Atomic data of tungsten for current and future uses in fusion and plasma science

Abstract

Abstract. Atomic physics has played an important role throughout the history of experimental plasma 5 physics. For example, accurate knowledge of atomic properties has been crucial for understanding the plasma 6 energy balance and for diagnostic development. With the shift in magnetic fusion research toward high-7 temperature burning plasmas like those expected to be found in the ITER tokamak, the atomic physics of 8 tungsten has become of importance. Tungsten will be a constituent of ITER plasmas because of its use as a 9 plasma-facing material able to withstand high heat loads with lower tritium retention than other possible 10 materials. Already, ITER diagnostics are being developed based on using tungsten radiation. In particular, 11 the ITER Core Imaging X-ray Spectrometer (CIXS), which is designed to measure the core ion temperature 12 and bulk plasma motion, is being based on the x-ray emission of neonlike tungsten ions (W 64+ ). In addition, 13 tungsten emission will at ITER be measured by extreme ultraviolet (EUV) and optical spectrometers to 14 determine its concentration in the plasma and to assess power loss and tungsten sputtering rates. On present-

Interpretation of EUV emissions observed by Mills et al.

“…From the similarity of the calculated low resolution curve and experiment, it is concluded that the pseudo-continuum discussed in references [1][2][3][4] is the result of overlapping and unresolved spectral lines. This interpretation is supported by experimental observations [5] 2 , [9] and , He, and O2 fill gases from figures 3e, 3c, and 3a, respectively, of [1]. For the He and O2 gas fills, a small background decreasing with wavelength (such as expected for scattered light) and ≤10% of the peak pseudo-continuum at 20 nm is subtracted from the original data.…”

“…These coincidences are confirmed by high resolution scans (not shown) with the EBIT source [5] 2 operating at an electron beam energy of 128 ± 10 eV. In particular, the line at 21.6 nm, dominating the EBIT data, is a strong line of W VII [12][13][14], while the calculated O V line intensity at nearly the same wavelength is predicted to be relatively weak 5 . Because tabulated spectra of W VIII and W IX are not available [12,13,15], these tests cannot be made on the shorter wavelength portion of the data.…”

“…In Figure 1a the spectrum of Mills et al is plotted together with W spectra observed by Clementson et al [5] 2 from an electron beam ion trap (EBIT). The data were acquired using a grazing-incidence instrument with a resolution of 0.04 nm full width half maximum (FWHM) at an EBIT electron-beam energy of 150 ± 10 eV.…”

“…The barely resolved structure in the Mills et al [2][3][4]] data of Figure 1a at wavelengths between 20 and 22 nm shows at least four coincidences between lines (or groups of lines) as observed using the EBIT device with a pure W plasma [5] 2 . These coincidences are confirmed by high resolution scans (not shown) with the EBIT source [5] 2 operating at an electron beam energy of 128 ± 10 eV.…”

Extreme Ultraviolet Spectra of Few-Times Ionized Tungsten for Divertor Plasma Diagnostics

“…The increased usage of tungsten as a wall material in magnetic fusion devices has led to the need for accurate atomic data of tungsten for essentially all ionization stages [1,2]. In addition to the large influence on the plasma power balance, tungsten emission may provide diagnostic information from all parts of the plasma, from the hot core to the cooler edge and divertor regions.…”