Experimental Investigations of the Electrothermal Instability using the Mykonos Linear Transformer Driver

The electrothermal instability (ETI) has been theorized to amplify density and temperature perturbations on ohmically heated surfaces that compromise magneto-inertial fusion and flyer plate applications. Only recently, facilitated by thin dielectric coatings which suppress plasma formation, has the ETI been demonstrated to exist on thick metal [1]. We present the results of new experimental investigations into the ETI performed in June on the Mykonos LTD, which delivers 850 kA to dielectric-coated 800-um-diameter aluminum rods in approximately 70 ns. Rods were carefully machined with different machining spectra, and several dielectric thicknesses were tested. 12-Frame ICCD imaging, Streaked Visible Spectroscopy and Photon Doppler Velocimetry diagnostics were fielded. These diagnostics permit calculation of surface temperature and early-time radial expansion of the rod surface, as well as ETI growth rates. The experimental setup, collected data, and analysis will be shown.

[1] T.M. Hutchinson, T.J. Awe, B.S. Bauer, K.C. Yates, E.P. Yu, W.G. Yelton, and S. Fuelling. Phys. Rev. E 97 053208 (2018).