High resolution investigations of the electrothermal instability using advanced light sources*

The electrothermal instability (ETI) occurs in all current-driven metals, leads to development of spatially correlated temperature and density perturbations, and is the primary mechanism that seeds hydrodynamic instabilities in many pulsed-power high-energy-density experiments. As an example, it seeds the magneto-Rayleigh-Taylor instability in magnetized liner inertial fusion (MagLIF) research, as well as undesired non-uniformities during electrical conductivity measurements within warm dense plasmas produced by the exploding wire method.

 

Despite the importance of understanding the ETI, experimental study of its structure has been largely confined to measurements of surface self-emission, with no direct measurements of the density distribution. High-quality X-ray imaging capabilities offered by advanced light sources such as 3^rd and 4^th generation synchrotron storage rings and X-ray free-electron lasers can address this knowledge gap by performing measurements of the instability development on spatial scales ranging from the micrometer to millimeter and time scales of ~100 ps.

 

In this talk, I will summarise results we obtained from imaging ETI development in underwater electrically exploding wires and metallic foils at the European Synchrotron ESRF (France). The imaging features in these measurements spanned sizes from 3.2 μm to 12 mm, and unveiled the spatial structure and characteristic azimuthal correlation length scale of the ETI during its development. In addition, I will discuss a set of proposed experiments to measure the ETI at unprecedented ~ 300 nm spatial resolution using X-ray free-electron lasers. These experiments should be able to resolve the minimum wavelength required for ETI stabilization by heat conductivity, which is predicted to be on the scale of a few micrometers.