Today I spent much of my time crawling around on hands and knees, picking pieces of rubbish from the innards of the ATLAS detector. It’s just one of those things that comes with the job and gives you a different view of the experiment (literally.) Before we start taking data we need to make sure that the ATLAS cavern is clean and safe. I call this process “Grooming the Beast”.
The ATLAS detector is housed in the ALTAS cavern, just behind the Globe at CERN. The journey down is long (more than 100 meters) and convoluted, with all kinds of doorways, locks, passages and elevators. Work has been taking place in the cavern during the winter shutdown to make improvements and sort out minor problems with the detector. Is a piece of the hardware getting damaged by interactions with matter? This is an excellent time to replace it!
Cleaning the cavern just as people start to leave it may seem like an unusual thing to do, but it serves a very important purpose. There has been a lot of work to improve the detector during the shutdown, and this leaves some debris. The engineers clear up as much as they can as they go along, but the odd screw or piece of wire goes missing, and over the months this builds up. The real danger to the machine is metal debris. The detector contains large magnets and these can interact with metallic objects lying around. They need to be removed before we turn on and take data!
The cleaning also serves a milestone in the life of the experiment. It serves as a reminder that the shutdown is over, the repairs are complete and that we need to look forward to the new data that’s going to arrive. It’s no coincidence that at the same time as we clean the cavern, we present our work at the Moriond conferences. (These two weeks are going to be my favorite of this year! So many interesting results, and getting the chance to poke around inside a large detector.)
As you would expect, health and safety are very important in this process. To get access to the cavern I had to pass 4 levels of safety training, get a dosimeter to monitor radioactive dose, a hardhat with a light, and hard boots. In addition we had to register our names and phone numbers in case anything happened while we were down there. There is an elaborate key system in place as well, which is mainly for safety. We each take a key as we enter, and the beams cannot pass through the cavern until every key is returned. We each get a pass (either on our CERN ID cards or a magnetic key fob) that is linked to our names and dosimeters, so that if a key is not returned we know who is still in the cavern and when they entered. Safety isn’t the only concern though, these systems have the added advantage of protecting the machinery. Everyone who goes down to the cavern has to have safety training and the correct permission, which significantly improves the quality of all the work down there. If we knew we could just pop along at any time to fix a minor problem there would be people down in the cavern all the time!
Most of the actual work involved picking pieces up off the floor and cleaning the areas that others can’t reach. It seems simple, but the shape and size of the detector make it very difficult. Balancing on one foot on a low friction floor as you lean into a crevice to see if that wire is actually attached to anything, while wearing a hard hat that makes your head bigger than usual is exactly as difficult as it sounds! For bonus points you can do this in a dark space with a special tool for grabbing objects in places too small for your hands to reach. Some of the “treasure” I found included a drill bit, a box of screws and tubes (“It’s good, but it’s not the Higgs”), a guide to some important looking apparatus, and some rusted metal in a box of rusty water. When faced with those objects it’s not always obvious what to do. Is it trash? Is it safe to move? Is somebody missing it?
This is the first time I’ve seen the ATLAS detector in person and it’s impressive. But on the other hand, I couldn’t relate to it very easily. I saw some piece of the toroid and some piece of the muon system, but from the outside it looked like an amorphous chunk of wires and pipes. My officemate, Julia, pointed out the muon systems, and showed me the sensors they used to calibrate their position. In addition to this, they also have geodetic instrumentation in the cavern so that they can work out the position of any part of the detector. That’s some neat hardware to have 100 meters underground! I’d hoped to be able to recognize a lot more of the detector, but it’s just not that kind of experiment. It’s far too huge to appreciate in a single day.
Towards the end of the day my friend Katie showed me the inside of the detector. At the bottom of the detector there’s a crawl space (mind your head on the muon system!) into a series of chambers and tunnels. These give access to some instruments and hardware so that we make some changes or repairs, and through an intricate set of ladders and tunnels you can actually get quite far into the outer parts of the detector. It’s warm down there, and you can see parts of the famous toroid, which is neat. It was around this time that Katie suggested that it would make the best clubhouse in the world. I can see myself enjoying somewhere like that as a 12 year old boy! (Actually, I can see my self enjoying it as an adult, but that’s just how amazing it looks when you’re inside.)
Right now I’m exhausted, and my throat is a little dry, but it’s been an awesome day and I’m glad to have the chance to share some photos of the ATLAS cavern with you!