Eddy current effects in an opposite-field septum

A large aperture, thin-septum, high-field opposite-field septum magnet has been developed for the injection of 50 GeV main ring of J-PARC. Due to the eddy current generated in septum conductor, magnet yoke and magnet end plate, the field quality was degraded. In the paper, eddy current effects on the field distribution are discussed. Correction methods and experiment results are introduced.