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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Extreme ultraviolet observations of white dwarfs

Observations shortward of the hydrogen Lyman limit provide sensitive determinations of stellar temperatures and interstellar absorption. Such data are of particular value in studies of hot white dwarfs, for which a large fraction of the emission occurs in the extreme-ultraviolet band (100-1000 A). Observations of HZ 43 and Feige 24 have been obtained with the Apollo-Soyuz extreme-ultraviolet telescope; both stars are copious EUV emitters, with four billionths and three billionths erg/sq cm sec in the 170-620-A band, respectively. The EUV data, combined with optical spectrophotometry, allow their temperatures to be estimated as 80,000 and 60,000 K, respectively. The corresponding interstellar neutral hydrogen column densities are about 4 by 10 to the 18th power per sq cm.

Lampton, M.↗
NASA NTRS1995

Extreme ultraviolet light curves of UZ Fornacis: Evidence for accretion stream absorption and vertical extent of the accretion spot

We report on two pointed observations of UZ For carried out by the imaging photometers aboard the Extreme Ultraviolet Explorer (EUVE), one as part of the EUVE Right Angle Program and one as an off-axis source during a guest observation. Both observations lasted approximately 3 days and covered a total of 72 orbits of the UZ For binary providing multiple coverage of all the orbital phases of UZ For. The resulting high signal-to-noise phase-folded light curve strongly constrains the emission and absorption geometry of UZ For. We have detected a narrow absorption dip that we attribute to the accretion stream at the location of the stagnation region many white dwarf radii away from the accretion spot and have also detected a broad dip caused by absorption much closer to the white dwarf surface. Both absorption effects are variable in time and phase. Based on the timescales of M-star eclipse ingress and egress, the angular spot size is constrained to be less than 5 deg; thus the ratio of spot area to white dwarf surface area is less than or equal to 0.0005. To explain the light curve phase duration given this small angular spot size, the extreme-ultraviolet (EUV) accretion spot must be raised vertically by approximately 5% of the white dwarf radius.

Warren, John K.↗
DOE OSTI2022

Tin removal by an annular surface wave plasma antenna in an extreme ultraviolet lithography source

Tin contamination of the collector mirror surface remains one of the crucial issues of EUV (Extreme Ultraviolet) sources, directly impacting the availability of the tool. Hydrogen plasma-based tin removal processes employ hydrogen radicals and ions to interact with tin deposits to form gaseous tin hydride (SnH 4 ), which can be removed through pumping. An annular surface wave plasma (SWP) source developed at the University of Illinois—Urbana Champaign is integrated into the cone and perimeter of the collection mirror for in situ tin removal. The SWP is characterized by high ion and radical densities, low electron temperature, and local generation where etching is needed. This method has the potential to significantly reduce downtime and increase mirror lifetime. Radical probe measurements show hydrogen radical densities in the order of 10 19 m -3 , while Langmuir probe measurements show electron temperatures of up to 6 eV and plasma densities on the order of 10 17–18 m -3 . The generated ions are essential to the tin cleaning and have sufficiently low energy to cause no damage to the collector capping layer. Tin etch rates of up to 270 nm/min were observed in a variety of experimental conditions, including various powers, pressures, flowrates, and temperatures. In conclusion, the high etch rates demonstrated in this study exceed the expected contamination rate of the EUV source.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1994

An operations and command systems for the extreme ultraviolet explorer

About 40% of the budget of a scientific spacecraft mission is usually consumed by Mission Operations & Data Analysis (MO&DA) with MO driving these costs. In the current practice, MO is separated from spacecraft design and comes in focus relatively late in the mission life cycle. As a result, spacecraft may be designed that are very difficult to operate. NASA centers have extensive MO expertise but often lessons learned in one mission are not exploited for other parallel or future missions. A significant reduction of MO costs is essential to ensure a continuing and growing access to space for the scientific community. We are addressing some of these issues with a highly automated payload operations and command system for an existing mission, the Extreme Ultraviolet Explorer (EUVE). EUVE is currently operated jointly by the Goddard Space Flight Center (GSFC), responsible for spacecraft operations, and the Center for Extreme Ultraviolet Astrophysics (CEA) of the University of California, Berkeley, which controls the telescopes and scientific instruments aboard the satellite. The new automated system is being developed by a team including personnel from the NASA Ames Research Center (ARC), the Jet Propulsion Laboratory (JPL) and the Center for EUV Astrophysics (CEA). An important goal of the project is to provide AI-based technology that can be easily operated by nonspecialists in AI. Another important goal is the reusability of the techniques for other missions. Models of the EUVE spacecraft need to be built both for planning/scheduling and for monitoring. In both cases, our modeling tools allow the assembly of a spacecraft model from separate sub-models of the various spacecraft subsystems. These sub-models are reusable; therefore, building mission operations systems for another small satellite mission will require choosing pre-existing modules, reparametrizing them with respect to the actual satellite telemetry information, and reassembling them in a new model. We briefly describe the EUVE mission and indicate why it is particularly suitable for the task. Then we briefly outline our current work in mission planning/scheduling and spacecraft and instrument health monitoring.

Muscettola, Nicola↗
NASA NTRS1982

X-ray and extreme ultraviolet imaging using layered synthetic microstructures

Up to now designers of X-ray optical instruments such as microscopes and telescopes have been compelled to use mirrors operating at small glancing angles. However, using vapor deposition techniques, it is now possible to build multilayered thin film structures in which the individual layers have thicknesses comparable with a wavelength of X-rays. These devices operate in a manner exactly analogous to multilayer dielectric coatings at visible wavelengths and can be used to increase the X-ray and extreme ultraviolet reflectivity of surfaces at large glancing angles. These X-ray mirrors have numerous potential applications in X-ray optics. Attention is given to X-ray images with a normal incidence mirror, and applications of multilayer optics. Single-mirror telescopes for solar/stellar astronomy are discussed, taking into account solar corona and transition region studies, and X-ray and extreme ultraviolet astronomy. Hybrid X-ray telescopes are also considered.

Underwood, J. H.↗
DOE OSTI2021

Table-top extreme ultraviolet second harmonic generation

The lack of available table-top extreme ultraviolet (XUV) sources with high enough fluxes and coherence properties has limited the availability of nonlinear XUV and x-ray spectroscopies to free-electron lasers (FELs). Here, we demonstrate second harmonic generation (SHG) on a table-top XUV source by observing SHG near the Ti M 2,3 edge with a high-harmonic seeded soft x-ray laser. Furthermore, this experiment represents the first SHG experiment in the XUV. First-principles electronic structure calculations suggest the surface specificity and separate the observed signal into its resonant and nonresonant contributions. The realization of XUV-SHG on a table-top source opens up more accessible opportunities for the study of element-specific dynamics in multicomponent systems where surface, interfacial, and bulk-phase asymmetries play a driving role.

47 OTHER INSTRUMENTATION↗
NASA NTRS1984

An extreme ultraviolet spectrometer experiment for the Shuttle Get Away Special Program

An extreme ultraviolet (EUV) spectrometer experiment operated successfully during the STS-7 mission in an experiment to measure the global and diurnal variation of the EUV airglow. The spectrometer is an F 3.5 Wadsworth mount with mechanical collimator, a 75 x 75 mm grating, and a bare microchannel plate detector providing a spectral resolution of 7 X FWHM. Read-out of the signal is through discrete channels or resistive anode techniques. The experiment includes a microcomputer, 20 Mbit tape recorder, and a 28V, 40 Ahr silver-zinc battery. It is the first GAS payload to use an opening door. The spectrometer's 0.1 x 4.2 deg field of view is pointed vertically out of the shuttle bay. During the STS-7 flight data were acquired continuously for a period of 5 hours and 37 minutes, providing spectra of the 570 A to 850 A wavelength region of the airglow. Five diurnal cycles of the 584 A emission of neutral helium and the 834 A emission of ionized atomic oxygen were recorded. The experiment also recorded ion events and pressure pulses associated with thruster firings. The experiment is to fly again on Mission 41-F.

Conway, R. R.↗
NASA NTRS1983

Solar irradiance variations. II - Analysis of the extreme ultraviolet measurements onboard the Atmosphere Explorer E satellite

Five of the extreme ultraviolet channels (L-alpha, L-beta, He I, He II, Fe XV) measuring irradiance fluctuations on board the AE-E satellite between 1977 and 1980 have been studied in detail. It is shown that the daily variations correspond very closely to the daily variations in solar radio emission (F10.7), but that the UV data are afflicted with serious and to date unrecognized calibration changes during the period of operation of the instruments. In order to correct for these changes, a statistical analysis is carried out, and a set of corrections to the raw data is suggested. The resulting, now uniform, data are then compared with rocket measurements (L-alpha) and data acquired onboard the AE-C satellite (L-beta). Finally the remaining discrepancies are discussed. After concluding that they are below the overall level of uncertainties, a first-order 10-year run of EUV irradiances derived from F10.7 data is proposed. This estimate includes the ratio of irradiance levels between the maxima of solar cycles 20 and 21 and the intervening minimum.

Oster, L.↗
NASA NTRS1985

Research in extreme ultraviolet and far ultraviolet astronomy

Instruments designed to explore different aspects of far and extreme ultraviolet cosmic radiation were studied. The far ultraviolet imager (FUVI) was flown on the Aries sounding rocket. Its unique large format 75mm detector mapped out the far ultraviolet background radiation with a resolution of only a few arc minutes. Analysis of this data indicates to what extent the FUVI background is extra galactic in origin. A power spectrum of the spatial fluctuations will have direct consequences for galactic evolution.

Labov, S. E.↗
NASA NTRS1986

An imaging extreme ultraviolet spectrometer for astrophysical investigations in space

A high-efficiency, extreme ultraviolet (EUV) imaging spectrometer has been constructed and tested. The spectrometer employs a concave toroidal grating illuminated at normal incidence in a Rowland circle mounting and has only one reflecting surface. The toroidal grating has been fabricated by a new technique employing an elastically deformable submaster grating which is replicated in a spherical form and then mechanically distorted to produce the desired aspect ratio of the toroidal surface for stigmatic imaging over the selected wavelength range. The fixed toroidal grating used in the spectrometer is then replicated from this surface. Photographic tests and initial photoelectric tests with a two-dimensional, pulse-counting detector system have verified the image quality of the toroidal grating at wavelengths near 600 A. The basic designs of two instruments employing the spectrometer for astrophysical investigations in space are described, namely, a high-resolution EUV spectroheliometer for studies of the solar chromosphere, transition region, and corona; and an EUV spectroscopic telescope for studies of nonsolar objects.

Huber, M. C. E.↗
NASA NTRS1993

Imaging the magnetosphere in the extreme ultraviolet

A final report on research on magnetosphere imaging in the extreme ultraviolet is presented. The objectives of the research contract can be summarized in three related items: (1) investigate the feasibility of the EUV imaging concept by using Lockheed in-situ ion measurement data; (2) investigate the technical resources required to make scientific interpretations of such EUV images by end-to-end simulations of the imaging concept; and (3) construct and test the key element for EUV magnetosphere imaging, the multilayer mirror with normal-incidence reflectance designed for the selected solar resonance line.

Chiu, Y. T.↗
DOE OSTI2021

Polymer thin films as universal substrates for extreme ultraviolet absorption spectroscopy of molecular transition metal complexes

Polystyrene and polyvinyl chloride thin films are explored as sample supports for extreme ultraviolet (XUV) spectroscopy of molecular transition metal complexes. Thin polymer films prepared by slip-coating are flat and smooth, and transmit much more XUV light than silicon nitride windows. Analytes can be directly cast onto the polymer surface or co-deposited within it. The M-edge XANES spectra (40–90 eV) of eight archetypal transition metal complexes (M = Mn, Fe, Co, Ni) are presented to demonstrate the versatility of this method. The films are suitable for pump/probe transient absorption spectroscopy, as shown by the excited-state spectra of Fe(bpy) 3 2+ in two different polymer supports.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1993

Extreme ultraviolet observations of G191-B2B and the local interstellar medium with the Hopkins Ultraviolet Telescope

During the Astro-l mission in 1990 December, the Hopkins Ultraviolet Telescope (HUT) was used to observe the extreme ultraviolet spectrum (415-912 A) of the hot DA white dwarf GI91-B2B. Absorption by neutral helium shortward of the 504 A He I absorption edge is clearly detected in the raw spectrum. Model fits to the observed spectrum require interstellar neutral helium and neutral hydrogen column densities of 1.45 +/- 0.065 x 10 exp 17/sq cm and 1.69 +/- 0.12 x 10 exp 18/sq cm, respectively. Comparison of the neutral columns yields a direct assessment of the ionization state of the local interstellar cloud surrounding the Sun. The neutral hydrogen to helium ratio of 11.6 +/- 1.0 observed by HUT strongly contradicts the widespread view that hydrogen is much more ionized than helium in the local interstellar medium, a view which has motivated some exotic theoretical explanations for the supposed high ionization.

Kimble, Randy A.↗
DOE OSTI2025

Optical design and efficiency measurement of an extreme ultraviolet high-resolution spectrometer for unresolved transition array research

Understanding the structures of the unresolved transition array (UTA) observed in extreme ultraviolet (EUV) spectra from many-electron atoms is crucial for various applications, including fusion science and nanolithography. Here, to measure the fine structure of the UTA from tungsten and tin at around 5 and 13.5 nm at the Tokyo electron beam ion trap, we developed a high-resolution EUV spectrometer. The designed spectrometer achieves a resolving power of λ/dλ > 5000 at 5 and 13.5 nm. The fabricated large-area grating was experimentally examined at beamline BL5B of the UVSOR synchrotron facility to evaluate the diffraction efficiencies and their variation across the ruled area. The measured diffraction efficiencies are 0.65% ± 0.07% at 5 nm (second order) and 7.9% ± 0.2% at 13.5 nm (first order). The variation in the diffraction efficiency across the ruled area is 2.2%, 13.6%, and 10.0% in zeroth, first, and second order diffractions, respectively. The discrepancies in diffraction efficiencies between the experiments and the calculations were 5.2%, 29%, and 35% for the zeroth, first, and second diffraction orders, respectively.

47 OTHER INSTRUMENTATION↗
NASA NTRS1977

The atmosphere of Sirius B. II - Extreme-ultraviolet observations

The letter reports an observation of Sirius in the extreme-ultraviolet (100-1000 A) band, using a grazing-incidence telescope flown aboard the Apollo-Soyuz mission. No positive flux is detected; under the arbitrary assumption of flat incident spectrum, an upper limit to the flux in the 170-620 A band is 5 billion erg/sq cm per sec. A detailed model-atmosphere analysis, when combined with the EUV limits, places severe constraints on models which attribute the previously reported soft X-ray (44-60 A) flux to thermal radiation from deep layers of the atmosphere of the white dwarf Sirius B. EUV radiation should be detectable from Sirius B just below the sensitivity threshold of the current data, or a thermal origin for the X-ray flux is untenable. If the X-ray flux is thermal, the present results provide extremely sensitive constraints on the temperature and helium abundance of Sirius B: the white dwarf has an effective temperature of 32,000 K to 32,500 K and a helium abundance (relative to hydrogen) of 0.0001 to 0.0002.

Shipman, H. L.↗
NASA NTRS1977

NRL-ATM extreme ultraviolet solar image TV monitor flown on Skylab

An instrument for recording extreme ultraviolet television images of the sun was flown in the Apollo Telescope Mount on Skylab. Solar radiation in the 171-630 A wavelength range, defined by the transmission band of three thin-film aluminum filters, was focused onto a p-quaterphenyl photon conversion layer by a platinum-coated mirror at normal incidence. The conversion layer was attached to the faceplate of a low light level SEC vidicon. An onboard video monitor enabled the Skylab crews to observe the images in real-time and to identify and follow the development of solar features. Images were also transmitted to the mission control center, where they were used in planning the ATM observing schedule.

Crockett, W. R.↗