Abstract
A large class of Laboratory, Space, and Astrophysical plasmas is nearly collisionless. When a localized energy or particle sink, such as a radiative cooling spot or a black hole, is introduced into such a plasma, it can trigger a plasma thermal collapse, also known as a thermal quench (TQ) in tokamak fusion. Such TQ in a tokamak disruption not only brings a thermal load management issue at device walls but also determines the runaway seeding for the subsequent current quench. Therefore, understanding the TQ in such an exotic regime with extreme plasma kinetics, which have been largely missed in previous studies, is critical for disruption mitigation.
By employing kinetic VPIC simulations and analytical theory, we have demonstrated an entirely different physical picture of how such TQ is accomplished, revealing three striking underlying parallel transport physics: 1) TQ is dominated by convective energy transport as opposed to the conductive one and thus TQ comes in the form of four propagating fronts with distinct characteristic physics; 2) the TQ inevitably has a transition from collisionless phase to collisional phase; 3) two collisionless mechanisms, including wave-particle interactions, enable fast perpendicular electron temperature cooling that closely track the crash of the parallel one.
Bio
Yanzeng Zhang, Ph.D.
Staff Scientist
Los Alamos National Lab
Dr. Yanzeng Zhang is a Staff Scientist in the Applied Mathematics and Plasma Physics Group in the Theoretical Division at the Los Alamos National Laboratory. Prior to this appointment, he was a Director’s Postdoc Fellow in the same group. He received a Ph.D. in Plasma Physics from the University of California San Diego (UCSD) in 2020.
His research interests span a wide range of topics in plasma physics leveraging theoretical analysis and numerical simulations, including the tokamak edge plasmas, tokamak disruptions, plasma particle and power exhaust, plasma instabilities, wave-particle interactions, and laser plasma interactions.