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Published: 1995
Total Pages: 19
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DOWNLOAD EBOOKRecent developments in detection of neutral atom imaging should enable imaging the global structure and dynamics of the terrestrial magnetosphere. The inherent technical challenge of imaging low energy neutral atoms (LENAs) with energy
Author: H. O. Funsten
Publisher:
Published: 1995
Total Pages:
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DOWNLOAD EBOOKAuthor: National Aeronautics and Space Administration (NASA)
Publisher: Createspace Independent Publishing Platform
Published: 2018-07-12
Total Pages: 48
ISBN-13: 9781722832704
DOWNLOAD EBOOKThis investigation has focused on development of key technology elements for low energy neutral atom imaging. More specifically, we have investigated the conversion of low energy neutral atoms to negatively charged ions upon reflection from specially prepared surfaces. This 'surface conversion' technique appears to offer a unique capability of detecting, and thus imaging, neutral atoms at energies of 0.01 - 1 keV with high enough efficiencies to make practical its application to low energy neutral atom imaging in space. Such imaging offers the opportunity to obtain the first instantaneous global maps of macroscopic plasma features and their temporal variation. Through previous in situ plasma measurements, we have a statistical picture of large scale morphology and local measurements of dynamic processes. However, with in situ techniques it is impossible to characterize or understand many of the global plasma transport and energization processes. A series of global plasma images would greatly advance our understanding of these processes and would provide the context for interpreting previous and future in situ measurements. Fast neutral atoms, created from ions that are neutralized in collisions with exospheric neutrals, offer the means for remotely imaging plasma populations. Energy and mass analysis of these neutrals provides critical information about the source plasma distribution. The flux of neutral atoms available for imaging depends upon a convolution of the ambient plasma distribution with the charge exchange cross section for the background neutral population. Some of the highest signals are at relatively low energies (well below 1 keV). This energy range also includes some of the most important plasma populations to be imaged, for example the base of the cleft ion fountain. Quinn, J. M. Unspecified Center NAS8-39950...
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Published: 1992
Total Pages: 15
ISBN-13:
DOWNLOAD EBOOKEnergetic neutral atom (ENA) and low energy neutral atom (LENA) imaging of space plasmas are emerging new technology which promises to revolutionize the way we view and understand large scale space plasma phenomena and dynamics. ENAs and LENAs are produced in the magnetosphere by charge exchange between energetic and plasma ions and cold geocoronal neutrals. While imaging techniques have been previously developed for observing ENAs, with energies above several tens of keV, most of the ions found in the terrestrial magnetosphere have lower energies. We recently suggested that LENAs could be imaged by first converting the neutrals to ions and then electrostatically analyzing them to reject the UV background. In this paper we extend this work to examine in detail the sensor elements needed to make an LENA imager. These elements are (1) a biased collimator to remove the ambient plasma ions and electrons and set the azimuthal field-of-view; (2) a charge modifier to convert a portion of the incident LENAs to ions; (3) an electrostatic analyzer to reject UV light and set the energy passband; and (4) a coincidence detector to measure converted LENAs while rejecting noise and penetrating radiation. We also examine the issue of LENA imager sensitivity and describe ways of optimizing sensitivity in the various sensor components. Finally, we demonstrate in detail how these general considerations are implemented by describing one relatively straightforward design based on a hemispherical electrostatic analyzer.
Author: James L. Burch
Publisher: Springer Science & Business Media
Published: 2012-12-06
Total Pages: 509
ISBN-13: 9401142335
DOWNLOAD EBOOKIMAGE (Imager for Magnetopause-to-Aurora Global Exploration) is the first NASA MIDEX mission and the first mission dedicated to imaging the Earth's magnetosphere. This volume offers detailed descriptions of the IMAGE instrumentation and of the image inversion techniques used to interpret the data. Also included are chapters on the IMAGE science objectives, the spacecraft design and capabilities, science and mission operations, and the processing and distribution of IMAGE's nonproprietary data products.
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Published: 1993
Total Pages: 11
ISBN-13:
DOWNLOAD EBOOKRecently proposed low energy neutral atom (LENA) imaging techniques use a collisional process to convert the low energy neutrals into ions before detection. At low energies, collisional processes limit the angular resolution and conversion efficiencies of these devices. However, if the intense ultraviolet light background can be suppressed, direct LENA detection is possible. We present results from a series of experiments designed to develop a novel filtering structure based on free-standing transmission gratings. If the grating period is sufficiently small, free standing transmission gratings can be employed to substantially polarize ultraviolet (UV) light in the wavelength range 300 Å to 1500 Å. If a second grating is placed behind the first grating with its axis of polarization oriented at a right angle to the first's, a substantial attenuation of UV radiation is achievable. ne neutrals will pass through the remaining open area of two gratings and be detected without UV background complications. We have obtained nominal 2000 Å period (1000 Å bars with 1000 Å slits) free standing, gold transmission gratings and measured their UV and atomic transmission characteristics. The geometric factor of a LENA imager based on this technology is comparable to that of other proposed LENA imagers. In addition, this of imager does not distort the neutral trajectories, allowing for high angular resolution.
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Published: 1992
Total Pages: 17
ISBN-13:
DOWNLOAD EBOOKMagnetospheric imaging has been proposed using remote detection of low energy neutral atoms (LENAs) of magnetospheric origin. In the detector, LENAs can be removed from the immense ambient EUV by charge modification (ionization) using a carbon stripping foil and can be subsequently deflected into an E/q analysis section. The detector sensitivity efficiency of LENAs is highly dependent on the ionization probability of neutrals as they transit the carbon foil. In this study, we present equilibrium charge state distributions and scatter distributions for 1-30 keV atomic hydrogen and oxygen transiting 0.5 [mu]g cm−2 carbon foils. The fraction of hydrogen exiting a foil as H ranges from approximately 5% at 1 keV to 41% at 30 keV. The fraction of oxygen exiting the foil as O+ ranges from 2% at 10 keV to 8% at 30 keV. Results obtained after coating the exit surface of foils with either aluminum (which forms aluminum oxide when exposed to air) or gold suggests that the exit surface chemistry has no effect on the charge state distributions due to foil contamination from exposure to air. Scattering resulting from the atom-foil interaction is shown to be independent of the charge state distribution, suggesting that the interaction mechanisms resulting in charge exchange and scattering are distinctly different.
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Published: 1993
Total Pages: 12
ISBN-13:
DOWNLOAD EBOOKLow energy neutral atoms (LENAs) are produced in space plasmas by charge exchange between the ambient magnetospheric plasma ions and cold neutral atoms. Under normal conditions these cold neutrals come from the terrestrial geocorona, a shroud of few-ev hydrogen atoms surrounding the Earth. As a consequence of this charge exchange, it has become possible to remotely image many regions of the magnetosphere for the first time utilizing recently developed LENA imaging technology. In addition to the natural hydrogen geocorona, conventional explosions and maneuvering thruster firings can also introduce large amounts of cold gas into the space environment. In this paper we examine whether such potentially clandestine activities could also be remotely observed for the first time via LENA imaging. First, we examine the fluxes of LENAs produced in the space environment from a conventional explosion. Then we review the present state of the art in the emerging field of LENA detection and imaging. Recent work has shown that LENAs can be imaged by first converting the neutrals to ions with ultra-thin (10s of [Angstrom]) foils and then electrostatically analyzing these newly created ions to reject the large (>10[sup 10] cm[sup [minus]2] [sup [minus]1]) UV background to which the low energy detectors are sensitive. We conclude that the sensitivities for present LENA imager designs may be just adequate for detecting some man-made releases. With additional improvements in LENA detection capabilities, this technique could become an important new method for monitoring for conventional explosions, as well as other man-made neutral releases, in the space environment.
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Published: 1993
Total Pages: 13
ISBN-13:
DOWNLOAD EBOOKThe potential scientific return from low energy neutral atom (LENA) imaging of the magnetosphere is extraordinary. The technical challenges of LENA detection include (1) removal of LENAs from the tremendous ambient UV without losing information of their incident trajectories, (2) quantification of their trajectories, and (3) obtaining high sensitivity measurements. Two techniques that have been proposed for this purpose are based on fundamentally different atomic interaction mechanisms between LENAs and a solid: LENA transmission through an ultrathin foil and LENA reflection from a solid surface. Both of these methods provide LENA ionization (for subsequent removal from the UV by electrostatic deflection) and secondary electron emission (for start pulse generation for time-of-flight and/or coincidence). We present a comparative study of the transmission and reflection techniques based on differences in atomic interactions with solids and surfaces. We show that transmission methods yield an order of magnitude greater secondary electron emission than reflection methods. Transmission methods are shown to be sufficient for LENA energies of approximately 1 keV to greater than 30 keV. Reflection methods using low work function surfaces could be employed for LENA ionization for energies less than several keV.
Author: Jamie Ryan Gardner
Publisher: Springer
Published: 2017-10-30
Total Pages: 121
ISBN-13: 3319684302
DOWNLOAD EBOOKThis book describes the design, construction, and characterization of a new type of aberration-corrected, neutral-atom lens. Atom beam control plays a crucial role in many different fields, ranging from fundamental physics research and materials science to applied nanotechnology. Despite this, atom-optical elements like lenses and mirrors remain relatively underdeveloped compared to their counterparts in other optics fields. Although aberration correction is addressed quite comprehensively in photon and electron lenses, no credible research efforts have yet produced the same technology for neutral atoms. It reports on progress towards a neutral atom imaging device that will be useful in a range of applications, including nanofabrication and surface microscopy. It presents a novel technique for improving refractive power and correcting chromatic aberration in atom lenses based on a fundamental paradigm shift from continuous, two-dimensional focusing to a pulsed, three-dimensional approach. Simulations of this system suggest that it will pave the way towards the long-sought goal of true atom imaging on the nanoscale. The book further describes the construction of a prototype lens, and shows that all of the technological requirements for the proposed system are easily satisfied. Using metastable neon from a supersonic source, the prototype was characterized for three different focal lengths and a diverse range of apertures. Despite some manufacturing imperfections, lower distortion and higher resolution than has been shown in any previous hexapole lens was observed. Comparison with simulations corroborates the underlying theory and encourages further refinement of the process.
