Study of impurity behaviour for first magnetic configuration changes in W7-X plasmas by means of PHA spectra

Abstract

Transport properties of impurities in stellarators are sensitive to potential variations on flux-surfaces, and thermodynamic forces from the bulk plasma which might be affected by changes in magnetic field properties. In this contribution, the effect of planar coil current changes on the core impurity behavior in the first operating phase of Wendelstein 7-X (W7-X) is described. Hydrogen plasmas, at different heating power levels were investigated showing Core-Electron-Root-Confinement (CERC) conditions, characterized by peaked Te profiles and positive radial electric fields in the plasma core. Impurity spectra in the x-ray emission range between 1 and 10 keV were measured by the Pulse Height Analysis (PHA) diagnostic. The line-integrated measurements of transitions in sulphur, chlorine and argon are in the focus of this analysis. First observations indicate that the scans of the magnetic configuration did not affect strongly the impurity concentration in the core. Clear differences in the impurity content, however, have been observed when the ECRH power was changed, which affects the bulk plasma properties.

First Results from the Soft X-ray Pulse Height Analysis System on Wendelstein 7-X Stellarator

“…Detailed studies of impurity behavior in W7-X is important in order to investigate e.g. the impact of different magnetic field configurations on impurity core and edge transport [22]. For this reason, the PHA system, with its good energy resolution, is significant W7-X diagnostic.…”

Electron temperature estimation using the Pulse Height Analysis system at Wendelstein 7-X stellarator

“…Measurements of Te can be also performed by the Pulse Height Analysis (PHA) [9][10][11][12] system installed at W7-X, which primary purpose is impurity content estimation [13][14] and additionally characterization of nonthermal features of the plasma spectral emission [15]. The PHA spectra also provide information about lineintegrated Te, along the line-of-sight, as opposed to measurements from TS and ECE diagnostics.…”