Electron density diagnostic for hot plasmas in coronal regime by using B-like ions

TL;DR

This paper develops an electron density diagnostic method using B-like ion line ratios in hot plasmas, validated with laboratory and stellar coronal data, enhancing plasma diagnostic capabilities in astrophysics.

Contribution

The study introduces a new diagnostic technique based on $3d-2p$ line ratios in B-like ions, extending plasma density measurements to coronal regimes and validating with both laboratory and astrophysical data.

Findings

Line ratios are sensitive to electron density in specified ranges.

Effective electron densities in EBIT plasmas are estimated and agree with other measurements.

The diagnostic method is validated with stellar coronal spectra, showing consistent results.

Abstract

Line ratio of $3d-2p$ transition lines in boron-like spectra of Si X, S XII, Ar XIV and Fe XXII has been investigated. Collisional-radiative model calculations reveal that the line ratio is sensitive to the electron density in ranges of $n_{\rm e}=4.0\times10^7-3.0\times10^{10}$ cm$^{-3}$, $4.0\times10^8-3.0\times10^{11}$ cm$^{-3}$, $3.0\times10^9-4.0\times10^{12}$ cm$^{-3}$ and $2.0\times10^{12}-3.0\times10^{15}$ cm$^{-3}$, respectively. This complements the K-shell diagnostics of helium-like ions. By comparison between the prediction and the measured values, effective electron densities in the electron beam ion trap (EBIT) plasmas performed by Lepson and collaborators at Lawrence Livermore EBIT, are estimated to be $n_{\rm e}=3.4^{+0.8}_{-0.6}\times10^{10}$ cm$^{-3}$ and $5.6^{+1.0}_{-1.1}\times10^{10}$ cm$^{-3}$ for sulphur and argon plasmas. In case of argon, a good agreement is shown with the actual electron density derived from N VI K-shell spectrum. We further explore the $3d-2p$ transition lines of Si X and S XII in the stellar coronal spectra measured with the Low Energy Transmission Grating Spectrometer combined with High Resolution Camera on board the {\it Chandra X-ray Observatory}. The constrained electron densities show a good agreement with the those determined from C V and O VII K-shell spectra.