Particle Accelerator That Can Fit on a Tabletop Opens New Chapter for Science Research

June 20, 2013

AUSTIN, Texas — laser plasma acceleratorPhysicists at The University of Texas at Austin have built a tabletop particle accelerator that can generate energies and speeds previously reached only by major facilities that are hundreds of meters long and cost hundreds of millions of dollars to build.

“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. “Until now that degree of energy and focus has required a conventional accelerator that stretches more than the length of two football fields. It’s a downsizing of a factor of approximately 10,000.”

The results, which were published this week in Nature Communications, mark a major milestone in the advance toward the day when multi-gigaelectronvolt (GeV) laser plasma accelerators are standard equipment in research laboratories around the world.

Downer said he expects 10 GeV accelerators of a few inches in length to be developed within the next few years, and he believes 20 GeV accelerators of similar size could be developed within a decade.

Downer said that the electrons from the current 2 GeV accelerator can be converted into “hard” X-rays as bright as those from large-scale facilities. He believes that with further refinement they could even drive an X-ray free electron laser, the brightest X-ray source currently available to science.

A tabletop X-ray laser would be transformative for chemists and biologists, who could use the bright X-rays to study the molecular basis of matter and life with atomic precision, and femtosecond time resolution, without traveling to a large national facility.

“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.”

To generate the energetic electrons capable of producing these X-rays, Downer and his colleagues employed an acceleration method known as laser-plasma acceleration. It 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.”

laser plasma accelerator - vacuum chamber interior

The interior of the vacuum chamber in which the acceleration occurs. The laser beam arrives from the right. The gas cell, within which the acceleration of electrons occurs, is in the center of the chamber. The actual acceleration occurs over a distance of about an inch.

Downer compared it to what would happen if you threw a motorboat into a lake with its engines churning. The boat (the laser) makes a splash, then creates a wave as it moves through the lake at high speed. During that initial splash some droplets (charged particles) break off, get 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.”

Former UT Austin physicist Toshiki Tajima and the late UCLA physicist John Dawson conceived the idea of laser-plasma acceleration in the late 1970s. Scientists have been experimenting with this concept since the early 1990s, but they’ve been limited by the power of their lasers. As a result the field had been stuck at a maximum energy of about 1 GeV for years.

Downer and his colleagues were able to use the Texas Petawatt Laser, one of the most powerful lasers in the world, to push past this barrier. In particular the petawatt laser enabled them to use gases that are much less dense than those used in previous experiments.

“At a lower density, that laser pulse can travel faster through the gas,” said Downer. “But with the earlier generations of lasers, when the density got too low, there wasn’t enough of a splash to inject electrons into the accelerator, so you got nothing out. This is where the petawatt laser comes in. When it enters low density plasma, it can make a bigger splash.”

Downer said that now that he and his team have demonstrated the workability of the 2 GeV accelerator, it should be only a matter of time until 10 GeV accelerators are built. That threshold is significant because 10 GeV devices would be able to do the X-ray analyses that biologists and chemists want.

“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.”

For more information, contact: Daniel Oppenheimer, Hogg Foundation, 512 745 3353; Michael Downer, Department of Physics, (512) 471-6054,

14 Comments to "Particle Accelerator That Can Fit on a Tabletop Opens New Chapter for Science Research"

1.  Neale said on June 20, 2013

What is it that limits the wavelength of the shock in the plasma? Is it merely the mean free path of the electrons or is it something else? If the 'shock-bubble' could be expanded to larger sizes (presumably at lower pressures?) it might be useful for accelerating objects (i.e. space ships through low density plasma clouds). And if higher density makes it easier to initiate acceleration, then would it be possible to use kerr effect laser plasma filamentation to produce particle acceleration a atmospheric pressures?

2.  J-Rod said on June 21, 2013

If the University of Texas attaches the particle accelerator to a meglinating variable intensity untranking finial, they will discover that the anomorgling subdivots will aquire nutrino mass-overload, which will cause the preneumanizing slotted synchrofusing synthetic toggle bearings to lose friction and they will incinerate the compressed velonoid camshanks and cause a disruption (i.e., tear) in the space-time continuim and the entire multiverse will be covered in ear wax.

3.  Nick B said on June 21, 2013

I'm guessing the limit to creating higher energy electrons is most likely the power density of the laser pulse. If the mean free path was an issue you'd likely just have a reduced number of electrons due to the collisions reducing the overall brightness. Creating a shock-bubble for larger objects would require spreading the beam out on a larger volume decreasing the power density, reducing the very high field you depend on to accelerate the object. This works for electrons as they're ridiculously light and are also charged.

4.  Seale said on June 21, 2013


5.  Dennis Towne said on June 21, 2013

Neale: My understanding was that it's the wavelength of the laser that gives the acceleration window. It would be completely and utterly unusable for spaceships and likely can never be used at atmospheric pressures.

6.  Mark Baker said on June 21, 2013

I think to get to the poit where we could use this to create a entanglement with different places in time both the electrons and the photons being accelerated through would need to be entangled ...
here is a simulation I made that should be redone at a future time
to refine the matter ...

7.  Ralph said on June 22, 2013

How low a gas density is too low?

8.  Stephen Paul King said on June 22, 2013

Neale, where can I learn more about this Kerr effect?

9.  Colin said on June 22, 2013

"Particle Accelerator That Can Fit on a Tabletop"

This system requires petawatt laser light as input -- which, in this case, is a whole other tabletop; a 34-foot optical tabletop just for that laser! (Source: Texas Petawatt Laser web page)

I think it would be reasonable to assume that "fit on a tabletop" would make most people think that the entire system would fit on something the size of a kitchen or dining room table. But, the reality is that at least two tables are involved here, and one of those tables is longer than 99.999% of tables in the world (e.g., rare things like boardroom tables are 34 feet long).

But, maybe the LHC will cut a one-inch gap under the floor area of their huge facility, and put tiny table legs, so they can boast that they also have a "tabletop" particle accelerator! LOL :-)

10.  David Hajicek said on June 22, 2013

If the target is cooled sufficiently, it can lead to a local higher density of the gas, while maintaining the low density elsewhere. This could allow higher velocities with less energy loss.

11.  Slambo said on June 23, 2013

Uh...huh, wha?

12.  jnally said on June 23, 2013

I can see the headlines now....teenager discovers the elusive BOSON on his laptop accelerator with videos to prove it.

13.  Parick said on July 1, 2013

Now just get one that we can strap to our backs and we can go Ghost busting.

14.  Sterling W. said on July 7, 2013

This is dag gum awesome. I love this university and not only am I amazed by the article and what students have discovered but the conversations that are spurred from the article. Truly the best place on the planet.