Modeling of eddy current effects in an opposite-field septum

An opposite-field septum magnet system has been developed at KEK; this system has advantages such as a force-free structure for the septum conductor and the easy pulsed operation. This system can be used for a 50-GeV main ring (MR) injection system, which delivers a high-intensity 3-GeV proton beam to the MR. To accommodate the large-sized injection beam, the magnet system is equipped with a large aperture and thin septum. The magnet system comprises three parts: a long opposite-field septum magnet and two short sub-bending magnets. However, the problem arising from this geometry is that the eddy current effects of individual magnets are different, which causes an error field for the circulating beam and affects the magnets’ performance. This study quantitatively investigates the eddy current behavior in two different ways: 3D transient simulation by the ELEKTRA code and an equivalent circuit simulation. We present a method for introducing an additional self-induced current to decrease the error field. Field measurements have been carried out, thereby confirming the simulation results.