The Description of Particle Transport Problems with Helical Symmetry

We show that three-dimensional (3-D) particle transport (or diffusion) problems having helical symmetry can be described by a transport (or diffusion) equation possessing only two independent spatial variables. The new two-dimensional (2-D) equations are closely related to the 2-D (r,) equations. These results will provide (a) more efficient computer simulations of 3-D transport and diffusion problems with helical symmetry, and (b) a useful technique for validating 3-D transport and diffusion codes.