• Some of the RE+4 chambers that have been recommisioned

  • The removal of a disk of the ECAL Preshower as a whole

  • A team from DESY working on the last YB0 sector

  • The ME+1/1 chambers installed and ready for commissioning

From the CMS experimental site at Cessy, France, located at Point 5 on the LHC ring


After a well-deserved Christmas break, work has resumed at Point 5 at an unabated pace. With an extremely busy 2013 behind us, all teams are now focusing their attention on the upcoming Tracker cold test, in which the cooling system will be operated at around –20 °C to validate the repairs made to the Tracker vapour barrier. Once this validation exercise is completed the entire LS1 schedule will be provided with a new baseline: each sub-system will be given a stable set of milestones with which its work can be planned. For this purpose, a Technical Coordination workshop is foreseen to take place on the last week of February. Since 13 January, the CMS detector has been in a configuration allowing for the preparation of the Tracker cold test. The vacuum tank is fully exposed with an access bridge positioned on top of it to allow easy access to the areas where CO2 cooling pipes are to be installed. These pipes are required for the cooling of the new Pixel Tracker, which is planned to be installed during the next year-end technical stop (YETS) in 2016–2017. To manage the installation during the YETS, the pipes must be installed now, since the time required to set up access to the vacuum tank is considerable. The Tracker crew members are also repairing the vapour barrier of the existing cooling distribution system and completing the dry-gas sealing inside the vacuum tank in order to lower the operating temperature of the Tracker itself. The target date for the kick-off of the cold test is 10 February. In the meantime, and since the last edition of this column, there are plenty of achievements in which to take pride. The Resistive Plate Chambers (RPC) activities planned for LS1 are making good progress. By mid-December all the RE+4 chambers had been installed on the fourth endcap station of the muon system, which is currently being assembled. Following this, the RE crew have been installing the associated gas and cooling services with testing almost complete. It is hoped, at the time of writing, that all 72 RE4 chambers should be commissioned with their final cabling, gas and cooling infrastructure by the end of January. The RPC team will access each part of the detector for maintenance; they have currently completed their work on the barrel region on the –z side of the CMS underground experimental cavern (underneath the main shaft) and the endcap region on the +z side. Repairs to the high-voltage connectors aim to restore chambers that did not carry power during the first run and optimise their performance. The number of active electronic channels has increased from 98.3% to 99.6%. Locating and repairing gas leaks in the barrel has also reduced the gas leak rate by 50%. Finally, on-detector electronic cards are also being replaced to fix low-voltage distribution and slow-control problems. The kick-off of the ME+1/1 Cathode Strip Chambers commissioning took place at the beginning of January and steady progress has been made ever since. Meanwhile, refurbishment and testing of the 36 ME‒1/1 chambers is continuing in the SX5 surface building with the aim of installing them in the early spring. Both ECAL Preshower disks have been successfully removed, to address a connector problem. Because the beam-pipe was already in place, the Preshower detectors were originally brought underground as half-disks, or "Dees". Fortunately, with no beam-pipe present during LS1, the team were able to crane them away more simply as complete disks. However, this operation was delicate, since neither this nor the reverse procedure had been carried out before. Both disks are now being refurbished on the surface in SX5. The target date for re-installation of the first (+z) disk is early April. The sourcing exercise of the ‒z HCAL endcap was completed on 7 December: a radioactive source was introduced into the detector in order to learn about the radiation damage to the front layers of the HCAL barrel region (HB). This was an interesting logistics challenge that required special radiation protection measures to be fully embedded in the UXC55 work plan so as to not delay other activities. The outcome of the sourcing tests was most useful and will remain a baseline for future sourcing activities. Thanks to the success of the tests, the team is now considering HB sourcing inside the vacuum tank. The installation of the two Gas Injection Systems has been completed, together with their injection and pumping lines. The leak-tightness of the beam pipes and the pumping system has been tested and their bake-out (i.e. the process used to clean the inner surfaces of the pipes by heating the system to remove any volatile compounds) is ongoing on both the positive and negative sides. With all these teams working in parallel, even things we usually take for granted have to be planned carefully and in detail. A prime example is the space needed for the crews to efficiently and safely access the detector. Taking advantage of the present configuration of the experiment, the crews of DT, RPC and HO have been able to rearrange some of their activities (DT chamber extraction + work on RBXs) and are currently working from the gap between the central YB0 barrel and YB+1. The CSC and RE crews are also pushing ahead with the installation of the services and cables for the ME–4/2 and RE–4 chambers. They are sharing the space between YE–3 and the cavern wall. The aim is to complete all detector infrastructures before the construction of the YE–4 disks will begin in early March followed by the ME–4/2 and then RE–4 chambers installation. Finally, and to confirm that life at Point 5 is never dull, as the colder and wetter winter weather settled in, the ground water level around the site has risen. There have been a few issues of water ingress in the PX56 main shaft. CMS Technical Coordination has been working together with CERN’s Civil Engineering group to diagnose and rectify the problem quickly and to also prevent such occurrences in the future. As said earlier: there are indeed plenty of achievements in which to take pride! — Submitted by Martin Gastal and Tom Marriott-Dodington

Tags / keywords: CMSTimes