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

Tetsutarou Oishi,Daiji Kato,Tomoko Kawate,Motoshi Goto,Izumi Murakami,Shigeru Morita,Yasuko Kawamoto,Hiroyuki A Sakaue

doi:10.3390/atoms9030069

Abstract

Spectroscopic studies for emissions released from tungsten ions have been conducted in the Large Helical Device (LHD) for contribution to the tungsten transport study in tungsten divertor fusion devices and for expansion of the experimental database of tungsten line emissions. Tungsten ions are distributed in the LHD plasma by injecting a pellet consisting of a small piece of tungsten metal wire enclosed by a carbon tube. Line emissions from W0, W5+, W6+, W24+–W28+, W37+, W38+, and W41+–W46+ are observed simultaneously in the visible (3200–3550 Å), vacuum ultraviolet (250–1050 Å), and extreme ultraviolet (5–300 Å) wavelength ranges and the wavelengths are summarized. Temporal evolutions of line emissions from these charge states are compared for comprehensive understanding of tungsten impurity behavior in a single discharge. The charge distribution of tungsten ions strongly depends on the electron temperature. Measurements of emissions from W10+ to W20+ are still insufficient, which is addressed as a future task.

Highlights

Tungsten (W) is considered as a candidate material for plasma-facing components (PFCs) in the divertor region of the international thermonuclear experimental reactor (ITER)and future fusion reactors because of its high melting point, low sputtering yield, and low tritium retention [1,2,3]
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]
Spectroscopic studies of emissions released from tungsten ions have been conducted in LHD for contribution to the tungsten transport study in tungsten divertor fusion devices and for expansion of the experimental database of tungsten line emissions

Summary

Introduction

Tungsten (W) is considered as a candidate material for plasma-facing components (PFCs) in the divertor region of the international thermonuclear experimental reactor (ITER). 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, W0 , as well as the singly ionized ions, W+ , were observed using visible spectroscopy in the wavelength range of 4000–4400 Å [11]. The line emissions from tungsten ions in low charge states, W2+ –W6+ , have been identified in the VUV range of 500–1500 Å [18]. Temporal evolution of emissions from tungsten ions in various charge states that are observed simultaneously will be demonstrated for comprehensive understanding of behavior of tungsten impurity

Tungsten Pellet Injection Experiment in LHD

Findings

Summary