Low-density laboratory spectra near the He iiλ304 line

Abstract

Aims. To interpret the EUV spectra of the solar corona, one hopes for laboratory data of specific chemical elements obtained under coronal conditions. Methods. EUV spectra of He, C, N, O, F, Ne, S, Ar, Fe, and Ni in a 40 Å wide wavelength interval near λ304 were excited in an electron beam ion trap. Results. We observe some two hundred lines about half of which are not yet identified and included in spectral models. Conclusions. Our data provide a check on the atomic data bases underlying the spectral models that are used to interpret solar corona data. However, a multitude of mostly weak additional lines taken together represent a flux that is comparable to that of various primary lines.

Low-density laboratory spectra near the λ335 channel of the SDO/AIA instrument

“…Moreover, EBIT spectra repeatedly have shown features that had either been missing from databases or that had not been listed in their natural wavelength positions. Our present measurements of SDO/AIA bands in the laboratory cover the λ335 band and, thus, join our earlier measurements of the lines in the λ131, λ171, λ193, and λ211 bands (Träbert et al 2014a,b;Beiersdorfer & Träbert 2018;Beiersdorfer et al 2014a) that have been carried out at high spectral resolution, and a moderate-resolution study of the vicinity of the He ii λ304 line (Träbert et al 2016). The latter study demonstrates the rich spectral content, which in the SDO/AIA λ304 band observations is masked by the strong He line.…”

“…Instead, we used a medium-resolution flat-field spectrograph, dubbed the long wavelength extreme ultraviolet spectrometer (LoWEUS; Beiersdorfer et al 1999b), which was equipped with a 1200 /mm R = 5 m grating, operating at an angle of incidence of 87 • . This instrument is the same as was used for the SDO/AIA λ304 band (Träbert et al 2016) and is similar to those employed on the National Spherical Torus Experiment (NSTX) and the Alcator C-Mod tokamak (Lepson et al 2012;Graf et al 2008;Reinke et al 2010). As was the case in our other measurements, we used a cryogenically cooled CCD camera of 1340 × 1300 pixels of 20 µm × 20 µm each to record the spectra.…”

EUV spectroscopy of highly chargedSn13+−Sn15+ions in an electron-beam ion trap

“…Experimental investigations are hampered by the fact that plasmas, including plasma in electron-beam ion traps (EBITs) [19][20][21][22][23][24], that are typically required to produce ions in intermediate charge states, contain a mixture of ions of different charge states with overlapping spectral features. Charge-state-resolved spectra can be obtained using suitable subtractions of spectra acquired under various plasma conditions [25][26][27][28] or by employing genetic algorithms [29]. In this work, we employ a matrix inversion method to obtain chargestate-resolved spectra using matrix inversion techniques on convoluted, mixed-charge-state EUV spectra experimentally obtained from an electron-beam ion trap.…”

Extreme ultraviolet spectra of highly charged Fe ions in the laboratory versus the excitation of spectra in astrophysical environments

“…For example, the He II line near 30.4 nm dominates a section of the solar EUV spectrum, and largely unfiltered exposures near this wavelength are sometimes used as a monitor of the full activity of the sun (an example is one of the eight channels of the Solar Dynamics Observatory (SDO) AIA instrument [37]). Out of scientific curiosity a recent set of measurements at the Livermore EBIT has demonstrated spectra of various elements with and without He [38], showing several prominent lines of other elements within the width of the He II line profile. Of course, the brightness of the He II line in the sun outshines all other lines in the particular SDO/AIA instrument channel.…”