A study of tungsten spectra using large helical device and compact electron beam ion trap in NIFS

Abstract

Tungsten spectra have been observed from Large Helical Device (LHD) and Compact electron Beam Ion Trap (CoBIT) in wavelength ranges of visible to EUV. The EUV spectra with unresolved transition array (UTA), e.g., 6g-4f, 5g-4f, 5f-4d and 5p-4d transitions for W +24-+33 , measured from LHD plasmas are compared with those measured from CoBIT with monoenergetic electron beam (d2keV). The tungsten spectra from LHD are well analyzed based on the knowledge from CoBIT tungsten spectra. The C-R model code has been developed to explain the UTA spectra in details. Radial profiles of EUV spectra from highly ionized tungsten ions have been measured and analyzed by impurity transport simulation code with ADPAK atomic database code to examine the ionization balance determined by ionization and recombination rate coefficients. As the first trial, analysis of the tungsten density in LHD plasmas is attempted from radial profile of Zn-like WXLV (W 44+ ) 4p-4s transition at 60.9Å based on the emission rate coefficient calculated with HULLAC code. As a result, a total tungsten ion density of 3.5x10 10 cm -3 at the plasma center is reasonably obtained. In order to observe the spectra from tungsten ions in lower-ionized charge stages, which can give useful information on the tungsten influx in fusion plasmas, the ablation cloud of the impurity pellet is directly measured with visible spectroscopy. A lot of spectra from neutral and singly ionized tungsten are observed and some of them are identified. A magnetic forbidden line from highly ionized tungsten ions has been examined and Cd-like WXXVII (W 26+ ) at 3893.7Å is identified as the ground-term fine-structure transition of 4f 2 3 H 5 -3 H 4 . The possibility of D particle diagnostic in D-T burning plasmas using the magnetic forbidden line is discussed.

Coronal lines and the importance of deep-core–valence correlation in Ag-like ions

“…Although the electron density in EBITs is lower than tokamak fusion * jon.grumer@teorfys.lu.se plasma densities, by around 2 orders of magnitude, M1 lines have been observed in fusion devices, e.g., as mentioned above the 2s 2 2p 3 2 D 5/2 -2 D 3/2 M1 decay in Fe XX [3]. Also, at the National Institute for Fusion Science in Japan, Morita et al [7] reported the observation of M1 transitions in the visible region for highly charged tungsten ions. Previously spectra from tokamaks made a great impact on the study of M1 and other forbidden transitions (see Ref.…”

Simultaneous Observation of Tungsten Spectra of W0 to W46+ Ions in Visible, VUV and EUV Wavelength Ranges in the Large Helical Device

“…UTAs consisting of W 24+ -W 33+ and W 27+ -W 42+ also appeared at 19-33 Å and 46-53 Å, respectively. The identification of charge states of the UTA was performed by comparing the spectra obtained in LHD and the compact electron beam ion trap (CoBIT) with CR model calculations [11,[37][38][39]. It is worth noting that the UTAs at around 50 Å have been used to evaluate tungsten ion concentrations in tokamak experiments [40].…”

“…Spectroscopic studies for emission from W ions in combination with a tungsten pellet injection technique have been intensively conducted on the Large Helical Device (LHD) for contribution to tungsten transport studies in tungsten divertor fusion devices represented by ITER and for expansion of the experimental database of tungsten line emissions [11][12][13][14]. The electron temperature, T e , of the LHD core plasmas with a tungsten pellet injection ranges from 0.5 keV to 3.5 keV, which is close to that of the edge plasmas in ITER around the last closed flux surface, including the scrape-off layer.…”

“…The current status of tungsten emission lines observed in LHD using visible, vacuum ultraviolet (VUV), and extreme ultraviolet (EUV) spectroscopy can be summarized as follows. The line emissions from the neutral atoms, W 0 , as well as the singly ionized ions, W + , were observed using visible spectroscopy in the wavelength range of 4000-4400 Å [11]. The visible spectroscopy has also observed magnetic dipole (M1) forbidden transition lines from W 26+ and W 27+ in the wavelength range of 3300-3900 Å [15][16][17].…”

Advanced multiconfiguration methods for complex atoms: I. Energies and wave functions

“…The complexity is also a hindrance to the necessary diagnostics of this contaminationvery little is known about the structure of the different ions of Tungsten. A major effort in later years on the spectroscopy of Tungsten, has been to understand these complex systems and be able to help in developing a new energy source [32,33,34].…”