Time dependence of magnetic periodic patterns measured on the MQXA magnets for the LHC-IR

Superconducting quadrupole magnets for the LHC-IR have been developed and tested by KEK in collaboration with CERN. Magnetic field measurements of the magnets were performed. The magnets satisfy the requirements for the accelerator operation. In addition to the field quality measurements, fine structures of the magnetic field along the magnet axis were measured at the beam injection current using a 25 mm long rotating harmonic coil. Periodic patterns of the magnetic field were observed in higher order multipole coefficients. The pitch of the periodic patterns is equal to the cable twist pitch. The time dependent change of the amplitude of the periodic pattern was also observed. In this paper, the measurement and results are reported. (8 refs)