Dynamo generated magnetic fields for various values of D and L when the seed field is concentrated solely in the inner disc. The ring half-width d = 1 kpc in all cases. The upper panel shows the magnetic field for t = 10¹⁰yr when the dynamo number D = 20, the lower shows the same for D = 50. The solid curves are for the gap extent L = 1 kpc, the dashed curves for L = 2 kpc, and the dot-dashed curves are for L = 3 kpc.