The dipole magnet of the Heavy Ion Synchrotron SIS is operated at fiel
ds of up to 1.8 T. Thus the non-linearity of the magnetisation and hys
teresis effects of the order of 0.1% cannot he neglected. The effectiv
e length is not constant, but varies with the magnetization of the mag
net. Eddy currents due to the planned high ramp rate of 4 T/s in the l
aminations, the magnet coil, and in the vacuum chamber affect the fiel
d quality of the magnet. Long time;constants of almost one second due
to field components orthogonal to tile laminations were observed.