests of all sectors.
In the meantime, electrical tests have continued on the first sector to be commissioned (sector 7-8), which was initially cooled down in April. On 25 May, the dipole circuits were successfully powered up to several thousand amps, followed by the quadrupole circuits on 20 June. This was still below the nominal values. Depending on the type of superconducting magnet, the nominal current of the electrical circuits varies between 60 A and 12 kA. During the tests, however, some circuits were powered up to the nominal current and quenches triggered deliberately to test the protection system as well as the system for extracting the stored energy in the magnets.
These power tests were the culmination of several weeks of electrical tests on sector 7-8. More than 100 electrical circuits for the superconducting magnets were checked one by one. An overall test, where all of the circuits were powered up overnight, also took place to ensure that they perform correctly over a prolonged period. Finally, a power cut was simulated at point 8 for the teams to verify that all of the systems were being supplied with power from the scheduled source – whether the normal or back-up power supply. Sector 7-8 will now be warmed up so that the triplet magnets to the left of point 8 can be connected up and some consolidation work can take place.
