The effect of magnetic field orientation on the structure and interaction of magnetised bow shocks in pulsed-power driven experiments

Summary form only given. We present results from magnetised bow shock experiments performed on the Magpie (~1 MA, 250 ns) pulsed-power facility. Bow shocks are formed around cylindrical conducting obstacles (diameter ~0.5 mm) positioned in a supersonic, super-Alfenic, plasma flow (M
_S
> 3, M
_A
> 2.5, V
_flow
~70 km/s). This radially diverging flow is produced by an exploding wire array z-pinch, and carries an embedded azimuthal magnetic field provided by the driving current. The bow shock structure is dramatically affected by the orientation of the obstacle with respect to the advected field. When the field lines are aligned parallel to the obstacle, the bow shock structure resembles that of a hydrodynamic bow shock. However, when the field lines lie perpendicular to the obstacle, we observe an additional bow-shaped sub-shock. This sub-shock has a large opening angle and a large stand-off distance (~1.5 mm) that is several times the obstacle radius. This sub-shock is mediated by a pileup and bending of magnetic field lines about the conducting obstacle, and appears to form indirectly via the preferential stopping of magnetised electrons in the region where the magnetic field piles up.We also discuss the interaction of multiple magnetised bow shock limbs at oblique angles. The limbs have oppositely oriented magnetic fields, and the observed geometry suggests a dramatic loss of pressure in the interaction region. This is consistent with magnetic flux annihilation lowering the magnetic pressure.