Abstract
Extreme ultraviolet spectra of the L-shell ions of highly charged yttrium (Y 26 + –Y 36 + ) were observed in the electron beam ion trap of the National Institute of Standards and Technology using a flat-field grazing-incidence spectrometer in the wavelength range of 4 nm-20 nm. The electron beam energy was systematically varied from 2.3 keV–6.0 keV to selectively produce different ionization stages. Fifty-nine spectral lines corresponding to Δ n = 0 transitions within the n = 2 and n = 3 shells have been identified using detailed collisional-radiative (CR) modeling of the non-Maxwellian plasma. The uncertainties of the wavelength determinations ranged between 0.0004 nm and 0.0020 nm. Li-like resonance lines, 2s– 2 p 1 / 2 and 2s–2 p 3 / 2 , and the Na-like D lines, 3s– 3 p 1 / 2 and 3s– 3 p 3 / 2 , have been measured and compared with previous measurements and calculations. Forbidden magnetic dipole (M1) transitions were identified and analyzed for their potential applicability in plasma diagnostics using large-scale CR calculations including approximately 1.5 million transitions. Several line ratios were found to show strong dependence on electron density and, hence, may be implemented in the diagnostics of hot plasmas, in particular in fusion devices.
Highlights
Multi-electron ions are under intense theoretical study as state-of-the-art calculations rival highly accurate measurements sensitive to higher order terms of quantum electrodynamics (QED) corrections to atomic energy levels [1]
In the past few years, the electron beam ion trap (EBIT) research program at the National Institute of Standards and Technology (NIST) has reported accurate measurements in the extreme ultraviolet (EUV) region that focus on systematic observations of transitions in L-shell, M-shell and N-shell ions [2,3,4,5,6,7,8,9,10,11,12,13,14]
Together with strontium, zirconium, niobium and molybdenum, yttrium has been injected into the Texas Experimental Tokamak (TEXT) [15,16], the Joint European Torus (JET) tokamak [17] and the Princeton tokamaks [18,19,20] and has been
Summary
Multi-electron ions are under intense theoretical study as state-of-the-art calculations rival highly accurate measurements sensitive to higher order terms of quantum electrodynamics (QED) corrections to atomic energy levels [1]. We report the first data for the wavelengths of the Na-like D1 and D2 yttrium lines measured with an EBIT to provide accurate experimental results that complement the previously reported measurements of Reader et al [45] in laser-produced and tokamak plasmas. In addition to the spectral analysis, we discuss the forbidden magnetic dipole (M1) transitions of highly charged yttrium ions that are potentially important for plasma diagnostics. The spectroscopy of forbidden magnetic dipole lines can help deduce important plasma parameters such as the density and temperature of plasmas These parameters are obtained in practice from intensity ratios of various atomic spectral lines rather than direct measurements, which are difficult or even impossible in fusion, laboratory and astrophysical plasmas [56]. The following sections describe the experimental method, the theoretical calculations that aided in line identifications, the list of the observed transitions and their uncertainties and a discussion of the diagnostic capabilities of some of the M1 transitions
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