First Laboratory Measurement of Magnetic-field-induced Transition Effect in Fe x at Different Magnetic Fields

Abstract

The magnetic field is extremely important for understanding the properties of the solar corona. However, there are still difficulties in the direct measurement of the coronal magnetic field. The magnetic-field-induced transition (MIT) in Fe x, appearing in coronal spectra, was discovered to have prospective applications in coronal magnetic field measurements. In this work, we obtained the extreme ultraviolet spectra of Fe x in the wavelength range of 174–267 Å in the Shanghai High-temperature Superconducting Electron Beam Ion Trap, and examined the effect of MIT in Fe x by measuring the line ratios between 257.262 Å and the reference line of 226.31 Å (257/226) at different magnetic field strengths for the first time. The electron density that may affect the 257/226 value was also obtained experimentally and verified by comparing the density-sensitive line ratio (175.266 Å/174.534 Å) measurements with the theoretical predictions, and there was good agreement between them. The energy separation between the two levels of 3s23p43d 4 D 5/2 and 3s23p43d 4 D 7/2, one of the most critical parameters for determining the MIT rate, was obtained by analyzing the simulated line ratios of 257/226 with the experimental values at the given electron densities and magnetic fields. Possible reasons that may have led to the difference between the obtained energy splitting and the recommended value in previous works are discussed. Magnetic field response curves for the 257/226 value were calculated and compared to the experimental results, which is necessary for future MIT diagnostics.

Application of a Magnetic-field-induced Transition in Fe x to Solar and Stellar Coronal Magnetic Field Measurements

“…The effect of the MIT in Fe X at different magnetic fields has been verified experimentally in the laboratory by Xu et al (2022).…”

“…They obtained a value of 3.5 cm −1 with an upper limit of 7.8 cm −1 . A similar method was employed by Xu et al (2022) and they determined ΔE = 8.6 ± 2.7 cm −1 , which is, however, much larger than that from Li et al (2016). The authors discussed the uncertainties from atomic data, spectrometer efficiency calibration and data statistics.…”

“…Li et al (2015) and Li et al (2021) presented systematic theoretical studies for the atomic properties needed to determine the dependence of the MIT rate on the strength of the magnetic field and proposed that the MIT in Fe X can be used to measure the magnetic field strengths in the solar corona. More recently, Xu et al (2022) measured the MIT of Fe X at different magnetic fields using the Shanghai Hightemperature Superconducting Electron Beam Ion Trap (Shanghai-Htsc EBIT).…”

“…Since this method is highly dependent on the accuracy of the collisional-radiative model (CRM), the atomic processes between different charge states, such as direct ionization, radiative recombination and charge exchange that may happen under EBIT plasma conditions can also affect the populations between energy levels and, therefore, change the derived ΔE value significantly. However, these processes were not included in the CRM model used by Li et al (2016) and Xu et al (2022). Hence all these considerations need to be carefully investigated in order to obtain an accurate value of ΔE from laboratory measurements in the future.…”

Solar coronal magnetic field measurements using spectral lines available in Hinode/EIS observations: Strong and weak field techniques and temperature diagnostics

“…Recently, Li et al (2015Li et al ( , 2016 noticed the magnetic-field-induced transition (MIT) in the Fe ion and suggested that it can be used to diagnose coronal magnetic field strength (also see Li et al 2021;Xu et al 2022). Si et al (2020) developed the direct line ratio technique and applied this method to spectral observations taken by EUV Imaging Spectrometer (EIS, Culhane et al 2007) onboard Hinode, and the suitability of the method has been validated through forward modeling with a series of MHD models (Chen et al 2021a(Chen et al ,b, 2023Liu et al 2022;Martínez-Sykora et al 2022).…”