Mini-accelerator breaks world record

Table-sized plasma laser accelerates particles for the first time to 4.25 Gigaelektronenvolt

In this setup, the laser pulses were shot to accelerate the electrons in the plasma. © Roy Kaltschmidt
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Lasers instead of magnets: With a particle-size laser particle accelerator, US researchers have for the first time accelerated electrons down to 4.25 galtaeletronvolts - a world record. This was achieved by ultrashort laser pulses shot in a plasma tube only a few centimeters long. The experiment proves that laser plasma accelerators may well be an alternative to the kilometer-long conventional particle accelerators, the researchers emphasize in the journal "Physical Review Letters".

Particle accelerators are usually one thing above all else: huge. To bring protons and other particles close to the speed of light, powerful electromagnets are used in kilometer-sized accelerator rings. Among other things, this technology is used in the world's largest accelerator, the Large Hadron Collider (LHC) at CERN, and for the generation of synchrotron radiation in free electron lasers).

But these particle accelerators have their limits: they can not reach more than 100 megaelectron volts (MeV) per meter of distance before the material gives way. Therefore, the more powerful they should be, the longer they have to be. But there is another way: with laser beams.

Laser pulses generate suction in the plasma

So-called laser plasma accelerators use no magnets, but short, extremely high-energy laser pulses, which are shot in a narrow channel with plasma. The pulses release electrons from the plasma and at the same time create a so-called electric field, dragging the particles behind them and thereby accelerating them.

This simulation shows the suction field of the laser pulse in the nine-centimeter plasma channel © Berkeley Lab

The big advantage: These laser plasma accelerators require only a few centimeters of pipe length. The entire structure therefore has room on a table. In addition, the restriction to 100 MeV per meter does not apply to this technique. The performance of these mini-accelerators has now been proven by Wim Leemans of the Lawrence Berkeley National Laboratory and his colleagues. display

World record in the plasma tube

For their experiment, the researchers sent ultra-short, only 40 femtosecond laser pulses of 300 Terawatt power through an extremely thin, about nine centimeters long tube with plasma. As it turned out, the electrons entrained in this way were accelerated to energies of 4.25 gigaelectronvolts more than ever before with a laser-plasma accelerator. This acceleration already corresponds to that achieved in synchrotron systems such as the accelerator ring DESY in Hamburg.

Due to the distance of only a few centimeters, the gradient of the acceleration is the distance that the particles need from zero to extremely fast which is a thousand times higher than the conventional large particle accelerator. "This experiment demonstrates that laser pulses of a few hundred terawatts can generate electron beams of several gigaelectron volts, " the researchers say.

Accelerator for all

"The results of Leemanns and his colleagues is a substantial step forward, " comments physicist Georg Korn of the European project Extreme Light Infrastructure (ELI). That's because the only table-sized laser accelerators achieve performances that compete with conventional technology. If one shifts several such laser units in succession, they could accelerate particles up to the terael electron volt range and thus as strongly as the LHC and other giant accelerators.

"The electron beam demonstrated here could, for example, be used to operate a free-electron laser in the X-ray region (XFEL), " explains Korn. Except that this laser-powered structure would only be about 30 meters long, instead of the otherwise necessary kilometer-long pipes. In addition, the small accelerators provide a wealth of new experiments that would otherwise be prohibitively expensive for many universities and research institutes. (Physical Review Letters, 2014; doi: 10.1103 / PhysRevLett.113.245002)

(DOE / Lawrence Berkeley National Laboratory, 10.12.2014 - NPO)