Design of tangential x-ray crystal spectrometer for Aditya-U tokamak

A tangential soft x-ray crystal spectrometer has been designed to measure the x-ray spectrum of He-like argon for the Aditya-U tokamak plasma. The system enables to measure electron temperature using the intensity ratio of the resonance line to the satellite line. For this purpose, an x-ray spectral line at 3.9494 Å from He-like argon, Ar¹⁶⁺, is considered. The spectrometer consists of a cylindrically bent silicon (111) crystal and a CCD detector to measure the resonance spectral line and its satellite lines in the wavelength region of 3.94-4.0 Å, viewing the plasma tangentially at an angle of 26° with respect to the toroidal direction in the magnetic axis. Considering Aditya-U tokamak plasma parameters and its geometrical constraints, plasma to crystal and crystal to detector distances have been kept at 1.47 m and 0.5 m, respectively, to detect a sufficient signal. The engineering design has been optimized after adequately addressing the issues related to port geometry and machine accessibility. Details on the design of the crystal spectrometer are presented in this paper.