High-resolution tungsten spectroscopy relevant to the diagnostic of high-temperature tokamak plasmas

The x-ray transitions in Cu- and Ni-like tungsten ions in the 5.19–5.26 Å wavelength range that are relevant as a high-temperature tokamak diagnostic, in particular for JET in the ITER-like wall configuration, have been studied. Tungsten spectra were measured at the upgraded Shanghai- Electron Beam Ion Trap operated with electron-beam energies from 3.16 to 4.55 keV. High-resolution measurements were performed by means of a flat Si 111 crystal spectrometer equipped by a CCD camera. The experimental wavelengths were determined with an accuracy of 0.3–0.4 mÅ. The wavelength of the ground-state transition in Cu-like tungsten from the $3p^{5}3d^{10}4s4d[{(3/2,{(1/2,5/2)}_2]}_{1/2}$ level was measured. All measured wavelengths were compared with those measured from JET ITER-like wall plasmas and with other experiments and various theoretical predictions including cowan, relac, multiconfigurational Dirac-Fock (MCDF), and fac calculations. To obtain a higher accuracy from theoretical predictions, the MCDF calculations were extended by taking into account correlation effects (configuration-interaction approach). It was found that such an extension brings the calculations closer to the experimental values in comparison with other calculations.

Figure 1

A general scheme of the experimental setup at the upgraded Shanghai EBIT.

Figure 2

X-ray spectra of Cu- and Ni-like tungsten ions measured on the upgraded Shanghai EBIT for electron-beam energies of 3.16, 3.76, 4.34, and 4.55 keV.

Figure 3

Tungsten $({\mathrm{W}}^{45+}$ and ${\mathrm{W}}^{46+})$ and molybdenum $\left({\mathrm{Mo}}^{32+}\right)$ x-ray lines observed in the spectrum measured at JET (shot #85909) at $T_e\approx 3.9$ keV and $n_e\approx 3.2\times {10}^{19}{\text{m}}^{-3}$.

Figure 4

Electron density and temperature profiles measured by LIDAR Thomson scattering at JET shot #85909 at a time between 16 and 17 s from the start of the discharge.

Figure 5

Fractional abundance for ${\mathrm{W}}^{44+}–{\mathrm{W}}^{47+}\text{tungsten}$ ions calculated for JET shot #85909 (time 16.0–17.0 s).

Figure 6

The MCDF-CI wavelength calculations for the Ni1 (upper) and Ni2 (bottom) tungsten lines as a function of the active set (ASn) compared with the experimental values. The dotted lines with diamond symbols represent the MCDF-CI calculations, while solid and dashed lines show the experimental values and their uncertainties.

Figure 7

Same as Fig. 6 but for Cu1, Cu2, and Cu3 tungsten lines.

Figure 8

Comparison of (a) previous and (b) present theoretical and experimental wavelengths of Ni1, Ni2 and Cu1, Cu2, Cu3 lines. The previous experimental wavelengths are taken from Refs. [15, 21], while the theoretical ones were taken from Refs. [25, 28]. The experimental uncertainties are represented by shaded area.