Method to obtain absolute impurity density profiles combining charge exchange and beam emission spectroscopy without absolute intensity calibration

Abstract

Investigation of impurity transport properties in tokamak plasmas is essential and a diagnostic that can provide information on the impurity content is required. Combining charge exchange recombination spectroscopy (CXRS) and beam emission spectroscopy (BES), absolute radial profiles of impurity densities can be obtained from the CXRS and BES intensities, electron density and CXRS and BES emission rates, without requiring any absolute calibration of the spectra. The technique is demonstrated here with absolute impurity density radial profiles obtained in TEXTOR plasmas, using a high efficiency charge exchange spectrometer with high etendue, that measures the CXRS and BES spectra along the same lines-of-sight, offering an additional advantage for the determination of absolute impurity densities.

Charge exchange recombination spectroscopy at Wendelstein 7-X

“…The primary measurements of the CXRS are made by a three colour channel high-étendue spectrometer 20 which was originally designed as a prototype for ITER and previously used on the TEXTOR 21 and ASDEX-Upgrade 22 tokamaks. The spectrometer, known as the 'ITER-Like spectrometer' (ILS) has 54 fibres, each of which are split into three colour channels to ultimately provide all the primary measurements at the same 54 spatial locations.…”

“…From this quantity, the impurity concentration n Z / i n i can be calculated if only a single impurity species is dominant in the plasma. The ILS spectrometer has been designed with this in mind, measuring both CX and BES signals on the same lines of sight 21 . Nonetheless, calculation of the absolute concentration must still take into account all energy components, the relative sensitivity of the spectrometer channels, the effective charge exchange and beam emission coefficients and their dependence on the local plasma parameters.…”

The tri-band high spectral resolution spectrometer with gratings in tandem for the charge-exchange recombination spectroscopy diagnostic system on HL-2A tokamak

“…For the He II, C VI and D α wavebands, the RLDs are 0.63 nm mm −1 , 0.72 nm mm −1 and 0.88 nm mm −1 , respectively, for the central fiber. The dispersions of the triband spectrometer at 468 nm and 529 nm are very similar to that of the spectrometer with reflective grating of 2160 grooves mm −1 [3]. However, the focal length of the latter is 400 mm.…”

“…Charge-exchange recombination spectroscopy (CXRS) is a powerful diagnostic system for the measurement of ion temperature, plasma rotation and impurity density, and CXRS is foreseen to be the major diagnostic monitoring the helium ash density on ITER [1][2][3]. The ion temperature and rotation velocity are determined by Doppler broadening and shift respectively of the active spectral lines such as C VI (529.1 nm) and He II (468.57 nm), while the local impurity concentration is derived by combining the line intensity of CXRS with that of beam emission spectroscopy (BES) [4].…”

Measurement of Absolute Carbon Ion Density Profile Based on CXRS Diagnostic on HL-2A Tokamak

“…There are mainly two methods to deduce the naked impurity ion density profiles based on CXRS diagnostic. One method is to couple the active spectral line intensity with neutral beam deposition calculation [5], the other one is to combine the CXRS and beam emission spectroscopy (BES) without beam deposition calculation [6].…”