June 23, 2020
By Audrey-Maude Vézina
An international team of researchers is the first to experimentally demonstrate the “Weibel” instabilities predicted by theory about 50 years ago, in the prestigious journal Nature Physics. These instabilities produce a magnetic turbulence which, in an astrophysical setting, could be responsible for the acceleration of cosmic rays and the emission of gamma photons in the famous “gamma-ray bursts”.
Julien Fuchs, a graduate of the Institut national de la recherche scientifique (INRS) and a researcher at the Laboratoire pour l’utilisation des lasers intenses (LULI) in France, INRS Professor Patrizio Antici, a specialist in laser-driven particle acceleration, and INRS Professor Emeritus Henri Pépin have succeeded in measuring the magnetic fields produced by Weibel instabilities created within a laser-driven plasma, an ionized gas. Their results were published on June 1 in the prestigious journal Nature Physics.
The researchers used laser accelerated protons radiography to be able to visualize this extremely rapid phenomenon. “Our protons accelerated by laser-plasma interaction are able to take a sequence of images of a very fast electromagnetic phenomena, in the order of pico seconds, with a resolution of a few microns. This allows us to probe instabilities with precision unmatched by other imaging techniques,” reports Patrizio Antici, who did his thesis under the supervision of Professor Fuchs, himself formerly under the direction of Professor Pépin.
These three generations of researchers recreated a “small-scale model” of astrophysical phenomena in the laboratory by irradiating a target with an intense laser. The magnetic fluctuations generated by the interaction can be probed by protons on a series of sensitive films, producing a sequence of images of the resulting magnetic structures.
The interpretation and modeling of these structures were conducted in collaboration with a team of physicists from the Commissariat à l’énergie atomique et aux énergies alternatives (CEA) led by Laurent Gremillet. By combining theoretical modelling and advanced numerical simulations, and after nine years of hard work, they highlighted two variants of Weibel’s instability according to the region of the plasma.
With more powerful lasers, researchers will be able to analyze even more extreme astrophysical phenomena with unrivaled resolution.