A new method for determining the magnetization of superconducting cables and its time dependence

A method is described for determining the average magnetization of several meters of Rutherford-type cable used in the superconducting magnets of the proton-electron collider HERA. Fifty-six cable sections of 300-mm length are mounted in two 90 degrees sectors on a stainless steel tube and inserted in a superconducting dipole coil, providing a magnetizing field of up to 5 T. The magnetized NbTi filaments in the sample generate dipole and decapole fields inside the tube of 1-2 mT. The dipole component is obtained from a longitudinal scan with a nuclear magnetic resonance (NMR) probe, subtracting the background field of the magnet. The superconductor magnetization was determined with a precision of 3%. The decapole field of the magnetized cable sample, measured with a fivefold rotating pickup coil, was well suited to study time dependences as it was almost two orders of magnitude larger than the persistent-current decapole of the dipole magnet. A weak logarithmic time dependence was observed, compatible with thermally activated flux creep in the superconductor.<
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