Analysis of EUV spectra of Sn XIX–XXII observed in low-density plasmas in the Large Helical Device

Abstract

We have measured extreme ultraviolet (EUV) spectra from highly charged tin ions in low-density and high-temperature plasmas produced in the Large Helical Device at the National Institute for Fusion Science. The EUV spectra emitted after injection of a tin pellet into a hydrogen plasma were monitored by a grazing incidence spectrometer whose wavelength resolution is about 0.01 nm. Two different types of spectral feature were measured in the 13-17 nm region depending on whether the discharge was stably sustained or underwent radiation collapse. The measured EUV spectra were analyzed by considering the difference in dominant charge states observed in the two types of spectra. Apart from the complex quasi-continuum structure around 13.5 nm, several strong lines occurring at wavelengths longer than 14 nm were found to originate from the transitions between excited states of Sn XXI and Sn XXII by comparison with the other experimental data including the charge exchange collisions experiments. Most of the strong spectral lines which were not identified as Sn XXI or Sn XXII were assigned to the resonance transitions of Sn XIX and Sn XX from comparison with the results of theoretical calculations.

Measurement of EUV Spectra from High Z Elements in the Large Helical Device

“…Many lines of Ge-like ions are also found and listed in ref. [8]. It should be emphasized that the lines from Ga-and Ge-like tin were identified for the first time in this work.…”

“…When the plasma edge is cooled as low as 200 eV, a broad spectral feature arising from UTA of open 4d subshell ions appears around 13.5 nm. As described in the next section, most of the sharp discrete lines in longer wavelength region are from higher charge states with open 4s or 4p subshell ions [8].…”

“…In this study, assignments of the strong discrete lines from tin and xenon ions, and the complicated broad features of tungsten ions have been performed with the help of comparisons with the previous experimental results, the experimental spectra in charge exchange collisions [21] and the theoretical calculations by Cowan code. Consequently, most of the strong discrete lines in longer wavelength side of the UTAs from tin and xenon have been assigned to the 4p-4d or 4d-4f transitions of higher charge states with open 4s or 4p subshell Cu-to Ge-like ions [8], which are partially summarized in table 1. It is noteworthy that the lines of Cu-like and Zn-like ions due to transitions between excited states are clearly observed in LHD, which are only very weakly observed in electron beam ion traps (EBITs) because of extremely low density.…”

“…Tin and xenon have been investigated as candidate elements in the development of EUV light source for the next generation semiconductor lithography [3,4], and tungsten has been determined as a plasma facing component in the forthcoming International Thermonuclear Experimental Reactor (ITER) project [5]. We have measured EUV spectra from these elements in LHD so far [6,7,8,9].…”

Plasma Diagnostics with Tracer-Encapsulated Solid Pellet

“…It has been done especially in the range of EUV spectra from Nd, Gd [44,45], Sn [46,47] and W [48][49][50] and also the other heavy atoms. For example, spectra of highly charged Neodymium is studied with Neodymium tracer in the TESPEL having a diameter of 900 µm under the plasma condition with T e (0) = 2 keV andn e = 4×10 19 m −3 .…”