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A. C. Gall

Publications and source records attributed to A. C. Gall.

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A Cryogen-Free Electron Beam Ion Trap for Astrophysically Relevant Spectroscopic Studies

The detailed design and operation of the Smithsonian Astrophysical Observatory's EBIT are described for the first time, including recent design upgrades that have led to improved system stability and greater user control, increasing the scope of possible experiments. Measurements of emission from highly charged Ar were taken to determine the spatial distribution of the ion cloud and electron beam. An optical setup consisting of two lenses, a narrow band filter, and a CCD camera was used to image visible light, while an X-ray pinhole and CCD camera were used to image X-rays. Measurements were used to estimate an effective electron density of 1.77 x 10$^{10}$ cm$^{-3}$. Additionally, observations of X-ray emission from background EBIT gases were measured with a Silicon Lithium detector. Measurements indicate the presence of Ba and Si, which are both easily removed by dumping the trap every 2 s or less.

astro-ph.IM

Dielectronic resonances of LMn and LNn (n $\geq$ 4) series in highly-charged M-shell tungsten ions

We present spectroscopic measurements and detailed theoretical analysis of inner-shell LMn and LNn (n $\geq$ 4) dielectronic resonances in highly-charged M-shell ions of tungsten. The x-ray emission from W$^{49+}$ through W$^{64+}$ was recorded at the electron beam ion trap (EBIT) facility at the National Institute of Standards and Technology (NIST) with a high-purity Ge detector for electron beam energies between 6.8 keV and 10.8 keV. The measured spectra clearly show the presence of strong resonance features as well as direct excitation spectral lines. The analysis of the recorded spectra with large-scale collisional-radiative (CR) modeling of the EBIT plasma allowed us to unambiguously identify numerous dielectronic resonances associated with excitations of the inner-shell 2s$_{1/2}$, 2p$_{1/2}$, and 2p$_{3/2}$ electrons.

physics.atom-ph