The Year-End Technical Stop (YETS) has been especially busy for CMS. In December 2017, part of the new pixel tracker installed in early 2017 was brought to a clean room on the surface at Point 5 to begin consolidation works in preparation for the 2018 data-collection run.
Members of CMS worked there every day of the closure, performing diagnostic tests to help develop maintenance and refit procedures for the pixel system, the rest of which was brought to the clean room early in the new year. During the pixel repair campaign, all pre-existing problems (~3% of channels) have been fixed, and 100% of DCDC converters have been exchanged, since about 5% failed in the last three months of the 2017 operation period. All components have now been re-inserted inside CMS. The system has been fully calibrated and recommissioned at final cold temperatures.
Another key ongoing task for the collaboration is the Phase-1 Upgrade of the hadron calorimeter (HCAL). The “forward” part of this calorimeter (around the beam pipe as it enters/leaves CMS) was upgraded a year ago, while the upgrade of the so-called “endcap” section is now almost complete. The central “barrel” components will be re-equipped during the long shutdown, ready for LHC Run 3 and, eventually, HL-LHC.
In preparation for the long shutdown, CERN’s Handling Engineering team and CMS have installed a second 20-tonne crane in the underground experimental cavern housing the detector. The installation was achieved in record time and will give CMS greater flexibility for moving sub-detector elements in the cavern during LS2 and beyond.
The last few weeks of the YETS continue to occupy the full attention of CMS Technical Coordination as the detector is readied for the next round of collisions.