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NASA NTRS1975

Cosmic ray propagation in interplanetary space

The validity of the test-particle picture, the approximation of static fields, and the spatial-diffusion approximation are discussed in a general way before specific technical assumptions are introduced. It is argued that the spatial-diffusion equation for the intensity per unit energy has a much wider range of applicability than the kinetic (Fokker-Planck) equation it is derived from. This gives strong weight to the phenomenological propagation theory. The general success (and possible failure at small energies) of the phenomenological theory for the modulation of galactic cosmic rays and solar events is described. Apparent effects such as the 'free boundary' are given disproportionate weight since they establish the connection with the detailed plasma physics of the solar wind. Greatest attention is paid to the pitch-angle diffusion theory. A general theory is presented which removes the well-known secularities of the quasi-linear approximation. The possible breakdown of any pitch-angle diffusion theory at very small energies is perhaps connected with the observed 'turn up' of the spectrum at low energies. A first attempt to derive the spatial dependence of the diffusion coefficient in the solar cavity, using such a divergence free scattering theory, is described and compared with recent observations out to 5 AU.

Voelk, H. J.↗

NASA NTRS1989

The thermal catastrophe model of substorms

Equations are presented for the physical mechanisms involved in the resonant absorption of Alfven waves in the plasma sheet boundary layer. It is shown that energy absorbed by the plasma-sheet particles is a function of the central plasma sheet temperature. The heating curve, when coupled with convective transport, yielded an equation of state for the steady state plasma sheet, whose solution has the form of a mathematical catastrophe. The master equation includes dynamic terms describing the transition across the thermal catastrophe, making it possible to evaluate the time scale for the catastrophe to occur.

Goertz, C. K.↗

NASA NTRS1991

The plasma environment of comets

U.S. research activities in the area of cometary plasma physics during 1987-1990 are reviewed. Consideration is given to mass loading and its consequences in the upstream region, the cometary shock, the cometosheath, the diamagnetic cavity boundary and the inner shock, and the plasma tail. Special attention is given to models and observations that have modified the pre-encounter understanding of cometary plasma environments.

Gombosi, Tamas I.↗

NASA NTRS1993

Physics of magnetospheric boundary layers

The central ideas of this grant are that the magnetospheric boundary layers link disparate regions of the magnetosphere together, and the global behavior of the magnetosphere can be understood only by understanding the linking mechanisms. Accordingly the present grant includes simultaneous research on the global, meso-, and micro-scale physics of the magnetosphere and its boundary layers. These boundary layers include the bow shock, magnetosheath, the plasma sheet boundary layer, and the ionosphere. Analytic, numerical and simulation projects have been performed on these subjects, as well as comparison of theoretical results with observational data. Very good progress has been made, with four papers published or in press and two additional papers submitted for publication during the six month period 1 June - 30 November 1993. At least two projects are currently being written up. In addition, members of the group have given papers at scientific meetings. The further structure of this report is as follows: section two contains brief accounts of research completed during the last six months, while section three describes the research projects intended for the grant's final period.

Cairns, I. H.↗

NASA NTRS1995

Physics of magnetospheric boundary layers

This final report was concerned with the ideas that: (1) magnetospheric boundary layers link disparate regions of the magnetosphere-solar wind system together; and (2) global behavior of the magnetosphere can be understood only by understanding its internal linking mechanisms and those with the solar wind. The research project involved simultaneous research on the global-, meso-, and micro-scale physics of the magnetosphere and its boundary layers, which included the bow shock, the magnetosheath, the plasma sheet boundary layer, and the ionosphere. Analytic, numerical, and simulation projects were performed on these subjects, as well as comparisons of theoretical results with observational data. Other related activity included in the research included: (1) prediction of geomagnetic activity; (2) global MHD (magnetohydrodynamic) simulations; (3) Alfven resonance heating; and (4) Critical Ionization Velocity (CIV) effect. In the appendixes are list of personnel involved, list of papers published; and reprints or photocopies of papers produced for this report.

Cairns, Iver H.↗

NASA NTRS2003

Kinetic Simulation of Inhomogeneous Plasma with a Variable Sized Grid System

Space plasmas are usually inhomogeneous and irregular. Particle in cell (PIC) plasma simulations, however, often consider the plasma to be homogeneous and periodic. Here non-periodic PIC simulations with inhomogeneities in the density, temperature and background magnetic field are considered. Boundary conditions and a variable sized grid system are discussed, along with an application to a magnetospheric plasma physics problem in the auroral zone.

Schriver, David↗

NASA NTRS1991

Electromagnetic ion/ion instabilities and their consequences in space plasmas - A review

This paper reviews recent research on the theory and computer simulations of electromagnetic ion/ion instabilities and their consequences in space plasmas. Ion/ion instabilities are growing modes in a collisionless plasma driven unstable by the relative streaming velocity v(0) of two distinct ion components such that v(0) is parallel or antiparallel to the uniform background magnetic field. The space physics regimes which display enhanced fluctuations due to these instabilities include the solar wind, the terrestrial foreshock, the plasma sheet boundary layer, and distant cometary environments.

Gary, S. Peter↗

NASA NTRS2018

The Martian Magnetosphere: Areas of Unsettled Terminology

The near-Mars space environment has a number of regions and boundaries that have numerous and confusing labels. The whole region is sometimes referred to as the induced Martian magnetosphere and sometimes as the solar wind interaction with Mars. The middle boundary where the shocked solar wind plasma gives way to predominately planetary-derived plasma has a variety of names. The region below that middle boundary and the top of the ionosphere also does not have a uniformly used name. There are several other regions and boundaries that also have naming confusion. The various terms that are currently used in the literature for these subjects are identified and discussed; regions and boundaries that have well-settled names are not discussed nor are the details of the physics involved.

Magnetosphere↗

NASA NTRS1979

Earth's magnetosphere - Global problems in magnetospheric plasma physics

Magnetospheric physics is presently in a transition from the exploratory stage to one in which satellite missions and ground-based observations are planned with the specific object of achieving a global understanding and self-consistent quantitative description of the cause-and-effect relationship among the principal dynamic processes involved. Measurements turn to lower and lower energies and to higher ion mass species, in order to encompass the entire particle population, and to a broader range of the frequency spectrum of magnetic and electric field variations. In the present paper, the current status of our knowledge on magnetospheric plasma physics is reviewed, with particular reference of such fundamental advances as the discovery of layers of streaming plasma in the magnetosphere beneath its boundary surface, the identification of the terrestrial magnetosphere as a celestial source of kilometric radiation and relativistic particles, the identification of parallel electric field regions within the magnetosphere and their role in auroral particle acceleration, and the discovery of large fluxes of energetic heavy ions trapped in the magnetosphere.

Roederer, J. G.↗

NASA NTRS1990

A satellite-ground study of the dynamics of the bulge region of the Earth's magnetosphere

Data from multiple ground stations and satellites were used to see how the plasmasphere in the dusk sector is modified during magnetic storms. There is clearly some type of erosion process, during which the plasmasphere is diminished in size, and it is believed that the excess plasma is peeled off and carried (convected) away toward the outer boundary of the magnetosphere (the magnetopause). However, very little is know about the physics of the erosion process, and about how the plasmasphere recovers during the quiet periods that follow such disturbances. Case studies from three multiday periods in 1982 produced a number of new findings which are summarized in this two page document.

Carpenter, Donald L.↗

NASA NTRS1979

Numerical methods for large-scale, time-dependent partial differential equations

A survey of numerical methods for time dependent partial differential equations is presented. The emphasis is on practical applications to large scale problems. A discussion of new developments in high order methods and moving grids is given. The importance of boundary conditions is stressed for both internal and external flows. A description of implicit methods is presented including generalizations to multidimensions. Shocks, aerodynamics, meteorology, plasma physics and combustion applications are also briefly described.

Turkel, E.↗

NASA NTRSDate not supplied

Development of Langmuir and Spatially Resolved OES Diagnostics for Arc Jet Shock and Boundary Layer Measurements Relevant to Atmospheric Re-Entry Environments

The second-generation miniature Arc Jet Research Chamber (mARC) ground testing facility at NASA Ames requires physical characterization of its supersonic plasma flow to verify numerical models and material sample testing. Two types of plasma diagnostics will be utilized: Langmuir probes and optical emission spectroscopy (OES). Several single and triple Langmuir probes have been constructed and will be inserted parallel to the flow via a sweep arm to measure post-shock electron temperature and number density along radial profiles at different axial distances. Due to the high heat flux (200-3000 W/cm2) sweep durations are necessarily short (< 0.1 s). Measuring these properties near the probe surface provide characterization of the post-shock environment. This is an important metric for validating coupled CFD-material codes, and will provide insight into longstanding thermocouple anomalies attributed to charging of heatshield surfaces. An OES system has also been assembled to obtain spatially resolved density and temperature for various flow species. The system consists of a convex lens that forms an image of the plasma onto a 16-channel linear fiber array, which will simultaneously capture the spectra from sixteen different locations. The light emission from the plasma is then focused by a spherical mirror into a spectrometer and recorded with a camera. These measurements non-intrusively provide a new spatially resolved flow characterization capability. This will initially be used to resolve issues with shock radiation interference in pyrometer measurements of material surface temperature. The design of each diagnostic and any initial results will be discussed.

Ethan Main-Loam Leong↗

NASA NTRS1979

Interplanetary gas. XXIV - Are cometary plasma tail disconnections caused by sector boundary crossings or by encounters with high-speed streams

The paper discusses and compares the original sector boundary model (Niedner and Brandt) and the alternative high-speed stream model (Ip and Mendis) suggested for explaining cometary plasma tail disconnection events (DE) within a largely observational framework not dependent on detailed plasma physics. Among the findings are: (1) the strong solar cycle phase dependence of the amplitude of the Rosenberg-Coleman effect (Svalgaard and Wilcox) yields inferred maximum latitudes of all of the DEs in the original survey to a one-time Rosenberg-Coleman effect measurement made by Pioneer 11, which indicated a disappearance of sectors above 16 deg latitude, and (2) approximately 70% of the post 1926 DEs in the expanded survey show a close association with corotated shorter-term polarity reversals. This result is difficult to reconcile with the predictions of the stream model, in which DEs should correlate more strongly with streams than with sector boundaries. It is concluded that the sector boundary model better describes the disconnection phenomenon and that the use of DEs as unique sector boundary markers is presently justified.

Niedner, M. B., Jr.↗

NASA NTRS1987

On the generation of field-aligned plasma flow at the boundary of the plasma sheet

A possible cause of the large plasma flow velocities parallel to the magnetic field (which were observed in spacecraft experiments) near the boundary of the plasma sheet in the earth's magnetotail is considered in the framework of a magnetohydrodynamic model. It is shown for steady-state configurations that high parallel flow velocities can be expected to exist on field lines connecting to a region of weak magnetic field. The physical mechanism causing large values of the parallel velocity component can be visualized as a strong imbalance of perpendicular mass flux into and out of magnetic flux tubes passing through regions where the magnetic field is weak and inhomogeneous. The value of the parallel velocity component is evaluated, and it is found that it can substantially exceed the perpendicular velocity (by as much as a factor of 40). The results are applied to the earth's magnetotail; it is found that this mechanism is able to explain the parallel flow velocities near the boundary of the plasma sheet in the range of several hundreds of km/s.

Schindler, K.↗

NASA NTRS2013

Radial Profiles of Plasma Electron Characteristics in a Low-Power Arcjet

Since 1960, the Arc Jet Complex at NASA Ames Research Center has been a source of long-duration, high-enthalpy flow for materials testing with application to the thermal protection of aerospace vehicle components. From their inception the facilities have played an integral role supporting many of NASA's space flight programs and numerous DoD projects. In recent years advancements in computational fluid dynamics (CFO) have made the resultant models a valuable tool for assessing and predicting performance, however, the inherent limitation of models to compensate for a dissociated, transitionally high temperature nonequilibrated flowfield have made further measurements necessary. The use of electrostatic probe diagnostics within similarly harsh plasma environments in previous studies have been met with much success. In this study, the use of a single Langmuir probe was implemented to characterize the plasma parameters of interest as they vary radially within a large volume of the plume. Classical Langmuir probe theory was applied to achieve first order estimates of the heavy particle temperature, the ratio T(sub i)/T(sub e), and the ionization fraction. As expected, both the electron temperature and electron density measurements show a dependence on radial distance from the plume centerline, with electron density profiles showing the largest dependence. This paper aims to validate and strengthen modeling work conducted at the NASA Ames Research Center by measuring the critical plasma parameters (electron temperature, electron density, and plasma potential) within the arc plume of a subscale arc jet. These parameters are intended to give physical insight into the flow characteristics while providing the necessary boundary conditions to validate full scale simulations.

Codron, Douglas↗

NASA NTRS1981

Boundary conditions which lead to excitation of instabilities in plasma simulations

Two examples of two-dimensional electrostatic particle-code simulations are shown in which one exhibits characteristics of a stable plasma while the other exhibits unstable, long wavelength plasma oscillations. The only difference between the two simulations is a change in the boundary condition on the electrostatic potential. An energy theorem is derived which shows that the rate of change of field and particle energy within a closed volume is related to a surface integral involving the electrostatic potential and the normal component of the electric current. An analytic theory is developed for a one-dimensional plasma to show how boundary effects can excite spurious plasma instabilities. The theory is tested with a series of one-dimensional plasma simulations. Finally, practical considerations on means of avoiding the non-physical instabilities in simulation plasmas are given.

Swift, D. W.↗

NASA NTRSDate not supplied

Thermomechanical Relaxation of Vibrationally Excited NO in a Hypersonic Turbulent Boundary Layer

The effects of thermal nonequilibrium are studied using a DC glow discharge plasma to selectively modify the vibrational temperature of an otherwise cold flow. These experiments were performed at 𝑴=5.7and 𝑹𝒆=6×10 6 /m in the Actively Controlled Expansion tunnel at Texas A&M University on a canonical 2.75° half-angle wedge test article. A∼47 W plasma was generated across spanwise electrodes, and removable trips produced either a laminar or turbulent boundary layer. NO planar laser-induced fluorescence (PLIF) quantified the extent of the NO 𝑿 2 𝚷 (𝒗=1) vibrational perturbation due to the plasma and its subsequent interplay with the boundary layer, the first such data of which the authors are aware. NOPLIF measurements were taken at three locations along the test article, and quasi-temperature measurements are reported at each. Despite not quantifiably perturbing the boundary layer, the plasma was shown to alter the NO vibrational temperature profile therein. Independent analysis of the thermodynamics and fluid mechanics of the system suggests each set of physics could explain the results observed near and far from the wall, respectively.

Casey J. Broslawski↗

NASA NTRSDate not supplied

Thermomechanical Relaxation of Vibrationally Excited NO in a Hypersonic Turbulent Boundary Layer

Casey J. Broslawski↗