Berkeley Lab Particle Accelerator Sets New World Record

Chuck Bednar for – Your Universe Online
Researchers from the US Department of Energy’s Lawrence Berkeley National Lab in California have set a new world record by exciting subatomic particles to the highest energies ever recorded from a compact accelerator.
According to the Berkeley Lab, the team that accomplished the feat used a specialized petawatt laser and charged-particle gas combination to accelerate electrons inside a nine-centimeter long plasma tube to an energy of 4.25 giga-electron volts.
This is known as a laser-plasma accelerator, an emerging class of particle accelerators that physicists believe can shrink traditional, miles-long accelerators to machines that can fit on a table, and the record-setting short-distance acceleration corresponds to an energy gradient 1000 times greater than traditional particle accelerators.
“This result requires exquisite control over the laser and the plasma,” explained Dr. Wim Leemans, director of the Accelerator Technology and Applied Physics Division at the Berkeley Lab and lead author of a new Physical Review Letters paper detailing the feat.
Traditional particle accelerators, such as CERN’s Large Hadron Collider, speed up particles by modulating electric fields inside a metal cavity, the researchers explained. This technique has a limit of approximately 100 mega-electron volts per meter before the metal breaks down, but laser-plasma accelerators take an entirely different approach.
In the Berkeley experiment, scientists injected a pulse of laser light into a thin, short straw-like tube that contained plasma. The laser creates a channel through the charged-particle gas as well as waves that trap free electrons and accelerate them to high energies. The record-setting effort was assisted by the Berkeley Lab Laser Accelerator (BELLA), a powerful laser capable of producing a quadrillion watts of power (a petawatt).
Dr. James Symons, associate laboratory director for Physical Sciences at Berkeley Lab, called it “an extraordinary achievement for Dr. Leemans and his team to produce this record-breaking result in their first operational campaign with BELLA.”
Dr. Leemans explained that he and his colleagues were “forcing this laser beam into a 500 micron hole about 14 meters away” and that “the BELLA laser beam has sufficiently high pointing stability to allow us to use it.” In addition, he said that the laser pulse, which fires once a second, is stable to within a fraction of a percent – something that “never could have happened” with less precise, harder-to-control lasers.
Considering the high energies required for the experiments, the researchers used computer simulations at the National Energy Research Scientific Computing Center (NERSC) to test the set-up of the accelerator and see how different parameters would alter the outcome. Eric Esarey, senior science advisor for the Accelerator Technology and Applied Physics Division at Berkeley Lab, noted that since small changes could have a drastic impact on the results, it was important to focus on the regions of operation and the best ways to control the accelerator.
“In order to accelerate electrons to even higher energies – Leemans’ near-term goal is 10 giga-electron volts – the researchers will need to more precisely control the density of the plasma channel through which the laser light flows,” the laboratory said. “In essence, the researchers need to create a tunnel for the light pulse that’s just the right shape to handle more-energetic electrons. Leemans says future work will demonstrate a new technique for plasma-channel shaping.”
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