A&A 416, 1139-1147 (2004)
Electrostatic instability in electron-positron pairs injected in an external electric fieldK. Asano and F. Takahara
Department of Earth and Space Science, Osaka University, Toyonaka 560-0043, Japan
(Received 17 September 2003 / Accepted 28 November 2003 )
Motivated by the particle acceleration problem in pulsars, we numerically investigate electrostatic instability of electron-positron pairs injected in an external electric field. The electric field is expected to be so strong that we cannot neglect effects of spatial variation in the 0th order distribution functions on the scale of the plasma oscillation. We assume that pairs are injected mono-energetically with 4-velocity u0>0 in a constant external electric field by which electrons (positrons) are accelerated (decelerated). By solving linear perturbations of the field and distribution functions of pairs, we find a new type of electrostatic instability. The properties of the instability are characterized by u0 and the ratio R of the braking time-scale (determined by the external electric field) to the time-scale of the plasma oscillation. The growth rate is as large as a few times the plasma frequency. We discuss the possibility that the excited waves prevent positrons from returning to the stellar surface.
Key words: instabilities -- plasmas -- stars: pulsars: general
Offprint request: K. Asano, email@example.com
© ESO 2004