Debye screening under non-equilibrium plasma conditions

¹ Argelander Institut für Astronomie, Universität Bonn Auf dem Hügel 71, 53121 Bonn, Germany
e-mail: hfahr@astro.uni-bonn.de
² Deutsches Zentrum für Luft und Raumfahrt (DLR), Königswinterer Str. 522–524, 53227 Bonn, Germany
e-mail: michael.heyl@DLR.de

Received: 6 January 2016
Accepted: 16 March 2016

Abstract

As has been revealed in a number of more recent astrophysical papers, in most of the tenuous space plasmas Maxwellian distribution functions cannot be expected for ions or electrons because of the lack of efficient relaxation processes. Many of the classical characteristics of plasmas, such as plasma frequency or Debye length, are calculated on the basis of the assumption, however, that Maxwellians prevail, which under most of the relevant astrophysical plasma conditions is not the case. We here therefore consider this specific problem of Debye shieldings of single charges in a plasma for the case of prevailing non-equilibrium distribution functions for ions and electrons. As typical non-equilibrium functions, so-called Kappa functions were considered with clear preference, and we therefore study here the Debye shielding in a plasma with Kappa-distributed electrons and ions. We show that the so-called Debye shielding increases with increasing extent of the high-velocity tail of the electron distribution function, or in other words, with lower Kappa index of the underlying Kappa function. In our calculations we demonstrate that the Debye lengths become enlarged by about a factor of 10 with respect to its classically expexted value if highly suprathermal electron distributions prevail with Kappa indices close to 1.5.