Review of highly charged tungsten spectroscopy research using low energy EBITs at the Shanghai EBIT laboratory

Abstract

We present an overview of recent work on the spectroscopy of tungsten ions, related to tokamak edge plasma. The spectra were recorded from the newly-built low energy electron beam ion traps (EBITs) in the Shanghai EBIT laboratory. By analyzing the spectra with the help of accurate theoretical calculations, using state-of-the-art techniques, we were able to identify term and fine structure splittings in the ground and the first excited configuration for a number of charge states. The theoretical models included a careful study of correlation and showed an excellent agreement with our experimental results for transition energies and rates. Some metastable levels which have extremely long lifetime and high population were found, and the influences of these levels on the charge state distribution of tungsten ions in tokamaks are discussed.

Extended Atomic Structure Calculations for W11+ and W13+

“…They confirmed that the ground state is 4f 13 5s 2 2 F 7/2 . Qiu et al [29] studied the visible and soft X-ray spectral regions and concluded that 4f collapse is not complete in W 13+ . According to them [29], four lines that were identified in the Berlin EBIT spectra [30] do not appear to originate from tungsten.…”

“…Qiu et al [29] studied the visible and soft X-ray spectral regions and concluded that 4f collapse is not complete in W 13+ . According to them [29], four lines that were identified in the Berlin EBIT spectra [30] do not appear to originate from tungsten. Kobayashi et al [31] observed extreme ultraviolet and visible spectra of W 13+ using EBIT.…”

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

“…Detailed laboratory measurements on tungsten ions are well suited for electron beam ion traps (EBITs), where charge-state selection is good and the ion temperature and electron density low. Several studies of tungsten in various ionization stages and spectral ranges have been conducted using EBITs; see, e.g., [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33]. Although designed to have a very wide electron-beam energy range, EBITs have mostly been used at energies above several hundred electron volts, leading to a focus on highly or moderately charged ions with little attention on the first few charge states.…”

Visible spectra of W8+ in an electron-beam ion trap

“…Electron-beam ion traps (EBITs) are one of the most versatile light sources for studying W spectroscopy (see, e.g., Refs. [20,[36][37][38][39][40]), since W ions in almost any charge state can be produced through successive ionization by a monoenergetic and energy-adjustable electron beam. However, the determination of charge states of lowly charged W ions is an intractable problem in EBIT measurements (see, e.g., Refs.…”

“…Over the last few years some progress has been made in spectroscopic data for lowly charged W ions (gap for W 7+ -W 26+ ), including W 7+ [4,33,34,36,46,47,48], W 11-15+ [24][25][26][27], and W 25-26+ [37,39]. In the present work we focus on the visible spectra lines from W 8+ , a more complicated case than W 7+ .…”