CMS Bulletin

TECHNICAL COORDINATION

LS1 overview

In general the LS1 project is progressing well and the workflow is holding to the original December 2012 schedule within two–three weeks, acceptable at this stage, with about 400 work packages already completed. In particular, the critical logistic configuration planned for summer 2013, giving simultaneous access to both ends of the vacuum tank interior and the exterior, plus the YE1 nose zones, was achieved significantly before the deadline at the end of June. The safety awareness of all those working on the CMS detector is currently very satisfactory and the general atmosphere at Point 5 is good, despite many concurrent activities and inevitable last minute adjustments to the day-to-day planning.

LS1 services infrastructure work

The “once-in-ten years” maintenance of the water-cooling infrastructure has been completed successfully by EN department teams; underground circuits were available again from 12 June. In the shadow of this activity, consolidation and maintenance of sub-detector water-cooling plants has been carried out, while fluorocarbon plants are being revised for lower-temperature operation of the tracking detectors. A further pre-requisite for this is the complete revision of the dry-gas supply and distribution system, which helps maintain low-humidity conditions in the Tracker and other subsystems. The external pipework installation and testing for this is now nearing completion. Finally, a vast programme of pipe-work and cabling modifications and additions in preparation for the installation of the fourth endcap muon stations has just passed the halfway mark.

Meanwhile, the re-cabling of the detector power distribution to extend UPS coverage to all the S1- and S2-based systems has also been completed.  Restoration of power throughout the USC awaits completion of the preventive replacement programme for turbine modules, expected to be complete by mid-July.

LS1 logistics and on-detector work

Since mid-June the solenoid vacuum tank outer surface has become accessible for the first time since 2008. Both endcaps are fully open and the YB-wheels of both ends are parked between the end of the vactank and the YE1s. The thermal shields of the vactank and YB0 have been removed and all ECAL cables covering sectors where DT chambers require maintenance have been disconnected from their patch panels and folded back. By the beginning of the CMS Week, access scaffolding will surround YB0, allowing installation of the on-detector pipe-work supplying dry gas (nitrogen or air, depending on operation conditions) to the tracker volume, additional sniffer pipes monitoring the dew point inside the vactank, cabling for additional temperature and humidity sensors, new HB low-voltage cables, with larger cross-section, for use with the Phase 1 upgraded electronics (foreseen for LS2) and an insulated cooling line at each end for the PLT. In addition, the path of the concentric vacuum-insulated CO₂ cooling lines for the Phase 1 Pixel detector upgrade can now be defined in detail. If available, the supports will be installed now, to minimise work during the actual pipe installation and testing at low temperature, planned for December 2013, which will take place without scaffolding. In parallel with these service installations, all HO photo-detectors on YB0 will be exchanged and maintenance on all accessible DT-mini-crates will be performed. Alongside this very packed programme on YB0 and the outside of the vactank, the humidity sealing of the Tracker’s service channels inside the vactank is about to start. This activity, the top priority task of LS1, will continue for up to one year.

On the YE1 nose zones, the extraction of ME1/1 chambers is progressing well, with two chambers per day being extracted, according to schedule. All chambers at the +Z end are expected to have been removed and transferred to the refitting laboratory in SX5, before the July CMS Week.

Phase 1 upgrade detector infrastructure

On 14 June, the assembly tooling for the YE4 endcap shielding walls successfully passed its safety inspection, after which three sectors were assembled vertically onto the support beam in the ISR, testing the underground installation procedure. From the middle of August, the barrel wheels at the +Z end will be temporarily moved back over the vacuum tank and the endcap will be closed by 6m, making space for the assembly of the first YE4 disk, after which a mirror-symmetrical logistic configuration will be set up to allow the second disk to be assembled.

All elements of the new central beam pipe (designed for the Phase 1 Pixel Tracker) are now complete at the manufacturer and the replacement support collars, for those lost in transit from CERN in May, have now also been delivered.

Authorisation to proceed with e-beam welding of the sections awaits a full understanding of the weld-test samples received recently.

Detector systems oversight

On 14 June, a follow-up took place of the ME1/1 Manufacturing Progress Review held in March 2013. The reviewers were pleased to note that the CSC laboratory in SX5 is fully operational with currently two refurbished spare chambers under test. In view of the excellent progress in nearly all areas that caused concern in the March MPR, the review committee was confident that the revision programme of the ME1/1 system is likely to conclude successfully. It was therefore concluded that the refurbishment of the removed ME1/1 chambers should start at the discretion of the endcap muon project manager, once details of the necessary testing infrastructure are complete.

The operation of the PLT demonstrator during the 2012 LHC physics run was extremely valuable in understanding the device and the conditions necessary for it to deliver an independent luminosity measurement. However a drawback became apparent with the diamond sensors currently used. Under irradiation they develop a rate-dependent signal shape and amplitude, most probably due to polarisation effects, leading to reduced efficiency. This would make an independent luminosity measurement impossible. As a consequence, on 28 June, a combined Engineering Change and Design Review was held, considering the proposal to change the sensor material from diamond to silicon. As the readout is the same for both sensors, the exchange of the sensor material is almost independent from the rest of the design. Silicon sensors and readout chips are available in the necessary quantities. The main difficulty arises from the necessity to cool the silicon sensors. The Integration Office is working with high priority to establish the routing of a cooling line from the Tracker SS2 distribution to the PLT carriage and the carriage itself, which also houses the BCM1F, is being re-designed to include cooling circuits. Though giving an overall positive recommendation, the committee has raised some questions and will require close monitoring of the progress through a series of subsequent reviews.

Other technical reviews since the last CMS Week include the ESR for the DAQ “Ferol” board, the PRR for the endcap radio-protection shielding and a follow-up to the pixel CO₂ cooling PRR, which endorsed the plan to install the new vacuum-insulated concentric distribution pipes mentioned above.

The review process for Phase 1 TDR detectors proper has started with a PRR authorising the procurement of all the barrel silicon sensors.

The recommendations arising from these recent reviews will be published shortly.

Phase 2 upgrade: logistics and planning

Following the TC workshop held on 23 May and the CMS-DESY workshop in June, Technical Coordination is focussing on three main issues: replacement of the HE scintillator (which may be forced by ageing), replacement of the whole endcap nose with a new calorimeter system and first muon station (with options to extend coverage of both to higher η) and comparative planning for completing the key elements of Phase 2 in a single shutdown (preferred) or two shutdowns.