Analytic model for the propagation of a collisionless Neutral beam
An analytical model is developed to compute the transport of col- lisionless particles in a Neutral beam system. It takes account both the spatial variation and velocity divergence at the beam source; also obstructions at the edge of the beam. Non-Gaussian distributions are modelled using a collection of Gaussian basis functions. Two- dimensional source distributions are taken into account in the limit that the distributions in orthoginal directions are separable. Results from the model agree well with those from ray-tracing calculations both in the spatial and veloicity domains. It is anticipated that the accuracy and speed of this new approach should make it well suited for Bayesian Inference calculations that require detailed knowledge of the neutral beam particle distribution.