D. Osin

Spectroscopy of diagnostically-important magnetic-dipole lines in highly-charged 3d n ions of tungsten

An electron beam ion trap (EBIT) is used to measure extreme ultraviolet spectra between 10 nm and 25 nm from highly-charged ions of tungsten with an open 3d shell (W XLVIII through W LVI). We found that almost all strong lines are due to the forbidden magnetic-dipole (M1) transitions within 3d n ground configurations. A total of 37 spectral lines are identified for the first time using detailed collisional-radiative (CR) modeling of the EBIT spectra. A new level-merging scheme for compactification of rate equations is described. The CR simulations for Maxwellian plasmas show that several line ratios involving these M1 lines can be used to reliably diagnose temperature and density in hot fusion devices.

EUV spectral lines of highly-charged Hf, Ta and Au ions observed with an electron beam ion trap

Extreme ultraviolet spectra of highly-charged hafnium, tantalum and gold were produced with an electron beam ion trap (EBIT) at the National Institute of Standards and Technology (NIST) and recorded with a flat-field grazing-incidence spectrometer in the wavelength range 4–20 nm. The beam energy was varied between 1.84 and 5.15 keV to selectively enhance spectra from specific ionization stages. Identifications of strong n = 4–n = 4 transitions from Rb-like hafnium (35+) to Co-like gold (52+) were determined with the aid of collisional-radiative modelling of the EBIT plasma. Good quantitative agreement between simulated and measured spectra was achieved. Over 150 spectral lines were identified, 115 of which are new.

Extreme ultraviolet spectra and analysis of Δn = 0 transitions in highly charged barium

Extreme ultraviolet spectra of highly charged barium atoms were produced with an electron beam ion trap (EBIT) and recorded with a flat-field grazing-incidence spectrometer. The spectra were measured in the wavelength range 4 nm–24 nm with the beam energies varying from 700 eV to 30 000 eV. The line identifications were performed with collisional-radiative modeling of the EBIT plasma that provided good quantitative agreement between simulated and measured spectra. In the energy range 700 eV–1750 eV, fifty three n = 4–n = 4 transitions in Se-like (Ba22+) to Cu-like (Ba27+) ions were identified, with forty seven corresponding to new lines. Almost all lines are due to electric-dipole transitions. For the beam energies of 3945 eV–7530 eV, we identified eight new n = 3–n = 3 transitions in Ba42+ (Si-like), Ba43+ (Al-like), and Ba44+ (Mg-like). At the highest beam energy, 30 000 eV, three new n = 2–n = 2 transitions of Ba51+ (B-like), Ba52+ (Be-like), and Ba53+ (Li-like) were identified. The measured wavelengths are compared with recent ab initio theoretical calculations. An improved ionization energy for Ba26+ (Zn-like), IE = 937.2 ± 0.8 eV, was determined by comparing theoretical values with measurements along the Zn isoelectronic sequence.

EUV magnetic-dipole lines from highly-charged high-Z ions with an open 3d shell

Abstract The electron beam ion trap (EBIT) at the National Institute of Standards and Technology was used to produce highly-charged ions of hafnium, tantalum and gold with an open 3d shell. The extreme-ultraviolet (EUV) spectra from these ions were recorded with a flat-field grazing-incidence spectrometer in the wavelength range of 4.5 nm to 25 nm. A total of 133 new spectral lines, primarily due to magnetic-dipole transitions within the ground-state 3dn configurations of the Co-like to K-like ions, were identified by comparing energy-dependent experimental spectra with a detailed collisional-radiative modeling of the EBIT plasma.

Magnetic-dipole lines in 3dn ions of high-Z elements: identification, diagnostic potential and dielectronic resonances

We present a review of measurements and analyses of extreme-ultraviolet magnetic-dipole (M1) lines in 50–60 times ionized atoms of tungsten, hafnium, tantalum and gold with an open 3d shell. The spectra were measured with the electron beam ion trap at the National Institute of Standards and Technology. Large-scale collisional–radiative modeling was instrumental in line identification and in analysis of their diagnostic potential. The M1 line ratios are shown to be an accurate and versatile tool for studying the LMN dielectronic resonances in 3dn ions.

Magnetic-dipole transitions in tungsten and other heavy elements observed with the NIST EBIT

We describe recent observations with the electron beam ion trap (EBIT) at the National Institute of Standards and Technology (NIST) in which we observed large numbers of magnetic dipole (M1) transitions within the 3dn ground configurations of the highly-ionized heavy metals Hf, Ta, W, and Au. The data are interpreted by means of collisional-radiative modeling of the EBIT plasma.

Physics of the interaction of pulsed magnetic fields with plasmas and relevance to applications

Summary form only given, as follows. Spatially and temporally resolved spectroscopic measurements of the ion velocities, electron density and temperature, non-thermal electric fields, and the magnetic field evolution in a current-carrying plasma, show that ion separation occurs in which a light-ion plasma is pushed ahead of a magnetic piston while a heavy-ion plasma lags behind the magnetic piston. The velocities of the heavier ions are determined from Doppler shifts and the proton velocity is obtained using charge-exchange spectroscopy. The width of the current channel, calculated from the spatial distribution of the magnetic field, determined from Zeeman splitting of doped helium lines, is significantly broader than expected from classical diffusion. A large electron and ion heating is observed during the field penetration, as predicted theoretically. Moreover, the formation of non-thermal fast electrons, associated with the field penetration is experimentally studied. Turbulent electric fields with a 10+-2 kV/cm amplitude are inferred from Stark broadening of hydrogen and helium lines. Explanations for the observed rapid magnetic field penetration into the heavy-ion plasma in the context of EMHD theory or turbulence-induced collisionality are discussed. It is shown that the presence of the light ions in the plasma significantly modifies the dissipated-magnetic-field-energy partitioning between electrons and ions. Furthermore, understanding the dynamics of different ion species allows for improving the switch opening and coupling to various loads. Relevance to astrophysics and magnetic fusion will also be discussed.

Spectroscopic study of the magnetic field penetration and electron density evolution in a POS

Summary form only given. We study the operation of a planar microsecond plasma opening switch (POS) in which a current of 140 kA is conducted by the plasma for a duration of 400 ns before opening into an inductive load within 90 ns. Spectroscopic measurements, local in 3D, are made by doping the plasma with various species and observing the characteristic emission of the doped particles. The electron density and temperature and the composition of the prefilled flashboard plasma are studied spectroscopically.