title: Self-consistent generation of superthermal electrons by beam-plasma interaction.
abstract: It has been known since the early days of plasma physics research that superthermal electrons are generated during beam-plasma laboratory experiments. Superthermal electrons (the kappa distribution) are also ubiquitously observed in space. To explain such a feature, various particle acceleration mechanisms have been proposed. However, self-consistent acceleration of electrons in the context of plasma kinetic theory has not been demonstrated to date. This Letter reports such a demonstration. It is shown that the collisionality, defined via the "plasma parameter" g=1/n(lambda(D)(3), plays a pivotal role. It is found that a small but moderately finite value of is necessary for the superthermal tail to be generated, implying that purely collisionless (g=0) Vlasov theory cannot produce a superthermal population.
authors.affiliation: Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742, USA.
authors.forename: Peter H
authors.initials: PH
authors.lastname: Yoon
authors.forename: Tongnyeol
authors.initials: T
authors.lastname: Rhee
authors.forename: Chang-Mo
authors.initials: CM
authors.lastname: Ryu