Journal of Plasma Physics


Resonant Weibel instability in counterstreaming plasmas with temperature anisotropies

M. LAZARa1a2, M. E. DIECKMANNa2a3 and S. POEDTSa1

a1 Center for Plasma Astrophysics, Celestijnenlaan 200B, 3001 Leuven, Belgium (

a2 Institut für Theoretische Physik, Lehrstuhl IV: Weltraum- und Astrophysik, Ruhr-Universität Bochum, D-44780 Bochum, Germany

a3 Department of Science and Technology (ITN), Linköping University, 60174 Norrköping, Sweden


The Weibel instability, driven by a plasma temperature anisotropy, is non-resonant with plasma particles: it is purely growing in time, and does not oscillate. The effect of a counterstreaming plasma is examined. In a counterstreaming plasma with an excess of transverse temperature, the Weibel instability arises along the streaming direction. Here it is proved that for large wave-numbers the instability becomes resonant with a finite real (oscillation) frequency, ωr ≠ 0. When the plasma flows faster, with a bulk velocity larger than the parallel thermal velocity, the instability becomes dominantly resonant. This new feature of the Weibel instability can be relevant for astrophysical sources of non-thermal emissions and the stability of counterflowing plasma experiments.

(Received February 24 2009)

(Accepted April 02 2009)

(Online publication May 19 2009)