Abstract
The intensity ratio of Fe XIV 264.765A/274.203A is useful to determine the electron density of solar corona, and the relationship between the electron density and the intensity ratio obtained from a model should be evaluated using laboratory plasmas to estimate the electron density more precisely. We constructed a new collisional–radiative model (CR-model) for Fe XIV (an Al-like iron ion) by considering the processes of proton-impact excitation and electron-impact ionization to the excited states of a Mg-like iron ion. The atomic data used in the CR-model were calculated using the HULLAC atomic code. The model was evaluated based on laboratory experiments using a compact electron beam ion trap, called CoBIT, and the Large Helical Device (LHD). The measured Fe XIV 264.785 Å/274.203 Å line intensity ratio with CoBIT was 1.869 ± 0.036, and it agreed well with our CR-model results. Concurrently, the measured ratio using LHD was larger than the results of our CR-model and CHIANTI. The estimated electron densities using our CR-model agreed with those from CHIANTI within a factor of 1.6–2.4 in the range of ne≈1010−11cm−3. Further model development is needed to explain the ratio in a high-electron density region.
Highlights
Spectroscopy provides various information on observed plasmas, and is important for obtaining their physical properties, of astrophysical plasmas
The extreme ultraviolet (EUV) spectrometer mounted on compact electron beam ion trap (CoBIT)-II was composed of a 1200 gr/mm grating (30-002 Shimadzu Corporation) and a charge coupled device
To avoid line blending of Fe XIV 264.785 Å and Fe XVI 265.000 Å, the beam energy was set as 400 eV, which is less than 456.2 eV, the ionization energy of Fe
Summary
Spectroscopy provides various information on observed plasmas, and is important for obtaining their physical properties, of astrophysical plasmas. Measuring a density-sensitive line intensity ratio is a good method for diagnosing the electron density of plasmas. The intensity ratios of Fe XIII line pairs, such as 203.8 Å/202.0 Å, are used to estimate the electron densities of solar plasmas [1]. The intensity ratio of Fe XIV 264.785 Å and 274.203 Å lines is sensitive to electron density, and it is one of the most measured line pairs by Hinode/EIS (e.g., References [5,6,7,8,9,10]). The ion fraction of the Al-like iron ion (Fe XIV) presents a peak in 106.3 K plasmas; measuring the Fe XIV 264.785 Å/274.203 Å line intensity ratio is a good method for electron density diagnosis for plasma phenomena in the solar corona
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