Abstract

The Pulse Height Analysis (PHA) system at Wendelstein 7-X (W7-X) is a broad energy range spectrometer dedicated to the observation of impurity behaviour during the plasma discharges. The system measures spectra in the range between 0.5 and 20 keV, from integrated signals along three lines of sight that pass close to the plasma center. During the recent operational phase of W7-X, the TESPEL (Tracer-Encapsulated Solid PELlet) injector has been commissioned. By this injector, polystyrene pellets with a single tracer impurity as well as multiple tracer impurities have been injected into the W7-X plasmas. The multiple tracer impurities injection allows studying the behavior of various impurities in the same plasma condition. The time resolution of the PHA system in the order of 60–100 ms, is smaller than typical confinement times and sufficient to observe differences in temporal behaviour of injected impurities. The collected PHA spectra consist of Kα lines of vanadium, manganese and nickel in case of the triple tracers, and of iron or copper in case of the single tracer. The temporal evolution of these Kα lines has been obtained in various plasma conditions, which will be presented and discussed in this paper.

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