CMS Bulletin

MUON DETECTORS: CSC

The earliest collision data in 2011 already show that the CSC detector performance is very similar to that seen in 2010. That is discussed in the DPG write-up elsewhere in this Bulletin. This report focuses on a few operational developments, the ME1/1 electronics replacement project, and the preparations at CERN for building the fourth station of CSC chambers ME4/2.

During the 2010 LHC run, the CSC detector ran smoothly for the most part and yielded muon triggers and data of excellent quality. Moreover, no major operational problems were found that needed to be fixed during the Extended Technical Stop. Several improvements to software and configuration were however made.
One such improvement is the automation of recovery from chamber high-voltage trips. The algorithm, defined by chamber experts, uses the so-called "Expert System" to analyse the trip signals sent from DCS and, based on the frequency and the timing of the signals, respond appropriately. This will make the central DCS shifters’ lives easier because they won't have to deal with the few channels (out of 9000) which occasionally trip in the CSC system. The algorithm has been implemented, fully tested at 904, and is being carefully evaluated in "listener-only" mode at Point 5 prior to activation.

The group also tried to minimise the impact of a potential downtime if one of the CSC computers were to die during running. Together with the CMS DAQ group, an exercise was performed on all CSC online computers to emulate this situation. On each computer, the operating system was completely wiped out, as if it were a new computer freshly installed in the rack. Then, the operating system was installed automatically from the network, including the CSC-specific libraries needed to run. This revealed a few problems on both the CMS DAQ side and on the CSC side, which would have taken hours to sort out if they had occurred during actual running. All such problems have been fixed.
Attention has recently focused on a CSC low voltage supply issue. Six of the 473 CSC chambers are not supplying data due to a 7.5 V “digital” power supply line that is read back as a value close to zero on the chambers themselves. There are two 7.5 V lines, one digital and one analogue, in the supply cables. We find the digital line is not working while the analogue line is working. Since they are in the same cable, it is hard to argue that there are cable disconnects. There were four chambers in such a state at the end of 2010 but, since the start of 2011, two more chambers have acquired this condition. The connectors/cables are inaccessible, so troubleshooting is going on using remote methods.

With respect to planning for the future, new ME1/1 cathode electronics is being developed to provide individual readout for every strip in ME1/1 and to ensure deadtimeless readout at higher luminosities. The original electronics for the readout of the ME1/1 chambers required a three-fold ganging of the cathode strips in the inner ME1/1a section of the chambers, which has been found to compromise the effectiveness of these chambers in triggering and pattern recognition.

Since December, the ME1/1 electronics work has progressed on multiple fronts. A prototype of the new digital front-end board for the CSCs, the DCFEB, was send for fabrication and assembly. The prototype of the Trigger Mother Board mezzanine was completed and has undergone extensive bench testing at Texas A&M. A new ASIC, the EMU_CC was submitted to the foundry in February. This ASIC will allow the clock, trigger and control signals to be transmitted optically to the new boards. Meanwhile, there was extensive work on other items needed for the project, including firmware, test beds, and long-range procurements. The plans and status of this upgrade were presented at the ATLAS-CMS Common Electronics Workshop for the LHC Upgrades (ACES2011) at CERN in March.

Meanwhile, the ME4/2 CSC upgrade project has moved into its setting-up and preparatory phase. The production of 71 chambers for the completion of the outer ME4 station ring located on the YE3 endcap disks will take place at CERN, in Prevessin building 904. The goal is to deliver fully tested CSC to P5 ready for installation in UXC during the long LHC shutdown of 2013-2014.

The 1000 m2 CSC factory area allocated to this task is being organised to meet all necessary requirements in terms of infrastructures (power, gas), factory equipment (storage, furniture, clean rooms) and chamber construction tooling (production machines, chambers tables and carts). A team of experts from CERN, PNPI, IHEP, US with the help of a few students and the CERN and CMS support services is actively involved at CERN in the preparations. In parallel, the procurement of all chamber mechanical parts and electronics components is underway in US.

The 904 factory will be equipped with two clean rooms which will be allocated to: 1) the wire winding of the anode panels and wire soldering and 2) the panel assembly and chamber sealing. The completion of the clean room construction is expected sometime by the end of April.

An important step of the production workflow will be the chamber leak and HV testing and the final assembly and testing of the on-chamber electronics. This represents the last step before the final chamber QC/QA inspection and packing. We are currently defining all hardware and software requirements for the optimisation of each individual sub-step.

Chamber production machines (tension, winding, automatic soldering, glue dispensers, tooling etc.) have been shipped from Fermilab late last year and are now being re-assembled and re-commissioned in 904. A complete set of chamber parts (including 21 FR4/Cu honeycomb panels) has also been delivered to CERN and will be used to construct three prototype chambers. These will allow to train the factory personnel and to assess the readiness of the construction facility for chamber mass production.

Assuming no show-stoppers, we should be able to start the prototype production early this summer. The subsequent start of the chamber mass production will depend very much on the lead times for delivery of chamber parts to 904. In this respect, chamber panels represent the item with the longest lead time. Indeed, after panel fabrication cathode strips have to be milled and all panels must be cleaned. This process will take place at Fermilab where the necessary tooling and adequate expertise is available. The expected chamber mass production rate is of 3-to-4 CSC/month.