Computerized Tomography for Sparse-Data Plasma Physics Experiments

Matrix inversion and least squares fitting have been used to recover two dimensional distribution functions from a small number of line integrals taken along chords across them. A self-consistent optimization procedure, free from reliance on comparison with a trial source function, for optimizing the configuration of these chords is described and used to demonstrate that an asymmetric arrangement usually leads to greater reconstruction accuracy than a regular array. Smoothing is incorporated by imposing auxiliary conditions relating to the second derivative ¿2f of the source function f, and its effect on reconstruction accuracy and resolution is investigated. These methods are applied to the ten-channel far-infrared interferometer being prepared for use on JET. Electron denisty contour shapes can be identified rather sensitively if the source function contours belong to a predetermined family.