Fitting measured emittance data

Emittance measurements have been made at several points in the 50-MEV Neutral Particle Beam Test Stand of the Argonne National Laboratory (ANL). These measurements were made with segmented Faraday cups that measure the angular distribution after passing the beam through a movable slit. Since measured distribution is very nonuniform, the Twiss parameters for the best fit at a given emittance depend on the ellipse area. A program that optimizes the Twiss parameters and the ellipse center as a function of the emittance is described. This is done separately in the two lateral phase planes. The β and α parameters and the ellipse center are adjusted such that the total count contained within the ellipse is maximized. The optimization method does not require evaluation of derivatives. Input data are read as a two-dimension array (displacement and angle). For cells containing the ellipse, the incremental count used is estimated by determining the intercepts of the ellipse in the two dimensions and approximating the portion of the curve by a straight line. Optional initial smoothing of the measured data is provided