New type of magneto-rotational instability in cylindrical Taylor-Couette flow

We study the stability of cylindrical Taylor-Couette flow in the presence of combined axial and azimuthal magnetic fields, and show that adding an azimuthal field profoundly alters the previous results for purely axial fields. For small magnetic Prandtl numbers Pm, the critical Reynolds number Re_c for the onset of the magneto-rotational instability becomes independent of Pm, whereas for purely axial fields it scales as Pm^{-1}. For typical liquid metals, Re_c is then reduced by several orders of magnitude, enough that this new design should succeed in realizing this instability in the laboratory.