CMS Bulletin

TECHNICAL COORDINATION

In this report we will review the main achievements of the Technical Stop and the progress of several centrally-managed projects to support CMS operation and maintenance and prepare the way for upgrades.

Overview of the extended Technical Stop 

The principal objectives of the extended Technical Stop affecting the detector itself were the installation of the TOTEM T1 telescopes on both ends, the readjustment of the alignment link-disk in YE-2, the replacement of the light-guide sleeves for all PMs of both HFs, and some repairs on TOTEM T2 and CASTOR. The most significant tasks were, however, concentrated on the supporting infrastructure. A detailed line-by-line leak search was performed in the C6F14 cooling system of the Tracker, followed by the installation of variable-frequency drives on the pump motors of the SS1 and SS2 tracker cooling plants to reduce pressure transients during start-up. In the electrical system, larger harmonic filters were installed in S4 to reduce CMS sensitivity to a variety of power transients. A public address system was installed and commissioned in UXC and USC, improving and simplifying significantly the communication from the surface to the underground, especially in the presence of magnetic field. On the surface the cooling power for the filter farm was enlarged from 600 kW to 1 MW to allow for a large increase in processor capacity over the coming years, so that the HLT bandwidth can be maintained or even enhanced against a background of increasing luminosity and pile-up. 

Just before the end of beam operation in 2010, the filters in the cold-box of the magnet cryo-system were regenerated for the first time at 3.8 T. In 2010, the majority of magnet on-off cycles were made necessary by the need to conduct this regeneration. Following the successful test at 3.8 T, the culmination of a progressive programme of work by the magnet team in the last quarter of 2010, it is expected that such cycles will now be avoided.

In the shadow of the activities highlighted above, the full annual maintenance of all electrical supply and water-cooling installations was completed.

Detail of critical path activity

The Technical Stop started with the dump of the last HI beam in the evening of 6^th December, 2010. By 10^th December, the beam pipe was at atmospheric pressure and filled with neon, allowing the lowering of HF to start. The HF at the –z end was lowered onto two risers on 15 ^th December. Two days later the HF+ was lowered to the floor, allowing the installation of cables and pipes for T1 to start. This infrastructure was already in place on the –z end and the remaining time before the end-of-year closure of the laboratory was used to install T1(–z) on top of the HF– for commissioning. This represented one of the key milestones of the Technical Stop. The holiday period was used to complete the installation of all infrastructure and services for T1(+z) and to test and commission T1(-z). On 6^th January, shortly after the end of the Christmas holidays, the alignment link disk was re-adjusted. This is a delicate operation, as it requires access to YE2 through YE3 with the beam pipe in place. The link disk has a sophisticated kinematic suspension. Unfortunately, one of its supports, which is inaccessible with the endcap closed, showed unexpected large friction, making the adjustment difficult. At the second attempt, on 7^th January, the adjustment was finally successful. Four out of six –z laser lines are now fully working, sufficient, considering built-in redundancy, to fully profit from the alignment system.

After several insertion tests with each half of the telescope, T1 was finally inserted into the –z endcap on 10^th January. In parallel, the HF+ was brought back onto two risers, allowing T1(+z) to be lifted into place on top of it. Following testing and commissioning, T1(+z) was successfully installed in the +z endcap on 14^th January. The HFs were the busiest place in UXC, since, in parallel to the T1 installation, all light-guide sleeves of both HFs were replaced. To reach all phototubes with the collar shielding still on the platform required complicated scaffolding constructions setup by our UXC crew. The HF work on –z and +z ends was finished on 18^th and 26^th January respectively.

On 27^th January, the detector was back in beam configuration and pump down of the beam pipe started reaching an acceptable operating vacuum just 13 days later, a clear demonstration that no damage had been caused. On 11^th February, the magnet was brought back up to 3.8 T. Though in principle the ramp-up was problem-free, with all components moving within safe limits, the final configuration of the large ensemble of heavy objects in the forward region is different to any configuration seen before, with a larger-than-usual gap between the rotating shield and the collar shield. To ensure a fully closed shielding around CASTOR, the collar will be shimmed at the next Technical Stop when the magnet is off. This observation of yet more variety in the detailed mechanical behaviour further supports the necessity of redesigning the entire region between HF and the Rotating Shielding.

After a week of tests and cosmic data-taking, CMS was declared ready for beam on 18^th February, exactly as foreseen by the planning and a tribute to the teams from the CMS collaboration, four CERN departments and various specialist contractors who took part in safely completing an intensive work programme, expertly scheduled by our experimental area management team.

Facilities for supporting operation, maintenance and upgrade

In parallel to the work on CMS and its infrastructure, the transformation of the SX5 surface assembly building into a service centre for CMS detector maintenance and repair continued. Progress has been made in the conversion of the SHL alcove into a clean room and laboratory for Pixel, BRM and fibre-optic monitoring systems. Floor and walls are being shielded, insulated and painted according to the requirements for a Class 100,000 clean-room inside an RP Zone. Although the upper floor laboratory has progressed satisfactorily, completion of the clean-/cold-room is delayed until March 2012 due to redirected resources in CERN and in CMS. Studies for a contingency plan in case of possible pixel tracker removal during 2011/12 are underway, relying on the relatively low activation levels to be expected at that stage.

Building 904 made further progress on its transformation into the future CMS Muon System assembly laboratory. The necessary renovation work on the roof, floor, fire detection, access systems and network has been finished. The gas system is under construction. The CSC production line sent from FNAL has arrived and is being re-commissioned. Temperature- and humidity-controlled laboratory units will start to be delivered during this CMS Week. Outside the laboratory, a 500 m² metallo-textile long-term storage building has been setup. Along with the temporary storage tent at Point 5, this will be used to store tooling and assembly equipment so that the ISR can be emptied and the interior of SX5 freed-up.

Facilities for supporting operation, maintenance and upgrade

Technical Coordination is involved in many aspects of the preparation of upgrade activities. The postponement of the first long LHC shutdown (LS1) until 2013 has many actual and potential implications. Indeed the revised overall plan for the next 10 years will not be clarified until the middle of this year and even then, many evolutions are possible, depending on the performance of the accelerator and experiments and the physics yield. The general planning philosophy being followed by Technical Coordination is similar to that during the construction phase, namely, be ready for all likely schedule evolutions including the official one, maximising the chances of exploiting the opportunities, or meeting the challenges, which may arise.

The likely delay of one or two years to the second long shutdown has implications for the Tracking upgrade project and has initiated a study of whether the four-layer pixel tracker could be installed in an extended year-end stop. This is only possible if the matching smaller-diameter beam pipe is pre-installed in LS1. High priority is therefore being given to completing the favoured design, which has an outer diameter of 45 mm to allow for a pixel detector with a 12-facet inner layer. The aim is to be able to order the pipe in September 2011. This gives enough time for intensive tests after delivery to CERN and for detailed study of the installation procedures of the pipe and the pixel tracker. Meanwhile the Pixel Luminosity Telescope is making good progress towards being ready-to-install in the year-end stop of 2011-’12 should the opportunity arise. Facilities for beam tests and final assembly at CERN are being prepared and a Manufacturing Progress Review will be held soon.

Meanwhile the delay to LS1 has mostly positive effects upon the Endcap Muon upgrade project, both in allowing more time for the assembly areas to be prepared and providing some contingency for the delivery of the YE4 shielding wall. Material for the disk sector cases is now being delivered to the manufacturer and the design of the complex assembly tooling is nearing completion. The engineering and electronics design review process for YE4, RPC4, CSC4 and the ME1/1 upgrade will be launched imminently.