AUTOMATIC FAST FITTING OF SINGLE LANGMUIR PROBE CHARACTERISTICS ON RFX

An array of single Langmuir probes is routinely used in the RFX revers ed field pinch for time-resolved measurements of edge electron density and temperature. In order to allow an automatic analysis of the large number of current-voltage characteristics, three different methods ha ve been developed, which consider restricted subsets of data with volt age lower than an upper cutoff value. The first one. determines this l imiting voltage by a neural network based technique, combined with cri teria for the rejection of too noisy characteristics. In the second on e a standard fitting routine is applied repeatedly to the data while v arying the upper cutoff voltage. The third one consists of a numerical technique, where the best fit is obtained by minimizing a properly de fined cost function. An error index is also calculated, which allows t he reliability of the results to be easily estimated. The best results have been achieved using the last two methods. (C) 1997 American Inst itute of Physics.