The ATLAS Liquid Argon Calorimeter has 183,296 separate channels, meaning it makes that many independent measurements of energy simultaneously all around the point where the protons collide in the LHC. It has to be able to reliably make these measurements millions of times per second for many years. Since we are expecting collisions very soon, the detector has now been closed up and we won’t have access to it again until December for any repairs.
Last week here at CERN was a Liquid Argon Week. These are weeks that happen about 4 times per year, and they are when the whole community (hundreds of people) get together to discuss the current status of the Liquid Argon Calorimeter project. There were presentations and discussions of how the calorimeter is working now that it is in the state it will be in for the eagerly awaited first proton-proton collisions.
It has taken a long time to get to this point. According to the article in Nuclear Instruments and Methods A 558 Issue 2, 15 March 2006, p 388:
The first studies of liquid argon calorimetry for LHC date back to 1990…the choice of the liquid argon technology by the ATLAS collaboration for its electromagnetic calorimetry [was made in] in 1995…The fabrication of some of the elements of the calorimeter…started in the beginning of 2000.
In order for the calorimeter to work, everything from design to construction to installation has to go right. The temperature and purity of the liquid argon must be maintained, the front end crates that receive the deposited energy and turn it into digital data cannot fail, the trigger and data-acquisition systems have to get the data to permanent storage, and of course there is plenty of other infrastructure including the high voltage and low voltage power, many custom-designed electronics boards, and cabling between all the systems. Basically, everything from this:
to this:
and beyond has to be working correctly.
So last week there was a tallying of “dead” channels; those that didn’t make it through this whole process and probably can’t ever be used. The great news is that more than 99.9% of all the channels are working and ready to find that Higgs boson, or whatever else awaits. This is a pretty impressive achievement!
Tags: ATLAS, calorimeter
