Evolution of the magnetic field, when the only source of magnetic energy in the ISM are stellar magnetic fields distributed by SN explosions. The curves show the results for a spherical halo in our fiducial model with a SN efficiency of α = 0.01. We show three different mean stellar field strengths: 10⁴ G (yellow dotted line), 10³ G (green dashed line) and 10² G (solid red line). With the thin gray line we further indicate the typical saturation strength of a magnetic field generated by a small-scale dynamo.