Start-up.

Today, some members of the Alice.

The schedule in the run up to the first beam circulating in the LHC is falling into place. Each of the eight sectors is in the final stages of cooling, electrical testing, equipment testing and powering. The current plan is to have the machines ready for the first circulation of a beam in a few weeks. Then the progressive commissioning of the machine for operation at 5 TeV will begin.

Once all the sectors have reached 1.9 K, around 1400 tests of varying complexity need to be done. These include: electrical quality assurance to double check all the wiring is in place after the magnets have undergone the contraction that is associated with cooling; individual testing of protection systems; power testing, the process of turning on individually and then in groups each of the magnetic circuits. These tests are being done by the Operations Group together with teams of equipment experts from the AB, AT and TS Departments. The programme is being coordinated by a dedicated Hardware Commissioning Team. After all these tests have been completed the sectors are handed over to the Operations Group to start doing ‘dry runs’, where the machine is run as it would be with the beam. There are also safety tests that have to be done before the beam can circulate, to prevent people from being in the tunnel at the same time as the beam. Ideally these tests can only be completed once the experiments are closed.

The decision to run the LHC at 5 TeV rather than 7 TeV this year is related to the need to ‘re-train’ the magnets in the tunnel. Superconducting magnets are complex devices that need to be ‘trained’ in order to reach the nominal field. Although all the magnets have been individually trained on the surface, small changes in their structure due to their transport and installation in the tunnel have caused some ‘de-training’. Therefore, although time-consuming, new quench tests in the tunnel are necessary before the field required by the 7 TeV operation can be reached.

Paul Collier, head of the machine Operations Group, explains the re-training process as it happened in sector 5-6: "It takes several hours for the cryogenic system to recover from a magnet quench at 5, 6 or 7 TeV. This means that the only real way to train the magnets is to increase the current level of a whole dipole chain [i.e. 154 magnets] until one dipole quenches, which then switches you off for several hours, and then repeat. In order to avoid this having an impact on this year’s schedule, the idea was to run it at a level below [i.e. 5 TeV] at which we are confident that there will not be any training quenches."

There could be a possibility of having an injection test to prepare the machine before the nominal beam makes a full circuit. This could happen either from TI 8 to point 6 or from TI 2 along to point 3. "If we can do it we will, not just to say we’ve done it, but because getting the beam to go around the LHC involves tuning up a lot of equipment, which requires quite a lot of work. Really, this is the first stage of commissioning the circulating beam"

adolfocanals@educ.ar