J. Plasma Physics (2000), vol. 64, part 4, pp. 427–431. Printed in the United Kingdom  2000 Cambridge University Press 427 Sheared-flow-driven vortices in a magnetized dusty electron–positron plasma P. K. SHUKLA, 1 T. FARID, 1 L. STENFLO 2 and O. G. ONISHCHENKO 3 1 Institut f ¨ ur Theoretische Physik IV, Fakult¨ at f¨ ur Physik und Astronomie, Ruhr-Universit¨ at Bochum, D-44780 Bochum, Germany 2 Department of Plasma Physics, Ume˚a University, S-90187 Ume˚a, Sweden 3 Institute of Physics of the Earth, 123810 Moscow, Russia (Received 16 May 2000) Abstract. It is shown that sheared plasma flows can generate nonthermal elec- trostatic waves in a magnetized dusty electron–positron plasma. Linearly excited modes attain large amplitudes and start interacting among themselves. Nonlinearly coupled modes self-organize in the form of coherent vortices comprising a vortex chain and a double vortex. Conditions under which the latter appear are given. The relevance of our investigation to space, astrophysical, and laboratory plasmas is pointed out. Dedication This paper is dedicated to John Dougherty on the occasion of his 65th birthday. 1. Introduction It is well known that electron–positron plasmas, which are composed of fully ionized charged particles with the same mass and opposite charge, are produced by high- energy particle and laser beams. Electron–positron plasmas are ubiquitous in the early universe (Misner et al. 1973: Rees 1983; Tajima and Taniuti 1990), in active galactic nuclei (Miller and Witta 1987), in pulsar magnetospheres (Goldreich and Julian 1969; Michel 1982), in the Van Allen radiation belts, and near the polar caps of rapidly rotating neutron stars (Lightman and Zdziarski 1987; Zdziarski 1987). Although in most astrophysical settings, pair plasmas are fully relativistic, recent laboratory experiments (Surko et al. 1989; Greaves and Surko 1995) show that non- relativistic electron–positron plasmas can be created. This possibility opens up new directions for investigating collective processes (Shukla et al. 1986; Yu et al. 1986; Rizzato 1988; Iwamoto 1993; Zhao et al. 1996; Sakai et al. 1999) that appear on time and space scales that are absent in electron–ion plasmas. Furthermore, both astrophysical and laboratory plasmas may contain high-Z ions (or charged dust particulates), which affect the dynamics of the pair plasma when it is embedded in an external magnetic field. For example, a number of authors (Rizzato 1988; Berezhiani et al. 1992; Jammalamadaka et al. 1996; Cho et al. 2000) have discussed the electromagnetic properties of a magnetized pair plasma containing heavy ions and stationary dust grains.