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Beiersdorfer, P

Publications and source records attributed to Beiersdorfer, P.

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Measurements of the effective electron density in an electron beam ion trap using extreme ultraviolet spectra and optical imaging

In an electron beam ion trap (EBIT), the ions are not confined to the electron beam, but rather oscillate in and out of the beam. As a result, the ions do not continuously experience the full density of the electron beam. To determine the effective electron density, n e,eff , experienced by the ions, the electron beam size, the nominal electron density n e , and the ion distribution around the beam, i.e., the so-called ion cloud, must be measured. We use imaging techniques in the extreme ultraviolet (EUV) and optical to determine these. The electron beam width is measured using 3 d → 3 p emission from Fe xii and xiii between 185 and 205 Å. These transitions are fast and the EUV emission occurs only within the electron beam. The measured spatial emission profile and variable electron current yield a nominal electron density range of n e ~ 10 11 –10 13 cm –3 . We determine the size of the ion cloud using optical emission from metastable levels of ions with radiative lifetimes longer than the ion orbital periods. Here, the resulting emission maps out the spatial distribution of the ion cloud. We find a typical electron beam radius of ~60 μm and an ion cloud radius of ~300 μ m. These yield a spatially averaged effective electron density, ne,eff, experienced by the ions in EBIT spanning ~ 5 × 10 9 –5 × 10 11 cm –3 .

47 OTHER INSTRUMENTATION↗
DOE OSTI2018

Electron-density-sensitive Line Ratios of Fe XIII--XVI from Laboratory Sources Compared to CHIANTI

We present electron-density-sensitive line ratios for Fe XIII–XVI measured in the spectral wavelength range of 200–440 Å and an electron density range of (1–4)×10 13 cm -3 . The results provide a test at the high-density limit of density-sensitive line ratios useful for astrophysical studies. The measurements were performed on the National Spherical Torus Experiment-Upgrade, where electron densities were measured independently by the laser Thomson scattering diagnostic. Spectra were collected with a flat-field grazing-incidence spectrometer, which provided a spectral resolution of up to 0.3 Å, i.e., high resolution across the broad wavelength range. The response of the instrument was relatively calibrated using spectroscopic techniques in order to improve accuracy. The line ratios are compared to other laboratory sources and the latest version of CHIANTI (8.0.2), and an agreement within 30% is found.

Spectroscopic techniques↗
DOE OSTI2017

Plasma measurements of the Fe XVII L-shell emission and blending with F VIII and F IX

We measured the L-shell emission spectrum of Fe XVII in a low-density, low-gradient magnetically confined laboratory plasma that contains predominantly C, O, Fe, and Ni as trace elements and find excellent agreement with the relative spectral emission obtained in solar and astrophysical observations. However, we obtained spectra that appear to have an usually large 1s^22s^22p^5_{1/2}3d_{3/2} --> 1s^22s^22p^6 Fe XVII resonance transition, commonly labeled 3C, from hot plasmas that also contain F. The wavelength of the Ly-alpha feature of F IX is coincident with the wavelength of the Fe XVII line 3C within one part in 538, and its flux, therefore, enhances the Fe XVII resonance line. Moreover, the resonance and forbidden lines of F VIII are close to the 3s --> 2p transitions in Fe XVII, and may further alter the inferred apparent Fe XVII line ratios, particularly in spectrometers with moderate spectral resolution. The enhanced emission of line 3C, thus, can serve as a new spectral diagnostic for the detection of fluorine in astrophysical plasmas.

Atomic processes↗
DOE OSTI2017

X-ray and extreme ultraviolet spectroscopy on DIII-D

Two spectrometers were installed to measure tungsten emission in the core of DIII-D plasmas during a metal rings experimental campaign. The spectral range of the high-resolution (1340 spectral channels), variable-ruled grating X-ray and Extreme Ultraviolet Spectrometer (XEUS) extends from10–71$\dot{A}$ . The spectral range of the second spectrometer, the Long-Wavelength Extreme Ultraviolet Spectrometer (LoWEUS), measures between 31–174$\dot{A}$ . Three groups of tungsten lines were identified with XEUS: W 38+ -W 45+ from 47–63$\dot{A}$ , W 27+ -W 35+ from 45–55$\dot{A}$ , and W 28+ -W 33+ from 16–30$\dot{A}$ . Emission lines from tungsten charge states W 28+ , W 43+ , W 44+ , and W 45+ are identified and the line amplitude is presented versus time. Peak emission of W 43+ -W 45+ occurs between core Te=2.5-3 keV, and peak emission of W28+ occurs at core Te 1:3 keV. One group of tungsten lines, W 40+ -W 45+ , between 120–140$\dot{A}$ , was identified with LoWEUS. W 43+ - W 45+ lines measured with LoWEUS track the sawtooth cycle. Furthermore, sensitivity to the sawtooth cycle and the correlation of the peak emission with core electron temperature show that these spectrometers track the on-axis tungsten emission of DIII-D plasmas.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗