The Instrumentation of the NMIMT Sodium α&#969-Dynamo Experiment

The NMIMT α&#969-Dynamo Experiment depends upon the formation of near-stable high speed Couette flow ( 60 m/s) in liquid sodium between a 60cm outer and 30cm inner co-rotating cylinders. The resulting high Reynolds number, Re 10⁷ means that the Ekman flow is small, 1/Re^1/2, so that both the turbulence and the resulting torque are small, both important for a sodium α&#969-dynamo experiment. We measure these initial conditions at two levels of signal gain, within the outer cylinder and in the rotating frame: the pressure and fluctuating pressure at 5 radii, the temperature in 4 locations, and the sodium level at one location. When a magnetic field is applied, either axial or radial, we measure three components of the magnetic field at 6 radial locations in the mid plane using Hall detectors (18). The cycle time of the sampling, digital conversion, and computer storage of all 28 signals is 10⁴ Hz. The electronics must operate in a centrifugal field of 1000g and temperatures up to 110 C. The differential analogue signals are selected by a multiplexer, amplified, digitized, converted to serial signals and capacitively transmitted across spaced slip rings to the computer. Stationary signals are similarly processed including two tachometers, the differential torque between inner and outer cylinders, three coil currents, differential magnetic flux, (dB/dt), DC torque motor current and voltage, AC motor current and torque, 9 temperatures, axis pressure, (27 channels of stationary data). This work was supported by the cooperative agreement between the New Mexico Institute of Mining and Technology, the University of California, Los Alamos National Lab, and the DOE.