  We present the first simultaneous mapping of two-dimensional, time-dependent
velocity and pressure fields in a plane Couette flow pervaded by a transverse
magnetic field. While electromagnetic forces are strongest in fluids of high
electric conductivity such as liquid metals, their opacity excludes optical
optical measurement methods. We circumvent this difficulty using a transparent
electrolyte (Sulfuric acid), whose weaker conductivity is offset by higher
magnetic fields. We describe an experimental rig based on this idea, where the
Couette flow is entrained by a tape immersed in sulfuric acid and positioned
flush onto the bore of large superconducting magnet, so that most of the flow
is pervaded by a sufficiently homogeneous transverse magnetic field. Velocity
and pressure fields are obtained by means of a bespoke PIV system, capable of
recording the fluid's acceleration as well as its velocity. Both fields are
then fed into a finite difference solver that extracts the pressure field from
the magnetohydrodynamic governing equations. This method constitutes the first
implementation of the pressure PIV technique to an MHD flow. Thanks to it, we
obtain the first experimental velocity and pressure profiles in an MHD Couette
flows and show that the transitional regime between laminar and turbulent
states is dominated by near-wall, isolated, anisotropic perturbations.
