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[en] The properties of highly charged ions and their interaction with electrons and atoms is being studied in-situ at the LLNL electron beam ion traps, EBIT-II and SuperEBIT. Spectroscopic measurements provide data on electron-ion and ion-atom interactions as well as accurate transition energies of lines relevant for understanding QED, nuclear magnetization, and the effects of relativity on complex, state-of-the-art atomic calculations
[en] X-ray spectra can provide valuable information on the atomic structure and the excitation mechanisms of highly charged ions, and their study is important for x-ray laser and fusion research as well as for the diagnosis of astrophysical and laser-produced plasmas. In the present work, high-resolution spectra of the n = 3 to n = 2 x-ray transitions in neonlike ions have been recorded on the Princeton Large Torus tokamak and are analyzed in detail. The observed spectra fall into the wavelength region 2.00-9.00 angstrom and originate from elements between Z = 34 (selenium) and Z = 63 (europium). A systematic determination of the wavelengths of the neonlike transitions has been made as function of atomic number. The wavelengths of the neonlike lines have been determined with the help of a large number of hydrogenlike and helium-like reference spectra. The hydrogen like and heliumlike spectra are also presented. The wavelength measurements are compared to results from advanced computer calculations, and the quantum electrodynamical contributions to the neonlike transition energies have been determined. The spectral line intensities of the neonlike transitions have been measured as a function of electron temperature and atomic number and are compared to theoretical lines ratios inferred from electron-impact excitation and radiative decay rates. In addition, the role of inner-shell ionization of sodiumlike ions in the excitation of neonlike ions is investigated. The process is shown to be significant for the excitation of certain neonlike levels, and its rate coefficient has been measured
[en] An overview is given of the current experimental effort to investigate the level structure of highly charged ions with the Livermore electron beam ion trap (EBIT) facility. The facility allows the production and study of virtually any ionization state of any element up to bare U92+. Precision spectroscopic measurements have been performed for a range of Δn = 0 and Δn = 1 transitions. Examples involving 3-4 and 2-3 as well as 3-3 and 2-2 transitions in uranium ions are discussed that illustrated some of the measurement and analysis techniques employed. The measurements have allowed tests of calculations of the the quantum electrodynamical contributions to the transitions energies at the 0.4% level in a regime where (Zα) ∼ 1
[en] Measurements of 2sl/2-2p3/2 electric dipole and 2p1/2-2p3/2 magnetic dipole and electric quadrupole transitions in U82+ through U89+ have been made with a high-resolution crystal spectrometer that recorded the line radiation from stationary ions produced and trapped in a high-energy electron beam ion trap. From the measurements we infer -39.21 ± 0.23 eV for the QED contribution to the 2s1/2-2p3/2 transition energy of lithiumlike U89+. A comparison between our measurements and various computations illustrates the need for continued improvements in theoretical approaches for calculating the atomic structure of ions with two or more electrons in the L shell
[en] Atomic physics of high-Z, heavy ions is very different from that encountered in low-Z or medium-Z ions. The reason is the ultra strong nuclear field found only in the heaviest ions. The highest-Z atomic systems available to physical investigation, the actinides, therefore, offer rich new physics that cannot be studied any other way. This ranges from new dominating forces in electron-ion collisions to tests of fundamental theories. A measurement of the two-loop Lamb shift in uranium is by many considered to be the ''holy grail'' of high-field QED tests of atomic systems. Such measurements have been attempted at heavy-ion accelerator facilities but have yet to succeed because of the difficulty to make measurements with the required accuracy. Also, electron collisions behave very differently in such tightly bound systems. The magnetic interaction between the ion and the incoming free electron (the so-called generalized Breit interaction) is essentially non-existent in collisions involving low and medium-Z ions. This interaction is therefore missing in essentially all electron collision codes. But in heavy, highly charged ions like uranium, the generalized Breit interaction readily is the dominant force, changing electron collision cross sections by a factor of two. This has never been experimentally observed. In fact, no K-shell emission spectrum of any heavy high-Z ion higher than krypton (Z=36) has ever been recorded from a collisional source. By studying the heaviest actinides such fundamental science can be extended to regimes where the highest precision tests can be made
[en] In the autumn of 1986, the first electron beam ion trap, EBIT, was put into service as a light source for the spectroscopy of highly charged ions. On the occasion of the twentieth anniversary of EBIT, we review its early uses for spectroscopy, from the first measurements of x rays from L-shell xenon ions in 1986 to its conversion to SuperEBIT in 1992 and rebirth as EBIT-I in 2001. Together with their sibling, EBIT-II, these machines have been used at Livermore to perform a multitude of seminal studies of the physics of highly charged ions.
[en] We give an overview of atomic spectroscopy performed on electron beam ion traps at various locations throughout the world. Spectroscopy at these facilities contributes to various areas of science and engineering, including but not limited to basic atomic physics, astrophysics, extreme ultraviolet lithography, and the development of density and temperature diagnostics of fusion plasmas. These contributions are accomplished by generating, for example, spectral surveys, making precise radiative lifetime measurements, accounting for radiative power emitted in a given wavelength band, illucidating isotopic effects, and testing collisional-radiative models. While spectroscopy with electron beam ion traps had originally focused on the x-ray emission from highly charged ions interacting with the electron beam, the operating modes of such devices have expanded to study radiation in almost all wavelength bands from the visible to the hard x-ray region; and at several facilities the ions can be studied even in the absence of an electron beam. Photon emission after charge exchange or laser excitation has been observed, and the work is no longer restricted to highly charged ions. Much of the experimental capabilities are unique to electron beam ion traps, and the work performed with these devices cannot be undertaken elsewhere. However, in other areas the work on electron beam ion traps rivals the spectroscopy performed with conventional ion traps or heavy-ion storage rings. The examples we present highlight many of the capabilities of the existing electron beam ion traps and their contributions to physics.
[en] Systematic studies of highs charged neonlike and nickellike ions as well as several open-shell ions performed on an electron beam ion trap are described and used to assess the accuracy of structure calculations of multi-electron ions. Discrepancies are found that can be attributed to inaccuracies in accounting for electron correlations and in estimating quantum electrodynamical effects. Documenting the effects of level crossings, we demonstrate that these discrepancies are compounded by uncertainties in assigning the respective contributions from quantum electrodynamics to each of the two strongly interacting levels undergoing the crossing
[en] The electron beam ion traps (EBIT) at Livermore were designed for studying the x-ray emission of highly charged ions produced and excited by a monoenergetic electron beam. The precision with which the x-ray emission can be analyzed has recently been increased markedly when it became possible to decouple the temperature of the ions from the energy of the electron beam by several orders of magnitude. By adjusting the trap parameters, ion temperatures as low as 15.8±4.4 eV for Ti20+ and 59.4±9.9 eV for Cs45+ were achieved. These temperatures were more than two orders of magnitude lower than the energy of the multi-keV electron beam used for the production and excitation of the ions. A discussion of the techniques used to produce and study low-temperature highly charged ions is presented in this progress report. The low ion temperatures enabled measurements heretofore impossible. As an example, a direct observation of the natural line width of fast electric dipole allowed x-ray transitions is described. From the observed natural line width and b making use of the time-energy relations of the uncertainty principle we were able to determine a radiative transition rate of 1.65 fs for the 2p-3d resonance transition in neonlike Cs45+. A brief discussion of other high-precision measurements enabled by our new technique is also given