To investigate the electrical properties of the joint between superconducting multifilamentary wires, we applied a radio frequency superconducting quantum interference device (r.f.-SQUID) voltmeter to measure the extremely small voltage induced across the joint. We measured the time variation of both the current induced in a loop of superconducting wire and the voltage induced across the joint. A voltage sensitivity in the pico-volt range was obtained with this apparatus. Comparisons of currentdecay between superconducting loops with soldered, spot-welded and cold-welded joints were made. A flux creep-like phenomena was seen in the current-decay for the coldwelded and spot-welded joints.
An optimal design method for magnets with double-layered coaxial coils to generate a uniform central magnetic field and a small stray magnetic field has been proposed. To find the optimal current density distribution, we used linear programming with constraints on the multipole field strengths, computed with analytical formulae, of the central and stray fields. The final coil positions were optimized with a quasi-Newton method, again taking into account the inner and outer multipole field strengths.Index Terms-Linear programming, optimization, quasiNewton method, uniform magnetic field.
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