Saturday, October 10, 2015

CERN Plans To Test Plasma Wakefield Accelerator

Particle Physics

Wakefield Accelerator: The SLAC National Accelerator Lab at Stanford University writes: “Experiments indicate that plasma wakefield machines could generate tens of billions of electron volts per meter—as much as 1000 times more acceleration potential per length of accelerator—allowing smaller accelerators of tremendous power. Such a system would use speeding electrons or a laser pulse to create a charge "wake" in a sea of ionized gas, or plasma. Like a surfer on a good wave, particles would ride this plasma wake to greater and greater speeds. But there are technical challenges to overcome before tabletop accelerators and plasma-driven turbo-chargers for larger accelerators can become a reality. Scientists must determine how to accelerate beams of particles—including electrons and their antimatter counterpart, positrons—that are suitable for a future collider.”
Photo Credit & Source: Nature

An article, by Elizabeth Gibney, in Nature News says that CERN will soon test a mini accelerator, which will be a slight departure from the ever-increasing size of particle accelerators. These are called Plasma wakefield accelerators, which were first proposed in the 1970s at UCLA, but only recently was this concept considered as viable.

There are a number of labs that have small prototype accelerators, including at the SLAC National Accelerator Laboratory at Stanford University in Menlo Park, California, which has proved this concept on a small scale [see Nov 6, 2014 article in Nature; 515, 92–95]. Its experimental model is just 12 inches long — or about 90,000 times smaller than CERN’s 27-kilometre (17-mile)-long Large Hadron Collider (LHC) in Switzerland.

The purpose of the experiment at CERN, writes University College, London, is to verify “the approach of using protons to drive a strong wakefield in a plasma which can then be harnessed to accelerate a witness bunch of electrons.” Or, in other words, to prove the concept at the world’s premier high-physics lab. In  “CERN prepares to test revolutionary mini-accelerator,” (October 7, 2015), Gibney writes:
Conventional colliders, such as the 27-kilometre-long LHC, use electric fields to move charged particles through a tunnel; the fields switch from positive to negative at a frequency that means the particles are constantly nudged forward, gaining energy with each push. But such colliders use metal-walled cavities that spark if the electric field is too strong. As a result, the only way to further increase the particles’ speed, and therefore energy, is to lengthen the tunnel.
Plasma wakefield accelerators, which were first proposed in the 1970s, are designed to break this cycle, says physicist Allen Caldwell at the Max Planck Institute for Physics in Munich, Germany, who will lead the AWAKE experiment. They send a pulse of charged particles or laser light through a plasma, which sets electrons and positively charged ions oscillating in its wake. The resulting regions of alternating negative and positive charge form waves that accelerate further charged particles. Injected at just the right time, these particles effectively surf the waves (see ‘Wakefield acceleration’). Crucially, as the electric fields are much stronger than those in a conventional collider, the acceleration can be as much as 1,000 times greater over the same distance.
If the experimental tests prove successful at CERN, it will likely change the way particle physics is done; smaller tabletop accelerators will be more widely used and at a fraction of the cost. The larger accelerators like LHC will still be necessary for more complex particle reactions, to better understand the subatomic world; but this approach might open up physics to many people and institutions that previously were unable to conduct such experiments, waiting for experimental time on large linear accelerators. Who knows what outcomes are possible?

For more, go to [NatureNews]

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