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NASA NTRS1977

Spectral analysis of a high-velocity meteor

A spectrogram of a fast optical meteor was reduced and analyzed, and 60 features were identified in the spectrum. Air and ionized elements in this meteor radiate throughout the spectrum from 3000 A to 6800 A. A mass of 9 mg and an effective radiation temperature of approximately 5700 K were computed for the meteor. Weight ratios of Ca:Fe, and Mg:Fe, and Na:Fe were computed. A plasma particle velocity distribution for meteors was derived, and the average collision speed obtained from this distribution was compared with the relative collision speed of a Fe-N2 gas mixture at 5700 K.

Harvey, G. A.↗

NASA NTRS2015

The Parameterization of Top-Hat Particle Sensors with Microchannel-Plate-Based Detection Systems and its Application to the Fast Plasma Investigation on NASA's Magnetospheric MultiScale Mission

The most common instrument for low energy plasmas consists of a top-hat electrostatic analyzer geometry coupled with a microchannel-plate (MCP)-based detection system. While the electrostatic optics for such sensors are readily simulated and parameterized during the laboratory calibration process, the detection system is often less well characterized. Furthermore, due to finite resources, for large sensor suites such as the Fast Plasma Investigation (FPI) on NASA's Magnetospheric Multiscale (MMS) mission, calibration data are increasingly sparse. Measurements must be interpolated and extrapolated to understand instrument behavior for untestable operating modes and yet sensor inter-calibration is critical to mission success. To characterize instruments from a minimal set of parameters we have developed the first comprehensive mathematical description of both sensor electrostatic optics and particle detection systems. We include effects of MCP efficiency, gain, scattering, capacitive crosstalk, and charge cloud spreading at the detector output. Our parameterization enables the interpolation and extrapolation of instrument response to all relevant particle energies, detector high voltage settings, and polar angles from a small set of calibration data. We apply this model to the 32 sensor heads in the Dual Electron Sensor (DES) and 32 sensor heads in the Dual Ion Sensor (DIS) instruments on the 4 MMS observatories and use least squares fitting of calibration data to extract all key instrument parameters. Parameters that will evolve in flight, namely MCP gain, will be determined daily through application of this model to specifically tailored in-flight calibration activities, providing a robust characterization of sensor suite performance throughout mission lifetime. Beyond FPI, our model provides a valuable framework for the simulation and evaluation of future detection system designs and can be used to maximize instrument understanding with minimal calibration resources.

Instrument-model↗

NASA NTRS1992

Fast ionospheric feedback instability and substorm onset

A study suggesting that the Alfven resonator can play an important role in modifying the ionosphere on the time and space scales required to play a significant role in substorm formation is presented. Although the effect of magnetosphere-ionosphere coupling on the onset of substorms has been studied, the effects due to gradients of the Alfven speed along auroral field line were neglected. The large increase of the Alfven speed with altitude above the ionosphere creates an effective resonant cavity, which can lead to fluctuations in the electric and magnetic fields as well as in particle fluxes in the range 0.1 to 1 Hz. Such fluctuations can be observed from the ground as PiB pulsations associated with substorm onset. These fluctuations can be excited by a fast feedback instability, which can grow on time scales much less than the Alfven travel time between the ionosphere and the plasma sheet. The instability enhances the value of both the Pedersen and Hall conductivity, and may play a role in preparing the ionosphere for substorm onset.

Lysak, Robert L.↗

NASA NTRS2011

Effect on the Lunar Exosphere of a CME Passage

It has long been recognized that solar wind bombardment onto exposed surfaces in the solar system will produce an energetic component to the exospheres about those bodies. Laboratory experiments have shown that the sputter yield can be noticeably increased in the case of a good insulating surface. It is now known that the solar wind composition is highly dependent on the origin of the particular plasma. Using the measured composition of the slow wind. fast wind. solar energetic particle (SEP) population. and coronal mass ejection (CME), broken down into its various components, we have estimated the total sputter yield for each type of solar wind. The heavy ion component, especially the He(++) component, greatly enhances the total sputter yield during times when the heavy ion population is enhanced, most notably during a coronal mass ejection. To simulate the etfect on the lunar exosphere of a CME passage past the Moon, we ran a Monte Carlo code for the species Na, K, Mg and Ca.

Killen, Roseamry M.↗

NASA NTRS1995

Centrifugal trapping in the magnetotail

Particles leving the neutral sheet in the distant magnetotail at times display adiabatic trajectory sequences characterized by an inflection toward the equator and subsequent mirroring in its vicinity. We demonstrate that this low-latitude mirroring results primarily from a centrifugal deceleration due to the fast direction-changing E x B drift. This effect which we refer to as 'centrifugal trapping' appears both in guiding centre and full particle treatments. It thus does not directly relate to nonadiabatic motion. However, pitch angle scattering due to nonadiabatic neutral sheet interaction does play a role in reducing the parallel speed of the particles. We show that centrifugal trapping is an important mechanism for the confinement of the slowest (typically below the equatorial E x B drift speed) plasma sheet populations to the midplane vicinity.

Delcourt, D. C.↗

NASA NTRS1986

Gas ionization induced by a high speed plasma injection in space

Gas ionization induced by a fast plasma injection has been observed with the Space Experiments with Particle Accelerators (SEPAC) Experiment on Spacelab-1. When an impulsive high-density plasma was injected from the orbiter, waves near the lower-hybrid frequency were enhanced, and the surrounding gas drifting with the orbiter was ionized for several tens of milliseconds after the plasma injection. The long-duration gas ionization was observed only when the plasma flux incoming to the orbiter cargo bay and the orbital velocity perpendicular to the magnetic field were relatively large. This effect has been explained by the concept of critical velocity ionization (CVI) for the gas drifting with the orbiter, although the gas velocity perpendicular to the magnetic field was less than the Alfven critical velocity.

Sasaki, S.↗

NASA NTRS1982

Early experiments in charged particle beams from the Space Shuttle

Characteristics of studies on board the Shuttle involving the interaction of particle beams with the atmosphere and the ionosphere, and the effects of the beams on the electrical potential of the platform, are discussed. Noting that the Shuttle allows greater weight and power demands by scientific payloads than previous satellite launches, the OSS-1 Vehicle Charging and Potential experiment and the Spacelab 1 Particle Accelerator and Phenomena Induced by Charged Particle Beams are described. Instrumentation details are provided, including charge and current probes, the Spherical Retarding Potential Analyzer, the Fast Pulse Electron Generator, and digital control and interface units. The SEPAC equipment, which comprises an electron beam accelerator, and MPD plasma jet, and diagnostic units are detailed, and operating procedures and experiment objectives are outlined.

Raitt, W. J.↗

NASA NTRS1985

The propagation of solar flare particles in a turbulent coronal loop

Energetic solar flare particles, both electrons and protons, must survive the turbulent environment of a flaring loop and propogate to the lower corona or chromosphere in order to produce hard X-ray and gamma ray bursts. This plasma turbulence, often observed in soft X-ray line widths to be in excess of 100 km/s, is presumably capable of efficiently scattering the fast flare particles. This prevents to some degree the free streaming of accelerated particles and depending on the amplitude of the turbulence, restricts the particles to diffusive propagation along the length of the loop to the target chromosphere. In addition this turbulence is capable of performing additional acceleration of the fast particles by the second order Fermi mechanism. For compact flares with rise times 10s, the acceleration effect is small and the propagation of the particles is governed by spatial diffusion and energy loss in the ambient medium. The solution of the time dependent diffusion equation with velocity dependent diffusion and energy loss coefficients yields for the case of nonrelativistic protons particle precipitation rates which are necessary for calculating thick target gamma ray emission and also yields the total thin target emissivity.

Ryan, J. M.↗

NASA NTRS1986

Quasi-stagnant plasmoid in the middle tail - A new preexpansion phase phenomenon

From the analysis of ISEE 3 data it is found that a plasmoid is sometimes formed in the middle tail outside the intervals of the substorm expansion phase. This plasmoid is produced by reconnection at the X-type neutral line, which is located earthward of the distant neutral line but beyond the substorm-associated near-tail neutral line, and it is almost stagnant in that the associated flow speed is less than 300 km/s. The blocking effect of the distant neutral line is the most probable reason for the slow movement. The quasi-stagnant plasmoid is observed at x = -60 to - 100 earth radii for a duration of a few tens of minutes, and in about one half of the cases it is followed by the fast tailward streaming. The onset of this streaming tends to coincide with the onset of the substorm expansion phase, and this probably occurs when the reconnection at the middle-tail neutral line comes close to processing the last closed field line. Intensification of the dawn-to-dusk electric field that causes the mantle plasma to reach the plasma sheet boundary closer to the earth is suggested as the reason for the formation of the middle-tail neutral line earthward of the distant neutral line. The effects on the energetic particle flux and relation to the near-tail reconnection are also discussed.

Nishida, A.↗

NASA NTRS2019

A Meteoroid Handbook for Aerospace Engineers and Managers

At the beginning of the Space Age, spacecraft designers and mission planners were very concerned about meteoroids. They envisioned vehicles being ripped to pieces by streams of fast-moving space rocks, a notion promoted by the science fiction novels and movies of the time. The reality is, of course, different—the meteoroid streams that produce meteor showers are not dense by laypeople’s standards, having spatial densities of just a handful of particles per cubic kilometer, even during meteor outbursts. The ever-present, diffuse, sporadic background, which produces observed meteor rates of only 5 to 8 meteors per hour, makes up 90% of the meteoroid risk to spacecraft that spend at least a year in low Earth orbit (LEO), whereas the visually spectacular but short-lived meteor showers make up the other 10%. Still, meteoroids do pose a significant risk to spacecraft. At Earth, they can travel 12 to 72 km/s. These high speeds cause even small meteoroids to carry enormous kinetic energy, making them capable of doing serious damage to spacecraft. For example, a 1-mm-diameter meteoroid moving at 25 km/s can inflict the same damage as a bullet fired from a 0.357 Magnum pistol. An exterior wire can be severed by a 0.1-mm (100 mm) particle, a spacesuit can be penetrated by a 0.5-mm meteoroid, and an unshielded pressure wall (like the cabin of the Space Shuttle) can be perforated by centimeter-sized particles. Along with mechanical damage, meteoroids can also cause other types of spacecraft anomalies. Meteoroids can transfer their momentum to the spacecraft, which can destroy or damage equipment such as shunt resistors and charge-coupled device (CCD) detectors with a clear view of space. Meteoroid impacts can also generate plasma. The impact vaporizes material, producing a crater and an expanding plasma, which can in turn provide a conductive path for any charge accumulated on the spacecraft. This effect is thought to be responsible for the demise of a satellite in one case: the OLYMPUS communications satellite was sent tumbling out of control during the 1993 Perseid outburst, and a Perseid meteoroid strike has been posited as a possible cause (McDonnell et al. 1993; Caswell et al. 1995). Other researchers have suggested that very fast meteoroids could produce a small electromagnetic pulse capable of disrupting spacecraft function (Close et al. 2010).

Moorhead, A.↗

NASA NTRS1997

Ponderomotive Force and Lower Hybrid Turbulence Effects in Space Plasmas Subjected to Large-Amplitude Low-Frequency Waves

In the auroral region, simultaneous occurrences of upward-flowing ions and field-aligned electrons have been observed by the Viking satellite. The occurrence is strongly correlated with large amplitude low frequency fluctuations of the electric field. Large-amplitude shear Alfven waves have also been observed by sounding rockets in the auroral ionosphere. When such LF waves are propagating in a plasma, a ponderomotive force and other types of waves are produced which may lead to significant effects on the plasma. This force is directed toward decreasing density, providing the electromagnetic lift of the background plasma and an increase of collisionless plasma expansion. We find that even for modest wave strengths, the influence on the outflowing oxygen ions can be dramatic, increasing the high-altitude density by orders of magnitude. It is also demonstrated that large-amplitude low-frequency waves (LFW) may generate lower hybrid waves (LHW) in the auroral zone. The excitation of LHW by a LF wave may lead to the appearance of an additional channel of energy transfer from, for example, Alfven or fast magnetosonic waves, to particles. This process then influences the formation of the plasma distribution function at the expense of acceleration in the tail of the distribution during the collapse of the LHW. The ion energization due to the LHW can be comparable with that produced by the ponderomotive force of the LFW. It is shown that the LH turbulence leads to equalization of the ponderomotive acceleration of the different ion species. The mechanism of LHW excitation due to the oxygen ion relative drift in a plasma subjected to low-frequency waves is used for analysis of Viking satellite data for events in the cusp/cleft region. It is found that, in some cases, such a mechanism leads to LHW energy densities and ion distribution functions close to those observed.

Khazanov, G. V.↗

NASA NTRS1985

Shock and statistical acceleration of energetic particles in the interplanetary medium

Definite evidence for particle acceleration in the solar wind came around a decade ago. Two likely sources are known to exist: particles may be accelerated by the turbulence resulting from the superposition of Alfven and Magnetosonic waves (Statistical Acceleration) or they may be accelerated directly at shock fronts formed by the interaction of fast and slow solar wind (CIR's) or by traveling shocks due to sporadic coronal mass ejections. Naurally both mechanisms may be operative. In this work the acceleration problem was tackled numerically using Helios 1 and 2 data to create a realistic representation of the Heliospheric plasma. Two 24 hour samples were used: one where there are only wave like fluctuations of the field (Day 90 Helios 1) and another with a shock present in it (Day 92 of Helios 2) both in 1976 during the STIP 2 interval. Transport coefficients in energy space have been calculated for particles injected in each sample and the effect of the shock studied in detail.

Valdes-Galicia, J. F.↗

NASA NTRS2018

Generation of Kappa Distributions in Solar Wind at 1 au

We examine the generation of kappa distributions in the solar wind plasma near 1 au. Several mechanisms are mentioned in the literature, each characterized by a specific relationship between the solar wind plasma features, the interplanetary magnetic field (IMF), and the kappa index-the parameter that governs the kappa distributions. This relationship serves as a signature condition that helps the identification of the mechanism in the plasma. In general, a mechanism that generates kappa distributions involves a single or a series of stochastic or physical processes that induces local correlations among particles. We identify three fundamental solar wind plasma conditions that can generate kappa distributions, noted as (i) Debye shielding, (ii) frozen IMF, and (iii) temperature fluctuations, each one prevailing in different scales of solar wind plasma and magnetic field properties. Moreover, our findings show that the kappa distributions, and thus, their generating mechanisms, vary significantly with solar wind features: (i) the kappa index has different dependence on the solar wind speed for slow and fast modes, i.e., slow wind is characterized by a quasi-constant kappa index, K (is) approx. 4.3 +/- 0.7, while fast wind exhibits kappa indices that increase with bulk speed; (ii) the dispersion of magnetosonic waves is more effective for lower kappa indices (i.e., further from thermal equilibrium); and (iii) the kappa and polytropic indices are positively correlated, as it was anticipated by the theory.

Livadiotis, G.↗

NASA NTRS1994

Particle acceleration in the dynamic magnetotail: Orbits in self-consistent three-dimensional MHD fields

The acceleration of protons in a dynamically evolving magnetotail is investigated by tracing particles in the fields obtained from a three-dimensional resistive magnetohydrodynamic (MHD) simulation. The MHD simulation, representing plasmoid formation and ejection through a near-Earth reconnection process, leads to cross-tail electric fields of up to approximately 4 mV/m with integrated voltages across the tail of up to approximately 200 kV. Energization of particles takes place over a wide range along the tail, due to the large spatial extent of the increased electric field together with the finite cross-tail extent of the electric field region. Such accelerated particles appear earthward of the neutral line over a significant portion of the closed field line region inside of the separatrix, not just in the vicinity of the separatrix. Two different acceleration processes are identified: a 'quasi-potential' acceleration, due to particle motion in the direction of the cross-tail electric field, and a 'quasi-betatron' effect, which consists of multiple energy gains from repeated crossings of the acceleration region, mostly on Speiser-type orbits, in the spatially varying induced electric field. The major source region for accelerated particles in the hundreds of keV range is the central plasma sheet at the dawn flank outside the reconnection site. Since this source plasma is already hot and dense, its moderate energization by a factor of approximately 2 may be sufficient to explain the observed increases in the energetic particle fluxes. Particles from the tail are the source of beams at the plasma sheet/lobe boundary. The temporal increase in the energetic particle fluxes, estimated from the increase in energy gain, occurs on a fast timescale of a few minutes, coincident with a strong increase in B(sub z), despite the fact that the inner boundary ('injection boundary') of the distribution of energized particles is fairly smooth.

Birn, Joachim↗

NASA NTRS2011

Modeling the Superstorm in November 2003

The superstorm on 20.21 November 2003 was the largest geomagnetic storm in solar cycle 23 as measured by Dst, which attained a minimum value of .422 nT. We have simulated this storm to understand how particles originating from the solar wind and ionosphere get access to the magnetosphere and how the subsequent transport and energization processes contribute to the buildup of the ring current. The global electromagnetic configuration and the solar wind H+ distribution are specified by the Lyon-Fedder-Mobarry (LFM) magnetohydrodynamics model. The outflow of H+ and O+ ions from the ionosphere are also considered. Their trajectories in the magnetosphere are followed by a test-particle code. The particle distributions at the inner plasma sheet established by the LFM model and test-particle calculations are then used as boundary conditions for a ring current model. Our simulations reproduce the rapid decrease of Dst during the storm main phase and the fast initial phase of recovery. Shielding in the inner magnetosphere is established at early main phase. This shielding field lasts several hours and then breaks down at late main phase. At the peak of the storm, strong penetration of ions earthward to L shell of 1.5 is revealed in the simulation. It is surprising that O+ is significant but not the dominant species in the ring current in our calculation for this major storm. It is very likely that substorm effects are not well represented in the models and O+ energization is underestimated. Ring current simulation with O+ energy density at the boundary set comparable to Geotail observations produces excellent agreement with the observed symH. As expected in superstorms, ring current O+ is the dominant species over H+ during the main to mid-recovery phase of the storm.

Fok, Mei-Ching↗

NASA NTRS1989

Computer simulations of cosmic-ray diffusion near supernova remnant shock waves

A plasma simulation model was used to study the resonant interactions between streaming cosmic-ray ions and a self-consistent spectrum of Alfven waves, such as might exist in the interstellar medium upstream of a supernova remnant shock wave. The computational model is a hybrid one, in which the background interstellar medium is an MHD fluid and the cosmic-rays are discrete kinetic particles. The particle sources for the electromagnetic fields are obtained by averaging over the fast cyclotron motions. When the perturbed magnetic field is larger than 10 percent of the background field, the macro- and microphysics are no longer correctly predicted by quasi-linear theory. The particles are trapped by the waves and show sharp jumps in their pitch-angles relative to the background magnetic field, and the effective ninety-degree scattering time for diffusion parallel to the background magnetic field is reduced to between 5 and 30 cyclotron periods. Simulation results suggest that Type 1 supernova remnants may be the principal sites of cosmic ray acceleration.

Max, C. E.↗

NASA NTRS1995

Observations of the solar wind speed near the sun

Two-antenna scintillation (IPS) observations can provide accurate measurements of the velocity with which electron density fluctuations drift past the line of sight. We will present recent IPS measurements made with the EISCAT and VLBA arrays. It is common, particularly during declining activity. for the line of sight to pass through plasma with a wide range of speed. Therefore it is important to account for the line of sight integration. It is clear from ULYSSES measurements that the speed is bimodal in nature, i.e., either 'fast' or 'slow.' Thus it is not necessary to model a continuous velocity distribution - one need only locate the 'fast-slow' interface. In addition one must consider the possibility that the density fluctuations are moving with respect to the flow of particles. Alfven waves propagating through field-aligned density fluctuations can mimic a sound wave in this respect, so the apparent IPS velocity can be the flow speed plus the Alfven speed. In modeling the IPS it is important that the scattering be 'weak,' because the weak scattering model requires only 1 spatial parameter instead of 3. Furthermore the effect of multiple velocities in much more distinct in weak scattering. EISCAT can only operate near 933 MHz, which limits the observations to outside of 17R(solar mass). The VLBA is the only facility with the combination of high frequency operation and long baselines required to observe inside of 15R(solar mass). A simple bimodal model has been successfully used to interpret our IPS observations near the sun. Farther out interaction regions have built up significantly and a two speed model is no longer valid. An apparent deceleration in the fast polar wind is sometimes evident when compared to the ULYSSES observation. The density variance delta N(exp 2)e in the fast wind appears to decrease from equator to pole.

Grall, R. R.↗

NASA NTRS2012

What Properties of CMEs are Most Important for Space Weather?

Severe space weather is characterized by intense particle radiation from the Sun and major geomagnetic storm caused by magnetized solar plasmas arriving at Earth. Coronal mass ejections (CMEs) are key players in both these aspects. CMEs traveling at super-Alfv nic speeds drive fast-mode MHD shocks that create the high levels of particle radiation. When a CME arrives at Earth, the CME-associated magnetic fields reconnect with Earth s magnetopause fields resulting in solar plasma entry into the magnetosphere and a geomagnetic storm depending on the magnetic structure of the CME. Particle radiation starts affecting geospace as soon as the CMEs leave the Sun and the geospace may be immersed in the radiation for several days. On the other hand, the geomagnetic storm happens only upon CME arrival at Earth. The requirements for the production of particles and magnetic storms by CMEs are different in a number of respects: solar source location, CME magnetic structure, conditions in the ambient solar wind, and shock-driving ability of CMEs. Intense shocks arriving at Earth have additional space weather effects such as sudden impulse that shrinks the magnetosphere often exposing satellites in geosynchronous orbit to the solar wind and energetic storm particle events. This paper highlights these space weather effects using CME observations space and ground based instruments during of solar cycles 23 and 24.

Gopalswamy, Nat↗