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

Joel Clementson,Peter Beiersdorfer,Thomas Lennartsson

doi:10.3390/atoms3030407

Joel Clementson, Peter Beiersdorfer + Show 1 more

Open Access

https://doi.org/10.3390/atoms3030407

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Journal: Atoms	Publication Date: Sep 9, 2015
Citations: 56	License type: CC BY 4.0

Affiliation: Lawrence Livermore National Laboratory, Lund University

Abstract

The extreme ultraviolet (EUV) emission from few-times ionized tungsten atoms has been experimentally studied at the Livermore electron beam ion trap facility. The ions were produced and confined during low-energy operations of the EBIT-I electron beam ion trap. By varying the electron-beam energy from around 30–300 eV, tungsten ions in charge states expected to be abundant in tokamak divertor plasmas were excited, and the resulting EUV emission was studied using a survey spectrometer covering 120–320 Å. It is found that the emission strongly depends on the excitation energy; below 150 eV, it is relatively simple, consisting of strong isolated lines from a few charge states, whereas at higher energies, it becomes very complex. For divertor plasmas with tungsten impurity ions, this emission should prove useful for diagnostics of tungsten flux rates and charge balance, as well as for radiative cooling of the divertor volume. Several lines in the 194–223 Å interval belonging to the spectra of five- and seven-times ionized tungsten (Tm-like W VI and Ho-like W VIII) were also measured using a high-resolution spectrometer.

Highlights

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]
Emission from low charge states of tungsten has been observed in magnetic fusion plasmas, not with enough resolution to allow for detailed spectroscopic measurements
The present measurements were performed using electron beam ion traps (EBITs)-I, which is the original electron beam ion trap developed at Livermore thirty years ago [35,36,37], by scanning the beam energy in the range of 30–300 eV and exciting the tungsten spectra expected from tokamak divertor plasmas

Summary

Introduction

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]. Based on the tungsten ionization energies [3], it can be expected that, neglecting transport, approximately the first ten charge states will have high abundances For divertor plasmas, it is the atomic data for few-times ionized tungsten that are needed. Sugar and Kaufman measured VUV and EUV lines from the closed-shell Er-like W6+ ion using a sliding-spark light source [13]. Emission from low charge states of tungsten has been observed in magnetic fusion plasmas, not with enough resolution to allow for detailed spectroscopic measurements. The present measurements were performed using EBIT-I, which is the original electron beam ion trap developed at Livermore thirty years ago [35,36,37], by scanning the beam energy in the range of 30–300 eV and exciting the tungsten spectra expected from tokamak divertor plasmas

EBIT Spectroscopy

Survey Measurements

High-Resolution Measurements

Spectral Analysis

Theoretical Atomic Data

Analysis

Results and Discussion