Axial Variations in the Magnetic Field of Superconducting Dipoles
Periodic variations in the field along the axis have been observed in a large number of superconducting dipoles. Both long and short versions of the SSC magnet have been examined as well as prototypes for the RHIC accelerator and coils from the CBA and ISABELLE projects. This field oscillation is present in all the components of the field. The period of the longitudinal pattern was found to match the conductor transposition length over a wide range of pitches. The amplitude of variation increases with time spent at high field and its decay has a complex time dependance. Unbalanced currents in the individual strands of the cable appear to be the cause of this effect and may also give rise to the unusually high sextupole drift observed near injection field in most dipoles.
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