Effect of the Prandtl number Pr on the instability. (a) Nonaxisymmetric (solid lines) and axisymmetric toroidal (dashed lines) magnetic energies as a function of time in runs S3–S6 (Re = 5 × 10⁴, Pm = 1, 𝒩 = 10, and different values of Pr as indicated in the legend). Only the nonaxisymmetric energy is shown for run S6 at Pr = 10⁻². (b) Toroidal magnetic energy at radius r/r_o = 0.5 as a function of time for the azimuthal modes m = 0 − 6 for the stable run S6.