*

The PBEX (Plasma Bubble Expansion EXperiment) utilizes a compact coaxial plasma gun and a linear plasma device  to  study magnetic  relaxation and other dynamics of dense plasma jets and bubbles propagating in background magnetized plasma. In previous experiments, high-speed multiframe imaging  suggested the presence of magneto-Rayleigh-Taylor (MRT) instabilities of cm- and microsecond-scales. Both  B-dot  and   multi-tip Langmuir probe in-situ measurements of the magnetic field, ion density and temperature are being used to characterize the instabilities, as well as the global dynamics.  These data are  also being compared with ongoing MHD Modeling of flux-rope expansion using the University of Michigan’s BATS-R-US code.  Measurement, simulations results, and comparisons, will be presented.