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NASA NTRS2019

Secondary Ion Mass Spectroscopy

Secondary Ion mass Spectroscopy (SIMS), as the name suggests, involves characterizing metallic and other materials trough the spectroscopic analysis of secondary ions emanating from the surface of the material to be characterized by the impact of the high energy primary ions. The primary ion source including the choice of its gun, voltage and current can be selected and used depending on the purpose of the analysis. In most instruments more than one primary ion gun is lined up to the sample stage and can be activated with selected accelerating parameters (voltage and beam intensity). The impingement of primary ions on to the sample surface generates positive, negative or neutral ions, electrons, atoms and atomic clusters. Majority of these sample fragments being neutral, could not be utilized as such fragments cannot be manipulated through the use of electromagnetic or electrostatic lenses. Secondary ions that are positively or negatively charged possess large variation in velocity, charge, and mass. These ionic fragments eventually travel through a system of several lenses in very high vacuum to reach detector/counter. Relative amounts of alloying elements or impurities in an alloy can be calculated from the counts of related ions accumulated in the detector/counter.

Panda, Binayak↗

NASA NTRS1993

Low Earth orbital atomic oxygen environmental simulation facility for space materials evaluation

Simulation of low Earth orbit atomic oxygen for accelerated exposure in ground-based facilities is necessary for the durability evaluation of space power system component materials for Space Station Freedom (SSF) and future missions. A facility developed at the National Aeronautics and Space Administrations's (NASA) Lewis Research Center provides accelerated rates of exposure to a directed or scattered oxygen beam, vacuum ultraviolet (VUV) radiation, and offers in-situ optical characterization. The facility utilizes an electron-cyclotron resonance (ECR) plasma source to generate a low energy oxygen beam. Total hemispherical spectral reflectance of samples can be measured in situ over the wavelength range of 250 to 2500 nm. Deuterium lamps provide VUV radiation intensity levels in the 115 to 200 nm range of three to five equivalent suns. Retarding potential analyses show distributed ion energies below 30 electron volts (eV) for the operating conditions most suited for high flux, low energy testing. Peak ion energies are below the sputter threshold energy (approximately 30 eV) of the protective coatings on polymers that are evaluated in the facility, thus allowing long duration exposure without sputter erosion. Neutral species are expected to be at thermal energies of approximately .04 eV to .1 eV. The maximum effective flux level based on polyimide Kapton mass loss is 4.4 x 10 exp 6 atoms/((sq. cm)*s), thus providing a highly accelerated testing capability.

Stidham, Curtis R.↗

NASA NTRS1995

Reliability assessment of multiple quantum well avalanche photodiodes

The reliability of doped-barrier AlGaAs/GsAs multi-quantum well avalanche photodiodes fabricated by molecular beam epitaxy is investigated via accelerated life tests. Dark current and breakdown voltage were the parameters monitored. The activation energy of the degradation mechanism and median device lifetime were determined. Device failure probability as a function of time was computed using the lognormal model. Analysis using the electron beam induced current method revealed the degradation to be caused by ionic impurities or contamination in the passivation layer.

Yun, Ilgu↗

NASA NTRS1975

Measurements on the development of cascades in a tungsten-scintillator ionization spectrometer

The response of a tungsten-scintillator ionization spectrometer to accelerated particle beams has been investigated. Results obtained from exposure of the approx. 1000 g/sq cm apparatus to 5, 10, and 15 GeV/c electrons and pions as well as to 2.1 GeV/nucleon C-12 and O-16 ions are presented. These results include cascade-development curves, fractions of the primary energy measured by the spectrometer, and resolutions of the apparatus for measuring the primary energies. For 15 GeV/c electrons, an average of about 82% of the incident energy is measured by the apparatus with resolution (normal standard deviation) of about 6%. For 15 GeV/c pions, an average of about 65% of the incident energy is measured with resolution of about 18%. The energy resolution improves with increasing energy and with increasing depth of the spectrometer.

Cheshire, D. L.↗

NASA NTRS2018

Parameterizations of Chromospheric Condensations in dG and dMe Model Flare Atmospheres

The origin of the near-ultraviolet and optical continuum radiation in flares is critical for understanding particle acceleration and impulsive heating in stellar atmospheres. Radiative-hydrodynamic (RHD) simulations in 1D have shown that high energy deposition rates from electron beams produce two flaring layers at T approximately 10 (exp 4) K that develop in the chromosphere: a cooling condensation (downflowing compression) and heated non-moving (stationary) flare layers just below the condensation. These atmospheres reproduce several observed phenomena in flare spectra, such as the red-wing asymmetry of the emission lines in solar flares and a small Balmer jump ratio in M dwarf flares. The high beam flux simulations are computationally expensive in 1D, and the (human) timescales for completing NLTE models with adaptive grids in 3D will likely be unwieldy for some time to come. We have developed a prescription for predicting the approximate evolved states, continuum optical depth, and emergent continuum flux spectra of RHD model flare atmospheres. These approximate prescriptions are based on an important atmospheric parameter: the column mass (m(sub ref)) at which hydrogen becomes nearly completely ionized at the depths that are approximately in steady state with the electron beam heating. Using this new modeling approach, we find that high energy flux density (>F11) electron beams are needed to reproduce the brightest observed continuum intensity in IRIS data of the 2014 March 29 X1 solar flare, and that variation in m(sub ref) from 0.001 to 0.02 g cm (exp -2) reproduces most of the observed range of the optical continuum flux ratios at the peak of M dwarf flares.

Kowalski, Adam F.↗

NASA NTRS1978

A new measurement of the cosmic ray electron spectrum from 10 GeV to 300 GeV

The spectrum of cosmic-ray electrons has been measured with an instrument that combines a transition-radiation detector with a shower detector. The transition-radiation detector provides unique identification of individual electrons and good discrimination against protons. At the same time, it allows the construction of a large-area instrument (0.48 sq m ? ster) and consequently makes possible a measurement of improved statistical accuracy. The instrument has been calibrated with electron beams of 5-300 GeV at Fermilab, thus eliminating energy-dependent biases. A first balloon flight yielded 30 hours of data at an altitude of 5 g/sq cm. The design of the instrument is described, along with the accelerator calibrations and the analysis of the balloon flight data. The spectrum of electrons is found to be significantly steeper than that of protons over the whole energy range.

Hartmann, G.↗

NASA NTRS1975

Production of hard X rays in a plasma focus

A model of a plasma focus is examined wherein large axial electric fields are produced by an imploding current sheet during the final nanoseconds of the collapse phase and where the fields provide a mechanism for creating a beam of electrons of highly suprathermal energies. The expected bremsstrahlung radiation above 100 keV is calculated for such a beam, which has a power-law spectrum, both from electron-deuteron collisions in the focused plasma and when the beam reaches the wall of the device. It is concluded that, since the experimental results indicate little or no radiation above 100 keV originating in the walls, that the electrons in the beam must be decelerated after leaving the plasma and before reaching the wall. Comparisons with the results and the total energy of the device yield qualitative agreement with the expected angular distribution of hard X-rays and reasonable agreement with the total energy in accelerated electrons required to produce the observed total energy in hard X-rays by this mechanism.

Newman, C. E.↗

NASA NTRS1994

The source of Jovian auroral hiss observed by Voyager 1

Observations of auroral hiss obtained from the Voyager 1 encounter with Jupiter have been reanalyzed. The Jovian auroral hiss was observed near the inner boundary of the warm Io torus and has a low-frequency cutoff caused by propagation near the resonance cone. A simple ray tracing procedure using an offset tilted dipole of the Jovian magnetic field is used to determine possible source locations. The results obtained are consistent with two sources located symmetrically with respect to the centrifugal equator along an L shell (L approximately = 5.59) that is coincident with the boundary between the hot and cold regions of the Io torus and is located just inward of the ribbon feature observed from Earth. The distance of the sources from the centrifugal equator is approximately 0.58 +/- 0.01 R(sub J). Based on the similarity to terrestrial auroral hiss, the Jovian is auroral hiss is believed to be generated by beams of low energy (approximately tens to thousands of eV) electrons. The low-frequency cutoff of the auroral hiss suggests that the electrons are accelerated near the inferred source region, possibly by parallel electric fields similar to those existing in the terrestrial auroral regions. A field-aligned current is inferred to exist at L shells just inward of the plasma ribbon. A possible mechanism for driving this current is discussed.

Morgan, D. D.↗

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 NTRS1990

High-Efficiency Klystron For Television Transmitters

Improved klystron designed for use as final amplifier in ultrahigh-frequency (UHF) television transmitter. New device incorporates multistage depressed collector (MSDC) of advanced design to increase efficiency by recovering, from spent electron beam, some of residual kinetic energy otherwise dissipated as heat. Concept applied to increase efficiencies of microwave communication, equipment, radar systems, and particle-beam accelerators.

Ramins, Peter↗

NASA NTRS1982

Extended-performance 8-cm ion thruster operation

The performance of an 8-cm ion thruster has been extended to 32-mN thrust, 4062-s specific impulse, and 0.033-mN/W thrust-to-power ratio. The design of this thruster is similar to the IAPS (Ion Auxiliary Propulsion System), which has a performance of 5-mN thrust, 3500-s specific impulse, and 0.036-mN/W thrust-to-power ratio. The above level of extended performance has been achieved by increasing the discharge power, ion-beam accelerating voltage, and propellant flowrate, and by modifying the propellant-vapor injection, discharge-chamber magnetic-field strength, high-voltage insulators, and electron baffle. This paper describes results obtained in characterizing the extended-performance operation of both the unmodified thruster (i.e., in an IAPS-like configuration) and the modified thruster. Lifetime-estimating measurements for the modified thruster at extended-performance conditions are also presented.

Wessel, F. J.↗

NASA NTRS1987

Advanced electric propulsion and space plasma contactor research

A theory of the plasma contacting process is described and experimental results obtained using three different hollow cathode-based plasma contactors are presented. The existence of a sheath across which the bulk of the voltage drop associated with the contacting process occurs is demonstrated. Test results are shown to agree with a model of a spherical, space-charge-limited double sheath. The concept of ignited mode contactor operation is discussed, which is shown to enhance contactor efficiency when it is collecting electrons. An investigation of the potentials in the plasma plumes downstream of contactors operating at typical conditions is presented. Results of tests performed on hollow cathodes operating at high interelectrode pressures (up to about 1000 Torr) on ammonia are presented and criteria that are necessary to ensure that the cathode will operate properly in this regime are presented. These results suggest that high pressure hollow cathode operation is difficult to achieve and that special care must be taken to assure that the electron emission region remains diffuse and attached to the low work function insert. Experiments conducted to verify results obtained previously using a ring cusp ion source equipped with a moveable anode are described and test results are reported. A theoretical study of hollow cathode operation at high electron emission currents is presented. Preliminary experiments using the constrained sheath optics concept to achieve ion extraction under conditions of high beam current density, low net accelerating voltage and well columniated beamlet formation are discussed.

Wilbur, Paul J.↗

NASA NTRS1992

Electrostatic ion thruster optics calculations

Calculations have been performed which encompass both a self-consistent ion source extraction plasma sheath and the primary ion optics including sheath and electrode-induced aberrations. Particular attention is given to the effects of beam space charge, accelerator geometry, and properties of the downstream plasma sheath on the position of the electrostatic potential saddle point near the extractor electrode. The electron blocking potential blocking is described as a function of electrode thickness and secondary plasma processes.

Whealton, John H.↗

NASA NTRS1994

Participation in the definition, conduct, and analysis of particle accelerator experiments for the first Spacelab Mission

The Space Experiments with Particle Accelerators (SEPAC) is a joint endeavor between NASA and the Institute of Space and Aeronautical Sciences (ISAS) in Japan. Its objectives are to use energetic electron beams to investigate beam-atmosphere interactions and beam-plasma interactions in the earth's upper atmosphere and ionosphere using the shuttle Spacelab. Two flights of SEPAC have occurred to date (Spacelab 1 on STS-9 in Nov.-Dec. 1983 and ATLAS 1 on STS-45 in Mar.-Apr. 1992). The SEPAC instrumentation is available for future missions, and the scientific results of the first two missions justify further investigations; however, at present there are no identifiable future flight opportunities. As specified in the contract, the primary purpose of this report is to review the scientific accomplishments of the ATLAS 1 SEPAC experiments, which have been documented in the published literature, with only a brief review of the earlier Spacelab 1 results. One of the main results of the Spacelab 1 SEPAC experiments was that the ejection of plasma from the magnetoplasmadynamic (MPD) arcjet was effective in maintaining vehicle charge neutralization during electron beam firings, but only for a brief period of 10 ms or so. Therefore, a xenon plasma contactor, which can provide continuous vehicle charge neutralization, was developed for the ATLAS 1 SEPAC experiments. Because of the successful operation of the plasma contactor on ATLAS 1, it was possible to perform experiments on beam-plasma interactions and beam-atmosphere interactions at the highest beam power levels of SEPAC. In addition, the ability of the plasma contactor to eject neutral xenon led to a successful experiment on the critical ionization velocity (CIV) phenomena on ATLAS 1.

Burch, J. L.↗

NASA NTRS1988

Measurements and calculations of the Coulomb cross section for the production of direct electron pairs by energetic heavy nuclei in nuclear track emulsion

Measurements and theoretical predictions of the Coulomb cross section for the production of direct electron pairs by heavy ions in emulsion have been performed. Nuclear track emulsions were exposed to the 1.8 GeV/amu Fe-56 beam at the Lawrence Berkeley Laboratory bevalac and to the 60 and 200 GeV/amu O-16 and the 200 GeV/amu S-32 beam at the European Center for Nuclear Research Super Proton Synchrotron modified to accelerate heavy ions. The calculations combine the Weizsacker-Williams virtual quanta method applicable to the low-energy transfers and the Kelner-Kotov relativistic treatment for the high-energy transfers. Comparison of the measured total electron pair yield, the energy transfer distribution, and the emission angle distribution with theoretical predictions revealed a discrepancy in the frequency of occurrence of the low-energy pairs (less than or = 10 MeV). The microscope scanning criteria used to identify the direct electron pairs is described and efforts to improve the calculation of the cross section for pair production are also discussed.

Derrickson, J. H.↗

NASA NTRS1977

Mass-dependent channel electron multiplier operation

The absolute counting efficiency and pulse height distributions of a continuous-channel electron multiplier used in the detection of hydrogen, argon and xenon ions are assessed. The assessment technique, which involves the post-acceleration of 8-eV ion beams to energies from 100 to 4000 eV, provides information on counting efficiency versus post-acceleration voltage characteristics over a wide range of ion mass. The charge pulse height distributions for H2 (+), A (+) and Xe (+) were measured by operating the experimental apparatus in a marginally gain-saturated mode. It was found that gain saturation occurs at lower channel multiplier operating voltages for light ions such as H2 (+) than for the heavier ions A (+) and Xe (+), suggesting that the technique may be used to discriminate between these two classes of ions in electrostatic analyzers.

Fields, S. A.↗

NASA NTRS1982

Electron heating within the earth's bow shock

High-temporal-resolution measurements of electron velocity distributions have been obtained for many transits through the earth's bow shock. Within all oblique shocks studied, the maximum of the electron velocity distribution is offset with respect to the ion rest frame parallel to the magnetic field vector and directed downstream. These observations indicate that electron thermalization within the bow shock consists first of a downstream acceleration parallel to the magnetic field vector by the macroscopic shock electric field, followed by beam-driven plasma instabilities.

Feldman, W. C.↗

NASA NTRS1985

Lead and uranium group abundances in cosmic rays

The importance of Lead and Uranium group abundances in cosmic rays is discussed in understanding their evolution and propagation. The electronic detectors can provide good charge resolution but poor data statistics. The plastic detectors can provide somewhat better statistics but charge resolution deteriorates. The extraterrestrial crystals can provide good statistics but with poor charge resolution. Recent studies of extraterrestrial crystals regarding their calibration to accelerated uranium ion beam and track etch kinetics are discussed. It is hoped that a charge resolution of two charge units can be achieved provided an additional parameter is taken into account. The prospects to study abundances of Lead group, Uranium group and superheavy element in extraterrestrial crystals are discussed, and usefulness of these studies in the light of studies with electronic and plastic detectors is assessed.

Yadav, J. S.↗