Accurate modeling of benchmark x-ray spectra from highly charged ions of tungsten

We present detailed collisional-radiative modeling for a benchmark x-ray spectrum of highly charged tungsten ions in the range between 3 and $10\mathrm{\AA }$ produced in an electron beam ion trap (EBIT) with a beam energy of $4.08\mathrm{keV}$. Remarkably good agreement between calculated and measured spectra was obtained without adjustable parameters, highlighting the well-controlled experimental conditions and the sophistication of the kinetic simulation of the non-Maxwellian tungsten plasma. This agreement permitted the identification of spectral lines from Cu-like ${\mathrm{W}}^{45+}$ and Ni-like ${\mathrm{W}}^{46+}$ ions, led to the reinterpretation of a previously known line in Ni-like ion as an overlap of electric-quadrupole and magnetic-octupole lines, and revealed subtle features in the x-ray spectrum arising from the dominance of forbidden transitions between excited states. The importance of level population mechanisms specific to the EBIT plasma is discussed as well.

Figure 1

(Color online) (a) Measured spectrum at beam energy $4.08\mathrm{keV}$; and (b) calculated spectrum at beam energy $4.06\mathrm{keV}$. Contributions from Cu-, Ni-, and Co-like ions of W are shown in different colors.

Figure 2

Energy diagram for the $3d^{10}$ (ground state configuration) and $3d^{9}4s$ (first excited configuration) levels in ${\mathrm{W}}^{46+}$. Solid lines: $M1$ transitions; dashed lines: $E2$ transitions; and dot-dashed line: $M3$ transition. Transition probabilities (in ${\mathrm{s}}^{-1}$) are given next to the corresponding lines. Notation $a\left(b\right)$ means $a\times {10}^b$.