Combining lasers could shrink particle accelerators from kilometers to meters

May 27, 2014
There are snapshots of the laser energy density at the beginning of the simulation for the array of laser pulse (left plot), and after some propagation distance of the beamlets in the plasma (right plot), where the laser field exhibits a clear incoherent pattern. Credit: Carlo Benedetti/LBL

It took every inch of the Large Hadron Collider's 17-mile length to accelerate particles to energies high enough to discover the Higgs boson. Now, imagine an accelerator that could do the same thing in, say, the length of a football field. Or less.

That is the promise of laser-plasma accelerators, which use lasers instead of high-power radio-frequency waves to energize in very short distances. Scientists have grappled with building these devices for two decades, and a new theoretical study predicts that this may be easier than previously thought.

The authors are Carlo Benedetti, Carl Schroeder, Eric Esarey, and Wim Leemans, physicists at Lawrence Berkeley National Laboratory's Berkeley Lab Laser Accelerator (BELLA) Center. Their paper, "Plasma wakefields driven by an incoherent combination of laser pulses: A path towards high-average power laser-plasma accelerators," appears in the May Special Issue of Physics of Plasmas.

If their models prove correct, they could help lower the cost of high-energy physics research—the Large Hadron Collider cost $9 billion—as well as many other industrial and medical applications of accelerators.

Laser-plasma accelerators work by blasting a powerful laser beam into a plasma, a cloud of unattached electrons and ions.

"The effect is like the wake of boat speeding down a lake. If the wake was big enough, a surfer could ride it," Leemans, who heads the BELLA Center, explained.

"Imagine that the plasma is the lake and the laser is the motorboat. When the laser plows through the plasma, the pressure created by its photons pushes the electrons out of the way. They wind up surfing the wake, or wakefield, created by the laser as it moves down the accelerator," he said.

The fast moving electrons leave the heavy ions behind. As they separate, they create gigantic electric fields, 100 to 1,000 times larger than those in conventional accelerators.

This is how they accelerate electrons so rapidly. For example, Stanford's Linear Accelerator Center takes two miles to drive an electron to 50 billion electron volts (GeV). Leemans' experimental laser-plasma accelerator takes electrons to more than 1 GeV in slightly more than 1 inch.

It takes a lot of laser power to generate a wakefield. For example, BELLA's petawatt (1 quadrillion watts) laser has a 10 meter x 10 meter footprint. It generates 400 times more power than all the world's power plants combined, though only for 40 femtoseconds (40 quadrillionths of a second).

Unfortunately, it takes BELLA's laser a full second to recharge and send a second pulse. High-energy physics research requires tens of thousands of pulses per second. Many other applications would benefit from multiple pulses per second.

BELLA's laser has the highest repetition rate of any petawatt laser in the world. Building a faster petawatt laser would require a heroic feat of engineering.

Several European researchers have suggested using an array of smaller lasers to produce one enormous pulse. Since less powerful lasers recharge faster, they could produce hundreds or even thousands of pulses per second and sustain a wakefield over many meters.

The hurdle they needed to overcome was how to synchronize hundreds of lasers so they all pulsed within less than a femtosecond of one another.

Such precision would be expensive and presents serious technical problems. But the concept of combining lasers got Leemans' team thinking.

What if the beam was not perfect? What if it were just good enough to rapidly raise the photon pressure on the electrons? Could we get away with it, they wondered.

According to the model presented in Physics of Plasmas, they could. Leemans compares it to pushing a swing.

"Instead of one big push, we would give it many smaller pushes at roughly the same time. It's not quite perfect, but the swing doesn't really care. It averages over all these little pushes and up it goes."

Laxer timing would make larger and more sustainable accelerators practical. Leemans hopes to power them with a new technology based on highly-efficient fiber lasers. The power that off-the-shelf welding lasers offer demonstrates multi-kW capabilities but much work is needed to pack the power into ultrashort pulses needed for plasma accelerators. The paper offers an approach that gets us a step closer.

The new accelerators would offer new options to physicists trying to unravel how the universe is put together. It could lower the cost of industrial uses, and make high-energy accelerators more affordable for hospitals.

Just think of it as dreaming big by thinking small.

Explore further: BELLA laser achieves world record power at one pulse per second

More information: "Plasma wakefields driven by an incoherent combination of laser pulses: a path towards high-average power laser-plasma accelerators" by C. Benedetti, C. B. Schroeder, E. Esarey, and W. P. Leemans. Physics of Plasmas May 27, 2014:

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5 / 5 (1) May 27, 2014
Belgium is working on creating an accelerator based sub-critical fission reactor.

Sounds like this would be perfect for it!

strong lasers + spallation target = neutron ray?
1 / 5 (3) May 27, 2014
There is no doubt in my mind that engineers will succeed in their endeavor here. This has all sorts of ramifications even perhaps to the point (in the century?) universities could have their own installations. The down side is that people employed to build the large accelerators would lose out although having said that, they could be employed to produce a larger number of smaller accelerators.
3.7 / 5 (3) May 27, 2014
Whenever I read articles about smaller accelerators, I think of a fantasy I once had of creating nano-scale accelerators that could each push a proton to 99% of the speed of light in a few microns, millions of times per second. It would be an advanced ion propulsion drive. Instead of balancing a payload on top of a long thin rocket that produced thrust by pushing hundreds of tons of propellant out a hundred sq ft of nozzle, the payload would be atop a several thousand sq ft disk covered with quadrillions of tiny accelerators powered by a fusion reactor and needing only a few thousand pounds of propellant to achieve earth orbit. It could carry enough propellant to slow back down before returning to the atmosphere, making a heat shield unnecessary, and allowing a fully controlled powered landing. It might look very similar to a 1950's style flying saucer.
2 / 5 (4) May 28, 2014
@dan42day who has been reading about Unconventional flying objects then? Actually I experimented with all sorts when I was much younger but I never had a proper lab. My launch site was an army parachute training ground (open ground in those days) and some official looking guys put a stop to my flights...and I never knew what happened to my drawings of my 'eletric bolt' rocket they confiscated. Like you I wondered about harnessing energy but...oh those were days.
As I mentioned in my previous post, the ramifications and benefits are almost limitless and feel sure it will be applied to space craft in the not too distant future. We already know that there is a military exploitation but that's something we have to live with in all fields.
1 / 5 (1) May 28, 2014
How would they phase the lasers? If they are not in phase, the beam could point in odd directions.
1.3 / 5 (3) May 28, 2014
Sounds like a variation of this would be good for space propulsion. Think maybe mimath's electric bolt rocket was actually a small scale 'rail gun'. No wonder the 'boys' at that field grabbed your stuff. The second grabbing was when they claimed it for their idea to some defense types who used the same tactics to grab it in turn from them. Rinse. Lather. Repeat until some megamonopoly stole it last.

Dan42...probably within our tech to use self assembling meta materials to make the mini accelerators. Yep and need some compact fusion machine like the focus fusion device now making its way to success via American and Iranian support.
2 / 5 (2) May 28, 2014
Whenever I read articles about smaller accelerators, I think of a fantasy I once had of creating nano-scale accelerators that could each push a proton to 99% of the speed of light in a few microns, millions of times per second.

antimater produced in CERN accelerator, imagine hundreds or thousands of laser accelerators of same power of CERN doing that simultaneously.
2 / 5 (4) May 28, 2014
@Osiris1 Oh well I can't claim anything unfortunately as it some was something I came upon by accident when I had made a long ramp out of metal meccano with wire coils (can't remember the details now) connect to dad's power point. Didn't realise that this was connected to household and managed cut supplies in the adjoining houses. 'Jeff King the Rocket Man' (American series) had nothing on me ha!
5 / 5 (2) May 28, 2014
Dude.... You don't have to lie to kick it.
2 / 5 (4) May 28, 2014
I understand that 'solar sails' are being considered
'A spacecraft equipped with a sail 1,300 feet (400 meters) wide, for example, could travel 1.3 billion miles (2.1 billion kilometers) per year...'
is one quote with other much larger sails being thought of for travel to other star systems. Perhaps a combination of both 'accelerator' and 'sail' could be designed too?
5 / 5 (3) May 29, 2014
I understand that 'solar sails' are being considered
'A spacecraft equipped with a sail 1,300 feet (400 meters) wide, for example, could travel 1.3 billion miles (2.1 billion kilometers) per year...'
is one quote with other much larger sails being thought of for travel to other star systems. Perhaps a combination of both 'accelerator' and 'sail' could be designed too?

Please just stop. You should write a fiction book instead of posting here. So far in this thread you have done nothing but lie in the hopes that anonymous people might think you are cool or something and pose wildly ignorant/naive ideas as if the random shit you dream up has any bearing on reality, here in the real world, where the universe has constraints and it actually matters whether you're talking out of your ass or designing something that can be built and operated. If you want to tell stories, then tell stories. Elsewhere. Yea dude, you silver-surfered around on some sheet of metal with coils that you built that you can't really remember the details about that the military dissappeared from you. And somehow you got this device functional with only some "drawings" as reference. COME ON DUDE. Oh, and this great thing that would take at least 20,000 years to reach the nearest system assuming it can do an insertion burn after accellerating for 20,000 years could totally be better if we attached this crazy propulsion that needs to active 4 billion little particle accellerators a million times a second(by the way the largest laser currently existing on earth has a MASSIVE power plant and infrastructure assembly, and can only fire one of them once per second, will somehow make that 20,000 years even betterer, even though if it actually did exert any meaningful force, the sail would collapse from the incoming interstellar medium... Right dude... Just stop
1.7 / 5 (3) May 29, 2014
@Requiem hey whats with then. There's no need to get vulgar, don't comment about someones life of which you have no idea. And I was quoting an article from http// about 'solar sails' written by Mike Wall. Yes it may be just dreaming but it's not mine. Ha, I didn't quote the most futuristic bit...' big as Texas...' that would be a big 'sail' would it not. Read the article then complain to Mike Wall...and I don't say that I believe it, in fact...but then why should I bother explain to in reality eh? Your walls must be long, high and narrow.
There was nothing cool about the things I mentioned and did many years my parents into a lot of trouble but I don't lie...say you don't believe it, OK, but no need to call me a liar.
3 / 5 (2) May 29, 2014
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