Solar spicules are small-scale jet-like structures in the lower solar atmosphere. Currently, the formation of these widely distributed structures lacks a complete explanation. It is still unclear whether they play an essential role in corona heating. Here, based on the magnetohydrodynamic scaling transformation relation, we perform experiments with the interaction of a high power laser with a one-dimensional sinusoidal modulated target to model solar spicules. We observe several spicule-like structures with alternating polarity magnetic fields around them. Magnetohydrodynamic simulations with similar parameters show the detail information during the spicules’ formation. The results suggest that the so-called strong pulse model can lead to the formation of the solar spicules. The magnetic reconnection process may also play a part and lead to additional heating and brightening phenomena.

Magnetic fields play a key role in driving a broad range of dynamic phenomena in the atmospheres of the Sun and other stars. Routine and accurate measurements of the magnetic fields at all the atmospheric layers are of critical importance to understand these magnetic activities, but in the solar and stellar coronae such a measurement is still a challenge due to the weak field strength and the high temperature. Recently, a magnetic-field-induced transition (MIT) of Fe X at 257.26 Å has been proposed for the magnetic field measurements in the solar and stellar coronae. In this review, we present an overview of recent progresses in the application of this method in astrophysics. We start by introducing the theory underlying the MIT method and reviewing the existing atomic data critical for the spectral modeling of Fe X lines. We also discuss the laboratory measurements that verify the potential capability of the MIT technique as a probe for diagnosing the plasma magnetic fields. We then continue by investigating the suitability and accuracy of solar and stellar coronal magnetic field measurements based on the MIT method through forward modeling. Furthermore, we discuss the application of the MIT method to the existing spectroscopic observations obtained by the Extreme-ultraviolet Imaging Spectrometer onboard Hinode. This novel technique provides a possible way for routine measurements of the magnetic fields in the solar and stellar coronae, but still requires further efforts to improve its accuracy. Finally, the challenges and prospects for future research on this topic are discussed.

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 3s 2 3p 4 3d 4 D 5/2 and 3s 2 3p 4 3d 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.

We study Hinode/EIS observations of an active region taken before, during, and after a small C2.0 flare in order to monitor the evolution of the magnetic field and its relation to the flare event. We find that while the flare left the active region itself unaltered, the event included a large magnetic field enhancement (MFE), which consisted of a large magnetic field strength increase to values just short of 500 G in a rather small region where no magnetic field was measured before. This MFE is observed during the impulsive phase of the flare at the footpoints of flare loops, its magnetic energy is sufficient to power the radiative losses of the entire flare, and has completely dissipated after the flare. We argue that the MFE might occur at the location of the reconnection event triggering the flare, and note that it formed within 22 minutes of the flare start (as given by the EIS raster return time). These results open the door to a new line of studies aimed at determining whether MFEs can be flare precursor events or used for Space Weather forecasts, what advance warning time they could provide and if this time is long enough to allow for mitigation procedures to be implemented; as well as to explore which physical processes lead to MFE formation and dissipation, whether such processes are the same in both long-duration and impulsive flares, and whether they can be predicted by theoretical models.

Observations and studies of what we call magnetic induced transitions have arguably re-opened a whole new area of atomic spectroscopy. There are transitions from upper levels that are sensitive to externally applied magnetic fields, such as those in tokamaks and the solar corona. So far only two types of ionic systems have been confirmed as leading to magnetic induced transitions, namely Ne-like Ar and Fe, and Cl-like Fe. We here propose a homologous system to Cl-like ions, namely Br-like ions, as a new candidate. These transitions are fed by close degeneracy between levels of relative short and long lifetimes, respectively. A similar close degeneracy as in Cl-like Fe is present in Br-like Sr and will give rise to an observable magnetic induced transition. We have predicted the magnetic induced transition rate for the D-4(7/2) level in Sr IV as a function of magnetic field strengths.

The 13th International Colloquium on Atomic Spectra and Oscillator Strengths for Astrophysical and Laboratory Plasmas (ASOS2019), co-hosted by Fudan and Lund Universities, was held at Fudan University from 23–27 June 2019 [...]

For all involved in astronomy, the importance of monitoring and determining astrophysical magnetic-field strengths is clear. It is also a well-known fact that the corona magnetic fields play an important part in the origin of solar flares and the variations of space weather. However, after many years of solar corona studies, there is still no direct and continuous way to measure and monitor the solar magnetic-field strength. We present here a scheme that allows such a measurement, based on a careful study of an exotic class of atomic transitions, known as magnetic induced transitions, in Fe9+. In this contribution we present a first application of this methodology and determine a value of the coronal field strength using the spectroscopic data from Hinode.

The present work illustrates the potential of a new diagnostic technique that allows the measurement of the coronal magnetic field strength in solar active regions by utilizing a handful of bright Fe x and Fe xi lines commonly observed by the high-resolution Hinode/EUV Imaging Spectrometer (EIS). The importance of this new diagnostic technique is twofold: (1) the coronal magnetic field is probably the most important quantity in coronal physics, being at the heart of the processes regulating space weather and the properties of the solar corona, and (2) this technique can be applied to the existing EIS archive spanning from 2007 to 2020, including more than one full solar cycle and covering a large number of active regions, flares, and even coronal mass ejections. This new diagnostic technique opens the door to a whole new field of studies, complementing the magnetic field measurements from the upcoming DKIST and UCoMP ground-based observatories, and extending our reach to active regions observed on the disk and until now only sampled by radio measurements. In this work, we present a few examples of the application of this technique to EIS observations taken at different times during the EIS mission, and we discuss its current limitations and the steps to improve its accuracy. We also present a list of EIS observing sequences whose data include all of the lines necessary for the application of this diagnostic technique, to help the solar community navigate the immense set of EIS data and to find observations suitable for measuring the coronal magnetic field.

It is normally assumed that induced transitions, by e.g. hyperfine, magnetic field or spin interaction, arise due to mixing in the upper levels. In this paper we discuss an example when mixing in the lower levels through an externally applied magnetic field gives rise to a magnetic field induced transition. We discuss the theory for such a transition and give an example from Fe X, which is relevant for the determination of the magnetic field of the solar corona. To make this possible, it is important to determine the energy difference between the 3p43d 4D5/2 and 4D7/2, which are accidentally very close in energy in Fe X. The splitting of these levels is expected to be around 3.5 cm−1 whereas their excitation energies are about 388 709 cm−1. We discuss how this fine structure can be determined, by observing transitions from levels that decay into this pair which have a longer wavelength than the resonance transition. Finally we discuss an experimental scenario based on an electron beam ion trap and a Fabry–Perot interferometer, to perform the measurement of this interval.

The multiconfiguration Dirac-Hartree-Fock theory is used to calculate the 3d9 2D3/2 - 2D5/2 transition energy for Co-like ions with Z = 28-100. We investigate how electron correlation, frequency-independent and -dependent Breit interactions, as well as QED corrections, vary along the sequence. The well-understood frequency-independent Breit contribution has the largest contribution for all ions. Among the corrections to this, correlation decreases rapidly with Z, the frequency-dependent Breit contribution is important especially for high-Z ions, and the self-energy contribution to the QED becomes the largest correction already for Z>50. We evaluate and compare results for the Self-energy in three different approximations, (i) the approach implemented in the GRASP2K package, (ii) the method based on Welton's concept and (iii) a model operator approach recently developed by Shabaev and coworkers. Through comparison with experimental values, it seems that the third set of results have the best agreement with experiments, but the difference from experiments for high-Z ions, is around 0.03%-0.04%, and therefore our results are outside the error bars of the experiments.

Theoretical calculations of Ga-like to Br-like gadolinium ions were performed by using the fully relativistic multi-configuration Dirac–Hartree–Fock (MCDHF) method. Extensive lists of excitation energies, wavelengths, line and oscillator strengths, and E1, M1, E2, M2, and E3 transition rates are presented. The effects of core–valence electron correlation from the deep subshells 3d and 3p are investigated and the accuracy of the results is confirmed by comparing with available theoretical and experimental data sets.

We propose that the ground term transition, 2p(5) P-2(3/2)-P-2(1/2), for ions in the F-like isoelectronic sequence could be used to accurately test current methods to compute Breit and quantum-electrodynamic (QED) effects. These systems are of interest since correlation is small due to what we will label Layzer quenching. Using the multiconfiguration Dirac-Hartee-Fock method, we investigate how correlation, Breit and QED corrections vary along the sequence and show that QED dominates over correlation already for Z approximate to 20. We also investigate the behavior of different QED effects as a function of the nuclear charge and find that the self-energy dominates for the mid-Z range (40-80), but then decreases to change sign for Z approximate to 90. For a few elements between Z = 85 and 90 the vacuum polarization is the leading term, while for higher Z the two QED contributions cancel. This opens up the possibility for these ions to carefully test the frequency-dependent transverse photon correction. The uncertainties of the treatment of the well-understood frequency-independent Breit correction and correlation are expected to be at least three orders of magnitude smaller than the QED and frequency-dependent transverse photon corrections for high Z. In this work we also compare and evaluate the results from three different methods to compute self-energies.

The multiconfiguration Dirac-Hartree-Fock theory is used to calculate the 3d(9) D-2(3/2)-> D-2(5/2) transition energy for Co-like ions with Z = 28-100. We investigate how electron correlation, frequency-independent and -dependent Breit interactions, as well as QED corrections vary along the sequence. The well-understood frequency-independent Breit contribution has the largest contribution for all ions. Among the corrections to this, correlation decreases rapidly with Z, the frequency-dependent Breit contribution is important especially for high-Z ions, and the self-energy contribution to the QED becomes the largest correction already for Z > 50. We evaluate and compare results for the Self-energy in three different approximations, (i) the approach implemented in the GRASP2K package, (ii) the method based on Welton's concept and (iii) a model operator approach recently developed by Shabaev and coworkers. Through comparison with experimental values, it seems that the third set of results have the best agreement with experiments, but the difference from experiments for high-Z ions, is around 0.03%-0.04%, and therefore our results are outside the error bars of the experiments.

Dielectronic recombination is an important process in high temperature plasmas. In the present work, the KLn (n = L, M, N and O) DR resonance strengths of He-like to O-like xenon ions are measured at the Shanghai electron beam ion trap using a fast electron beam energy scanning method. The experiment uncertainty reaches about 6% with significant improvement of statistics. A relativistic configuration interaction calculation is also made. Theoretical results agree with the experiment results within 15% in most cases.

We report on a flat crystal spectrometer (FCS) featuring a differently pumped rotary feedthrough and double detectors connected to a crystal chamber by extendable bellows built at the Shanghai EBIT Laboratory. It was designed to overcome defects such as oil contamination, little distance from the detector to the crystal and others of an early FCS equipped at the same laboratory, but still keeps a large detectable angle range of detectors and brings new features and functions such as the Bond method measurement and double-crystal measurement which are based on the two-detector and large bellow design. This new FCS could cover an energy range of measurable photons from 570 eV to 10 keV and reach a vacuum better than 6 × 10−10 Torr and thus is compatible for coupling directly to ultra-high vacuum light sources. Off-line tests of the FCS were undertaken where Kα x-rays from solid titanium were measured and analyzed. Measurements of transitions in He-like argon ions were performed when the spectrometer was directly connected to Shanghai EBIT, and the width of the x-ray source was monitored simultaneously using an x-ray slit imaging system. An observed spectral line broadening was 0.869 eV corresponding to a resolving power of 3600, including Doppler broadening of the x-ray source. Taking account of the measured source width, we made simulations using the SHADOW 3 code and got a nominal resolving power of 6500 for the spectrometer. This high nominal resolving power is due to a longer distance from the crystal to the detector, comparing with that in the early FCS.

In this work, we investigate the magnetic-field-and hyperfine-induced P-3(0) -> S-1(0) transitions in Be-and Ne-like ions along the respective isoelectronic sequence by using the multiconfiguration Dirac-Hartree-Fock method. The transition probabilities are in this case dependent on the magnetic hyperfine quantum number M-F of the upper state. We show that it is important to include perturbers with Delta(F) = +/- 1. The calculated transition rates are compared to experimental results, when available. The discrepancies between the resulting magnetic-fieldand hyperfine-induced transition rates and the experimental values in Be-like ions are discussed as well as the observability of the hyperfine-induced transitions in Ne-like ions.

In this work, we investigate the magnetic-field- and hyperfine-induced $^{3}P_{0}\phantom{\rule{4pt}{0ex}}\ensuremath{\rightarrow}\phantom{\rule{4pt}{0ex}}^{1}S_{0}$ transitions in Be- and Ne-like ions along the respective isoelectronic sequence by using the multiconfiguration Dirac-Hartree-Fock method. The transition probabilities are in this case dependent on the magnetic hyperfine quantum number ${M}_{F}$ of the upper state. We show that it is important to include perturbers with $\mathrm{\ensuremath{\Delta}}F=\ifmmode\pm\else\textpm\fi{}1$. The calculated transition rates are compared to experimental results, when available. The discrepancies between the resulting magnetic-field- and hyperfine-induced transition rates and the experimental values in Be-like ions are discussed as well as the observability of the hyperfine-induced transitions in Ne-like ions.

In this contribution we will discuss a single spectral line in W 27+ an M1 line between the two ground state fine structure levels 4d 10 4f 2 F7/2 and 2 F5/2. This is the only transition within the ground configuration of this ion and therefore a challenge to identify spectroscopically. We have studied this line both experimentally using an EBIT and theoretically using the GRASP2K code [1]. These investigations were done independently and the results only compared when both methods had reached a conclusive wavelength, from careful and systematic considerations. One of the motivation for this work was the fact that earlier predictions for this transition showed a spread of over 400 Å for the wavelength [2, 3]. Our experiments were performed using the Shanghai permanent magnet EBIT and an Andor 303 Shamrock spectrometer equipped with an Andor Newton CCD camera. Tungsten was injected into the EBIT using the vaporous compound W(CO)6. Spectra were recorded at several electron beam energies to isolate the W 27+ line. The spectra were wavelength calibrated using a number of calibration lamps and the final experimental wavelength was determined to be 3377.43 ± 0.26 Å. To confirm the line was really from W 27+ we determined the lifetime of the upper level of the 2 F term and compared our value with one from a calculation. As the line is from an M1 transition the lifetime of the upper level it is trivial to calculate the rate and thereby the lifetime. Our theoretical studies are systematic in two senses – first we investigate the contributions to the wavelength from different core subshells. These studies implies it is important to include core valence correlation even between the valence 4f and deep subshells – as a matter of fact, the correlation contribution from 3d is more pronounced than from 4d. The second dimension of the systematic approach is an increase of the active set of orbitals, and thereby the space of configuration state functions (CSFs) to show convergence of the final results.

Three visible lines of M1 transitions from In-like tungsten were recorded using the Shanghai Permanent Magnet Electron Beam Ion Trap. The experimental wavelengths were measured as 493.84 ± 0.15, 226.97 ± 0.13 and 587.63 ± 0.23 nm (vacuum wavelengths). These results are in good agreement with theoretical predictions obtained using the large-scale relativistic many-body perturbation theory, in the form of the flexible atomic code.

We have investigated the visible spectrum of W11+ and found a very strong line at the wave length of 527.61 nm from the 4f135s25p2 (2F7/2-2F5/2) transition. We show that this line is strong since the excitation energy of the upper level opens up the possibility to capture a large population. We discuss the possibility that this strong line could be the unknown line seen in charge exchange spectra recorded at the JET fusion facility.