A new mechanism for parallel electric fields in space and laboratory plasmas

Summary form only given. The existence of a new kind of pamllel electric fields supported by electron inertia has been demonstmted theoretically as well as by numerical simulations and has been successfully applied to previously unexplained space plasma observations. The essence of the mechanism is as follows. If a net positive charge is imposed locally in a plasma, it attracts neutmlizing electrons. If the plasma is collisionless, the inertia of the electrons prevents them from stopping at the point of maximum positive potential, as they would in the presence of collisions. As a consequence, the neutmlization will be incomplete. One-dimensional numerical simulations have shown that in a magnetized plasma this allows formation of stable magnetic-field aligned potentials that are tens of times as large as those which can be supported in a collisional plasma at he same electron tempemture. The voltage is established on the electron transit time and is stably maintained on the much larger time scale on which the ions are redistributed in response to the resulting positive potential. The stability is a consequence of the particular phase space distribution, which the tmpped electrons develop. Unlike previously known mechanisms, this one is tied neither to the (small-scale) Debye-length nor to the (large-scale) geomagnetic mirrors, but allows electric fields on a meso-scale determined by the imposed excess charge, which may, for example be due to artificially injected ion clouds or to natumlly occcurring waves. Unlike the case of the electric double layer, this mechanism preserves quasineutmlity.