High-resolution measurement, line identification, and spectral modeling of the K beta spectrum of heliumlike Ar16+

Abstract

High-resolution crystal spectrometer measurements of the K\ensuremath{\beta} spectrum of heliumlike ${\mathrm{Ar}}^{16+}$ covering the wavelength region from 3.34 to 3.50 \AA{} are presented and compared with detailed theoretical analyses. The measurements were made on the Princeton Large Torus tokamak and test the theoretical atomic data in the low-density limit at an electron density ${\mathit{n}}_{\mathit{e}}$\ensuremath{\le}2\ifmmode\times\else\texttimes\fi{}${10}^{13}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ and temperature ${\mathit{T}}_{\mathit{e}}$=2.3 keV. Satellite transitions of the type 1${\mathit{s}}^{2}$2l-1s2l3l' and 1${\mathit{s}}^{2}$3l-1s3l3l' from lithiumlike ${\mathrm{Ar}}^{15+}$ and 1${\mathit{s}}^{2}$2l2l'-1s2l2l'3l'' from berylliumlike ${\mathrm{Ar}}^{14+}$ are identified that are produced by either dielectronic recombination or electron-impact excitation. Good overall agreement between the predicted and measured intensities of the strong dielectronic satellites is found. The agreement demonstrates the utility of K\ensuremath{\beta} spectra as a diagnostic of the electron temperature of low-density plasmas, such as those found in the Sun or magnetic fusion facilities. Poorer agreement is found for the weaker dielectronic satellite transitions, including the 1s3l3l' satellites that play an important role in the analysis of high-density plasma produced in laser fusion. Their intensity is underestimated by the calculations by about 50%. Moreover, it is shown that direct electron-impact excitation rates underestimate the relative intensity of the 1${\mathit{s}}^{2}$ $^{1}$${\mathit{S}}_{0}$--1s2p $^{3}$${\mathit{P}}_{1}$ transition in heliumlike ${\mathrm{Ar}}^{16+}$ by a factor of 2, indicating the need for including additional excitation processes and possible blends with high-lying dielectronic satellites of the type 1${\mathit{s}}^{2}$nl'-1s3lnl' with n\ensuremath{\ge}4 in the theoretical models.