Disruption of Current Filaments and Isotropization of the Magnetic Field in Counterstreaming Plasmas

We study the stability of current filaments produced by the Weibel, or current filamentation, instability in weakly magnetized counterstreaming plasmas. It is shown that a resonance exists between the current-carrying ions and a longitudinal drift-kink mode that strongly deforms and eventually breaks the current filaments. Analytical estimates of the wavelength, growth rate, and saturation level of the resonant mode are derived and validated by three-dimensional particle-in-cell simulations. Furthermore, self-consistent simulations of counterstreaming plasmas indicate that this drift-kink mode is dominant in the slow down of the flows and in the isotropization of the magnetic field, playing an important role in the formation of collisionless shocks.