Rest-wavelength Fiducials for the ITER Core Imaging X-ray Spectrometer

Absolute wavelength references are needed to derive the plasma velocities from the Doppler shift of a given line emitted by a moving plasma. We show that such reference standards exist for the strongest x-ray line in neonlike W64+, which has become the line of choice for the ITER (Latin the way) core imaging x-ray spectrometer. Close-by standards are the Hf L3 line and the Ir L2 line, which bracket the W64+ line by 30 eV; other standards are given by the Ir L1 and L2 lines and the Hf L1 and L2 lines, which bracket the W64+ line by 40 and 160 eV, respectively. The reference standards can be produced by an x-ray tube built into the ITER spectrometer. We present spectra of the reference lines obtained with an x-ray microcalorimeter and compare them to spectra of the W64+ line obtained both with an x-ray microcalorimeter and a crystal spectrometer