Cumulative effect of the filamentation and Weibel instabilities in counterstreaming thermal plasmas

Introducing a thermal particle distribution is important for a realistic investigation of counterstreaming plasmas with finite temperatures. Such counterstreaming thermal plasmas are described by the particle distributions, which include the counterstreams and thermal distribution as well. Two nonrelativistic counterstreams are considered here, with a bi-Maxwellian thermal anisotropy for each of them. This type of distribution is often expected to be found in both laboratory or cosmic plasmas, and it is able to cumulate the effects of the filamentation and Weibel instability. Comparing with the growth rates of each of these instabilities, the cumulative effect provides larger values, if they are emitted in the same direction. If the thermal anisotropy is negative, which means that Weibel instability develops on a perpendicular direction with respect to the filamentation instability, then their cumulative effect will suppress the instability. In both of these cases, the cumulative effect of the filamentation and Weibel instabilities can modify significantly the effective growth rate of the electromagnetic unstable modes. (c) 2006 American Institute of Physics.