Theoretical analysis and computer simulation of eddy-current septum magnets

The stray field of eddy current septum magnets is analyzed theoretically and also simulated by a computer program. The results from theoretical analysis agree well with those simulated from OPERA program. The maximum of stray field varies inversely with the thickness of septum. It delays some time with respect to the maximum of main field, and the delay time is proportional to square of the thickness of the septum. After stray field increases to its maximum, it starts to decrease very slowly to zero. To reduce stray field fast, one can adopt full sine wave pulse current to power the magnet, The stray field can be reduced to 0.2% at any position and any time by using composite septum (2. 4mm Cu + 0. 6mm Fe). The homogeneity of the main field is superior to 1 %.