Dynamics of the Magnetoviscous Instability

In dilute astrophysical plasmas, the collisional mean free path of a particle can exceed its Larmor radius. Under these conditions, the thermal conductivity and viscosity of the plasma can be dramatically altered. This alteration allows outwardly decreasing angular velocity or temperature gradients to become strongly destabilizing. This paper generalizes an earlier, simple analysis of the viscosity instability by including the dynamical effects of magnetic field line tension. Such effects lower the growth rates found in the absence of such tension but still allow growth rates in excess of the maximum of the standard magnetorotational instability. We find very good quantitative agreement with more complex kinetic treatments of the same process. The combination of large growth rates and large magnetic Prandtl number suggests that protogalactic disks are powerful dynamos.