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Walker, Arthur B. C., Jr.

Publications and source records attributed to Walker, Arthur B. C., Jr..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Optical configurations of H I Lyman-alpha coronagraph/polarimeters

The Multi-Spectral Solar Telescope Array (MSSTA) has obtained numerous high-resolution soft X-ray/EUV/FUV solar images with multilayer telescopes; these show dramatic prominences, spicules, and threadlike limb structures. There is excellent correlation between faint Lyman-alpha coronal structures seen in the digitized MSSTA images and prominences seen in H-alpha images gathered by ground-based observatories. The MSSTA has established the feasibility of an all-reflecting, imaging Ly-alpha coronagraph/polarimeter.

Hoover, Richard B.↗
NASA NTRS1992

Design and test of a High-Resolution EUV Spectroheliometer

The HiRES High-Resolution EUV Spectroheliometer is a sounding rocket instrument yielding very high spatial, spectral, and temporal resolution images of the solar outer atmosphere, on the basis of a 45-cm Gregorian telescope feeding a normal-incidence stigmatic EUV spectrometer with imaging multianode microchannel-array detector system, as well as an IR spectrometer with imaging CCD detector system. Attention is given to the expected performance of this system, including the effects of vibrational misalignments due to the sounding rocket flight environment.

Berger, Thomas E.↗
NASA NTRS1992

The Objective Double Crystal Spectrometer

The solar corona, supernova remnants, the hot diffuse interstellar gas in the Galaxy, galactic halos, and the hot intracluster gas in rich clusters of galaxies, are examples of extended astrophysical plasmas which emit line-rich spectra in the X-ray spectral range from 1.5 to 25 A. These phenomena represent a significant fraction of the baryonic matter in the universe. The study of the composition, structure and dynamics of these astrophysical plasmas requires observations with both high spectral and spatial resolution simultaneously. The Objective Double Crystal Spectrometer, coupled with a grazing incidence X-ray telescope, represents a stigmatic instrument which is highly efficient for the study of such sources. We describe the configuration and performance (spatial resolution, spectral resolution and efficiency) of the Objective Double Crystal spectrometer.

Walker, Arthur B. C., Jr.↗
NASA NTRS1991

Multi-Spectral Solar Telescope Array. II - Soft X-ray/EUV reflectivity of the multilayer mirrors

The Multispectral Solar Telescope Array is a rocket-borne observatory which encompasses seven compact soft X-ray/EUV, multilayer-coated, and two compact far-UV, interference film-coated, Cassegrain and Ritchey-Chretien telescopes. Extensive measurements are presented on the efficiency and spectral bandpass of the X-ray/EUV telescopes. Attention is given to systematic errors and measurement errors.

Barbee, Troy W., Jr.↗
NASA NTRS1991

EUV/FUV response characteristics of photographic films for the Multi-Spectral Solar Telescope Array

The photographic film employed by NASA's Multi-Spectral Solar Telescope Array must have high-to-ultrahigh resolution; since the spacecraft bearing the telescope must be evacuated to prevent the failure of delicate EUV and soft X-ray filters due to acoustic vibration during launch, the films must also have very low outgassing rates. An account is presently given of the properties of important new emulsions selected for flight, together with response-characteristics data for the experimental XUV 100 film and an uncoated Spectroscopic 649 emulsion.

Hoover, Richard B.↗
NASA NTRS1991

Multi-Spectral Solar Telescope Array. V - Temperature diagnostic response to the optically thin solar plasma

The compact soft X-ray/EUV/FUV multilayer coated telescopes developed for solar chromosphere, corona, and corona/solar-wind interface studies permit the use of conventional (Cassegrain, Herschelian, etc.) configurations. The multilayer coatings also allow a narrow-wavelength band to be selected for imaging. NASA's Multi-Spectral Solar Telescope Array is composed of 17 of these compact telescopes; attention is given to their ability to obtain temperature-diagnostic information concerning the solar plasma.

Deforest, Craig E.↗
NASA NTRS1991

Multi-Spectral Solar Telescope Array. IV - The soft X-ray and extreme ultraviolet filters

NASA's Multi-Spectral Solar Telescope Array uses various combinations of thin foil filters composed of Al, C, Te, Be, Mo, Rh, and phthalocyanine to achieve the requisite radiation-rejection characteristics. Such rejection is demanded by the presence of strong EUV radiation at longer wavelengths where the specular reflectivity of multilayer mirrors can cause 'contamination' of the image in the narrow band defined by the Bragg condition.

Lindblom, Joakim F.↗
NASA NTRS1991

Polarimetry of extreme ultraviolet lines in solar astronomy

Ways are suggested in which recent advancements in the fabrication of ultrasmooth, low scatter flow-polished mirror substrates and high-quality multilayer and interference film coatings can be used to create novel optical instruments for observing linear-polarization effects in the outer solar atmosphere. Attention is given to the observational parameters of all-reflective FUV/EUV imaging polarimeters; such a coronagraph/polarimeter, operating at Ly-alpha, could yield the first measurements of coronal vector magnetic fields.

Fineschi, Silvano↗
NASA NTRS1991

Imaging polarimeters for solar extreme ultraviolet astronomy

Accounts are given of EUV/FUV polarimetric instrument concepts for solar research which observe linear polarization in the spectral lines which originate in the outer solar atmosphere. The coronagraph/polarimeter instruments discussed employ all-reflective optical systems using ultrasmooth, low-scatter normal incidence mirrors and reflective polarization analyzers. The reflecting polarization analyzers operate at the Brewster angle.

Hoover, Richard B.↗
NASA NTRS1991

X ray imaging microscope for cancer research

The NASA technology employed during the Stanford MSFC LLNL Rocket X Ray Spectroheliograph flight established that doubly reflecting, normal incidence multilayer optics can be designed, fabricated, and used for high resolution x ray imaging of the Sun. Technology developed as part of the MSFC X Ray Microscope program, showed that high quality, high resolution multilayer x ray imaging microscopes are feasible. Using technology developed at Stanford University and at the DOE Lawrence Livermore National Laboratory (LLNL), Troy W. Barbee, Jr. has fabricated multilayer coatings with near theoretical reflectivities and perfect bandpass matching for a new rocket borne solar observatory, the Multi-Spectral Solar Telescope Array (MSSTA). Advanced Flow Polishing has provided multilayer mirror substrates with sub-angstrom (rms) smoothnesss for the astronomical x ray telescopes and x ray microscopes. The combination of these important technological advancements has paved the way for the development of a Water Window Imaging X Ray Microscope for cancer research.

Hoover, Richard B.↗
NASA NTRS1991

X-ray/EUV optics for astronomy, microscopy, polarimetry, and projection lithography; Proceedings of the Meeting, San Diego, CA, July 9-13, 1990

Topics discussed in this issue include the fabrication of multilayer X-ray/EUV coatings; the design, characterization, and test of multilayer X-ray/EUV coatings; multilayer X-ray/EUV monochromators and imaging microscopes; X-ray/EUV telescopes; the test and calibration performance of X-ray/EUV instruments; XUV/soft X-ray projection lithography; X-ray/EUV space observatories and missions; X-ray/EUV telescopes for solar research; X-ray/EUV polarimetry; X-ray/EUV spectrographs; and X-ray/EUV filters and gratings. Papers are presented on the deposition-controlled uniformity of multilayer mirrors, interfaces in Mo/Si multilayers, the design and analysis of an aspherical multilayer imaging X-ray microscope, recent developments in the production of thin X-ray reflecting foils, and the ultraprecise scanning technology. Consideration is also given to an active sun telescope array, the fabrication and performance at 1.33 nm of a 0.24-micron-period multilayer grating, a cylindrical proportional counter for X-ray polarimetry, and the design and analysis of the reflection grating arrays for the X-Ray Multi-Mirror Mission.

Hoover, Richard B.↗
NASA NTRS1991

The Ultra High Resolution XUV Spectroheliograph. II - Predicted performance

The phenomena to be studied with the Ultra-High Resolution XUV Spectroheliograph (UHRXS) which will be included into the instrumental load of the Space Station Freedom are discussed together with the characteristics of the nine multilayer Ritchey-Chretien telescopes constituting the UHRXS system. The telescopes will cover a spectral range from about 70 A to about 300 A. Each telescope will be able to isolate emission line multiplets excited over a narrow temperature range, providing images of diagnostic quality covering structures in the solar atmosphere ranging from T of about 50,000 K to 30,000,000 K. One of the nine UHRXS telescopes is configured as a coronagraph to allow observations to 6 solar radii beyond the solar limb. The paper presents an analysis of the expected sensitivity and resolving power of the UHRXS telescopes, and the diagnostic response of the various UHRXS instruments to structures in the solar atmosphere between 10,000 K and 100,000,000 K.

Walker, Arthur B. C., Jr.↗
NASA NTRS1991

The Active Sun Telescope Array

The concept of the Active Sun Telescope Array (ASTA) designed as a part of the NASA Orbiting Solar Laboratory is described together with the details of the ASTA instrument package. The ASTA, which will investigate the phenomenology of the solar chromosphere and the corona, consists of six EUV/XUV solar telescopes designed to provide wide field solar images in narrow wavelength bands, high-resolution spectroheliograms, and line profiles of the solar plasma in the temperature range from 10,000 K to 30,000 K. The detectors used in the ASTA are of the multianode multichannel array photon-counting array detector type.

Walker, Arthur B. C., Jr.↗
NASA NTRS1991

Solar EUV/FUV line polarimetry. I - Observational parameters and theoretical considerations. II - Instruments and methods

The paper discusses theoretical considerations and presents the observational parameters for the development of reflective FUV coronagraph/polarimeter and EUV imaging polarimeter instruments. New EUV/FUV polarimeter instrument concepts for solar research are described. One of these is a new coronagraph/polarimeter operating at 1215.6 A, which could observe the neutral hydrogen Ly-alpha line in the near solar corona and lead to the first direct measurements of both the strength and the direction of coronal magnetic fields. The other is a new multilayer EUV imaging polarimeter, operating at the wavelengths of strong He emission lines, which could observe impact polarization phenomena and provide information concerning the relative importance of thermal and nonthermal processes in solar flares.

Fineschi, Silvano↗
NASA NTRS1991

High resolution imaging with multilayer soft X-ray, EUV and FUV telescopes of modest aperture and cost

The development of multilayer reflective coatings now permits soft X-ray, EUV and FUV radiation to be efficiently imaged by conventional normal incidence optical configurations. Telescopes with quite modest apertures can, in principle, achieve images with resolutions which would require apertures of 1.25 meters or more at visible wavelengths. The progress is reviewed which has been made in developing compact telescopes for ultra-high resolution imaging of the sun at soft X-ray, EUV and FUV wavelengths, including laboratory test results and astronomical images obtained with rocket-borne multilayer telescopes. The factors are discussed which limit the resolution which has been achieved so far, and the problems which must be addressed to attain, and surpass the 0.1 arc-second level. The application of these technologies to the development of solar telescopes for future space missions is also described.

Walker, Arthur B. C., Jr.↗
NASA NTRS1990

The ultra high resolution XUV spectroheliograph: An attached payload for the Space Station Freedom

The principle goal of the ultra high resolution XUV spectroheliograph (UHRXS) is to improve the ability to identify and understand the fundamental physical processes that shape the structure and dynamics of the solar chromosphere and corona. The ability of the UHRXS imaging telescope and spectrographs to resolve fine scale structures over a broad wavelength (and hence temperature) range is critical to this mission. The scientific objectives and instrumental capabilities of the UHRXS investigation are reviewed before proceeding to a discussion of the expected performance of the UHRXS observatory.

Walker, Arthur B. C., Jr.↗
NASA NTRS1990

The Advanced Solar Observatory

A conceptual plan for the development of a comprehensive long duration solar space observatory, The Advanced Solar Observatory (ASO) is described. The ASO is intended to provide solar astronomers with the observational power necessary to address fundamental problems relating to the solar convection zone and activity cycle; the thermal and nonthermal processes that control the transport of energy, mass, and magnetic flux in the solar atmosphere; the generation of the solar wind; and the dynamics of the inner heliosphere. The ASO concept encompasses three proposed Space Station-based instrument ensembles: (1) the High Resolution Telescope Cluster, which includes far ultraviolet, extreme ultraviolet, and X-ray telescopes; (2) the Pinhole/Occulter Facility, which includes Fourier transform and coded aperture hard X-ray and gamma ray telescopes and occulted ultraviolet and visible light coronagraphs; and (3) the High Energy Facility, which contains neutron, gamma ray, and low frequency radio spectrometers. Two other facilities, the Orbiting Solar Laboratory, and a package of Global Dynamics Instrumentation, will, with the Space Station ensembles, form a comprehensive capability for solar physics. The scientific program of the ASO, current instrument concepts for the Space Station based ASO instrument ensembles, and plans for their accommodation on the Space Station are described.

Walker, Arthur B. C., Jr.↗