Quantitative spectroscopy of x-ray lines and continua in tokamaks (abstract)

Abstract

Crystal and synthetic multilayer diffractors, deployed either as flat Bragg reflectors, or curved, as in the Johann configuration, have been used to study the spectrum of COMPASS-D and other tokamaks in the wavelength region 1–100 Å. In particular, line emission from CIXVI and other He-like ions of the third atomic period elements have been shown to be a rich source of diagnostic information on ion transport and impurity ion accumulation, ion and electron temperatures, and plasma fluid velocities. In this article, we concentrate on the measurement of absolute photon fluxes and the derivation of volume emissivities of the lines and continua in the x-ray region. The sensitivities of these instruments to absolute photon flux are constructed from the individual component efficiencies, including published values of the diffractor reflectivities. Where diffractors have been used for which there is no published information, the reflectivity is measured using a double-axis goniometer or from line branching ratios. Changes in the effective ion charge state, Zeff, have been derived for different operating conditions, from the absolute intensity of the continuum at ∼4 Å in COMPASS-D. From the irradiances of the line emission, changes in the absolute level of impurities following “boronization” of the vacuum vessel have been documented.