Highly ionized atoms in tokamak discharges

TLDR

Tokamak discharges have electron densities of ~0.3–1.0×10¹⁴ cm⁻³, temperatures of a few hundred eV to several keV, and contain fully stripped light impurities and partially stripped heavy elements that radiate and are used for diagnostics via resonance lines. The study aims to improve atomic data—wavelengths, transition probabilities, excitation, ionization, and recombination rates—for heavy elements to enable more accurate analysis of plasma temperature and confinement time. The authors plan to refine these atomic data by calculating or measuring the relevant parameters for the heavy elements present in tokamak plasmas.

Abstract

Tokamak discharges are characterized by electron densities usually \ensuremath{\sim}(0.3-1.0)\ifmmode\times\else\texttimes\fi{}${10}^{14}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ and temperatures from a few hundred eV to several keV. In addition to the working gas (H or He), the plasma normally contains some light impurities (\ensuremath{\sim}${10}^{12}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ O or C) that are completely stripped except at the outer periphery, and heavier elements from the vacuum wall and current-aperture limiter (Fe, Cr, Ni, W, Mo, and others, \ensuremath{\sim}${10}^{10}$-${10}^{11}$ ${\mathrm{cm}}^{\ensuremath{-}3}$) that remain partly stripped, hence relatively strongly radiating, throughout the discharge. Other elements, especially noble gases, may be deliberately added for diagnostic purposes. Resonance lines of Fe and Ar in the beryllium and lithium sequences, of Fe, Kr, and Mo in the magnesium and sodium sequences, and of Mo and Xe in the zinc and copper sequences have been used for rough determination of plasma composition. Since crucial plasma characteristics such as temperature and confinement time are sensitively affected by the local composition, it is essential to improve the available atomic data necessary for more accurate analysis: wavelengths, transition probabilities, excitation, ionization, and recombination rates, especially for the heavier elements.