Fig. 2From: Non-invasive assessment of plasma parameters inside an ion thruster combining optical emission spectroscopy and principal component analysisSchematic description of our measurement-based correlation between optical emission spectrum and plasma parameters. First, a reference data set is measured consisting of simultaneously performed OES and Langmuir diagnostics. The measured spectrum is transferred into a simplified coordinate system using PCA, which yields the axes PCE,i and the coordinates or scores PCi of the spectra on these axes. The scores PCi are then correlated with the measured plasma parameters. The correlation can then be used to extract plasma parameters from a measured spectrum S′(λ) by calculating its scores PCi′ and inserting them into the correlationBack to article page