$L$-shell x-ray emission from neonlike W${}^{64+}$

We present high-resolution crystal spectroscopy measurements of the $n=3\to n=2$ $L$-shell x-ray transitions of neonlike W${}^{64+}$, which include seven electric-dipole–allowed transitions, two electric quadrupole transitions, and one magnetic quadrupole transition. The resulting wavelength data are compared to recent calculational results, allowing us to clearly distinguish between different theoretical approaches which need to take into account not only substantial electron correlations effects but also radiative contributions, which in case of the transition from the upper level ${\left(1s^{2}2s_{1/2}2p^{6}3p_{3/2}\right)}_{J=1}$ to the closed-shell neonlike ground state exceeds 20 eV. Best agreement is found with calculations utilizing the relativistic multireference Møller-Plesset approach. In addition to the emission from W${}^{64+}$, we observed several inner-shell collisional satellite lines associated with oxygenlike W${}^{66+}$, fluorinelike W${}^{65+}$, sodiumlike W${}^{63+}$, and magnesiumlike W${}^{62+}$, which provide benchmarks for future calculations as well as for recent calculations using the relativistic many-body perturbation theory. The present measurements also provide accurate rest wavelengths for establishing the instrumental dispersion needed for future measurements of the core plasma motion in the ITER tokamak and show that the candidate W${}^{64+}$ line for such measurements remains well isolated from neighboring collisional satellite lines even when broadened by the expected high temperatures in this device.

Figure 1

Top: x-ray spectrum of neonlike W${}^{64+}$ calculated with FAC assuming an electron-beam energy of 16 keV and an electron density of $1\times {10}^{12}$ cm${}^{-3}$. The lines are labeled using the notation of Parkinson [66], augmented by the notation of Beiersdorfer et al. [33] for denoting the electric-dipole–forbidden lines. Bottom: Schematic location of the reference lines from heliumlike and hydrogenlike ions used for calibration. The heliumlike lines denoted $w$ and $z$ refer to the transitions from levels $1s2p^1{P}_1$ and $1s2s^3{S}_1$ to the $1s^2$ ${}^1{S}_0$ ground state, respectively. Ly-${\alpha }_1$ and Ly-${\alpha }_2$ refer to the $2p_{3/2}\to 1s_{1/2}$ and the $2p_{1/2}\to 1s_{1/2}$ transitions in the hydrogenlike ions, respectively.

Figure 2

Spectral emission of (a) sodiumlike W${}^{63+}$, (b) magnesiumlike W${}^{62+}$, and (c) aluminumlike W${}^{61+}$ calculated with FAC. The electron energy is assumed to be 16 keV, and the electron density is set to ${10}^{12}$ cm${}^{-3}$.

Figure 3

Spectral emission of (a) fluorinelike W${}^{65+}$ and (b) oxygenlike W${}^{66+}$ calculated with FAC. The electron energy is assumed to be 21 keV, and the electron density is set to ${10}^{12}$ cm${}^{-3}$.

Figure 4

X-ray emission of neonlike W${}^{64+}$ between 8200 and 8800 eV excited at an electron-beam energy of (a) 15 keV and (b) 21 keV. The reference spectra of heliumlike and hydrogenlike copper produced at a beam energy of 17.5 keV are shown in panel (c).

Figure 5

(a) X-ray emission of neonlike W${}^{64+}$ between 8800 and 9500 eV excited at an electron-beam energy of 21 keV. The reference spectra of heliumlike and hydrogenlike zinc produced at an electron energy of 17.5 keV are shown in panel (b).

Figure 6

(a) X-ray emission of neonlike W${}^{64+}$ between 9300 and 10,200 eV excited at an electron-beam energy of 17 keV. The spectrum was recorded in second-order Bragg reflection. The reference spectra of heliumlike and hydrogenlike titanium, which were recorded in first order, are shown in panel (b).

Figure 7

(a) X-ray emission of neonlike W${}^{64+}$ between 10 100 and 11 200 eV excited at an electron-beam energy of 17 keV. The spectrum was recorded in second-order Bragg reflection. The reference spectra of heliumlike and hydrogenlike vanadium obtained at an electron energy of 7 keV and recorded in first order are shown in panel (b).

Figure 8

Comparison between the measured and calculated transition energies of neonlike W${}^{64+}$. The transitions are labeled in the notation used in Table  and are given in order of increasing wavelength. The shaded area indicates the measurement uncertainty. The calculated values are from Ref. [49] (long-dashed trace), from Ref. [39] (solid trace), and from our own predictions using FAC (short-dashed trace).