A Technique for Wavelength Calibration of a Multichannel Polychromator Spectrometer Using the Fabry–Perot Etalon

The Active spectroscopy plasma diagnostics (CXRS, charge eXchange recombination spectroscopy) and plans for its use in the ITER tokamak are described. A technique for the wavelength calibration of a multichannel polychromator spectrometer using a Fabry–Perot etalon is presented. This idea of the wavelength calibration of the spectrometer was originally used for the CXRS diagnostics in the JET tokamak. Using this technique, a high-resolution tri-band polychromator spectrometer, which was created for the CXRS diagnostics at the ITER facility, was calibrated. This polychromator spectrometer allows simultaneous measurements in three spectral ranges: 469–477, 529–538, and 650–661 nm. The obtained error of the calibration for various wavelengths was evaluated, which was on average 0.003 nm. The resulting calibration accuracy for different wavelengths is enough to meet the requirements for the CXRS diagnostics in the ITER tokamak with a margin.