News from the pit

25 January 2011

Working on the Tile Calorimeter electronics draws

They say that the number of construction cranes littering the skyline of a city is an accurate indicator of its economic well-being. Over at Point 1, ATLAS has its own peripheral productivity-meter: the lift down to the pit notched up over 11,000 journeys between December 7th and January 18th, ferrying people and parts to and from the detector for testing, maintenance and upgrades.

According to Technical Coordinator Marzio Nessi, 70 per cent of all the work scheduled was routine yearly maintenance the electronics, ventilation, cooling, gas and cryogenics systems have all gone through the standard motions and been tweaked back to their optimum states.

The powered-down detector saw three days without cooling, while the external cooling towers were cleaned, and the electronics underwent many small additions and improvements including a new Uninterruptable Power Supply that, in the event of a power cut, will extend the emergency cover for the cryogenics and magnets to two hours.

The whole detector took just four weeks to fully open one week faster than foreseen and hundreds of work requests were completed. Other than December 25th, and 26th, the detector was worked on constantly over the Christmas break, with around 30 to 40 people underground each day, and more once CERN re-opened.

Several adjustments and improvements were made to the ventilation systems in order to achieve better air circulation and avoid 'hot spots' within the detector volume. And speaking of hot spots, thermal problems with some of the Toroid's electrical bus bar connections were addressed by reworking the copper-aluminium joints with new silver pads to increase the surface contact area.

A multitude of little jobs were tackled on the Muon system, but the Tile and Liquid Argon calorimeters were the focus of most of the big active-detector changes. The former had 32 of its electronics drawers pulled out for work, 23 of which had their low voltage power supplies refurbished or replaced to reduce noise and make them more robust against trips. The latter had a lot of work done on the front-end boards, specifically the plagued optical transmitters; 30 failed modules, plus 24 deemed likely-to-fail, were replaced.

All systems migrated to the latest, more streamlined, core trigger and data acquisition software release and began testing out how it runs for them.

Radiation safety was a big focus and, according to Operations Manager Martin Jäkel, the whole shutdown period was “an excellent dry run for the next openings”. The replacement of the (by then) heavily irradiated beam pipe is scheduled for the next big shutdown period, expected in 2013. The Christmas shutdown was an opportunity to practice applying the principles of the ALARA (as low as reasonably achievable) radiation safety guidelines, and all of the detector manoeuvrings and interventions were filmed for later detailed analysis for how to improve on the current procedures.

The detector began to be re-closed on January 18th, and should all be back in place by February 14th, poised and ready for 2011's first beams.


Ceri Perkins

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