In situ wavelength calibration system for the X-ray Imaging Crystal Spectrometer (XICS) on W7-X

Area of Science:

• Plasma Physics
• Spectroscopy
• Fusion Energy Research

Background:

• The X-ray Imaging Crystal Spectrometer (XICS) is crucial for determining plasma flow profiles in fusion devices.
• Accurate wavelength calibration is essential for precise Doppler shift measurements of highly charged impurity ions.

Purpose of the Study:

• To develop and present a novel in situ wavelength calibration system for the W7-X XICS.
• To enable routine, high-accuracy calibration of XICS instruments independent of plasma conditions.

Main Methods:

• Implementation of an x-ray tube with a cadmium anode positioned before a diffracting spherically bent crystal.
• Generation of calibration lines across the full detector extent for Ar¹⁶⁺ and Ar¹⁷⁺/Fe²⁴⁺ spectrometer channels.

Main Results:

• Achieved relative wavelength accuracy of 3 × 10^-7 Å (50 m/s velocity resolution) across the detector.
• Expected absolute wavelength accuracy of 1 × 10^-5 Å (1 km/s velocity resolution).

Conclusions:

• The developed calibration system provides routine, high-accuracy wavelength calibration for XICS.
• This system is adaptable for XICS instruments on both stellarators and tokamaks, simplifying calibration procedures.