Mechanisms of conversion of kinetic into magnetic energy in partially ionized plasmas

The processes involved in the transformation of kinetic into magnetic energy in partially ionized compressible plasmas are not limited to the well-known mechanism of transport and diffusion of single-fluid magnetohydrodynamics. The induction equation, in this new case, may be written for any mean of the ion and electron velocities, and it possesses a natural scaling parameter equal to the ratio of the electron and ion masses. This produces a hierarchy of sources able to generate a magnetic field. The first of these sources corresponds to the classical stretching of magnetic field lines by the flow and ohmic diffusion, and a compressional effect due to the flow of electromagnetic energy into the regions of higher density. A potentially important effect is caused by dragging of electrons by neutral particles through collisions; this term could dissipate as well as enhance the magnetic field depending on the geometry of the neutral flow. Finally, there exists a term analogous to the stretching one, this time involving the current density and with the opposite effect. Its presence implies that not only the magnetic field but also the current density grows at most exponentially with a growth rate bounded by the maximum of the strain matrix. While the effect of these nonclassical sources, acting alone, is in all probability extremely small, they could be relevant in the creation of seed magnetic fields for subsequent dynamo action.