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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS2016

APES: Acute Precipitating Electron Spectrometer - A High Time Resolution Monodirectional Magnetic Deflection Electron Spectrometer

We present a description of the Acute Precipitating Electron Spectrometer (APES) that was designed and built for the Ground-to-Rocket Electron Electrodynamics Correlative Experiment (GREECE) auroral sounding rocket mission. The purpose was to measure the precipitating electron spectrum with high time resolution, on the order of milliseconds. The trade-off made in order to achieve high time resolution was to limit the aperture to only one look direction. The energy selection was done by using a permanent magnet to separate the incoming electrons, such that the different energies would fall onto different regions of the microchannel plate and therefore be detected by different anodes. A rectangular microchannel plate (MCP) was used (15 mm x 100 mm), and there was a total of 50 discrete anodes under the MCP, each one 15 mm x 1.5 mm, with a 0.5 mm spacing between anodes. The target energy range of APES was 200 eV to 30 keV.

Michell, R. G.↗
NASA NTRSDate not supplied

Experimental Characterization of Surface Roughness and Geometric Evaluations of Thin-Wall Laser Powder Directed Energy Deposition

Additive Manufacturing (AM) has offered many new design and manufacturing opportunities for components across various industries. As AM evolves there is a need to better understand outputs of the process including geometric limitations and surface roughness based on specific application requirements. One possible application area of AM are components using thin-wall (<2 mm) microchannel heat exchangers for subsystems across aerospace, and industrial applications. AM offers the opportunity to significantly reduce the cost and lead time associated with fabricating these complex parts with internal features such as an array of cooling channels. Laser Powder Bed Fusion (L-PBF) has been continuously demonstrated as a technique to fabricate heat exchangers with internal geometric complexities. However, L-PBF is limited in the scale at which parts can be fabricated. Laser Powder Directed Energy Deposition (LP-DED) has been demonstrated as an AM technology to significantly increase the scale of which thin-wall microchannel heat exchangers could be manufactured. Successful deployment of the LP-DED technology requires critical understanding of the resulting features from the build process. Surface roughness is one of the critical areas that effects the friction factor and pressure drop within a heat exchanger and must be well understood. This presentation will provide an overview of the characterization work completed to understand the LP-DED process for thin-walls representative of hydrogen resistant alloy NASA HR-1 that would be used in a Hydrogen-environment application. An overview of the experiments conducted with varying LP-DED parameters, evaluation of various geometric channel and geometric build features and resulting surface finish will be provided along with a summary of conclusions from these experiments. Results indicate that powder size is a major contributor and surface roughness varies between closed channel shapes and external surfaces.

Directed Energy Deposition↗
NASA NTRS1974

Negative affinity X-ray photocathodes

A new X-ray image intensifier is described. The device should eventually have a quantum efficiency which is an order of magnitude greater than that of presently available high spatial resolution X-ray detectors, such as microchannel plates. The new intesifier is based upon a GaAs crystal photocathode which is activated to achieve negative electron affinity. Details concerning the detector concept are discussed together with the theoretical relations involved, X-ray data, and optical data.

Vanspeybroeck, L.↗
NASA NTRS1974

The Ranicon - A resistive anode image converter

A versatile photon and charged particle imaging system is described. The Ranicon employs a microchannel electron multiplier plate to convert each detected event into a charge signal. This charge pulse is proximity-focused onto a large-area resistive anode plate equipped with pickup electrodes on its edges. Each event is located electronically by the ratios of the charges collected at the edges or by the differences of the signals' risetimes. One- or two-dimensional pictures are built up by storing events digitally (e.g., a core memory) or in analog form (e.g., a storage oscilloscope). Compact laboratory models have been constructed and tested. Operating characteristics, applications, limitations, and advantages of the Ranicon are discussed.

Lampton, M.↗
NASA NTRS1976

Two-dimensional photon detector

Device incorporates set of cascaded microchannel-array plates in proximity focus with two sets of mutually-orthogonal linear anodes. Technique allows data from N x M picture elements to be recorded with only N + M amplifiers.

Timothy, J. G.↗
NASA NTRS1976

Resistive anode image converter

The invention of an apparatus for imaging soft X-ray and ultraviolet electromagnetic radiation and charged particles was described. The apparatus includes a pair of microchannel electron multiplier plates connected in a cascaded chevron configuration which intercepts an incident beam of radiation or charged particles. Incident photons or charged particles strike the front surface of the chevron configuration causing emission of electrons. The electrons are accelerated by a voltage gradient and strike the inner side walls of the individual channels, causing emission of secondary electrons. Accelerated and multiplied secondary electrons impinge upon a resistive anode after they transverse the chevron configuration. A pulse position circuit converts the magnitude or transit time of the currents flowing from the point of impact of the electrons on the resistive anode to four contact electrodes mounted on their periphery of the resistive anode into the spatial coordinates of electron impact.

Lampton, M. L.↗
NASA NTRS1976

Spectroscopic survey of the far-ultraviolet /1160-1700 A/ emissions of Capella

A far-ultraviolet spectral survey of Capella (Alpha Aur, G5 III + G0 III) has been obtained using a highly sensitive rocketborne spectrograph with a microchannel plate detector. The spectral distribution is very similar to that of the sun; however, if the line surface fluxes are due to the primary (G5 III), then, except for Ly-alpha, they are about an order of magnitude greater than those of the quiet sun

Vitz, R. C.↗
NASA NTRS1977

The Photicon

The Photicon is a novel imaging optical detector utilizing a conventional semitransparent photocathode, imaging electrostatic optics, microchannel plates, and a crossed-wire-grid position-sensitive charge detector. Its sensitivity to single optical photons over a two-dimensional area, high-resolution imaging, and timing capability render it useful for recording scintillations from X-ray image converters in X-ray astronomy. A digital word indicating the position of a single photon event is produced; the image can be stored in an array or serially. Spatial resolution to 20 microns in a 25 mm diam active area detector is reported, and modifications to achieve a spectral range of 120-730 nm are mentioned.

Kellogg, E.↗
NASA NTRS1978

The High Resolution Imaging Instrument for HEAO-B

The High Resolution Imaging Instrument for the HEAO-B X-ray Telescope satellite is designed to reproduce images of celestial X-ray sources in the range of 0.2 to 4.0 keV. It provides both imaging and temporal data. The basic detector is a two-stage microchannel plate with a crossed-grid charge detector. Preamplifiers, detector bias supplies, and some processing circuits are colocated with the detector. The remaining electronic circuits are located in a remote central electronic assembly. The processing system is designed for single-photon processing. The imaging data rate is limited to 100 data points per second. Non-imaging total-field count rate is acquired with a maximum dead time of 14 microseconds per event.

Kubierschky, K.↗
NASA NTRS1978

A rocket observation of the far-ultraviolet spectrum of Saturn

Far-ultraviolet (1160-1750 A) spectra of the Saturnian disk and the ring system have been obtained by using a very sensitive rocket-borne spectrograph with a microchannel plate detector. The use of two apertures of different diameter in the telescope focal plane permitted the separation of the contribution of the planetary disk from that of the rings. H I lambda 1216 was the only atomic spectral line emission detected in the planet and the rings. A weak signal from the disk between 1300 A and 1500 A was observed. Geometric disk albedos, averaged over 50 A, were determined from 1500 A to 1700 A. Measurements of the ring reflectivity longward of 1650 A are compatible with H2O frost but not NH3 frost.

Weiser, H.↗
NASA NTRS1978

Crossed grid anode and its image partitioning

Measurements on an imaging crossed grid anode following a pair of microchannel plates indicate fast charge propagation via wire-to-wire capacitances, suggesting a temporal resolution of 100 ns. A figure of merit for partitioned systems has been suggested that provides an estimate of the position uncertainty of photoelectrons in the image plane of an anode. Solutions for two-, three-, and four-amplifier position algorithms are given, and basic system requirements are discussed.

Knapp, G.↗
NASA NTRS1979

Time-of-flight technique for particle identification at energies from 2 to 400 keV/nucleon

The time of flight technique for particle identification was extended to 2 keV/nucleon and the size of the start-time detector was reduced considerably by the use of carbon foils of few micrograms/cm square in thickness combined with microchannel plates for detecting secondary electrons. Time of flight telescopes incorporating this start-time device were used to measure the stopping power of a number of low energy heavy ions in thin carbon foils and the charge states of these ions emerging from such foils. Applications for the detection and identification of low energy interplanetary and magnetospheric particles are suggested.

Gloeckler, G.↗
NASA NTRS1979

A low-energy gamma-ray imaging detector

We describe a hard-X-ray/soft-gamma-ray imaging detector, incorporating a microchannel-plate (MCP) electron multiplier for possible use in future telescopes. In contrast to previous attempts using MCP's this approach promises to achieve high quantum detection efficiencies in addition to high spatial and temporal resolution. Preliminary results indicate not only the capability of simultaneous imaging and single-photon counting, but also coarse energy resolution.

Yin, L. I.↗
NASA NTRS1979

Electrographic instrumentation for ultraviolet imaging and spectrography

The latest results in the NRL program of far-UV electrographic camera development, and application of these cameras to astrophysical and upper-atmospheric investigations, are presented. A new large electrographic Schmidt camera, of 15 cm aperture and f/2 focal ratio, has been successfully used in two sounding rocket flights, one for direct imagery in the 1230-2000 A wavelength range and the second for objective spectrography in the 950-2000 A range, of stars and nebulae in the Cygnus region of the sky. The camera has an 11 deg field of view and better than 30 arcsec resolution (2 A spectral resolution with 600 line/mm objective grating). A nebular spectrograph, based on a microchannel-intensified electrographic Schmidt camera, is the payload of a May 1979 rocket flight. It will reach emission line features as faint as 5 Rayleighs in 100 second exposures in the 1050-2000 A range, with 5 A spectral resolution.

Carruthers, G. R.↗
NASA NTRS1979

A rocket-borne faint object spectrograph with a codacon detector

A rocket payload, consisting of a Rowland circle spectrograph with a multi-anode, microchannel plate detector, located at the focus of a 40 cm mirror, has been constructed to observe faint astronomical objects in the 900 to 1800 A spectral region. It can obtain the spectrum of an unreddened, V = 10m OB star with 3 A resolution and + or 3% precision in a 60 second observation.

Lillie, C. F.↗
NASA NTRS1979

Low-distortion resistive anodes for two-dimensional position-sensitive MCP systems

Microchannel plates (MCPs) are frequently used with resistive anodes to detect charged particles or photons and yield analog signals from which event positions can be decoded. The paper discusses a four-corner concave circular arc terminated resistive anode that permits theoretically distortionless encoding of Cartesian event positions into pulse charge ratios. The theory of the circular arc terminated anode is discussed along with anode design and performance. Electron beam images obtained by using such an anode are presented to confirm the usefulness of the approach.

Lampton, M.↗
NASA NTRS1980

Crossed-grid charge locator

Circuit locates center of cloud of charge on wire grid to within 6.5 micrometers. Wires in vicinity of charge cloud develop voltages that are processed by priority encoders to develop coarse and fine position codes. Device is used with microchannel plate amplifier in X-ray photon detectors, electron microscopes, and closed-circuit television.

Harrison, D. C.↗