Team Creates 2 GeV Laser-Plasma Accelerator
June 20, 2013

Scientists Create Tabletop Particle Accelerators

Lee Rannals for — Your Universe Online

The Large Hadron Collider (LHC) is the world's largest and highest-energy particle accelerator. It lies in a tunnel with a 17-mile circumference 574-feet beneath mountains near Geneva, Switzerland. However, technology like this could one day be simply sitting on a tabletop.

Physicists at the University of Texas at Austin have built a tabletop particle accelerator capable of potentially generating speeds up to 2 multi-gigaelectronvolt (GeV). This output is still shy of the LHC's 7 teraelectronvolts (TeV) expected to take place in 2015, but 2 GeV has previously only been done on technology that stretches more than the length of two football fields.

"We have accelerated about half a billion electrons to 2 gigaelectronvolts over a distance of about 1 inch," said Mike Downer, professor of physics in the College of Natural Sciences. "It's a downsizing of a factor of approximately 10,000."

This is a huge feat for scientists because it opens up the door to one day make GeV laser-plasma accelerators a standard piece of laboratory equipment. A tabletop X-ray laser would be transformative for chemists and biologists, who would use it to study the molecular basis of matter and life with atomic precision without having to travel somewhere like the LHC to do it.

"The X-rays we'll be able to produce are of femtosecond duration, which is the time scale on which molecules vibrate and the fastest chemical reactions take place," said Downer. "They will have the energy and brightness to enable us to see, for example, the atomic structure of single protein molecules in a living sample."

The team had to use an acceleration method known as laser-plasma acceleration, which involves firing a brief but intensely powerful laser pulse into a puff of gas.

"To a layman it looks like low technology," said Downer. "All you do is make a little puff of gas with the right density and profile. The laser pulse comes in. It ionizes that gas and makes the plasma, but it also imprints structure in it. It separates electrons from the ion background and creates these enormous internal space-charge fields. Then the charged particles emerge right out of the plasma, get trapped in those fields, which are racing along at nearly the speed of light with that laser pulse, and accelerate in them."

He said it is like throwing a motorboat into a lake with its engines churning. The boat makes a splash, then creates a wave as it moves through the lake at high speed. During the initial splash, droplets break off, getting caught up in the wave and accelerate by surfing on it.

"At the other end of the lake they get thrown off into the environment at incredibly high speeds," said Downer. "That's our 2 GeV electron beam."

The researchers have been able to demonstrate the workability of the 2 GeV accelerator, and Downer said it is only a matter of time until 10 GeV accelerators are built. The scientist said he expects accelerators capable of this output will be developed within a few years, while 20 GeV tabletop accelerators could be developed within a decade.

"I don't think a major breakthrough is required to get there," he said. "If we can just keep the funding in place for the next few years, all of this is going to happen. Companies are now selling petawatt lasers commercially, and as we get better at doing this, companies will come into being to make 10 GeV accelerator modules. Then the end users, the chemists and biologists, will come in, and that will lead to more innovations and discoveries."