Study and optimization of 15-cm Kaufman thruster discharges
Kaufman thrustor performance dependence on transmission of ion extraction optics and magnetic field shape
Knauer, W.↗
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Radiative transfer of X-rays in the solar corona
The problem of resonance scattering of X-ray emission lines in the solar corona is investigated. For the resonance lines of some helium-like ions, significant optical depths are reached over distances small compared with the size of typical coronal features. A general integral equation for the transfer of resonance-line radiation under solar coronal conditions is derived. This expression is in a form useful for modeling the complex three-dimensional temperature and density structure of coronal active regions. The transfer equation is then cast in a form illustrating the terms which give rise to the attenuation or enhancement of the resonance-line intensity. The source function for helium-like oxygen (O VII) under coronal conditions is computed and discussed in terms of the relative importance of scattering.
Acton, L. W.↗
Small scale structure in the interstellar medium: Orion's threadbare cloak
The interstellar medium in the central portion of the Orion Cloak dynamical feature was examined for evidence of fine structure. Four stars in the Ori OB I association, HD 37017, 37468, 37479, and 37776 bracket the stars in the lower belt region that were studied previously. Two are members of the sigma Ori subcluster. A lower limit to the scale inhomogeneity can be set using these at 0.1 pc, while on a scale of about 10 pc, the high velocity component of the second spectrum ions shows optical depth variation of more than a factor of 5. Neutral lines do not display the high velocity component. Some preliminary abundances are also given.
Shore, S. N.↗
A comparison of experimental and computer model results on the charge-exchange plasma flow from a 30 cm mercury ion thruster
Ion thrusters can be used in a variety of primary and auxiliary space-propulsion applications. A thruster produces a charge-exchange plasma which can interact with various systems on the spacecraft. The propagation of the charge-exchange plasma is crucial in determining the interaction of that plasma with the spacecraft. This paper compares experimental measurements with computer model predictions of the propagation of the charge-exchange plasma from a 30 cm mercury ion thruster. The plasma potentials, and ion densities, and directed energies are discussed. Good agreement is found in a region upstream of, and close to, the ion thruster optics. Outside of this region the agreement is reasonable in view of the modeling difficulties.
Gabriel, S. B.↗
A simplified optical model description of heavy ion fragmentation
The abrasion-ablation model of heavy-ion frgmentation by target nuclei of Townsend (1983) and the EVAP Monte Carlo computer program (Guthrie, 1970) for decay probabilities are applied to calculate the production cross sections of isotopes of S, P, Si, and Al for the fragmentation of 213-MeV/nucleon Ar-40 ions by C-12 targets and of Fe, Mn, Cr, V, Ti, Sc, and Ca for 1.88-GeV Fe-56 fragmentation by Pb-208 and by C-12. The results are presented in tables and graphs and shown to be in good agreement with the experimental data of Viyogi et al. (1979) and Westfall et al. (1979). The implications of these studies for the design of radiation shielding for long-term manned space missions are indicated.
Townsend, L. W.↗
Local oscillator induced degradation of medium-term stability in passive atomic frequency standards
As the performance of passive atomic frequency standards improves, a new limitation is encountered due to frequency fluctuations in an ancillary local oscillator (L.O.). The effect is due to time variation in the gain of the feedback which compensates L.O. frequency fluctuations. The high performance promised by new microwave and optical trapped ion standards may be severely compromised by this effect. Researchers present an analysis of this performance limitation for the case of sequentially interrogated standards. The time dependence of the sensitivity of the interrogation process to L.O. frequency fluctuations is evaluated for single-pulse and double-pulse Ramsey RF interrogation and for amplitude modulated pulses. The effect of these various time dependencies on performance of the standard is calculated for an L.O. with frequency fluctuations showing a typical 1/f spectral density. A limiting 1/sq. root gamma dependent deviation of frequency fluctuations is calculated as a function of pulse lengths, dead time, and pulse overlap. Researchers also present conceptual and hardware-oriented solutions to this problem which achieve a much more nearly constant sensitivity to L.O. fluctuations. Solutions involve use of double-pulse interrogation; alternate interrogation of multiple traps so that the dead time of one trap can be covered by operation of the other; and the use of double-pulse interrogation for two traps, so that during the time of the RF pulses, the increasing sensitivity of one trap tends to compensate for the decreasing sensitivity of the other. A solution making use of amplified-modulated pulses is also presented which shows nominally zero time variation.
Dick, G. John↗
Recombination line intensities for hydrogenic ions. III - Effects of finite optical depth and dust
The effect on the recombination spectrum of hydrogen arising from: (1) finite optical thickness in the Lyman lines; (2) the overlapping of Lyman lines near the series limit; (3) the absorption of Lyman lines by dust or photoionization, and (4) the long-wave radiation emitted by dust is examined. Full account is taken of electron and heavy particle collisions in redistributing energy and angular momentum. It is seen that each of these deviations from the classical Case B leads to observable effects, and that dust influences the recombination spectrum in characteristic ways that may make possible new observational constraints on dust properties in nebulosities. On the basis of these calculations it is believed that the uncertainty in the determination of the helium-to-hydrogen abundance ratio in the universe may be larger than currently claimed.
Hummer, D. G.↗
Large carbon-carbon grids for high power, high specific impulse ion thrusters
This paper reports performance and lifetime predictions based on numerical modeling and issues associated with fabrication of carbon-carbon composite grids for high power, high ISP grids.
ion thrusters ion optics carbon-carbon↗
Operating Characteristics of a 15-cm dia. Ion Engine for Small Planetary Spacecraft
A 15-cm diameter, scaled-down version of the NASA light-weight 30-cm ion engine has been developed for potential application to very small planetary spacecraft. Integration of the 15-cm ion source into 4x15-cm segmented engine configuration results in a 30-cm equivalent engine which can be throttled over a 7-to-1 input power variation with a constant beam current in each of the four segments. Throttling the segmented engine by turning off individual segments can result in a significant decrease in the required service life (and qualification requirements) of the ion source components.
grids segmented ion engine↗
Optical Properties of Tm(3+) Ions in Alkali Germanate Glass
Tm-doped alkali germanate glass is investigated for use as a laser material. Spectroscopic investigations of bulk Tm-doped germanate glass are reported for the absorption, emission and luminescence decay. Tm:germanate shows promise as a fiber laser when pumped with 0.792 m diodes because of low phonon energies. Spectroscopic analysis indicates low nonradiative quenching and pulsed laser performance studies confirm this prediction by showing a quantum efficiency of 1.69.
Walsh, Brian M.↗
Colorimetric and Label-Free Optical Detection of Pb 2+ Ions via Colloidal Gold Nanoparticles
The detection of Lead (Pb) heavy metal in water is crucial in many chemical processes as it is associated with serious health hazard. Here, we report the selective and precise colorimetric detection of Pb 2+ ions in water exploiting the mechanisms of aggregation and self-assembly of Glutathione (GSH) functionalized gold nanoparticles (GNPs). The carboxyl functional groups are available to create coordination complexes with Pb 2+ inducing aggregation amongst the GSH-GNPs in the presence of Pb 2+ due to the chelation of the GSH ligands. The resulting aggregation of amongst the GSHGNPs in the presence of Pb2+ increases the aggregate size depending on available Pb 2+ ions affecting the plasmonic coupling. This causes in a substantial shift in the plasmon wavelength to a longer wavelength side with increasing Pb 2+ concentration, resulting in a red-to-blue colorimetric or visual change, enabling instant determination of lead content in water.
calorimetric detection↗
(abstract) Optical Scattering and Surface Microroughness of Ion Beam Deposited Au and Pt Thin Films
Thin films of gold and platinum have been deposited onto superpolished fused silica substrates using thermal evaporation, ion assisted deposition (IAD), and ion assisted sputtering. The influence of ion beam flux, thin film material, and deposition rate on the films microroughness have been investigated. Short range surface microroughness of the films has been examined using scanning tunneling microscopy (STM) and atomic force microscopy (AFM). Long range surface microroughness has been characterized using an angle resolved optical scatterometer. Results indicate that ion beam deposited coatings have improved microstructure over thermally evaporated films.
assisted sputtering fused silica ion beam microrou↗
Optical-model abrasion cross sections for high-energy heavy ions
Within the context of eikonal scattering theory, a generalized optical model potential approximation to the nucleus-nucleus multiple scattering series is used in an abrasion-ablation collision model to predict abrasion cross sections for relativistic projectile heavy ions. Unlike the optical limit of Glauber theory, which cannot be used for very light nuclei, the abrasion formalism is valid for any projectile target combination at any incident kinetic energy for which eikonal scattering theory can be utilized. Results are compared with experimental results and predictions from Glauber theory.
Townsend, L. W.↗
Ion beam deposited silicon carbide on glass optics and replica gratings
The results of an attempt to coat optical flats and replace echelle gratings with ion-deposited SiC are reported. Deposition was performed by bombarding a SiC target with an ion beam angled 45 deg relative to the target. Half the target was covered with stainless steel to furnish a comparison opportunity. After precleaning SiC coatings of 300-2200 A thickness were deposited. The specimens had previously been coated with either Au or Al or were left blank. Reflectance and diffraction data were taken of the finished flats and gratings. The SiC-coated flats performed as well as uncoated flats while the echelles exhibited deteriorating performance with increasing coating thickness. Further studies are indicated on the effect of coating thickness on surface roughness.
Windt, D. L.↗
Advanced ion thruster and electrochemical launcher research
The theoretical model of orificed hollow cathode operation predicted experimentally observed cathode performance with reasonable accuracy. The deflection and divergence characteristics of ion beamlets emanating from a two grid optics system as a function of the relative offset of screen and accel grids hole axes were described. Ion currents associated with discharge chamber operation were controlled to improve ion thruster performance markedly. Limitations imposed by basic physical laws on reductions in screen grid hole size and grid spacing for ion optics systems were described. The influence of stray magnetic fields in the vicinity of a neutralizer on the performance of that neutralizer was demonstrated. The ion current density extracted from a thruster was enhanced by injecting electrons into the region between its ion accelerating grids. Theoretical analysis of the electrothermal ramjet concept of launching space bound payloads at high acceleration levels is described. The operation of this system is broken down into two phases. In the light gas gun phase the payload is accelerated to the velocity at which the ramjet phase can commence. Preliminary models of operation are examined and shown to yield overall energy efficiences for a typical Earth escape launch of 60 to 70%. When shock losses are incorporated these efficiencies are still observed to remain at the relatively high values of 40 to 50%.
Wilbur, P. J.↗
Ion-beam-textured and coated surfaces experiment (S1003)
The objective of this LDEF experiment is to measure the effects of exposure to the shuttle launch and near Earth space environments on the optical properties of ion beam textured high absorptance solar thermal control surfaces, the optical and electrical properties of ion beam sputtered conductive solar thermal control surfaces, and the weight loss of ion beam deposited oxide polymer films. The various types of surfaces to be tested include six major categories: (1) ion beam textured surfaces suitable for space solar thermal (solar concentration) application; (2) painted and/or state of the art solar thermal surfaces; (3) ion beam sputtered conductive coatings for thermal and space charge control (e.g., indium-oxide coated metalized FEP Teflon); (4) ion beam sputtered conductive coated solar sail materials for space charge control and cooling through emittance; (5) micrometeoroid sensitive samples whose optical properties change only as a result of micrometeoroid impact; and (6) Kapton coated with oxide polymer films to minimize oxygen degradation at near Earth orbit altitudes.
Mirtich, M. J., Jr.↗
Optical model calculations of heavy-ion target fragmentation
The fragmentation of target nuclei by relativistic protons and heavy ions is described within the context of a simple abrasion-ablation-final-state interaction model. Abrasion is described by a quantum mechanical formalism utilizing an optical model potential approximation. Nuclear charge distributions of the excited prefragments are calculated by both a hypergeometric distribution and a method based upon the zero-point oscillations of the giant dipole resonance. Excitation energies are estimated from the excess surface energy resulting from the abrasion process and the additional energy deposited by frictional spectator interactions of the abraded nucleons. The ablation probabilities are obtained from the EVA-3 computer program. Isotope production cross sections for the spallation of copper targets by relativistic protons and for the fragmenting of carbon targets by relativistic carbon, neon, and iron projectiles are calculated and compared with available experimental data.
Townsend, L. W.↗
Universal characteristics of transverse momentum transfer in intermediate energy heavy ion collisions
A microscopic optical model formalism for estimating momentum transfer in intermediate energy heavy ion collisions predicts universal behavior of the transverse component. In particular, for symmetric systems heavier than niobium, it appears that values of P(perpendicular)/A are independent of the mass and charge of the colliding nuclei and vary only with impact parameter and incident beam energy. This suggests that momentum transfer per nucleon saturates to some limiting value with increasing mass.
Khan, F.↗