The ATLAS teams are wrapping things up and prepare for Run 2, as Long Shutdown 1 is coming to an end. The collaboration has made major upgrades to increase the efficiency, safety, and environmental impact of the detector; 2014 was a really busy year.

The ATLAS detector is now a brand new machine, as its basic infrastructure and all its subdetectors underwent several upgrades. The technical teams refurbished the cooling and ventilation systems, installed new aluminium beam pipes, and fixed electrical and optoelectronic issues. The upgrades, besides improving the detector's performance, protect it from unexpected power glitches that used to inhibit data taking.

On May 7, a new subdetector, the Insertable B–Layer (IBL), was installed in the heart of ATLAS and is now the fourth layer in the inner detector region. It was designed to improve the tracking efficiency, as radiation damage, caused by the higher luminosity of Run 2, might reduce it. The IBL will measure with precision the momentum and trajectories of particles and, more specifically, help scientists identify heavy particles, produced by the decay of short–lived particles, such as the Higgs boson. The installation of this new detector was very challenging, due to the tiny insertion gap (only 0.2 mm) between the Inner Supporting Tube and the IBL, and the team had been practising the procedure for two years before carrying it out.

The big wheel of the muon spectrometer as it is moved halfway through to its final position before the closing of the ATLAS detector. (IMAGE: Claudia Marcelloni, The ATLAS Experiment/CERN)

The aim of several upgrades was to make ATLAS more eco–friendly. The IBL, uses CO2 for cooling instead of fluorocarbons, reducing its greenhouse effect and its ecological footprint in case of leaks. In addition, leaks in the Muon Spectrometer chambers have been repaired and parts of the beam pipes have been replaced to limit the use of materials that are easily activated in the experimental environment.

In closing ATLAS for the next LHC run, with a weight of 1000 tonnes and a diameter of 9 m, the endcap calorimeter, top left, is one of the most difficult objects to move. However, thanks to a system of air pads, the orange discs seen lower left, it can be moved with a force of only 23 tonnes. At the right, the endcap can be seen on the air-pad system at the start of its journey back into the toroid barrel.  (Image credits: ATLAS Collaboration.)

Upgrades were made to detector electronics as well, to increase the acceptance rate of events from 70kHz to 100kHz. As a result, the computer farms also increased in size. A hardware–based topological trigger, in the form of an electronics board, was also introduced to raise the selectivity of events at the earliest stage. In addition, faster readout chips were developed for Run 2, as the IBL will collect substantially more data. The new Trigger structure was then tested to ensure that the system will continue to efficiently select interesting data in the challenging environment of the next runs.

In the end of November, many ATLAS people spent five days cleaning and inspecting the detector and the experimental cavern. They had to wipe and vacuum every surface, as well as search for any metallic object that remained from the LS1 work, before the powerful toroid magnets start again.

Careful cleaning of the cavern is needed to ensure that there are no loose metallic objects around, which could move under ATLAS’ powerful magnetic field and damage the detector (Image Credit: ATLAS Collaboration)

The closing activities started in early August and will finish by next Friday December 19^th. Two long and intense years passed very quickly with many work packages, many interventions, a lot of nice stories to remember, a lot more experience for everybody involved. LS1 will remain in our memories. Thousands of scientists eagerly anticipate the restart of the experiment in the spring of 2015 to continue their research, further study the Higgs boson, and tackle the unsolved mysteries of the universe. The only drawback is that the experimental site, which welcomed more than 37,000 people in the past two years, will remain closed to visitors until LS2.