Interaction between Current Imbalance and Magnetization in LHC cables

Abstract-The quality of the magnetic field in superconduc-ting accelerator magnets is associated with the properties of the superconducting cable. Current imbalances due to coupling cur-rents AI, as large as 100 A, are induced by spatial variations of the field sweep rate and contact resistances. During injection at a constant field all magnetic field components show a decay beha-vior. The decay is caused by a diffusion of coupling currents into the whole magnet. This results in a redistribution of the trans-port current among the strands and causes a demagnetization of the superconducting cable. As soon as the field is ramped up again after the end of injection, the magnetization rapidly re-covers from the decay and follows the course of the original hys-teresis curve. In order to clarify the interactions between the changes in current and magnetization during injection we per-formed a number of experiments. A magnetic field with a spa-tially periodic pattern was applied to a superconducting wire in order to simulate the coupling behavior in a magnet. This model system was placed into a stand for magnetization measurements and the influence of different powering conditions was analyzed. Index Terms-Field component decay, Magnetization mea-surements, Snapback, Superconducting accelerator magnets