Protostars and Planets VI, Heidelberg, July 15-20, 2013

Poster 2S051

Nonlinear Ohm’s Law: Electric-Field Heating of Plasmas in Protoplanetary Disks

Okuzumi, Satoshi (Tokyo Institute of Technology)
Inutsuka, Shu-ichiro (Nagoya University)

Abstract:
Magnetic resistivity plays crucial roles in MHD of protoplanetary disks. It is commonly assumed that electric fields (in the neutral-gas rest frame) are so weak that they have no effect on the kinetics of ionized gases. However, an estimate shows that the E-field induced by MRI turbulence can become strong enough to heat up free electrons (Inutsuka & Sano 2005). We construct a simple charge-reaction model that takes into account the E-field heating of weakly ionized plasmas as well as the impact ionization of the gas by hot electrons. Our model calculations show that the heating promotes the adsorption of electrons onto dust grains, resulting in an enhancement of the resistivity up to factor 10^3. This “anomalous” resistivity may perhaps determine the saturation level of MRI-driven turbulence.We also find that a very high E-field causes an abrupt increase in the electric current (“electron avalanche”) as predicted by Inutsuka & Sano. However, this solution is found to be unstable in some cases.

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