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Monday
Aug082011

Whiz-Bang Science: Particle Accelerators

A few days ago, Brooke wrote about the creation of two new elements--ununquadium and ununhuexium  (which, by virtue of the double negatives, should be called quadium and hexium)

If these are elements that aren't found in nature,
a) why do we care about them?
b) how do we create the conditions that lead to their synthesis?

We, believe it or not, do not live in an extreme world. We've got all kinds of equilibria; our sun is in the middle of its life; we're in the galactic suburbs, nothing about our corner of the universe is too hot, too dense, too radiative, too variable.

Most of the physics-based action of the universe takes place elsewhere--and lucky for us, or there would be no "us."

But that doesn't mean that us--uh, we--aren't interested in knowing about extreme conditions, or that those conditions are irrelevant to us.

After all, the same physical laws that produce notnotquadium and notnothexium produced us. Supernovae produce the heavy elements that give us irises, as well as irises. Before our planet was around a star around a galaxy around a galaxy cluster, it was a dense mass of plasma, with all the other pre-galaxies and pre-labradors.

As scientists, humans always want to know where we came from, where we are, where we're going, and how, and why.

Particle physics--high-energy physics, condensed matter physics, collision science--can help us figure that out.

The laboratories of particle physicists can either be very far away, where we can't manipulate or choose parameters--quasars and neutron stars--or they can be in Batavia, Illinois, at a particle accelerators.




Gold atom + gold atom + momentum = slightly distasteful
living room art (credit).

Particle accelerators do as promised--they accelerate particles.




The Stanford Linear Accelerator, aka the long
white strip down the middle of this picture.
There are two basic kinds of modern accelerators: linear and circular.




Part of the Large Hadron Collider at CERN, which may produce tiny black
holes sometime but will not cause the Earth to be "sucked in." I personally
promise.
Accelerators use electromagnetism to bring particles to relativistic velocities (ones that are significant fractions of the speed of light), meaning that these particles have energies on the order of giga-electron-volts, where an electron-volt is the amount of energy gained by one electron encountering a potential of one volt. These speeds and energies are required if nuclear-type reactions are to occur. For more on the specific behavior of these charged particles at these energies/velocities, see "Nonlinear Dynamics of Relativistic Charged Particle Beams.")


But to get high energy, you have to put in high energy. The key here is that the particles with which physicists work are charged, meaning that they are attracted and repelled by electric fields. We are pretty good at creating E fields. A technique called "oscillating voltage" allows accelerators to accelerate to the energies we need to investigate conditions we don't understand yet. The electric plates are the opposite charge from the particles of interest while the particle approaches them, and after the particle passes through, the plates change polarity so that the particle is repelled, giving it a boost away The electric plates are arranged to accelerate particles along a particular path, preferably the path that leads to a sensor that leads to a scientist's computer. 

That path is either a line, in a linear accelerator, or a circle, in a circular accelerator. The latter requires that a magnetic field also influence the particles, causing their paths to curve. The degree and direction of that curve (as well as the degree and direction of the line) are due to the electromagnetism (electricity + magnetism) selected by the particle accelerator engineers. Circular accelerators have the advantage that particles can pass go and collect $200 multiple times before ending its journey, whereas a line segment always ends in the same number of meters. (In a circular accelerator, a separate dipole magnet is used to divert particles from the circular track and toward the detector/target).

By accelerating particles to relativistic velocities, we can manufacture conditions that don't exist in our epoch, when the universe has calmed down considerably. We can force atoms and subatomic particles into uncomfortable situations into which they wouldn't put themselves, into which they long ago stopped putting themselves, ones they occupy so rarely (or for such a short period of time) that there's ~0 probability we would ever happen to see them like this in nature.

We can play particle sociologist and see how they behave, compare it to how we predicted they would behave.

High-energy, Earth-based physics gives us a spyglass for our smallest parts, the things that make us--and make everything--anything at all, a time machine that can be dialed to 13.7 billion years, the power to distinguish between "never, impossible" and "unstable to the tune of 6.4x10-4 s."

To learn more about the science particle accelerators do, check out



To learn more about the current science being done with particle accelerators, check out the High-Energy Physics arXiv, which provides free pre-prints of articles.

ResearchBlogging.org

Nunes, R., & Rizzato, F. (2011). Nonlinear dynamics of relativistic charged particle beams Applied Physics Letters, 98 (5) DOI: 10.1063/1.3549690

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Reader Comments (3)

Excellent follow-up post! All I knew about particle accelerators were late nights with Tripp Jones & Dan Brown books.

August 8, 2011 | Unregistered CommenterBrooke N.

Thanks.

February 12, 2012 | Unregistered CommenterAnonymous

This is what we should know about particle accelerators. I agree, why do we have to care about them if they're not really found in nature?
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February 12, 2012 | Unregistered CommenterFrank Hendon

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