Separation-of-variables approximation to the Boltzmann equation

We have tested a separation-of-variables approximation for the electron velocity distribution function in the Boltzmann equation. In this approximation, the distribution function fe(z,νz,νr,t) is represented as the product of two functions F(z,νz,t) and G(z,νr,t). This approximation can represent very anisotropic distributions, while effectively reducing the dimensionality of the calculation. We have implemented this approximation using a method of characteristics, and have applied it to argon and neon gas for a wide range of applied electric fields