Optimal Geometry for Neutral-Beam-Based Optical Diagnostics in Tokamaks
Authors: J. Goldston and R. Goldston
Spatial resolution is an important issue for neutral-beam-based optical diagnostics in tokamak plasmas, such as charge-exchange-recombination spectroscopy (measuring Ti, and v) and motional Stark effect (measuring Bp). The key geometrical constraint is that the optical sightlines of these diagnostics must be as nearly tangent as possible to magnetic surfaces at the point were they cross the path of the neutral beam. This minimizes the effect of the width of the neutral beam on the spatial resolution of the diagnostic in the direction perpendicular to the flux surfaces. (See figure 1).