The effect of axial magnetic field on electrothermal instability-driven overheating: simulation and experiment

An externally applied axial magnetic field (B_z) benefits performance of magneto-inertial fusion concepts (e.g., MagLIF) by reducing thermal losses from the fuel and possibly mitigating magnetohydrodynamic (MHD) instabilities in the imploding metallic liner. However, the physics of B_z applied to current-driven metal requires deeper understanding. For instance, MagLIF implosions exhibit a helical mode, the origin of which remains an open research question. The engineered defect (ED) platform on the 1-MA Mykonos Facility at Sandia National Laboratories has proven to be an effective tool for understanding the early-time physics of current-driven metal. Hemispherical divots machined onto ultrasmooth metal rods drive enhanced Joule heating due to the electrothermal instability, resulting in distinctive visible emission patterns. Recently, the ED platform has been upgraded to allow application of time-varying B_z. In this work, we report on simulations (using the MHD code ALEGRA) of ED evolution modified by B_z and compare these predictions with recent experiments.