start-up for the LHC
A new schedule for the commissioning of the LHC was presented to the Council at its Session in June. The start-up of the accelerator is scheduled for May 2008, to allow all technical problems to be resolved.
Positionning work in the LHC tunnel. Four metal cartridges, like this one held by Juan Carlos Perez, who is responsible for the operations in Building 181, will be inserted in the Q1 and Q2 magnets of the inner triplets. In the background, a Q1 magnet which has already been modified.
Delegates to the 142nd Session of the CERN Council, which took place on 21-22 June, were informed of the new schedule for the commissioning of the LHC. The machine will be closed in April 2008, followed by beam commissioning in May 2008. First collisions at 14 TeV are expected to take place in July. In the end, the pilot run at 900 GeV, which was initially planned for the end of this year, has been cancelled and will be a normal stage in commissioning in 2008.
A number of problems have contributed to the delay in commissioning the LHC. However, they are well on their way to being resolved. An innovative solution is currently being implemented to address the problem affecting the "inner triplets" (see box on the following page). These quadrupole magnets failed during a pressure test at the end of March (further information can be found on the CERN intranet page). As a result, the defective inner triplets have had to be isolated to allow commissioning of the first two sectors to go ahead.
In collaboration with Fermilab, a working group led by Ranko Ostojic (AT/MEL) was rapidly set up at CERN. The damaged magnets from Point 5L (L stands for Left) have been brought back up to the surface and examined. The longitudinal forces generated by the pressure test had broken the support which keeps the Q1 cold mass in position inside the cryostat. There was also slight damage to the magnet’s electrical feed box.
The working group, and in particular Cédric Garion, a young CERN engineer, have come up with the idea of reinforcing the structure using metal cartridges. These cartridges consist of an invar rod inserted into an aluminium tube. When a longitudinal force acts on the cold mass, the cartridges keep it in position inside the cryostat. The cartridges’ thermal and mechanical properties allow the system to function at a wide range of temperatures from room temperature to 1.9K (-271°C), the operating temperature of the superconducting magnets.
One of the major difficulties posed by the repair was that it had to be performed in the tunnel to avoid having to bring the magnets up to the surface. The cartridge design, which required more than a month and a half of development work, meets this requirement. An assembly of four metal cartridges will be fitted to each of the inner triplets’ Q1 and Q3 magnets. The cartridges will be inserted through the interconnections of each cryostat. With the exception of the inner triplet from Point 5L, which was damaged, no other magnet will be brought back up to the surface.