Scaling law for diffused magnetic field in an eddy current passive copper septum magnet

A scaling law for predicting diffused magnetic fields in an eddy current passive copper septum magnet, which is used for beam injection and extraction for accelerators, are examined both experimentally and theoretically. Experiments are performed with a transformer type copper septum magnet fabricated on a MnZn ferrite core. The diffusion properties of the magnetic field are measured with a pick-up coil. With a 1-mm copper septum, the measured peak leakage field level is 0.94% of the peak primary field level. To explain the leakage field level, a simple one-dimensional theoretical model, which is corrected to account for the finite size effects, is given. The model explains experimental results well, and suggests methods for reducing the leakage field level.