Scientists working at Berkeley Lab's BELLA Center nearly double their previous record set in 2014
Combining a first laser pulse to heat up and "drill" through a plasma, and another to accelerate electrons to incredibly high energies in just tens of centimeters, scientists have nearly doubled the previous record for laser-driven particle acceleration.
A snapshot of a plasma channel's electron density profile (blue) formed inside a sapphire tube (gray) with the combination of an electrical discharge and an 8-nanosecond laser pulse (red/yellow).
Credit: Gennadiy Bagdasarov/Keldysh Institute of Applied Mathematics; Anthony Gonsalves, and Jean-Luc Vay/Lawrence Berkeley National Laboratory
The laser-plasma experiments, conducted at the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab), are pushing toward more compact and affordable types of particle acceleration to power exotic, high-energy machines - like X-ray free-electron lasers and particle colliders - that could enable researchers to see more clearly at the scale of molecules, atoms, and even subatomic particles.
The new record of propelling electrons to 7.8 billion electron volts (7.8 GeV) at the Berkeley Lab Laser Accelerator (BELLA) Center surpasses a 4.25 GeV result at BELLA announced in 2014. The latest research is detailed in the Feb. 25 edition of the journal Physical Review Letters. The record result was achieved during the summer of 2018.
The experiment used incredibly intense and short "driver" laser pulses, each with a peak power of about 850 trillion watts and confined to a pulse length of about 35 quadrillionths of a second (35 femtoseconds). The peak power is equivalent to lighting up about 8.5 trillion 100-watt lightbulbs simultaneously, though the bulbs would be lit for only tens of femtoseconds.
Each intense driver laser pulse delivered a heavy "kick" that stirred up a wave inside a plasma - a gas that has been heated enough to create charged particles, including electrons. Electrons rode the crest of the plasma wave, like a surfer riding an ocean wave, to reach record-breaking energies within a 20-centimeter-long sapphire tube.
"Just creating large plasma waves wasn't enough," noted Anthony Gonsalves, the lead author of the latest study. "We also needed to create those waves over the full length of the 20-centimeter tube to accelerate the electrons to such high energy."
To do this required a plasma channel, which confines a laser pulse in much the same way that a fiber-optic cable channels light. But unlike a conventional optical fiber, a plasma channel can withstand the ultra-intense laser pulses needed to accelerate electrons. In order to form such a plasma channel, you need to make the plasma less dense in the middle.
In the 2014 experiment, an electrical discharge was used to create the plasma channel, but to go to higher energies the researchers needed the plasma's density profile to be deeper - so it is less dense in the middle of the channel. In previous attempts the laser lost its tight focus and damaged the sapphire tube. Gonsalves noted that even the weaker areas of the laser beam's focus - its so-called "wings" - were strong enough to destroy the sapphire structure with the previous technique.
Eric Esarey, BELLA Center Director, said the solution to this problem was inspired by an idea from the 1990s to use a laser pulse to heat the plasma and form a channel. This technique has been used in many experiments, including a 2004 Berkeley Lab effort that produced high-quality beams reaching 100 million electron volts (100 MeV).
Both the 2004 team and the team involved in the latest effort were led by former ATAP and BELLA Center Director Wim Leemans, who is now at the DESY laboratory in Germany. The researchers realized that combining the two methods - and putting a heater beam down the center of the capillary - further deepens and narrows the plasma channel. This provided a path forward to achieving higher-energy beams.
In the latest experiment, Gonsalves said, "The electrical discharge gave us exquisite control to optimize the plasma conditions for the heater laser pulse. The timing of the electrical discharge, heater pulse, and driver pulse was critical."
The combined technique radically improved the confinement of the laser beam, preserving the intensity and the focus of the driving laser, and confining its spot size, or diameter, to just tens of millionths of a meter as it moved through the plasma tube. This enabled the use of a lower-density plasma and a longer channel. The previous 4.25 GeV record had used a 9-centimeter channel.
The team needed new numerical models (codes) to develop the technique. A collaboration including Berkeley Lab, the Keldysh Institute of Applied Mathematics in Russia, and the ELI-Beamlines Project in the Czech Republic adapted and integrated several codes. They combined MARPLE and NPINCH, developed at the Keldysh Institute, to simulate the channel formation; and INF&RNO, developed at the BELLA Center, to model the laser-plasma interactions.
"These codes helped us to see quickly what makes the biggest difference - what are the things that allow you to achieve guiding and acceleration," said Carlo Benedetti, the lead developer of INF&RNO. Once the codes were shown to agree with the experimental data, it became easier to interpret the experiments, he noted.
"Now it's at the point where the simulations can lead and tell us what to do next," Gonsalves said.
Benedetti noted that the heavy computations in the codes drew upon the resources of the National Energy Research Scientific Computing Center (NERSC) at Berkeley Lab. Future work pushing toward higher-energy acceleration could require far more intensive calculations that approach a regime known as exascale computing.
"Today, the beams produced could enable the production and capture of positrons," which are electrons' positively charged counterparts, said Esarey.
He noted that there is a goal to reach 10 GeV energies in electron acceleration at BELLA, and future experiments will target this threshold and beyond.
"In the future, multiple high-energy stages of electron acceleration could be coupled together to realize an electron-positron collider to explore fundamental physics with new precision," he said.
Also participating in this research were researchers from UC Berkeley and the National Research Nuclear University in Russia.
This work was supported by the Department of Energy's Office of Science, the Alexander von Humboldt Foundation, and the National Science Foundation.
Founded in 1931 on the belief that the biggest scientific challenges are best addressed by teams, Lawrence Berkeley National Laboratory and its scientists have been recognized with 13 Nobel Prizes. Today, Berkeley Lab researchers develop sustainable energy and environmental solutions, create useful new materials, advance the frontiers of computing, and probe the mysteries of life, matter, and the universe. Scientists from around the world rely on the Lab's facilities for their own discovery science. Berkeley Lab is a multiprogram national laboratory, managed by the University of California for the U.S. Department of Energy's Office of Science.
DOE's 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 science.energy.gov.
Glenn Roberts Jr. | EurekAlert!
21.03.2019 | Max-Planck-Institut für Polymerforschung
Levitating objects with light
19.03.2019 | California Institute of Technology
Nano- and microtechnology are promising candidates not only for medical applications such as drug delivery but also for the creation of little robots or flexible integrated sensors. Scientists from the Max Planck Institute for Polymer Research (MPI-P) have created magnetic microparticles, with a newly developed method, that could pave the way for building micro-motors or guiding drugs in the human body to a target, like a tumor. The preparation of such structures as well as their remote-control can be regulated using magnetic fields and therefore can find application in an array of domains.
The magnetic properties of a material control how this material responds to the presence of a magnetic field. Iron oxide is the main component of rust but also...
Due to the special arrangement of its molecules, a new coating made of corn starch is able to repair small scratches by itself through heat: The cross-linking via ring-shaped molecules makes the material mobile, so that it compensates for the scratches and these disappear again.
Superficial micro-scratches on the car body or on other high-gloss surfaces are harmless, but annoying. Especially in the luxury segment such surfaces are...
The Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) at the Large Binocular Telescope (LBT) in Arizona released its first image of the surface magnetic field of another star. In a paper in the European journal Astronomy & Astrophysics, the PEPSI team presents a Zeeman- Doppler-Image of the surface of the magnetically active star II Pegasi.
A special technique allows astronomers to resolve the surfaces of faraway stars. Those are otherwise only seen as point sources, even in the largest telescopes...
Researchers at Chalmers University of Technology and the University of Gothenburg, Sweden, have proposed a way to create a completely new source of radiation. Ultra-intense light pulses consist of the motion of a single wave and can be described as a tsunami of light. The strong wave can be used to study interactions between matter and light in a unique way. Their research is now published in the scientific journal Physical Review Letters.
"This source of radiation lets us look at reality through a new angle - it is like twisting a mirror and discovering something completely different," says...
New research group at the University of Jena combines theory and experiment to demonstrate for the first time certain physical processes in a quantum vacuum
For most people, a vacuum is an empty space. Quantum physics, on the other hand, assumes that even in this lowest-energy state, particles and antiparticles...
11.03.2019 | Event News
01.03.2019 | Event News
28.02.2019 | Event News
21.03.2019 | Life Sciences
21.03.2019 | Physics and Astronomy
21.03.2019 | HANNOVER MESSE