You can’t do particle physics experiments in a room, or a building, or even a city block. The Large Hadron Collider measures a staggering five miles in diameter. Stanford’s Linear Accelerator is two miles long. These giant machines get the job done, but scientists at CERN are testing a machine that could do the same job, but in a lot smaller area.
The AWAKE experiment may have the potential to scale down the size of particle physics experiments by a factor of a hundred or more. On June 16 scientists ran the first in a series of tests that will be performed over the next few decades in the experiment.
The reason that colliders are currently so big has to do with just how much happens inside a particle collider. In order to work, they need to have room to store the particles, accelerate them to incredibly high speeds, smash them together, and then look at the resulting particle bits that come out of the explosion.
To get particles up to speed in these large colliders, they get pushed through a series of alternating electric fields. As the need for speed increases, scientists have tended to build longer and longer colliders rather than more powerful ones.
The AWAKE experiment takes a different tack. Instead of being pushed through electric fields, a process that requires large amounts of space and longer and longer colliders, AWAKE will use a concept called wakefield acceleration to get particles moving much faster in a shorter amount of time.
Here’s Ryan F. Mandelbaum with Popular Science, explaining how the process works:
First, a packet of protons from CERN’s proton accelerator, the Super Proton Synchrotron, will pass through a field of plasma. The electrons in the plasma are negatively charged, so they fly towards the positively charged proton bunch. By that point, though, the protons have flown away, so the electrons keep flying. The electrons leave positively charged plasma in their absence, though, so they’re pulled back to where they came from. The process continues and makes a wave. If you plop another electron into the wave, it will surf along to avoid all the other negative electrons crashing down, causing our surfer dude to accelerate really quickly through the wake field, as much as a thousand times faster than the traditional method, according to an article published in Nature.
As of now, scientists have successfully passed the proton bunches through the main beam line in preparation for the experiment, but they are still working getting the plasma and accelerated electrons, which probably won’t happen until 2018.
AWAKE is the first attempt at producing a wakefield accelerator, but scientists at Stanford Linear Accelerator lab and Brookhaven National Lab are working on similar concepts. However, of the three, AWAKE is the only one to use protons, which may produce a more powerful wave.
According to a CERN press release, we could even see tabletop-size accelerators one day, but it would be several decades before we see these much smaller devices being used regularly in particle physics.