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Christine Nattrass | USLHC | USA

View Blog | Read Bio

Inside ALICE

I am currently at CERN to work on getting the electronics for the electomagnetic calorimeter working now that the rest of it is installed.  I got to see the ALICE detector in person for the first time on Thursday, which was very exciting.

This is a picture of me in front of the detector:

But that was part of a tour and to work in the detector I needed a lot of training.  I needed to take

  • Radiation safety training – there can always be residual radiation from things that have been activated by the beam and there may be radioactive sources in the area.  I have to recognize the appropriate placards and understand any dangers that may be present.
  • Working at heights training – the electromagnetic calorimeter is not at ground level and working on the electronics requires me to work well above ground.  I have to know how to use a harness properly.
  • Confined space training – the doors of the magnet are closed now so that they can start replacing the shielding around ALICE and I need to work inside the magnet.  This is a confined space.  There is a risk of oxygen deficiency – the amount of oxygen can drop rapidly and I have to to be aware of potential dangers and ready to respond.
  • Biocell training – The biocell is a small container of oxygen which I have to carry with me at all times in case the oxygen levels rapidly drop.  I have to be trained to use this properly because I may need to use it to save my life.

I also have to wear a dosimeter (which measures how much radiation I’ve been exposed to), a hardhat with a headlamp (in case the power goes out), and safety (steel-toed) shoes.  No shorts are allowed.  Inside the magnet there are high voltage sources, risks of falling, risks of falling objects, and detectors using flammable and/or toxic gases which could leak.  We are required to have at least two people working inside the magnet at a time – so that if someone gets hurt, the other person knows and can get help – and to have a 3rd person outside the magnet as a watcher keeping track of who is inside and where they are so that if anyone gets hurt or there is an emergency there is someone who can call the fire brigade and tell them how many people are inside and where they are.

I haven’t had the opportunity to take any pictures inside ALICE yet – and safety always has to come first so I may not be able to – but this is the hole we use to enter the magnet:

It is about 60 cm in diameter.  To get down to ALICE, you first have to go through this door:

(This is Soren Sorensen, my boss, coming down to see ALICE.) To go through this door, I have to scan my dosimeter on a card reader.  This says who I am and whether or not I have access to “the cavern” – the space underground where the detector is.  Then the outer doors open, I walk in, and I’m closed inside.  They scan one of my eyes and weigh me to make sure that I really am the person who owns the dosimeter.  Only then am I allowed in.  Inside there’s an elevator that takes us the 70m down to ALICE.  (It is easier to go down to see the cavern as a visitor than to work on the detector – one does not need training but must be supervised.)

This is why we tested as many components of the electromagnetic calorimeter  as possible before the EMCal was installed.  However, there will always be something which doesn’t work quite right and we want to fix it if we can.  It’s really exciting work, but we have to stay alert and stay safe.

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