Atomic-Level Pseudo-Degeneracy of Atomic Levels Giving Transitions Induced by Magnetic Fields, of Importance for Determining the Field Strengths in the Solar Corona

Abstract

We present a measured value for the degree of pseudo-degeneracy between two fine-structure levels in Fe9+ from line intensity ratios involving a transition induced by an external magnetic field. The extracted fine-structure energy difference between the and levels, where the latter is the upper state for the magnetic-field induced line, is needed in our recently proposed method to measure magnetic-field strengths in the solar corona. The intensity of the line at 257.262 Å is sensitive to the magnetic field external to the ion. This sensitivity is in turn strongly dependent on the energy separation in the pseudo-degeneracy through the mixing induced by the external magnetic field. Our measurement, which uses an Electron Beam Ion Trap with a known magnetic-field strength, indicates that this energy difference is 3.5 cm−1. The high abundance of Fe9+ and the sensitivity of the line’s transition probability to field strengths below 0.1 T opens up the possibility of diagnosing coronal magnetic fields. We propose a new method to measure the magnetic field in the solar corona, from similar intensity ratios in Fe9+. In addition, the proposed method to use the line ratio of the blended line with another line from Fe x as the density diagnostic should evaluate the effect of the magnetic-field-induced transition line.

ON THE FINE STRUCTURE SPLITTING OF THE 3p43d 4D5/2 AND 3p43d 4D7/2 LEVELS OF Fe x

“…The value of 3.6 ± 2.7 cm −1 is an independent verification of the small estimate of the splitting ≈ 3.5 cm −1 obtained entirely independently by Li et al (2016) from the Shanghai EBIT device. Our work rejects some of the larger values examined by Li et al (2015).…”

“…The latter authors estimated the value of E j − E i for levels 3p 4 3d 4 D 5/2 and 3p 4 3d 4 D 7/2 using a known magnetic field and the observed intensity ratio. At present, the splitting is believed to be on the order of 3.5 cm −1 from the Shanghai EBIT measurement, by measurement of the EUV spectrum with a known magnetic field (Li et al 2016). But given the high sensitivity of the derived magnetic field to the zero-field splitting, it is important to try to constrain the energy splitting through other techniques.…”

“…For this method to be of practical use, the energy difference E j − E i must be known with sufficient accuracy (Li et al 2016). The latter authors estimated the value of E j − E i for levels 3p 4 3d 4 D 5/2 and 3p 4 3d 4 D 7/2 using a known magnetic field and the observed intensity ratio.…”

“…and Li et al (2015Li et al ( , 2016 have presented a novel method by which mixing of atomic states by the Zeeman effect can in principle be used to determine magnetic field strengths in the solar corona. The method is readily illustrated by non-degenerate first order quantum perturbation theory.…”

Responsivity calibration of the extreme ultraviolet spectrometer in the range of 175-435 Å

“…5,6 In addition, the intensity ratios of iron lines are good candidates to determine the plasma density or even the magnetic field strength in the solar corona. 7,8 For the extensive utilization in plasma diagnostics, a portable high-resolution extreme ultraviolet spectrometer has been designed and developed at Shanghai electron beam ions trap (EBIT) laboratory 9 Much work has been done using EUV spectrometer at EBIT devices for identification of new lines and plasma diagnostics. [5][6][7][8][10][11][12][13] The line intensity ratios of Fe xiv 264.8 Å/274.2 Å, 219.1 Å/211.3 Å and 270.5 Å/274.2 Å and Fe xv 233.9 Å/243.8 Å were studied in Ref.…”