Study of time dependent magnetic field variation due to current redistribution in Rutherford cable

Time-varying magnetic field quality of superconducting accelerator magnets is a important issue of accelerator operation at particle injection. This is induced by magnetization changes of superconductors due to redistributions of imbalance current of superconducting strands in cables. Because the imbalance current and its redistributions induce time variations of magnetic periodic patterns, to clarify the mechanism of time-varying magnetic field, we performed periodic pattern measurements on quadrapole magnets for the LHC insertion regions developed by KEK in collaboration with CERN. We report the results of the measurements with various excitation processes, and describe estimation of imbalance current using numerical calculation. 10 Refs.