Quantification of systematic errors in the electron density and temperature measured with Thomson scattering at W7-X

Philipp Nelde; Golo Fuchert; Ekkehard Pasch; Marc N. A. Beurskens; Sergey A. Bozhenkov; Kai Jakob Brunner; Udo Höfel; Sehyun Kwak; Jens Meineke; Evan R. Scott; Robert C. Wolf; W7-X team

arXiv · 2111.03562

Quantification of systematic errors in the electron density and temperature measured with Thomson scattering at W7-X

Philipp Nelde·Golo Fuchert·Ekkehard Pasch·Marc N. A. Beurskens·Sergey A. Bozhenkov·Kai Jakob Brunner·Udo Höfel·Sehyun Kwak·Jens Meineke·Evan R. Scott·Robert C. Wolf·W7-X team

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Abstract

The electron density and temperature profiles measured with Thomson scattering at the stellarator Wendelstein 7-X show features which seem to be unphysical, but so far could not be associated with any source of error considered in the data processing. A detailed Bayesian analysis reveals that errors in the spectral calibration cannot explain the features observed in the profiles. Rather, it seems that small fluctuations in the laser position are sufficient to affect the profile substantially. The impact of these fluctuations depends on the laser position itself, which, in turn, provides a method to find the optimum laser alignment in the future.

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Philipp Nelde, Golo Fuchert, Ekkehard Pasch, Marc N. A. Beurskens, Sergey A. Bozhenkov, Kai Jakob Brunner, Udo Höfel, Sehyun Kwak, Jens Meineke, Evan R. Scott, Robert C. Wolf, W7-X team. 2021-11-05. Quantification of systematic errors in the electron density and temperature measured with Thomson scattering at W7-X. https://arxiv.org/abs/2111.03562

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