Published Online: 27 September 2018 | Accepted: July 2018
Review of Scientific Instruments 89, 10F111 (2018); https://doi.org/10.1063/1.5038850
M. Kubkowska, A. Czarnecka, T. Fornal, M. Gruca, S. Jabłoński, N. Krawczyk, L. Ryć, R. Burhenn, B. Buttenschön, B. Geiger, O. Grulke, A. Langenberg, O. Marchuk, K. J. McCarthy, U. Neuner, D. Nicolai, N. Pablant, B. Schweer, H. Thomsen, Th. Wegner, P. Drews, K.-P. Hollfeld, C. Killer, Th. Krings, G. Offermanns, G. Satheeswaran, F. Kunkel, and W7-X team
The paper reports on the optimization process of the soft X-ray pulse height analyzer installed on the Wendelstein 7-X (W7-X) stellarator. It is a 3-channel system that records X-ray spectra in the range from 0.6 to 19.6 keV. X-ray spectra, with a temporal and spatial resolution of 100 ms and 2.5 cm (depending on selected slit sizes), respectively, are line integrated along a line-of-sight that crosses near to the plasma center. In the second W7-X operation phase with a carbon test divertor unit, light impurities, e.g., carbon and oxygen, were observed as well as mid- to high-Z elements, e.g., sulfur, chlorine, chromium, manganese, iron, and nickel. In addition, X-ray lines from several tracer elements have been observed after the laser blow-off injection of different impurities, e.g., silicon, titanium, and iron, and during discharges with prefill or a gas puff of neon or argon. These measurements were achieved by optimizing light absorber-foil selection, which defines the detected energy range, and remotely controlled pinhole size, which defines photon flux. The identification of X-ray lines was confirmed by other spectroscopic diagnostics, e.g., by the High-Efficiency XUV Overview Spectrometer, HEXOS, and high-resolution X-ray imaging spectrometer, HR-XIS.