The Braginskii model of the Rayleigh-Taylor instability. I. Effects of self-generated magnetic fields and thermal conduction in two dimensions

TL;DR

This study uses the Braginskii model to simulate the Rayleigh-Taylor instability in two dimensions, revealing the significant roles of self-generated magnetic fields and thermal conduction in the instability's evolution and structure.

Contribution

It implements and verifies Braginskii physics modules in RTI simulations, demonstrating the effects of magnetic fields and thermal conduction on instability dynamics and morphology.

Findings

Magnetic fields reach up to 11 MG without thermal conduction.

Thermal conduction reduces RTI growth rate by about 20%.

Self-generated magnetic fields are comparable to experimental observations.

Abstract

(abridged) There exists a substantial disagreement between computer simulation results and high-energy density laboratory experiments of the Rayleigh-Taylor instability Kuranz et al. (2010). We adopt the Braginskii formulation for transport in hot, dense plasma, implement and verify the additional physics modules, and conduct a computational study of a single-mode RTI in two dimensions with various combinations of the newly implemented modules. We find that magnetic fields reach levels on the order of 11 MG in the absence of thermal conduction. We observe denting of the RT spike tip and generation of additional higher order modes as a result of these fields. Contrary to interpretation presented in earlier work Nishiguchi (2002), the additional mode is not generated due to modified anisotropic heat transport effects but due to dynamical effect of self-generated magnetic fields. The main effects of thermal conduction are a reduction of the RT instability growth rate (by about 20% for conditions considered here) and inhibited mixing on small scales. In this case, the maximum self-generated magnetic fields are weaker (approximately 1.7 MG). These self-generated magnetic fields are of very similar strength compared to magnetic fields observed recently in HED laboratory experiments Manuel et al. (2012). We find that thermal conduction plays the dominant role in the evolution of the model RTI system considered. It smears out small-scale structure and reduces the RTI growth rate. This may account for the relatively featureless RT spikes seen in experiments, but does not explain mass extensions observed in experiments. Resistivity and related heat source terms were not included in the present work, but we estimate their impact on RTI as modest and not affecting our main conclusions. Resistive effects will be discussed in detail in the next paper in the series.