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  • 1
    Publication Date: 2018-06-06
    Description: Even in the relatively small region of space that is the Earth's magnetosphere, ion and electron fluxes can vary by several orders of magnitude. Top-hat electrostatic analyzers currently do not possess the dynamic range required to sample plasma under all conditions. The purpose of this study was to compare, through computer simulation, three new electrostatic methods that would allow the sensitivity of a sensor to be varied through control of its geometric factor (GF) (much like an aperture on a camera). The methods studied were inner filter plates, split hemispherical analyzer (SHA) and top-cap electrode. This is the first discussion of the filter plate concept and also the first study where all three systems are studied within a common analyzer design, so that their relative merits could be fairly compared. Filter plates were found to have the important advantage that they facilitate the reduction in instrument sensitivity whilst keeping all other instrument parameters constant. However, it was discovered that filter plates have numerous disadvantages that make such a system impracticable for a top-hat electrostatic analyzer. It was found that both the top-cap electrode and SHA are promising variable geometric factor system (VGFS) concepts for implementation into a top-hat electrostatic analyzer, each with distinct advantages over the other.
    Keywords: Instrumentation and Photography
    Type: Measurement Science and Technology (ISSN 0957-0233); Volume 21
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  • 2
    Publication Date: 2019-07-13
    Description: We report the first observations of Spontaneous Hot Flow Anomalies (SHFAs) at Venus and Mars, demonstrating their existence in the foreshocks of other planets beyond Earth. Using data from the ESA Venus Express and the NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft, we present magnetic and plasma observations from events at both planets, exhibiting properties similar to classical Hot Flow Anomalies, with bounding shock-like compressive regions and a hot and diffuse core. However, these explosive foreshock transients were observed without any attendant interplanetary magnetic field discontinuity, consistent with SHFAs observed at Earth and our hybrid simulations.
    Keywords: Space Radiation
    Type: GSFC-E-DAA-TN53853 , Journal of Geophysical Research: Space Physics (ISSN 2169-9402) (e-ISSN ); 122; vember 10; 9910-9923
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  • 3
    Publication Date: 2019-07-13
    Description: We report our findings comparing the geometric factor (GF) as determined from simulations and laboratory measurements of the new Dual Electron Spectrometer (DES) being developed at NASA Goddard Space Flight Center as part of the Fast Plasma Investigation on NASA's Magnetospheric Multiscale mission. Particle simulations are increasingly playing an essential role in the design and calibration of electrostatic analyzers, facilitating the identification and mitigation of the many sources of systematic error present in laboratory calibration. While equations for laboratory measurement of the Geometric Factpr (GF) have been described in the literature, these are not directly applicable to simulation since the two are carried out under substantially different assumptions and conditions, making direct comparison very challenging. Starting from first principles, we derive generalized expressions for the determination of the GF in simulation and laboratory, and discuss how we have estimated errors in both cases. Finally, we apply these equations to the new DES instrument and show that the results agree within errors. Thus we show that the techniques presented here will produce consistent results between laboratory and simulation, and present the first description of the performance of the new DES instrument in the literature.
    Keywords: Spacecraft Instrumentation and Astrionics
    Type: GSFC-E-DAA-TN9709 , Review of Scientific Instruments (ISSN 0034-6748); 83; 3; 033303
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  • 4
    Publication Date: 2019-07-13
    Description: Many space plasmas (especially electrons generated in planetary ionospheres) exhibit fine-detailed structures that are challenging to fully resolve with the energy resolution of typical space plasma analyzers (10% 20%). While analyzers with higher resolution have flown, generally this comes at the expense of sensitivity and temporal resolution. We present a new technique for measuring plasmas with extremely high energy resolution through the combination of a top-hat Electrostatic Analyzer (ESA) followed by an internally mounted Retarding Potential Analyzer (RPA). When high resolutions are not required, the RPA is grounded, and the instrument may operate as a typical general-purpose plasma analyzer using its ESA alone. We also describe how such an instrument may use its RPA to remotely vary the geometric factor (sensitivity) of a top hat analyzer, as was performed on the New Horizons Solar Wind at Pluto and MAVEN SupraThermal and Thermal Ion Composition instruments. Finally, we present results from laboratory testing of our prototype, showing that this technique may be used to construct an instrument with 1.6% energy resolution, constant over all energies and angles.
    Keywords: Plasma Physics
    Type: GSFC-E-DAA-TN66020 , Review of Scientific Instruments (ISSN 0034-6748) (e-ISSN 1089-7623); 89; 11; 113306
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  • 5
    Publication Date: 2019-07-13
    Description: We present high-resolution Hall MHD simulations of Ganymede's magnetosphere demonstrating that Hall electric fields in ion-scale magnetic reconnection layers have significant global effects not captured in resistive MHD simulations. Consistent with local kinetic simulations of magnetic reconnection, our global simulations show the development of intense field-aligned currents along the magnetic separatrices. These currents extend all the way down to the moon's surface, where they may contribute to Ganymede's aurora. Within the magnetopause and magnetotail current sheets, Hall J x B forces accelerate ions to the local Alfven speed in the out-of-plane direction, producing a global system of ion drift belts that circulates Jovian magnetospheric plasma throughout Ganymede's magnetosphere. We discuss some observable consequences of these Hall-induced currents and ion drifts: the appearance of a sub-Jovian 'double magnetopause' structure, an Alfvenic ion jet extending across the upstream magnetopause, and an asymmetric pattern of magnetopause Kelvin-Helmholtz waves.
    Keywords: Physics of Elementary Particles and Fields; Mathematical and Computer Sciences (General); Lunar and Planetary Science and Exploration
    Type: GSFC-E-DAA-TN32381 , Journal of Geophysical Research: Space Physics (e-ISSN 2169-9402); 120; 7; 5377-5392
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  • 6
    Publication Date: 2019-07-13
    Description: Using data from the National Aeronautics and Space Administration Mars Atmosphere and Voltatile EvolutioN and the European Space Agency Mars Express spacecraft, we show that transient phenomena in the foreshock and solar wind can directly inject energy into the ionosphere of Mars. We demonstrate that the impact of compressive ultralow frequency waves in the solar wind on the induced magnetospheres drive compressional, linearly polarized, magnetosonic ultralow frequency waves in the ionosphere, and a localized electromagnetic "ringing" at the local proton gyro frequency. The pulsations heat and energize Ionospheric plasmas. A preliminary survey of events shows that no special upstream conditions are required in the interplanetary magnetic field or solar wind. Elevated ion densities and temperatures in the solar wind near to Mars are consistent with the presence of an additional population of Martian ions, leading to ion-ion instabilities, associated wave-particle interactions, and heating of the solar wind. The phenomenon was found to be seasonal, occurring when Mars is near perihelion. Finally, we present simultaneous multipoint observations of the phenomenon, with the Mars Express observing the waves upstream, and Mars Atmosphere and Voltatile EvolutioN observing the response in the ionosphere. When these new observations are combined with decades of previous studies, they collectively provide strong evidence for a previously undemonstrated atmospheric loss process at unmagnetized planets: ionospheric escape driven by the direct impact of transient phenomena from the foreshock and solar wind.
    Keywords: Solar Physics
    Type: GSFC-E-DAA-TN62778 , Journal of Geophysical Research: Space Physics (ISSN 2169-9402) (e-ISSN 2169-9380); 123; 9; 7241-7256
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  • 7
    Publication Date: 2019-07-13
    Description: Abstract Parallel electric fields and their associated electric potential structures play a crucial role inionospheric-magnetospheric interactions at any planet. Although there is abundant evidence that parallel electric fields play key roles in Martian ionospheric outflow and auroral electron acceleration, the fields themselves are challenging to directly measure due to their relatively weak nature. Using measurements by the Solar Wind Electron Analyzer instrument aboard the NASA Mars Atmosphere and Volatile EvolutioN(MAVEN) Mars Scout, we present the discovery and measurement of a substantial (Phi) Mars 7.7 +/-0.6 V) parallel electric potential drop on closed magnetic field lines spanning the terminator from day to night above the great impact basin of Utopia Planitia, a region largely free of crustal magnetic fields. A survey of the previous 26 orbits passing over a range of longitudes revealed similar signatures on seven orbits, with a mean potential drop (Phi) Mars of 10.9 +/- 0.8 V, suggestive that although trans-terminator electric fields of comparable strength are not ubiquitous, they may be common, at least at these northerly latitudes.
    Keywords: Lunar and Planetary Science and Exploration
    Type: GSFC-E-DAA-TN42412 , Journal of Geophysical Research: Space Physics (ISSN 2169-9380) (e-ISSN 2169-9402); 122; 2; 2260-2271
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  • 8
    Publication Date: 2019-07-11
    Description: We report for the first time, simultaneous ion, electron, magnetic field vector and electric field wave measurements made possible by Mars Atmosphere and Volatile EvolutioN, during ion energy flux spikes in lowaltitude radial crustal magnetic fields on the Mars dayside. Observations show energetic electrons and ions (E 〉 25 eV) precipitating on magnetic field lines assumed as closed. Ions (E 〈 1.4 keV) display broad velocity distributions toward Mars, showing ions flowing from higher altitude possibly after magnetic reconnection or loss cone filling from pitch angle scattering effects. Precipitating ions (E 〈 1.4 keV) show nonadiabatic features depending on ion mass and energy and returning ions (E 〈 1.4 keV) show evidence of conserving the first adiabatic invariant in a mirror field. We observe magnetic field perturbations up to 60 nT, electric field wave amplitudes up to 38 mV/m, and brief periods of peaked electron spectra. At 175 km and at times Mars Atmosphere and Volatile EvolutioN is below the mirroring altitude of electrons, we observe mirroring and transverse heating of H+ ions alongside increased electric field wave amplitude fluctuations. It suggests field aligned potential drops result from different mirror altitudes of ions and electrons. Ions E 〉 1.4 keV (O+) occur as injected accelerated ion beams and ions heated after energization or deceleration. Energy dispersed kiloelectronvolt ions suggest a selection effect in radial magnetic fields for lowerenergy Marsward ions, compared to reflection of higherenergy antiSunward ions. Precipitating kiloelectronvolt ions show energy deposition rates of 3.6 10(exp -6) W/sq m and sputtering escape rates from precipitating O+ ions of 1.5 10(exp 5)/(sq cm.s) and 2.1 10(exp 6)/(sq cm.s) are calculated.
    Keywords: Lunar and Planetary Science and Exploration
    Type: GSFC-E-DAA-TN68737 , Journal of Geophysical Research: Space Physics (e-ISSN 2169-9402); 124; 2; 1239-1261
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  • 9
    Publication Date: 2019-07-19
    Description: The Magnetospheric Multiscale mission (MMS) is designed to study fundamental phenomena in space plasma physics such as a magnetic reconnection. The mission consists of four spacecraft, equipped with identical scientific payloads, allowing for the first measurements of fast dynamics in the critical electron diffusion region where magnetic reconnection occurs and charged particles are demagnetized. The MMS orbit is optimized to ensure the spacecraft spend extended periods of time in locations where reconnection is known to occur: at the dayside magnetopause and in the magnetotail. In order to resolve fine structures of the three dimensional electron distributions in the diffusion region (reconnection site), the Fast Plasma Investigation's (FPI) Dual Electron Spectrometer (DES) is designed to measure three dimensional electron velocity distributions with an extremely high time resolution of 30 ms. In order to achieve this unprecedented sampling rate, four dual spectrometers, each sampling 180 x 45 degree sections of the sky, are installed on each spacecraft. We present results of the comprehensive tests performed on the DES Engineering & Test Unit (ETU). This includes main parameters of the spectrometer such as energy resolution, angular acceptance, and geometric factor along with their variations over the 16 pixels spanning the 180-degree tophat Electro Static Analyzer (ESA) field of view and over the energy of the test beam. A newly developed method for precisely defining the operational space of the instrument is presented as well. This allows optimization of the trade-off between pixel to pixel crosstalk and uniformity of the main spectrometer parameters.
    Keywords: Plasma Physics
    Type: GSFC.ABS.5724.2011 , 2011 American Geophysical Union Fall Meeting; 5-9 Dec. 2011; San Francisco, CA; United States
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  • 10
    Publication Date: 2019-07-20
    Description: On 27 June 1996, the NASA Galileo spacecraft made humanitys first flyby of Jupiters largest moon, Ganymede, discovering that it is the only moon known to possess an internally generated magnetic field. Resurrecting the original Galileo Plasma Subsystem (PLS) data analysis software, we processed the raw PLS data from G01 and for the first time present the properties of plasmas encountered. Entry into the magnetosphere of Ganymede occurred near the confluence of the magnetopause and plasma sheet. Reconnection-driven plasma flows were observed (consistent with an Earth-like Dungey cycle), which may be a result of reconnection in the plasma sheet, magnetopause, or might be Ganymedes equivalent of a Low-Latitude Boundary Layer. Dropouts in plasma density combined with velocity perturbations afterward suggest that Galileo briefly crossed the cusps into closed magnetic field lines. Galileo then crossed the cusps, where field-aligned precipitating ions were observed flowing down into the surface, at a location consistent with observations by the Hubble Space Telescope. The density of plasma outflowing from Ganymede jumped an order of magnitude around closest approach over the north polar cap. The abrupt increase may be a result of crossing the cusp or may represent an altitude-dependent boundary such as an ionopause. More diffuse, warmer field-aligned outflows were observed in the lobes. Fluxes of particles near the moon on the nightside were significantly lower than on the dayside, possibly resulting from a diurnal cycle of the ionosphere and/or neutral atmosphere.
    Keywords: Lunar and Planetary Science and Exploration
    Type: GSFC-E-DAA-TN63498 , Geophysical Research Letters ; 45; 8; 3382-3392
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