Highly charged ions in magnetic fusion plasmas: research opportunities and diagnostic necessities

Abstract

Highly charged ions play a crucial role in magnetic fusion plasmas. These plasmas are excellent sources for producing highly charged ions and copious amounts of radiation for studying their atomic properties. These studies include calibration of density diagnostics, x-ray production by charge exchange, line identifications and accurate wavelength measurements, and benchmark data for ionization balance calculations. Studies of magnetic fusion plasmas also consume a large amount of atomic data, especially in order to develop new spectral diagnostics. Examples we give are the need for highly accurate wavelengths as references for measurements of bulk plasma motion, the need for accurate line excitation rates that encompass both electron-impact excitation and indirect line formation processes, for accurate position and resonance strength information of dielectronic recombination satellite lines that may broaden or shift diagnostic lines or that may provide electron temperature information, and the need for accurate ionization balance calculations. We show that the highly charged ions of several elements are of special current interest to magnetic fusion, notably highly charged ions of argon, iron, krypton, xenon, and foremost of tungsten. The electron temperatures thought to be achievable in the near future may produce W70+ ions and possibly ions with even higher charge states. This means that all but a few of the most highly charged ions are of potential interest as plasma diagnostics or are available for basic research.

Energy levels and transition rates for helium-like ions withZ = 10–36

“…Aggarwal et al (2005Aggarwal et al ( , 2008Aggarwal et al ( , 2009Aggarwal et al ( , 2010Aggarwal et al ( , 2011Aggarwal et al ( , 2012aAggarwal et al ( ,b,c,d, 2013a included level energies and multipole rates for transitions within 1snl (n ≤ 5, l ≤ (n − 1)) configurations of helium-like ions with Z = 3−36 (except for Ne IX) using the GRASP code ). However, we show below that because they treated correlation only in a limited way, their energies differ from the experimental values by more than 3 eV, which does not meet the accuracy requirement in the fitting of observed spectra (Kharchenko & Dalgarno 2001;Kallman & Palmeri 2007;Smith 2014;Beiersdorfer 2015).…”

Electron impact excitation for He-like ions withZ= 20–42

“…These diagnostics have been widely used for solar plasmas Full Table 1 is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/600/A85 (Doschek & Meekins 1970;Doyle 1980;McKenzie et al 1980;Pradhan & Shull 1981;McKenzie & Landecker 1982;Wolfson et al 1983;Keenan et al 1984Keenan et al , 1987Doyle & Keenan 1986) and tokamak plasmas (Doyle & Schwob 1982;Källne et al 1983;Keenan et al 1989). Reliable line interpretation and plasma modeling require a large amount of accurate atomic data, including energy levels, radiative rates, and collisional rate coefficients related to states up to the n = 5 configurations (Porquet et al 2010;Kallman & Palmeri 2007;Smith & Brickhouse 2014;Beiersdorfer 2015).…”

Advanced multiconfiguration methods for complex atoms: I. Energies and wave functions

“…This is the realm of theoretical atomic physics, where one predicts the light-emission of ions and how it is affected by the property of the plasma. If data for atomic transitions are known, the spectra from the plasma can give information about its fundamental properties, e.g., temperature and density (if they are well-defined), as well as the abundance of different elements and the balance between different ionization stages [18]. In some cases we are also able to determine magnetic fields -their strengths and polarization [19,20].…”

“…The value of ω ij can be interpreted in terms of differences in orbital oneelectron energies. In the low photon energy limit (or the long wavelength approximation), when ω ij → 0, the expression (18) reduces to the Breit interaction [66,64] …”