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

Abstract

Aims. For a more complete interpretation of the extreme-ultraviolet (EUV) spectra of the solar corona, it is beneficial to acquire laboratory data of specific chemical elements obtained under coronal conditions. Methods. The EUV spectra of He, C, N, O, F, Ne, S, Ar, Fe, and Ni in a 30 Å wide wavelength interval near 335 have been excited in an electron beam ion trap. Results. We observe just under 200 lines, almost half of which are not yet identified and included in spectral models. Conclusions. Our data serve as a check on atomic databases that are used to interpret solar corona data such as collected by the Solar Dynamics Observatory spacecraft or the EUNIS instrument on sounding rockets. Our findings largely corroborate the databases. However, the accumulated flux of a multitude of mostly weak additional lines is comparable to that of various primary lines.

EUV Beam-Foil Spectra of Titanium, Iron, Nickel, and Copper

“…A laboratory light source that comes close to the ultrahigh vacuum and electron density conditions of parts of the solar corona is the electron beam ion trap (EBIT) [101]. Consequently, EBIT spectra have been used to help interpret solar corona spectra (for example, [24][25][26][27][28][29]102]. The appearance of the spectra depends on the measurement conditions [103,104], as discussed with examples below.…”

“…The experiment required about a day (and night) of accelerator time. The EBIT experiment [28,29] used a grazingincidence flat-field spectrograph (variable line-spacing grating of R = 5 m and approximately 1200 L/mm) [110,111]; the spectrum was recorded on a CCD chip with an exposure time of 30 min. The spectrograph has no entrance slit but images the 60 µm wide zone of the stored ion cloud exposed to the energetic electron beam directly onto the detector.…”

“…A further section of the highresolution spectrum has been added recently [113]. The wavelength interval 28-35 nm investigated with a medium resolution spectrograph has been discussed in [28,29]. In this wavelength band, the difference between the high-electron density excitation in the beam-foil interaction (Figures 14a and 15a) and the excitation by a low-density electron beam (Figures 14b and 15b) is particularly striking.…”

“…As mentioned above in the subsection on Fe, high-resolution nickel spectra have been recorded at the Livermore electron beam ion trap EBIT (see, for example, [27]). The spectrograph used [112] produced highly resolved spectra of wavelength bands that matched the individual detection bands of the SolarDynamicsObservatory spacecraft, but it did not permit observation beyond wavelengths of about 25 nm, where a smaller, mediumresolution flat-field spectrograph [110,111] was employed instead [28,29]. The spectra obtained with this instrument are close in resolution to the beam-foil survey spectra of Ni [56] that have been discussed above.…”

“…A laboratory effort at the Livermore EBIT therefore attempted to support the SDO project by recording element-specific high-resolution EUV spectra of the wavelength bands of the low-resolution SDO detectors [24][25][26][27][28][29]. The laboratory spectra were intended to clarify the blending situation with lines of other elements, and, in addition, they revealed a multitude of mostly weak unidentified lines of identifiable elements as well.…”