Friday, March 8th, 2024, 12:30 pm
Title: Fast magnetic reconnection experiments at the National Ignition Facility: flux annihilation and electron heating
Speaker: Vicente Valenzuela Villaseca (Princeton University)
Abstract: Magnetic reconnection is a fundamental plasma process whereby two merging flows with oppositely oriented magnetic fields drive the reconfiguration of the field topology inside a current sheet, which rapidly converts magnetic into kinetic energy. This ubiquitous process is key to understanding a wide range of systems, such as coronal mass ejections in the Sun, Active Galactic Nuclei flares, and sawtooth crashes in tokamaks. One of the outstanding questions in magnetic reconnection regards the energy partition between thermal heating, bulk acceleration, and non-thermal particles.
In this talk, I will present results from a dedicated laser-driven magnetic reconnection laboratory platform fielded at the National Ignition Facility (NIF). Two highly extended plasma plumes are produced by tiling a total of 40 laser beams which become self-magnetized through the Biermann battery effect. As they collide, they form a reconnecting current sheet in the interaction region with a high aspect ratio ~100.
The magnetic field structure and evolution is probed using proton radiography with inertial confinement fusion capsules as backlighters, which show a peak plume line-integrated magnetization ~ 7.5 T⋅mm. The out-of-plane dynamics was studied using gated X-ray detectors, finding significant electron heating; however we also find that conversion of magnetic to thermal energy is insufficient to explain the observed temperature increase. I will discuss the role of electron-ion Coulomb collisions in a background of free-streaming ions and show that they may account for the anomalous heating found in these experiments.