Friday, May 15, 2009

CERN and the LHC

hello sir, i am a junior and I was wondering if you have ever visited the particle accelerator at CERN, and if you have how does it compare to any other particle accelerator you've seen. Also do you know if Fremi-Lab have any anti-matter? From what I know anti-matter is a result of a particle accelerator experiment.



Yes, I have visited CERN and seen their particle accelerators. The LHC at CERN is about 5 times bigger than our biggest accelerator here in the U.S., at Fermilab where I work. It is the largest machine in the world, and when it turns on and runs full steam, it will become the highest energy accelerator. Right now, that honor belongs to the Tevatron at my lab. The LHC is indeed a very impressive sight.

As for your second question, yes Fermilab has lots of antimatter, though "lots" is a relative word. The LHC at CERN will collide protons heading one direction with protons heading in the other direction. These protons travel in side-by-side pipes, and then are brought together at "collision points." In the Tevatron, we collide protons with "antiprotons" going in opposite directions within a single pipe. So for this to work, we need to constantly be making antiprotons every day, all day long. We have the biggest anti-matter factory in the world!

We can make about 300 billion antiprotons every hour of operation. We accelerate protons to a high energy, and then steer them into a target. A lot of debris gets generated from the energy of the collision. For every million protons that hit our target, about 20 antiprotons come out and get collected. We repeat this process over and over until we get enough to collide with the protons in our big accelerator.

But like I said, even though we make lots of anti-matter, it's really not that much. Suppose we run our machines 150 hours a week, and 40 weeks during the year. Then, we'd make 1.8 x 10^15 antiprotons each year. A big number, eh? But an antiproton weighs the same as a proton, which is only 1.7x10^-27 kg. So, in a year we only make a couple of nanograms of antimatter at most; in a good year! In one billion years of constant running we'd make two grams of antimatter...

Fun to think about though!

Thanks for your questions!

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