Tabletop-sized particle accelerator sets new record

A tabletop-sized device has accelerated subatomic particles to an energy gradient 1,000 times greater than traditional particle accelerators such as the Large Hadron Collider at CERN.
The team, from the US Department of Energy's Lawrence Berkeley National Lab (Berkeley Lab), used a specialised petawatt laser and a charged-particle gas called plasma to get the particles up to speed.
The setup 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.
The researchers sped up the particles - electrons in this case - inside a nine-centimetre long tube of plasma. The speed corresponded to an energy of 4.25 giga-electron volts.

The acceleration over such a short distance corresponds to an energy gradient 1000 times greater than traditional particle accelerators and marks a world record energy for laser-plasma accelerators.
"This result requires exquisite control over the laser and the plasma," said Dr Wim Leemans, director of the Accelerator Technology and Applied Physics Division at Berkeley Lab and lead author on the paper.

Traditional particle accelerators, like the Large Hadron Collider at CERN, which is 17 miles in circumference, speed up particles by modulating electric fields inside a metal cavity.
It is a technique that has a limit of about 100 mega-electron volts per meter before the metal breaks down.

Laser-plasma accelerators take a completely different approach. In the case of this experiment, a pulse of laser light is injected into a short and thin straw-like tube that contains plasma.
The laser creates a channel through the plasma as well as waves that trap free electrons and accelerate them to high energies. It's similar to the way that a surfer gains speed when skimming down the face of a wave.
The record-breaking energies were achieved with the help of BELLA (Berkeley Lab Laser Accelerator), one of the most powerful lasers in the world. BELLA, which produces a quadrillion watts of power (a petawatt), began operation just last year.

In addition to packing a high-powered punch, BELLA is renowned for its precision and control.
"We're forcing this laser beam into a 500 micron hole about 14 meters away," said Leemans.
Moreover, Leemans said, the laser pulse, which fires once a second, is stable to within a fraction of a per cent.
"With a lot of lasers, this never could have happened," he added.
The study was published in the journal Physical Review Letters.