Magnetic Field Generation and Reconnection in High Energy Density Plasmas

Abstract

Throughout this thesis, we investigate the dynamics of magnetized high energy density (HED) plasmas. This work focuses on magnetic field generation via the Biermann battery effect and the Weibel instability, as well as magnetic reconnection; our findings have significant implications for recent and on-going HED magnetic reconnection experiments as well as more broadly for astrophysical plasmas and inertial confinement fusion. In particular, we develop the first 3-D fully kinetic simulations of self-magnetized ablating plasmas, characterizing magnetic field generation in recent experiments due to the Biermann battery effect at modest laser focal radii (R_h >> 10 d_i). We proceed to discover and investigate how the ion Weibel instability dominates field generation at larger system size (R_h >> d_i), and quantitatively verify how the filamentation is driven by counterstreaming between the ablation plasma and a sparse background. We find evidence of this instability in recent Omega EP shots in quantitative agreement with simulation predictions; such filamentation (~ 100 T, 300 um) will likely be present in large HED systems such as in inertial confinement fusion experiments. In 3-D simulations, we observe how the ablation of the two adjacent plasmas drives the formation of a current sheet, where magnetic reconnection occurs in a strongly time-and-space-dependent manner. We find evidence of a novel 3-D reconnection mechanism, which we refer to as Biermann-mediated reconnection, where localized heating in the reconnection layer coupled with the out-of-plane ablation density profile conspires to reconnect flux via the Biermann battery effect. We quantify this effect and explore its relevance in space reconnection scenarios. In comparing 2-D and 3-D simulations, we find that a relative lack of compression in 3-D leads to slower reconnection rates. Finally, we provide insight into two recent HED reconnection campaigns at the NIF and Omega EP facilities, yielding predictions of development of the current sheet at NIF, and exploring the current sheet development conditions that led to the likely observation of a multi-plasmoid reconnection on Omega EP.