Shocks and Instabilities in Stagnated Supersonic Magnetised Plasmas

The structure of stagnation regions formed in the interaction of supersonic plasmas with obstacles can be strongly affected by the presence of the advected magnetic field in the flow. Here, we present an investigation of stagnation layer and MHD shocks formed from super magnetosonic plasmas (□ ~ 5□, □ A ~ 2 , □ S ~ 6) colliding against planar conducting obstacles. The plasma flow (n e ~ 10 18 cm -3 , □ ~ 70 km/s) is generated by the ablation of metallic wires (Al, Cu, Ag, W) using an inverse Z-Pinch cylindrical array at MAGPIE facility (1.4MA, 240ns). In the case of Aluminium, we observe a well-defined stand-off shock at ~ 3 mm from the planar Cu wall due to the pile-up of the advected magnetic field and the development of small-scale instabilities at the stagnated plasma. No presence of stand-off shock is instead observed in Tungsten flows, where the magnetic precursor is mainly dominated by strong density perturbations with k-vector parallel to [V x B] direction, extending for ~ 5 mm from the obstacle in both the stagnation layer and the magnetic precursor. A detailed analysis of the data in the magnetic precursor region, including also Cu and Ag, suggests that resistivity and radiative cooling are responsible for the observed shock structure. These measurements will be compared with properties of stagnated plasmas formed by the collision of two counter-streaming flows in an X-Ray driven ablation platform [1] .