| 1. |
- Grumer, Jon, et al.
(author)
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Magnetic field induced transition rates in Ne- and Be-like ions for plasma diagnostics and E1M1 two-photon decay rate determination
- 2014
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In: XXVIII International Conference on Photonic, Electronic and Atomic Collisions (ICPEAC 2013). - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 488, s. 152005-152005
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Journal article (other academic/artistic)abstract
- We report on theoretical results of magnetic field induced transitions (MITs) in Ne- and Be-like ions without nuclear spin for two applicalions. Firstly, MITs are promising candidates in the determination of magnetic fields in plasmas. In our work on Ne-like ions we present accurate theoretical MIT rates for 2p(6 1)S(O) - 2p(5)3s 3P(O),2 [11. Purthermore, for Be-like ions, it has been proposed to extract the rate of the BIM1 two-photon transition 2s(2 1)S(O) - 2s2p P-3(O) by measuring the lifetime of the 'Po state using a storage ring, which involves an external magnetic field. The MIT rates are carefully evaluated and shown to be of the same order as the ElMI rates [2].
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| 2. |
- Grumer, Jon, et al.
(author)
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Unexpected transitions induced by spin-dependent, hyperfine and external magnetic-field interactions
- 2014
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In: Physica Scripta. - : IOP Publishing. - 0031-8949 .- 1402-4896. ; 89:11
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Journal article (peer-reviewed)abstract
- Unexpected transitions are induced by weaker interactions not included in the gross structure model of the ion under investigation. We discuss different examples of such decay channels, starting with relativistic spin-induced transitions. These represented an important field of study a few decades ago, and we illustrate how some challenging cases can be treated very accurately with today's computational techniques, while close degeneracy sometimes still prevents ab initio methods from obtaining accurate results. For hyperfine induced transitions we review some recent results and discuss remaining challenges for experiment and theory. Finally, we discuss the newly opened field of accurate calculations for transitions induced by an external magnetic field and point to some examples of where these are accessible for experimental tests.
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| 3. |
- Grumer, Jon, et al.
(author)
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Coronal lines and the importance of deep-core-valence correlation in Ag-like ions
- 2014
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In: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 89:6
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Journal article (peer-reviewed)abstract
- We report on large-scale and critically evaluated ab initio multiconfiguration Dirac-Hartree-Fock calculations of the wavelength and transition rate of the "coronal," M1 transition 4f F-2(5/2)o-F-2(7/2)o in Ag-like ions. The transition between these two fine-structure levels, which makes up the ground term for Z >= 62 in the isoelectronic sequence, has recently been observed in Yb23+ and W27+, where the latter could be of great importance for fusion plasma diagnostics. We present values for all members of the sequence between Z = 50 and 94, which are supported by excellent agreement with values from recent experiments. The importance of including core-valence correlation with the n = 3 shell in the theoretical model is emphasized. The results show close-to-spectroscopic accuracy for these forbidden lines.
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| 4. |
- Grumer, Jon, et al.
(author)
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Magnetic-field Induced Transitions : the Search for Close Degeneracies
- 2014
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In: Ninth International Conference on Atomic and Molecular Data and Their Applications: book of abstracts. ; , s. 54-54
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Conference paper (other academic/artistic)abstract
- Magnetic fields play a crucial role in numerous astrophysical and experimental plasma, such as solar protuberances, tokamaks, ion traps and storage rings. It is well-known that external fields affects ions by breaking the spherical symmetry, resulting in non-degenerate magnetic sublevels (the Zeeman effect). A more intriguing consequence is that the field will introduce new decay channels through off-diagonal interactions. We call these magnetic-field induced transitions (MITs). Such exotic lines could have a significant impact on the spectrum under investigation, especially for systems containing close degeneracies or when otherwise strictly forbidden one-photon channels are opened up. These transitions have attracted new attention recently due to the development of accurate and systematic methods of calculations of their rates [1,2] and the possible application as a tool for measuring plasma magnetic fields in cases when conventional methods, such as measurements of Zeeman separation energies, are beyond reach. We are currently developing a module for general atomic systems [3] based on wave-functions and transition matrix elements calculated with the well-established multiconfiguration Dirac-Hartree-Fock program package GRASP2K [4]. The code also supports ions with non-zero nuclear spin (and therefore also pure hyperfine induced transitions) and the aim is to eventually make it available to the general public as an extension module to GRASP2K. We will give an overview and recent progress in this field and present some new results. One interesting example is our ongoing investigation of enhanced MITs appearing due to close degeneracies, and the possible application of these as probes of magnetic fields in solar flares of which no direct measurements yet exists. The origin of these eruptions is connected to regions in the Solar corona with comparatively strong magnetic fields (sunspots) and it is believed that the energy released in a flare has been stored in these fields. It is therefore of great importance to measure the magnetic field strength and we propose a method based on MIT intensities.
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| 5. |
- Shi, Zhan, et al.
(author)
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A portable high-resolution soft x-ray and extreme ultraviolet spectrometer designed for the Shanghai EBIT and the Shanghai low energy EBITs
- 2014
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In: Review of Scientific Instruments. - : AIP Publishing. - 1089-7623 .- 0034-6748. ; 85:6
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Journal article (peer-reviewed)abstract
- A portable high resolution soft x-ray and extreme ultraviolet (EUV) spectrometer has been developed for spectroscopic research at the Shanghai Electron Beam Ion Trap (EBIT) laboratory. A unique way of aligning the grazing incidence spectrometer using the zero order of the grating is introduced. This method is realized by extending the range of the movement of the CCD detector to cover the zero order. The alignment can be done in a few minutes, thus leading to a portable spectrometer. The high vacuum needed to be compatible with the EBITs is reached by mounting most of the translation and rotation stages outside the chamber. Only one high vacuum compatible linear guide is mounted inside the chamber. This is to ensure the convenient interchange of the gratings needed to enable wavelength coverage of the whole range of 10 to 500 angstrom. Spectra recorded with one of our low energy EBITs shows that a resolving power of above 800 can be achieved. In the slitless configuration used in this work, we found the resolving power to be limited by the width of the EBIT plasma. When mounted on the Shanghai EBIT which is a high energy EBIT and has a narrower EBIT plasma width, the estimated resolving power will be around 1400 at 221.15 angstrom. (C) 2014 AIP Publishing LLC.
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