Observations of Alcator C-Mod plasmas from a five chord high energy resolution x-ray spectrometer array

Abstract

X-ray spectra from Alcator C-Mod plasmas have been collected using a high wavelength resolution, five spectrometer array during a wide range of operating conditions, providing a large variety of diagnostic information. Each independently scannable von Hamos type spectrometer has a wavelength range of 2.8–4.0 Å, and the complete Rydberg series of helium- and hydrogenlike argon have been observed. Spectra of Δn=1 ground state transitions and satellites taken along different chords have been simulated using the results from a collisional-radiative model and the mist transport code. Line ratios are very sensitive to the electron temperature and deduced profiles are in good agreement with ECE profiles. Line intensities have been utilized to obtain absolute argon densities. The widths of the strongest lines have been used to deduce ion temperature profiles. Transitions from around n=9 to the ground state are populated by charge exchange in the outer regions of the plasma and these line intensities have been used to determine the neutral hydrogen density profile. Spectra from heliumlike scandium have been obtained during injection experiments and time histories and line intensities have been utilized to determine impurity transport coefficients.