Fig. 9From: Non-invasive assessment of plasma parameters inside an ion thruster combining optical emission spectroscopy and principal component analysisPlots of the time evolution of electron density (a) and temperature (b) for a xenon plasma driven by 1.2 MHz RF excitation for various operation parameters calculated from the PCA scores (see Fig. 8b) of time-resolved optical spectra (see Fig. 7). Mass flow, RF input power, frequency as well as average electron temperature and density are given in the legend. Parameters resulting from data points outside the mapped region (see Fig. 8a) are ill defined and plotted as smaller symbols connected by a dotted line. The plasma parameters oscillate with twice the radio frequencyBack to article page