Impression d’artiste (pas à l’échelle) idéalisant la façon dont le vent solaire façonne les magnétosphères de Vénus (en haut), de la Terre (au milieu) et de Mars (en bas). Crédit : ESA
Première mesure expérimentale des écoulements d’électrons purs associés à la reconnexion magnétique pilotée par la dynamique des électrons dans des plasmas produits par laser.
Les reconnexions magnétiques dans les plasmas produits par laser ont été étudiées afin de mieux comprendre la dynamique microscopique des électrons, qui est pertinente pour les phénomènes spatiaux et astrophysiques. Des scientifiques de l’université d’Osaka, en collaboration avec des chercheurs du National Institute for Fusion Science et d’autres universités, ont rapporté les mesures directes des flux d’électrons purs liés à la reconnexion magnétique à l’aide d’un laser de haute puissance, Gekko XII, à l’Institute of Laser Engineering de l’université d’Osaka au Japon. Leurs résultats seront publiés aujourd’hui (30 juin 2022) dans Springer Nature, Scientific Reports.
La reconnexion magnétique est un processus fondamental dans de nombreux phénomènes spatiaux et astrophysiques tels que les éruptions solaires et les sous-orages magnétiques, où l’énergie magnétique est libérée sous forme de plasma energy. It is known that electron dynamics play essential roles in the triggering mechanism of magnetic reconnection. However, it has been extremely challenging to observe the tiny electron scale phenomena in the vast universe.
(a) Schematics of the experiment. By irradiating a plastic target with the Gekko XII laser, plasma flow is generated in the presence of a weak magnetic field. The weak magnetic field is distorted by the dynamic pressure of the plasma flow and the anti-parallel magnetic configuration is created. (b) The insert schematically shows that the elongated magnetic field reconnects and releases the magnetic field energy as the reconnection outflows. Pure electron outflows have been measured with CTS for the first time in laser-produced plasmas. Credit: 2022 K. Sakai et al. Direct observations of pure electron outflow in magnetic reconnection. Scientific Reports
Therefore, the scientists created situation-only electrons directly coupled with a magnetic field in laser-produced plasmas. The so-called laboratory astrophysics allows scientists to access the miniature universe.
“In space plasmas, the key players sometimes hide in the small scale. It is very difficult to see their actions in large-scale space phenomena, even via cutting-edge numerical simulations,” study author Toseo Moritaka explains. “Now laser experiments can arrange a new stage to shed light on their actions. The results will bridge various observations and simulations in macroscopic and microscopic points of view.”
By using collective Thomson scattering measurements, the pure electron outflow associated with the electron-scale magnetic reconnection has been measured in laser-produced plasmas for the first time.
“The outcomes of this research are applicable not only to space and astrophysical plasmas, but also to magnetic propulsion of spacecrafts and also fusion plasmas,” study lead author Yasuhiro Kuramitsu explains. “Microscopic electron dynamics governs macroscopic phenomena, such as magnetic reconnections and collisionless shocks. This is a unique and universal property of plasma, which is not seen in ordinary gas and liquid.
“Now we can address this in laboratories by direct local measurements of the plasma and magnetic field. We will tackle long-standing open problems in the universe by modeling them in laboratories. Knowing the nature of plasmas may lead us to realize, for example, fusion plasma.”
Reference: “Direct observations of pure electron outflow in magnetic reconnection” 30 June 2022, Scientific Reports.
DOI: 10.1038/s41598-022-14582-3
Funding: Japan Society for the Promotion of Science, Ministry of Education, Culture, Sports, Science and Technology-Japan
