Spectroscopy of diagnostically-important magnetic-dipole lines in highly-charged 3d$^n$ ions of tungsten

TL;DR

This study uses EBIT to measure EUV spectra of highly-charged tungsten ions, identifying 37 new spectral lines from magnetic-dipole transitions, which can help diagnose plasma conditions in fusion devices.

Contribution

First identification of 37 spectral lines from magnetic-dipole transitions in highly-charged tungsten ions using collisional-radiative modeling.

Findings

Most strong lines are due to forbidden M1 transitions.

Line ratios can diagnose temperature and density in fusion plasmas.

Introduces a new level-merging scheme for rate equations.

Abstract

An electron beam ion trap (EBIT) is used to measure extreme ultraviolet spectra between 10 nm and 25 nm from highly-charged ions of tungsten with an open 3d shell (W XLVIII through W LVI). We found that almost all strong lines are due to the forbidden magnetic-dipole (M1) transitions within $3d^n$ ground configurations. A total of 37 spectral lines are identified for the first time using detailed collisional-radiative (CR) modeling of the EBIT spectra. A new level-merging scheme for compactification of rate equations is described. The CR simulations for Maxwellian plasmas show that several line ratios involving these M1 lines can be used to reliably diagnose temperature and density in hot fusion devices.