A fast numerical method to calculate drift instability growth rate in multispecies inhomogeneous plasmas

In this paper we use a new accurate method for solving the linear dispersion relation in an inhomogeneous Vlasov multispecies plasmas. This method takes into account the four poles fractional approximation for the Z dispersion function published elsewhere, where by using that approximation a polynomial form for the dispersion relation was obtained. By this way, arbitrary values for the argument of Z can be used (i.e. large or small frequency - wave number ratio). For a one ion species plasma, the maximum growth rate is calculated and analyzed for the relevant parameters: density gradient, ion mass, electron - ion temperature ratio, electron cyclotron frequency, parallel and perpendicular wave length. The optimum value of the parallel wave length for which the growth rate reaches a maximum is found and discussed. For multispecies plasmas, two unstables modes of propagation are excited and the dependance of the growth rate against several parameters (as for example the relative concentration of the ion species) is calculated. (author)