Validation of the ITER CXRS design by tests on TEXTOR

Measurement performance assessment for the ITER CXRS Edge diagnostic system

Measurement performance assessment has been carried out for the latest design of the ITER Charge Exchange Recombination Spectroscopy (CXRS) Edge diagnostic system. Several plasma scenarios, covering all expected baseline operation regimes for ITER, were used. Various impurity (He, Be, C, and Ne) concentrations for the system whole spatial range (0.5 < r/a < 1.0) were considered. Statistical errors for the measurements of low-Z impurity temperature, density, and rotation velocity were calculated. Other non-statistical error sources were reviewed, including the presence of wall reflections, effects on the active charge-exchange line shape, calibration, and positioning uncertainties. Minimal impurity concentrations, allowing measurements with required accuracy, were obtained. It was shown that the CXRS Edge system will be able to measure primary plasma parameters with required accuracy, space, and time resolution.

Measurements of the internal magnetic field using the B-Stark motional Stark effect diagnostic on DIII-D (inivited)

Results are presented from the B-Stark diagnostic installed on the DIII-D tokamak. This diagnostic provides measurements of the magnitude and direction of the internal magnetic field. The B-Stark system is a version of a motional Stark effect (MSE) diagnostic based on the relative line intensities and spacing of the Stark split D(α) emission from injected neutral beams. This technique may have advantages over MSE polarimetry based diagnostics in future devices, such as the ITER. The B-Stark diagnostic technique and calibration procedures are discussed. The system is shown to provide accurate measurements of B(θ)/B(T) and ∣B∣ over a range of plasma conditions. Measurements have been made with toroidal fields in the range of 1.2-2.1 T, plasma currents in the range 0.5-2.0 MA, densities between 1.7 and 9.0×10(19) m(-3), and neutral beam voltages between 50 and 81 keV. The viewing direction and polarization dependent transmission properties of the collection optics are found using an in situ beam into gas calibration. These results are compared to values found from plasma equilibrium reconstructions and the MSE polarimetry system on DIII-D.

An integrated charge exchange recombination spectroscopy/beam emission spectroscopy diagnostic for Alcator C-Mod tokamak

A novel integrated charge exchange recombination spectroscopy (CXRS)/beam emission spectroscopy (BES) system is proposed for C-Mod, in which both measurements are taken from a shared viewing geometry. The supplementary BES system serves to quantify local beam densities and supplants the common calculation of beam attenuation. The new system employs two optical viewing arrays, 20 poloidal and 22 toroidal channels. A dichroic filter splits the light between two spectrometers operating at different wavelengths for impurity ion and beam neutrals emission. In this arrangement, the impurity density is inferred from the electron density, measured BES and CXRS spectral radiances, and atomic emission rates.

Charge exchange spectroscopy as a fast ion diagnostic on TEXTOR

An upgraded charge exchange spectroscopy diagnostic has been taken into operation at the TEXTOR tokamak. The angles of the viewing lines with the toroidal magnetic field are close to the pitch angles at birth of fast ions injected by one of the neutral beam injectors. Using another neutral beam for active spectroscopy, injected counter the direction in which fast ions injected by the first beam are circulating, we can simultaneously measure a fast ion tail on the blue wing of the D(alpha) spectrum while the beam emission spectrum is Doppler shifted to the red wing. An analysis combining the two parts of the spectrum offers possibilities to improve the accuracy of the absolute (fast) ion density profiles. Fast beam modulation or passive viewing lines cannot be used for background subtraction on this diagnostic setup and therefore the background has to be modeled and fitted to the data together with a spectral model for the slowing down feature. The analysis of the fast ion D(alpha) spectrum obtained with the new diagnostic is discussed.