Remote sensing of Induced Current in Magnetic Czochralski Crystal Growth

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(1) Establishment of the Measurement PrincipleBased on Biot-Savart Law and the current induced by the movement of a conducting top in magnetic field, we have calculated the induced secondary magnetic field at arbitrary points outside of the top.(2) Measurement of the Induced FieldUsing solid gallium and liquid gallium as specimen materials, we have measured the induced magnetic field. Solid gallium made a symmetrical large field which is predicted by the theory involving shunt effect. But liquid gallium made a small, nonsymmetrical, complex field. which requires more comprehensive analysis.(3) Measurement of Temperature Rising by the Joule's HeatSince the estimation of the induced current through magnetic field is an inverse problem, we need another way of estimation to assure the uniqueness of the solution. As another approach we measured the surface temperature of the top with time by the infrared thermometer and compared the data with the electric current data. Both data coincide qualitatively. We are continuing more quantitative examination.(4) Development in FutureBy analyzing the saturation and the decrease effect of the induced current density with increasing applied magnetic field, we would understand the suppression mechanism of the flow by the magnetic field. We are also planning to catch the induced current more directly by probing the potential of the surface of rotating top and to calibrate the remote sensing data.