With the pressure tests now complete, we are coming to the equally important phase of cleaning the machine. With all the work performed over the past year, quite a lot of dust and dirt has accumulated in certain areas of the accelerator.
A simple and efficient solution, known as helium flushing, has been devised by the Cryogenics group (TE-CRG) to clean up these areas. "We circulate helium gas around the machine in both the cryogenic distribution lines and the magnets," explains Gérard Ferlin, who is responsible for the flushing operations. "This blows all the debris into a filter at the outlet."
The flow-rate needs to be high enough to ensure that everything is swept away, so the helium is injected at rates of between 15 and 40 metres per second, much higher than in normal operation. "There’s still a chance of leaving some debris behind even so," says Ferlin, "but if it’s not dislodged by the helium flush it's very unlikely to be dislodged by anything else. This 'floating debris' does remain a concern for us."
Another bugbear is metallic waste such as chippings or brazing residues, which can create short circuits. "These are our greatest enemies," says Ferlin. "They could cause the whole machine to shut down, with massive consequences." So to avoid any problems in the accelerator due to metallic waste, the Cryogenics Group hands over to the TE-MPE team, which is responsible for the electrical quality assurance (ELQA) testing. By measuring the electrical parameters of the machine, the team can identify non-conformities caused by any metallic residues.
On Monday 24 February, after two weeks of intensive flushing, the Cryogenics Group completed the cleaning of Sector 6-7. "We’re very pleased with the state of this sector," says Ferlin. "The filters were particularly clean and this shows how carefully the teams conducted the repair and consolidation operations." Next on the list is Sector 8-1. If it turns out to be as clean as the previous sector, the teams intend to reduce the flushing time. "That would save us time with respect to the schedule, which would be no bad thing," he says.
At the LHC, the delays in the SMACC project have been made up and all operations are once again proceeding according to schedule. The electrical feed boxes (DFBA) at Points 6 and 8 are still being reconnected. The consolidation of the DFBAs in the remaining sectors of the accelerator is also proceeding at a very good pace, and some operations are even a few weeks ahead of schedule.
The electrical quality assurance tests have been carried out in all sectors of the machine. No fewer than 10,000 electrical connections have been tested, which equates to an impressive 100,000 electrical measurements.
In the injectors, the access system is in the process of being re-commissioned. At the PS Booster, the teams are working on the instrumentation for the beam-line and the vacuum. Some of the work currently being performed, such as cable identification and a few civil engineering jobs, is in preparation for the second long shutdown (LS2).