EUV Wavelength Range Research Articles

Commissioning of a gas monitor detector for an undulator beamline in the VUV and EUV wavelength range

A gas detector system was implemented to monitor the absolute photon flux at the insertion device beamline of the Metrology Light Source. This system should overcome the drawbacks in the use of traceably calibrated semiconductor photodiodes, which are prone to radiation-induced degradation and not qualified for permanent real-time monitoring during the measurements at the beamline endstation. Gas monitor detectors are based on atomic photoionization. They do not suffer from radiation-induced degradation, and their transparency makes them suitable for real-time monitoring of the photon flux. We calibrated and commissioned such a monitor at the insertion device beamline in the vacuum- and extreme ultraviolet spectral range from 14 eV to 111 eV photon energy. The resulting photon flux measurement was compared to measurements made with a photodiode and shows deviations below 5 %, which agrees well with the calculated relative uncertainty of 4.7 %.

Large-scale Multiconfiguration Dirac–Hartree–Fock Calculations for Astrophysics: C-like Ions from O iii to Mg vii

Large-scale multiconfiguration Dirac–Hartree–Fock calculations are provided for the n ≤ 5 states in C-like ions from O iii to Mg vii. Electron correlation effects are accounted for by using large configuration state function expansions, built from sets of orbitals with principal quantum numbers n ≤ 10. An accurate and complete data set of excitation energies, wavelengths, radiative transition parameters, and lifetimes is offered for the 156 (196, 215, 272, 318) lowest states of the 2s 22p 2, 2s2p 3, 2p 4, 2s 22p3s, 2s 22p3p, 2s 22p3d, 2s2p 23s, 2s2p 23p, 2s2p 23d, 2p 33s, 2p 33p, 2p 33d, 2s 22p4s, 2s 22p4p, 2s 22p4d, 2s 22p4f, 2s2p 24s, 2s2p 24p, 2s2p 24d, 2s2p 24f, 2s 22p5s, 2s 22p5p, 2s 22p5d, 2s 22p5f, and 2s 22p5g configurations in O iii (F iv, Ne v, Na vi, Mg vii). By comparing available experimental wavelengths with the MCDHF results, the previous line identifications for the n = 5, 4, 3 → n = 2 transitions of Na vi in the X-ray and EUV wavelength range are revised. For several previous identifications discrepancies are found, and tentative new (or revised) identifications are proposed. A consistent atomic data set including both energy and transition data with spectroscopic accuracy is provided for the lowest hundreds of states for C-like ions from O iii to Mg vii.

Система визуализации плазменного факела бетатронного источника рентгеновского излучения

The paper describes the design of a microscope for studying a betatron radiation source based on the PEARL femtosecond laser complex in the SXR and EUV wavelength range. The main optical element of the microscope is a spherical Schwarzschild objective a x5 magnification. The device allows to study the size and spatial structure of the interaction area of laser radiation with matter, at a selected wavelength in the EUV or SXR range with a resolution of δx = 2.75 microns. The operation wavelength (=13.5 nm) is set by multilayer X-ray mirrors. Thin-film absorption filters are used to suppress the background component of the signal.

Imaging system of a plasma torch of a Betatron X-ray source

The paper describes the design of a microscope for studying a betatron radiation source based on the PEARL femtosecond laser complex in the SXR and EUV wavelength range. The main optical element of the microscope is a spherical Schwarzschild objective a x5 magnification. The device allows to study the size and spatial structure of the interaction area of laser radiation with matter, at a selected wavelength in the EUV or SXR range with a resolution of delta x=2.75 μm. The operation wavelength (λ=13.5 nm) is set by multilayer X-ray mirrors. Thin-film absorption filters are used to suppress the background component of the signal. Keywords: SXR and EUV radiation, betatron radiation, imaging x-ray optics, SXR microscope.

SPARKLING EXTREME-ULTRAVIOLET BRIGHT DOTS OBSERVED WITH Hi-C

Observing the Sun at high time and spatial scales is a step towards understanding the finest and fundamental scales of heating events in the solar corona. The Hi-C instrument has provided the highest spatial and temporal resolution images of the solar corona in the EUV wavelength range to date. Hi-C observed an active region on 11 July 2012, which exhibits several interesting features in the EUV line at 193\AA: one of them is the existence of short, small brightenings ``sparkling" at the edge of the active region; we call these EUV Bright Dots (EBDs). Individual EBDs have a characteristic duration of 25s with a characteristic length of 680 km. These brightenings are not fully resolved by the SDO/AIA instrument at the same wavelength, however, they can be identified with respect to the Hi-C location of the EBDs. In addition, EBDs are seen in other chromospheric/coronal channels of SDO/AIA suggesting a temperature between 0.5 and 1.5 MK. Based on their frequency in the Hi-C time series, we define four different categories of EBDs: single peak, double peak, long duration, and bursty EBDs. Based on a potential field extrapolation from an SDO/HMI magnetogram, the EBDs appear at the footpoints of large-scale trans-equatorial coronal loops. The Hi-C observations provide the first evidence of small-scale EUV heating events at the base of these coronal loops, which have a free magnetic energy of the order of 10$^{26}$ erg.

Spectroscopic measurements of EUV ejecta in a CME: a high-blueshift trailing thread

AbstractThe mass of erupting prominence material can be inferred from the obscuration of emission behind this mass of cool plasma thanks to the rapid cadence of SDO/AIA images in the short EUV wavelength range (Carlyle et al. 2013, these proceedings). In comparing this approach with spectral observations from Hinode/EIS, to monitor contributions from emission seen around the erupting prominence material, we have found an intriguing component of blue-shifted emission, trailing the erupting prominence, with Doppler shifts on the order of 350 km s−1 in bright lines of both He ii and Fe xii.

Non-astigmatic imaging with matched pairs of spherically bent crystals or reflectors

This paper defines the exact conditions for the application of a previously proposed, general, non-astigmatic, imaging scheme, consisting of a matched pair of spherically bent crystals or reflectors, to x rays. These conditions lead to two specific experimental arrangements, of which one can provide large magnifications. Potential applications include the x-ray diagnosis of laser-produced plasmas and x-ray imaging of, e.g., biological samples, using the highly monochromatic radiation at synchrotron light sources. The results obtained for x rays are, however, valid for a wide spectrum of the electromagnetic radiation so that, for instance, an application of one of the imaging schemes to lithography in the EUV wavelength range should also be possible, if the spherically bent crystals are replaced by appropriate spherical reflectors. Also described is the design of an x-ray crystal spectrometer, which meets the here defined, necessary requirements for the observation of the x-ray spectra of helium-like argon.

Extreme solar EUV flares and ICMEs and resultant extreme ionospheric effects: Comparison of the Halloween 2003 and the Bastille Day events

Extreme solar flares can cause extreme ionospheric effects. The 28 October 2003 flare caused a ∼25 total electron content units (TECU = 1016 el/m2 column density), or a ∼30%, increase in the local noon equatorial ionospheric column density. The rise in the TEC enhancement occurred in ∼5 min. This TEC increase was ∼5 times the TEC increases detected for the 29 October and the 4 November 2003 flares and the 14 July 2000 (Bastille Day) flare. In the 260–340 Å EUV wavelength range, the 28 October flare peak count rate was more than twice as large as for the other three flares. Another strong ionospheric effect is the delayed influence of the interplanetary coronal mass ejection (ICME) electric fields on the ionosphere. For the 28 and 29 October flares, the associated ICMEs propagated from the Sun to the Earth at particularly high speeds. The prompt penetration of the interplanetary electric fields (IEFs) caused the dayside near‐equatorial ionosphere to be strongly uplifted by E × B convection. Consequential diffusion of the uplifted plasma down the Earth's magnetic field lines to higher magnetic latitudes is a major plasma transport process during these IEF (superstorm) events. Such diffusion should lead to inverted midlatitude ionospheres (oxygen ions at higher altitudes than protons). The energy input into the midlatitude ionospheres by this superfountain phenomenon could lead to local dayside midlatitude disturbance dynamos, features which cannot propagate from the nightside auroral zones.

The extreme Halloween 2003 solar flares (and Bastille Day, 2000 Flare), ICMEs, and resultant extreme ionospheric effects: A review

Extreme solar flares can cause extreme ionospheric effects. The Oct 28, 2003 flare caused a ∼25 TECU (a total electron content unit is 10 16 electron/m 2 column density), or a ∼30%, increase in the local noon equatorial ionospheric column density. This enhancement occurred within ∼5 min. This TEC increase was ∼5 times the TEC increases detected for the Oct 29, 2003, Nov 4, 2003, and the July 14, 2000 (Bastille Day) flares. In the 260–340 Å EUV wavelength range, the Oct 28 flare peak count rate was more than twice as large as for the other three flares. Another strong ionospheric effect is the delayed influence (due to solar wind propagation) of interplanetary coronal mass ejection (ICME) electric fields on the ionosphere. For the Oct 28 and 29 flares, the associated ICMEs propagated from the sun to the Earth at particularly high speeds. The prompt penetration of the interplanetary electric field caused the dayside equatorial ionospheric to be strongly convected upward. This led to enhanced TEC to values >300% nominal values in ∼2 h. Proposed mechanisms for this TEC enhancement will be discussed.

Transition region oscillations above sunspots

We present observations of three sunspots made in the EUV wavelength range with the Coronal Diagnostic Spectrometer (CDS) on SOHO. We examine time series of line intensities obtained with a 15-s cadence and calculate their Fourier power spectra and the wavelet transforms. We find oscillations in the chromosphere and transition region above sunspots in the temperature range 2 10 4 -4 10 5 K. Most of the spectral power is contained in the 5-8 mHz frequency range, and the dominant frequency is 5.9 mHz (170 s period). We find a relationship between the oscillations and sunspot plumes which are compact features located above sunspots and bright in the transition region lines emitted between 1.7 10 5 and 4 10 5 K. When the CDS slit crosses a sunspot plume, the bright O IV 554.5 Aand O V 629.7 Alines show clear 3 min oscillations. An extreme alternative interpretation that excludes the presence of oscillations in sunspot plumes carries the requirement that the adjacent low-intensity plasma oscillate with high relative amplitudes greater than 50 percent. We also observe oscillations in a fainter area above a sunspot, outside the sunspot plume. The oscillations seen at different temperatures are compared. Using the wavelet transform, we find variability of the oscillation period in the range 120-200 s.

Simultaneous Extreme-Ultraviolet Explorer and Optical Observations of AD Leonis: Evidence for Large Coronal Loops and the Neupert Effect in Stellar Flares

We report on the first simultaneous Extreme-Ultraviolet Explorer (EUVE) and optical observations of flares on the dMe flare star AD Leonis. The data show the following features: (1) Two flares (one large and one of moderate size) of several hours duration were observed in the EUV wavelength range; (2) Flare emission observed in the optical precedes the emission seen with EUVE; and (3) Several diminutions (DIMs) in the optical continuum were observed during the period of optical flare activity. To interpret these data, we develop a technique for deriving the coronal loop length from the observed rise and decay behavior of the EUV flare. The technique is generally applicable to existing and future coronal observations of stellar flares. We also determine the pressure, column depth, emission measure, loop cross-sectional area, and peak thermal energy during the two EUV flares, and the temperature, area coverage, and energy of the optical continuum emission. When the optical and coronal data are combined, we find convincing evidence of a stellar 'Neupert effect' which is a strong signature of chromospheric evaporation models. We then argue that the known spatial correlation of white-light emission with hard X-ray emission in solar flares, and the identification of the hard X-ray emission with nonthermal bremsstrahlung produced by accelerated electrons, provides evidence that flare heating on dMe stars is produced by the same electron precipitation mechanism that is inferred to occur on the Sun. We provide a thorough picture of the physical processes that are operative during the largest EUV flare, compare and contrast this picture with the canonical solar flare model, and conclude that the coronal loop length may be the most important factor in determining the flare rise time and energetics.

Representations of solar EUV fluxes for aeronomical applications

The development of significantly improved representations of solar EUV inputs for computer-aided investigations of the terrestrial thermosphere and ionosphere has become attractive particularly for the present solar cycle which has been covered by reasonably complete and continuous EUV observations from the AE-E Satellite. These representations try to satisfy some rather incongruous requirements of spectral detail , regarding (a) the strong wavelength-dependence in the terrestrial atmospheric cross sections of the various types of EUV photon interactions, (b) the great differences in the relative amplitudes of the various types of variations in the full-disk fluxes of solar emissions at different wavelengths, and (c) the persisting desire to use only a small number of daily indices as actual input variables for computational models supposed to cover the entire EUV wavelength range (remembering the great success of empirical thermospheric models using only two indices). These general physical and specific aeronomical demands indeed outline a very difficult task. The present study, based mainly on AE-E satellite observations during 1976–1979, represents an exploratory step, only clarifying some important developmental aspects, without recommending any specific formulations for immediately practicable adoption in aeronomical modelling at this time.