Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Beams to Order from Table-Top Accelerators

23.08.2011
Berkeley Lab scientists achieve tunable, high-quality electron beams for laser plasma accelerators

Laser plasma accelerators offer the potential to create powerful electron beams within a fraction of the space required by conventional accelerators – and at a fraction of the cost.

Their promise for the future includes not only compact high-energy colliders for fundamental physics but diminutive sources of intensely bright beams of light, spanning the spectrum from microwaves to gamma rays – a new kind of ultrafast light source for investigating new materials, biological structures, and green chemistry.

Compared to today’s giant science facilities, “table-top” laser plasma accelerators may eventually be able to do equally powerful research with minimal environmental impact.

To reach these goals, laser plasma accelerators must be able to produce high-quality, stable electron beams and tune those beams to the users’ needs. The LOASIS program at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) has already demonstrated high-quality beams up to a billion electron volts in a mere 3.3 centimeters; the BELLA project will reach 10 billion electron volts in a single meter.

Now the LOASIS team has demonstrated a simple way to tune highly stable beams through a wide range of energies. They describe their methods in the journal Nature Physics.

Surfing the wave

“To describe how a laser plasma accelerator works, I use the analogy of a surfer riding a wave,” says Wim Leemans, who heads the LOASIS program in Berkeley Lab’s Accelerator and Fusion Research Division. “The surfers are the electrons themselves. The waves form when a laser pulse plows through a plasma.”

In a plasma, atomic nuclei (ions) are separated from electrons, and immensely strong electric fields can build up between the oppositely charged particles when they are separated by the waves behind a powerful laser pulse. Some of the electrons in the plasma are swept up by the waves and are quickly accelerated to high energy.

“In this case the wave is a tsunami, and it doesn’t much matter what the surfers do; they’ll be carried along,” Leemans says. “That’s called self-trapping. But there are other ways a surfer can catch a wave. Real surfers can gauge the size and speed of an oncoming wave and start paddling to match its momentum.”

A laser plasma accelerator uses a laser pulse (red and blue disks, extreme right) to create a wake through a plasma, creating strong electric fields. Like surfers on a wave, free electrons ride the wake and are accelerated to high energies. Only the electron bunch propelled by the first wave (white glow) is shown in this simulation. (Simulation by Jean-Luc Vay and Cameron Geddes)

Attempts to create tunable electron beams through momentum-matching have been tried, by injecting electrons into the accelerating field – first giving them a boost using colliding laser pulses to catch the wave, then using a different drive-laser pulse to excite a wave on which those surfing electrons can be accelerated to high energies. It’s an approach that demands sophisticated timing and synchronization, and along with other tuning methods for one-stage accelerators, requires electron injection that’s localized in space and time.

“But there’s a third way of helping a surfer catch a wave,” Leemans says, “and that’s by slowing the wave until even slow surfers can catch it – then increasing the speed of the wave.” In other words, a two-stage process – and this turns out to be the secret to tunable, high-quality electron beams.

For their experiments the Berkeley Lab scientists modified the same 3.3-centimeter LOASIS accelerator and the same 40-trillion-watt peak-power drive laser, dubbed TREX, they used to produce the first billion-electron-volt beam. The accelerator is a block of titanium sapphire with a narrow capillary through it, filled with hydrogen gas that’s ionized to a plasma by a jolt of electricity, just before the drive-laser pulse enters.

“Two-stage” acceleration

Slowing the laser wake and then speeding it up requires controlling the wake’s phase velocity. To modify the LOASIS system for “two-stage,” tunable acceleration, the researchers introduced a supersonic jet of helium gas that passes through the accelerator’s hydrogen-filled capillary at the upstream front end. This sharply increases the density of electrons in the subsequent plasma. The plasma density then falls off rapidly downstream.

“The extra density itself serves as a lens to focus the laser to higher intensity, and the laser is focused right where the extra density is beginning to decrease,” says Leemans. Here at the edge of the “density downramp,” the slower waves trap electrons more readily. “The waves in the wake are falling farther behind the laser pulse as it enters the region of lower density.”

Density control is only one way to control wave velocity, however. Another method is through laser intensity – an unexpected gift from Albert Einstein’s Special Theory of Relativity. Leemans explains, “The particles in the plasma waves have slowed because of the increased density, but they’re still moving relativistically, near the speed of light,”

A supersonic jet of helium gas (red, upper panel) greatly increases plasma density upstream of the hydrogen-filled capillary (blue). In the lower panel, the black curve shows density increasing, then falling off downstream. The blue curve indicates the phase velocity of the wake, slowing where the laser pulse (pink) is focused, then increasing again as density decreases.

Carl Schroeder, a theoretician with LOASIS and an author of the Nature Physics paper, says that “as the laser is focused, its intensity increases, driving larger and larger plasma waves. Larger waves increase the relativistic mass effect. This reduces the frequency of the wave and stretches the wavelength. The peaks of the waves fall even farther behind the laser pulse.”

Says experimenter Tony Gonsalves, first author of the Nature Physics paper, “If we simply end the plasma there, we have a stable low-energy accelerator. But with a second stage we can accelerate the electron beam to much higher energy, and we can tune that energy.”

The same drive-laser pulse whose wake has been slowed by plasma density and laser intensity now powers into the low-density region of the accelerator; the following waves, carrying their extra load of electron “surfers,” rapidly catch up.

“Tuning the energy is possible because by changing the density or location of the higher-density plasma, we can change its focusing power, the intensity of the laser pulse, and how much the pulse spreads out in the following lower-density plasma,” Gonsalves says. “This allows us to tune the acceleration length and the final beam energy. The stability we achieve over our tunable range is quite amazing.”

By tailoring plasma density in the two zones over the length of the accelerator, the LOASIS researchers were able to tune the energy of the electron beams over a range from 100 million electron volts to 400 million electron volts, while maintaining energy stability to within a few percent.

Leemans says, “Tailoring plasma density longitudinally this way is a concept that shows a new path to the level of sophisticated tuning for accelerators and light sources that users of conventional facilities just take for granted. It’s a major step toward perfecting the laser plasma light sources and accelerators of the future.”

“Tunable laser plasma accelerator based on longitudinal density tailoring,” by Anthony Gonsalves, Kei Nakamura, Chen Lin, Dimitriy Panasenko, Satomi Shiraishi, Thomas Sokollik, Carlo Benedetti, Carl Schroeder, Cameron Geddes, Jeroen van Tilborg, Jens Osterhoff, Eric Esarey, Csaba Toth, and Wim Leemans, appears in Nature Physics and is available online at http://www.nature.com/nphys/journal/vaop/ncurrent/full/nphys2071.html

This work was supported principally by the U.S. Department of Energy’s Office of Science, as well as the National Science Foundation and the Defense Advanced Research Projects Agency. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit http://science.energy.gov.

Lawrence Berkeley National Laboratory addresses the world’s most urgent scientific challenges by advancing sustainable energy, protecting human health, creating new materials, and revealing the origin and fate of the universe. Founded in 1931, Berkeley Lab’s scientific expertise has been recognized with 12 Nobel prizes. The University of California manages Berkeley Lab for the U.S. Department of Energy’s Office of Science. For more, visit www.lbl.gov.

Paul Preuss | EurekAlert!
Further information:
http://www.lbl.gov

More articles from Physics and Astronomy:

nachricht Engineering team images tiny quasicrystals as they form
18.08.2017 | Cornell University

nachricht Astrophysicists explain the mysterious behavior of cosmic rays
18.08.2017 | Moscow Institute of Physics and Technology

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Fizzy soda water could be key to clean manufacture of flat wonder material: Graphene

Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.

As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...

Im Focus: Exotic quantum states made from light: Physicists create optical “wells” for a super-photon

Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.

Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...

Im Focus: Circular RNA linked to brain function

For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.

While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...

Im Focus: RAVAN CubeSat measures Earth's outgoing energy

An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.

The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...

Im Focus: Scientists shine new light on the “other high temperature superconductor”

A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.

Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Call for Papers – ICNFT 2018, 5th International Conference on New Forming Technology

16.08.2017 | Event News

Sustainability is the business model of tomorrow

04.08.2017 | Event News

Clash of Realities 2017: Registration now open. International Conference at TH Köln

26.07.2017 | Event News

 
Latest News

A Map of the Cell’s Power Station

18.08.2017 | Life Sciences

Engineering team images tiny quasicrystals as they form

18.08.2017 | Physics and Astronomy

Researchers printed graphene-like materials with inkjet

18.08.2017 | Materials Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>