Ilija Draganic

EUV spectra of highly-charged ions W54+?W63+ relevant to ITER diagnostics

We report the first measurements and detailed analysis of extreme ultraviolet (EUV) spectra (4–20 nm) of highly-charged tungsten ions W54+ to W63+ obtained with an electron beam ion trap (EBIT). Collisional-radiative modelling is used to identify strong electric-dipole and magnetic-dipole transitions in all ionization stages. These lines can be used for impurity transport studies and temperature diagnostics in fusion reactors, such as ITER. Identifications of prominent lines from several W ions are confirmed by the measurement of isoelectronic EUV spectra of Hf, Ta and Au. We also discuss the importance of charge-exchange recombination for the correct description of ionization balance in the EBIT plasma.

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.