Speaker
Description
The electrothermal instability (ETI), ubiquitous in materials which carry large currents, is driven by the dependence of the material resistivity on temperature. The filamentation mode of the instability occurs in plasmas, where the gradient of the Spitzer resistivity with temperature is negative, and results in non-uniform filaments of hot, current-dense plasma. The ETI is potentially significant for a variety of pulsed power applications since its growth rate depends on the current density squared.
Previous studies have shown that this instability may limit the utility of exploding wires, z-pinches, and magnetized liner implosions. However, these studies often neglect losses such as Coulomb collisions, thermal conductivity, and radiation. Furthermore, the saturation mechanism of the instability has not been carefully studied, so it is unclear what the final state of the plasma will be.
In this study, we conduct idealized 2D simulations of a current-carrying plasma subject to the electrothermal instability. A steady state plasma is initialized in the domain, where Ohmic heating is balanced by collisional and/or radiative losses. The growth rate predicted by linear theory is assessed, where a peak growth rate appears that is dependent on the wavenumber, k. The instability is triggered by a small sinusoidal perturbation in the current density at this peak wavenumber and the resulting growth rate is compared with linear theory. Later in the simulation, harmonics of the original perturbation wavelength appear, leading to nonlinear saturation of the instability. Implications of this saturation and the final state of the plasma are discussed in the context of pulsed power plasmas.
Acknowledgements: This work was sponsored by the US Naval Research Laboratory Base Program.
Distribution Statement A. Approved for public release. Distribution is unlimited.
