Novel passive spectroscopy system for absolutely referenced plasma rotation measurements in clean plasmas

A novel method for measuring absolutely calibrated rotation velocities in fusion plasmas by means of passive spectroscopy, using a single plasma view, is presented. The method consists of simultaneously recording the emission lines from the plasma and from a calibration lamp by means of a double fiber-fiber guide. A software simultaneously analyzes the plasma and calibration lines, which are obtained with a high-resolution spectrometer equipped with an intensified linear detector array, and provides absolute rotation measurements. Experimental results of carbon impurity ion rotation measured in the TJ-II stellarator are reported, demonstrating an accuracy of better than $0.3\mathrm{km}∕\mathrm{s}$ .