Observation of Rayleigh-Taylor instability growth and evolution toward longer wavelengths at a decelerating magnetized-plasma interface

The interaction of a high-Mach-number plasma jet propagating into a background magnetic field is studied experimentally on the Plasma Liner Experiment [1]. The jets, generated by plasma railguns, have densities and temperatures of order $10^{14}$~cm$^{-3}$ and 1~eV, respectively, at the time of interaction with the magnetic field ($\sim$ few hundred G). Due to ringing railgun current, the jet is comprised of a series of ``blobs'' traveling at $\sim 40$--70~km/s, arriving at the region with the applied field at $\sim 20$--30~$\mu$s intervals. When a trailing jet arrives and interacts with the remnants of the leading jet and compressed magnetic field, growing fingers are observed with a multi-frame camera at the front of the trailing jet. The fingers evolve toward longer mode wavelength ($\sim$ few cm) as the incoming jet penetrates into the magnetized region. Spectrometer and interferometer data show deceleration of the incoming jets against the lower-density magnetized background at approximately $10^{10}$~m/s$^2$. We compare experimental results to theoretical and computational predictions, showing consistency of the observations with Rayleigh-Taylor instabilities with magnetic and/or viscous stabilization.\\[4pt] [1] S. C. Hsu et al., Phys. Plasmas 19, 123514 (2012).