The latest from the LHC
Work on closing up sectors in the LHC tunnel.
The foreseen shutdown work on the LHC is proceeding well, including the powering tests with the new quench protection system. However, during the past week vacuum leaks have been found in two "cold" sectors of the LHC. The leaks were found in Sectors 8-1 and 2-3 while they were being prepared for the electrical tests on the copper stabilizers at around 80 K. In both cases the leak is at one end of the sector, where the electrical feedbox, DFBA, joins Q7, the final magnet in the sector.
Unfortunately, the repair necessitates a partial warm-up of both sectors. This involves the end sub-sector being warmed to room temperature, while the adjacent sub-sector "floats" in temperature and the remainder of the sector is kept at 80 K. As the leak is from the helium circuit to the insulating vacuum, the repair work will have no impact on the vacuum in the beam pipe. However the intervention will have an impact on the schedule for the restart. It is now foreseen that the LHC will be closed and ready for beam injection by mid-November.
All planned repairs have been completed in Sector 4-5 and the final ‘W bellow’ - the large accordion-shaped sleeve that covers the interconnections between two magnets - was closed on Wednesday 15 July. Sector 6-7 was closed two days earlier.
Over the past three weeks, during which Sector 4-5 was at room temperature, two sets of 300 K measurements on the copper busbars were taken. The second set was taken at the end of the three-week period to reduce inaccuracy caused by temperature fluctuations. With these accurate room-temperature measurements, the relationship between the 80 and 300 K tests can be determined more accurately. The three busbar segments with the highest resistance were opened and direct measurements taken across each electrical joint (or splice) to confirm the 300 K measurements. The individual splices with high resistance in these three sections were repaired, 15 in total.
The last of the remaining three cold sectors will be tested at 80 K in the first week of August.
During the last three weeks, in the shadow of the other work in Sector 4-5, as many new pressure release nozzles as possible have been installed in the Sector, focusing on the most critical areas. In total 60 have been fitted, roughly a third of the total planned in the sector. Four other sectors are fully equipped with the new larger pressure release ports.
In the remaining cold sectors, where the new ports cannot be installed, the bolts that fix the existing (standard) pressure release ports to the machine are being replaced with spring release clips. In the event of a sudden increase in pressure caused by helium, the whole port will be released, allowing the helium to escape much more quickly.
Sector 3-4 has been successfully pressure tested. The 14 vacuum subsections have also been tested, revealing 3 with minor leaks, which are being repaired.
Following the closure of Sector 3-4 the teams involved held a small celebration to mark the end of the repair work in the sector on 8 July. Watch the video below: