July 27, 2011
Exploring the Universe on a Break
Undergrads stop by CERN for a tour
By Katrina Wisdom, Pratt 2012
A longer version of this post originally appeared on Katrina Wisdom's personal blog
Having heard somewhere during physics class last year that there was a Duke team working at CERN, I decided to see what I could find out, and possibly arrange. I started sending emails within a few weeks of arriving here in Metz, France (at Georgia Tech in Lorraine) and discovered that not only was there a team working at CERN, but that one of my former physics professors could put me directly into contact with the team.
I sent a few more emails to see if it would be possible to arrange a tour, and soon enough I was in touch with Andrea Bocci, a member of the Duke ATLAS team who volunteered to show us around CERN. I was able to gather eight other students, who were as excited as I was, to come as well.
We arrived a bit early and were able to read a little about CERN and walk through the museum portion a bit before we met up with Andrea. CERN was conceived of in the 1950’s as a major European hub of particle physics, ideally located in “neutral” Geneva, Switzerland.
Andrea and the Duke team work on the ATLAS project, which involves 38 countries, 174 institutions, and 3000 scientists. (And this is just one part of CERN!) ATLAS is one of the particle detector experiments using the Large Hadron Collider (LHC). It is described best by those who work there:
“[This unique machine] consists of an enormous cylindrical skeleton, with pixels at its heart and calorimeters in its entrails, completed by an outer skin of muon chambers, and the entire structure immersed in a powerful magnetic field. Assembling subsystems within subsystems, like a Russian doll, called for feats of ingenuity, skill, and inventiveness.”
These particle accelerators use ENORMOUS magnets and currents to manipulate the movements of beams (clumps) of particles, smash them into each other violently, and “see what happens”. I put that last bit in quotes because it really doesn’t work that way; most often the physicists start with rigorous theory, discern what the theory predicts must happen in real life, find a way to detect what must or might be happening specifically, and then run the experiment to see if they find what must be there, according to theory.
Duke’s involvement in the ATLAS project is with their contributed component, called TRT (Transition Radiation Tracker). From what Andrea told us, the TRT is very reliable and works with far fewer accidents than the other components (which is to say that the “TRT” status is rarely the blinking red one. Phew! Go Duke!)
A few amazing facts:
- When the beam is running, there is a collision every 25 nanoseconds, or 40 million collisions per second.
- Each collision produces 10 Megabytes of information. (Which is A LOT…my computer has 285 GB of hard drive space…this is 34 times less than the information needed in 25 nanoseconds)
- They can only save data of 300 collisions per second to a disk (99.9% of the collisions are lost). And deciding which collisions to keep and which ones to save is an endeavor in and of itself!
- The LHC runs at an energy level of 14 Teravolts, which is seven times more energy than Fermilab, a particle accelerator in the U.S.
- The LHC operates at a magnetism of 2 Teslas. This is HUGE, just like the solenoids and magnets needed to produce this field!
- It was here at CERN that antimatter was discovered. Project LEIR first produced an atom of antimatter from antiparticles.
Typically, you’d think that a bunch of physicists looking to confirm their crackpot theories by hurling particles at each other has just about nothing to do with the real world, other than inspiring the rumor that they might cause the apocalypse by producing a black hole that will devour the entire universe. But we learned about two examples of practical application. First, a beam of neutrons is thought to be much more exact than x-rays in medical use, making it ideal for killing a brain tumor, for example. Further, there is a current theory that by bombarding radioactive waste with a beam of neutrons, one can speed up the process of radioactive decay. This immediately excited me—could this contribute to a solution to the present problem of what on earth to do with radioactive waste?! By speeding up the decay, it would not take thousands of millions of years for the material to be (for all intents and purposes) harmless, but perhaps on tens or hundreds of years. WOW! I wonder how these experiments are going.
We saw where the HUGE magnets are rigorously tested before they can be implemented. Here things must be unbelievably precise, or else the electron beam will be lost. Consider the following criterion: measurements must have a precision (of the magnetic field, for example) of 10^-4. However, rarely in engineering is such precision needed; order of magnitude estimates and models are usually sufficient. No wonder physicists feel skeptical of the magnets that the engineers make for them…and no wonder why they must test them judiciously!
Or consider the precision required for the vacuum inside different layers of the beam chamber. The leakage rate into the secondary beam chamber must be slow enough to fill a 1 Liter bottle in 300 years. In the primary beam chamber, it must leak in at the rate that would be equivalent to 300 million years to fill a 1 Liter bottle. Think of that next time you lift up your milk bottle!
Another awesome fact: in the vacuum of outer space, between galaxies, where there is NOTHING whatsoever, the temperature is still 3 degrees Kelvin (3 degrees above absolute zero). Inside the beam chamber, the temperature is 1.9 degrees Kelvin. Achieving this temperature requires an incredibly strong vacuum.
There is so little bureaucracy that teams of psychologists come to study CERN's organizational structure to understand how thousands of scientists (and thousands of arrogant physicists) can work so well together. All though there are people designated as heads of certain positions, there is almost no hierarchy.
Learn about Undergrad Joshua Loyal's LHC experiments here: http://research.duke.edu/stories/down-quantum-hole