Development of a diagnostic array for the measurement of velocity profiles across open-channel liquid metal flows

An array of potential probes utilizing the Hall effect to measure liquid metal flow velocity is developed and implemented in the Liquid Metal Experiment (LMX) at PPPL, a study of magnetohydrodynamic (MHD) stability in open-channel flow. The channel experiment has applications in the study of the dynamics of ``plasma oceans'' on the surface of neutron stars. Furthermore, liquid metal is studied as a possible material for plasma-facing components in fusion reactors, an avenue of research requiring an understanding of turbulent liquid metal flow under the influence of magnetic fields. Liquid gallium alloy circulates with a flow height of 1 cm through the open channel of dimensions 15 cm wide by 70 cm long within a uniform perpendicular magnetic field of strength up to 0.7 T. A series of 16 electrode pairs, one per centimeter from wall to wall across the width of the channel, detect potential differences across 2 mm sections of flow normal to the mean velocity and the magnetic field. For flow speeds of 0.2 m/s and magnetic field strengths of 0.1 T, a raw signal of about 40 $\mu $V is expected, which will be amplified with a gain of 1000. Velocity profiles will be measured at various heights in the flow. Design considerations, calibration procedures and results will be presented.