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At least 109 records · Page 6

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NASA NTRS1994

Extended test of a xenon hollow cathode for a space plasma contactor

Implementation of a hollow cathode plasma contactor for charge control on the Space Station has required validation of long-life hollow cathodes. A test series of hollow cathodes and hollow cathode plasma contactors was initiated as part of the plasma contactor development program. An on-going wear-test of a hollow cathode has demonstrated cathode operation in excess of 4700 hours with small changes in operating parameters. The discharge experienced 4 shutdowns during the test, all of which were due to test facility failures or expellant replenishment. In all cases, the cathode was reignited at approximately 42 volts and resumed typical operation. This test represents the longest demonstrated stable operation of a high current (greater than 1A) xenon hollow cathode reported to date.

Sarver-Verhey, Timothy R.↗

NASA NTRS1994

Life test of a xenon hollow cathode for a space plasma contractor

A plasma contacting device using a hollow cathode for plasma production has been baselined for use on the Space Station. This application will require reliable, continuous operation of the cathode at electron emission currents of between 0.75 and 10 A for two years (17,500 hours). In order to validate life-time capability, a hollow cathode, operated in a diode configuration, has been tested for more than 8600 hours of stable discharge operation as of March 30, 1994. This cathode is operated at a steady-state emission current of 12.0 and a fixed xenon flow rate of 4.5 sccm. Discharge voltage and cathode temperature have remained relatively stable at approximately 12.9 V and 1260 C during the test. The test has experienced 7 shutdowns to date. In all instances, the cathode was reignited at about 42 V and resumed stable operation. This test represents the longest demonstration of stable operation of high current (greater than 1A) xenon hollow cathodes reported to date.

Sarver-Verhey, Timothy R.↗

NASA NTRS1981

Experimental simulation of space plasma interactions with high voltage solar arrays

Operating high voltage solar arrays in the space environment can result in anomalously large currents being collected through small insulation defects. Tests of simulated defects have been conducted in a 45-cm vacuum chamber with plasma densities of 100,000 to 1,000,000/cu cm. Plasmas were generated using an argon hollow cathode. The solar array elements were simulated by placing a thin sheet of polyimide (Kapton) insulation with a small hole in it over a conductor. Parameters tested were: hole size, adhesive, surface roughening, sample temperature, insulator thickness, insulator area. These results are discussed along with some preliminary empirical correlations.

Stillwell, R. P.↗

NASA NTRS1992

Analysis of Waves in Space Plasma (WISP) near field simulation and experiment

The WISP payload scheduler for a 1995 space transportation system (shuttle flight) will include a large power transmitter on board at a wide range of frequencies. The levels of electromagnetic interference/electromagnetic compatibility (EMI/EMC) must be addressed to insure the safety of the shuttle crew. This report is concerned with the simulation and experimental verification of EMI/EMC for the WISP payload in the shuttle cargo bay. The simulations have been carried out using the method of moments for both thin wires and patches to stimulate closed solids. Data obtained from simulation is compared with experimental results. An investigation of the accuracy of the modeling approach is also included. The report begins with a description of the WISP experiment. A description of the model used to simulate the cargo bay follows. The results of the simulation are compared to experimental data on the input impedance of the WISP antenna with the cargo bay present. A discussion of the methods used to verify the accuracy of the model is shown to illustrate appropriate methods for obtaining this information. Finally, suggestions for future work are provided.

Richie, James E.↗

NASA NTRS2000

Global MHD Simulations of Space Plasma Environments: Heliosphere, Comets, Magnetospheres of Plants and Satellites

Magnetohydrodynamics (MHD) provides an approximate description of a great variety of processes in space physics. Accurate numerical solutions of the MHD equations are still a challenge, but in the past decade a number of robust methods have appeared. Once these techniques made the direct solution of MHD equations feasible, a number of global three-dimensional models were designed and applied to many space physics objects. The range of these objects is truly astonishing, including active galactic nuclei, the heliosphere, the solar corona, and the solar wind interaction with planets, satellites, and comets. Outside the realm of space physics, MHD theory has been applied to such diverse problems as laboratory plasmas and electromagnetic casting of liquid metals. In this paper we present a broad spectrum of models of different phenomena in space science developed in the recent years at the University of Michigan. Although the physical systems addressed by these models are different, they all use the MHD equations as a unifying basis.

Kabin, K.↗

NASA NTRS1985

Current collection from the space plasma through defects in solar array insulation

Operating high-voltage solar arrays in the space environment can result in anomalously large currents being collected through small insulation defects. Tests simulating the electron collection have shown that there are two major collection modes. The first involves current enhancement by means of a surface phenomenon involving secondary electron emission from the surrounding insulator. In the second mode, the current collection is enhanced by vaporization and ionization of the insulator material, in addition to the surface enhancement of the first mode. The electron collection due to surface enhancement (first mode) has been modeled. Using this model, simple calculations yield realistic predictions.

Robinson, R. S.↗

NASA NTRS1987

Effects of space plasma discharge on the performance of large antenna structures in low Earth orbit

The anomalous plasma around spacecrafts in low Earth orbit represents the coma of an artificial comet. The plasma discharge is caused by an energetic disturbance of charged particles which were formerly in a state of equilibrium. The plasma can effect the passive and active radio frequency operation of large space antennas by inducing corona discharge or strong arcing in the antenna feeds. One such large space antenna is the 15-meter hoop column antenna which consists of a mesh membrane material (tricot knitted gold plated wire) reflector and carbon fiber tension cords. The atomic oxygen in the plasma discharge state can force the wire base metal particles through the gold lattice and oxydize the metal particles to build a Schottky-barrier contact at the point where the wires meet. This effect can cause strong deviations in the reflector performance in terms of antenna pattern and losses. Also, the carbon-fiber cords can experience a strength reduction of 30 percent over a 40-hour exposure time.

Blume, Hans-Juergen C.↗

NASA NTRS1986

Some consequences of intense electromagnetic wave injection into space plasmas

The future possibility of actively testing the current understanding of how energetic particles may be accelerated in space or dumped from the radiation belts using intense electromagnetic energy from ground based antennas is discussed. The ground source of radiation is merely a convenience. A space station source for radiation that does not have to pass through the atmosphere and lower ionosphere, is an attractive alternative. The text is divided into two main sections addressing the possibilities of: (1) accelerating electrons to fill selected flux tubes above the Kennel-Petscheck limit for stably trapped fluxes, and (2) using an Alfven maser to cause rapid depletion of energetic protons or electrons from the radiation belts.

Burke, William J.↗

NASA NTRS2007

Space Plasma Ion Processing of Ilmenite in the Lunar Soil: Insights from In-Situ TEM Ion Irradiation Experiments

Space weathering on the moon and asteroids results largely from the alteration of the outer surfaces of regolith grains by the combined effects of solar ion irradiation and other processes that include deposition of impact or sputter-derived vapors. Although no longer considered the sole driver of space weathering, solar ion irradiation remains a key part of the space weathering puzzle, and quantitative data on its effects on regolith minerals are still in short supply. For the lunar regolith, previous transmission electron microscope (TEM) studies performed by ourselves and others have uncovered altered rims on ilmenite (FeTiO3) grains that point to this phase as a unique "witness plate" for unraveling nanoscale space weathering processes. Most notably, the radiation processed portions of these ilmenite rims consistently have a crystalline structure, in contrast to radiation damaged rims on regolith silicates that are characteristically amorphous. While this has tended to support informal designation of ilmenite as a "radiation resistant" regolith mineral, there are to date no experimental data that directly and quantitatively compare ilmenite s response to ion radiation relative to lunar silicates. Such data are needed because the radiation processed rims on ilmenite grains, although crystalline, are microstructurally and chemically complex, and exhibit changes linked to the formation of nanophase Fe metal, a key space weathering process. We report here the first ion radiation processing study of ilmenite performed by in-situ means using the Intermediate Voltage Electron Microscope- Tandem Irradiation facility (IVEM-Tandem) at Argonne National Laboratory. The capability of this facility for performing real time TEM observations of samples concurrent with ion irradiation makes it uniquely suited for studying the dose-dependence of amorphization and other changes in irradiated samples.

Christoffersen, R.↗

NASA NTRS2019

Revealing the Multiscale Nature of Turbulence in Space Plasmas with an Innovative Swarm of Spacecraft

Abstract: Turbulence is fundamentally a multiscale phenomena, with energy, mass, and momentum being transported across both spatial and temporal scales. In a magnetized collisionless plasma, there are unresolved questions about the structure of the turbulent transfer of energy, as well as how the energy is extracted from the cascade and dissipated as heat in the constituent charged particles. The plasma in the solar wind acts as an accessible natural laboratory to study these processes, and much progress has indeed been made since the dawn of the space age in understanding turbulence via in situ observations of turbulent plasmas near Earth. However, to date, these observations have been limited to a single, or at best, a tight cluster of points, leading to ambiguities in at what scales energy is contained, how it is transported, and by what mechanism it is dissipated. In this presentation, we describe a heliophysics mission concept aimed at understanding turbulence that is enabled by a swarm of small satellites. The proposed "HelioSwarm" mission will measure turbulent fields and flows and charged particles simultaneously at many points spanning size and time scales from the fluid to sub-ion regime. In doing so, we will be able to disentangle how the turbulence depends on time and space, directly observe the change in internal energy in the plasma, and definitively capture the dynamic relation between turbulence and structures. While the processes under examination are universal, arising throughout our solar system and universe, they are difficult to reproduce in either terrestrial laboratories or numerical simulations, meaning that the only a multipoint observatory in the near-Earth heliosphere will be able to study them in sufficient detail to discern the underlying physics. In this talk, we highlight the enabling role that small satellites play in providing closure on these long-standing but critically important science questions.

Spence, H. E.↗

NASA NTRS1995

Making sense from space-time data in laboratory experiments on space plasma processes

A number of visualization techniques are discussed in a laboratory experiment designed to study phenomena that occur in space. Visualization tools are used to design the apparatus, collect data, and make one-, two-, and three-dimensional plots of the results. These tools are an indispensable part of the experiment because the data sets are hundreds of megabytes in size and rapid turnaround is required.

Gekelman, Walter↗

NASA NTRS2002

Mechanisms for the Dissipation of Alfven Waves in Near-Earth Space Plasma

Alfven waves are a major mechanism for the transport of electromagnetic energy from the distant part of the magnetosphere to the near-Earth space. This is especially true for the auroral and polar regions of the Earth. However, the mechanisms for their dissipation have remained illusive. One of the mechanisms is the formation of double layers when the current associated with Alfven waves in the inertial regime interact with density cavities, which either are generated nonlinearly by the waves themselves or are a part of the ambient plasma turbulence. Depending on the strength of the cavities, weak and strong double layers could form. Such double layers are transient; their lifetimes depend on that of the cavities. Thus they impulsively accelerate ions and electrons. Another mechanism is the resonant absorption of broadband Alfven- wave noise by the ions at the ion cyclotron frequencies. But this resonant absorption may not be possible for the very low frequency waves, and it may be more suited for electromagnetic ion cyclotron waves. A third mechanism is the excitation of secondary waves by the drifts of electrons and ions in the Alfven wave fields. It is found that under suitable conditions, the relative drifts between different ion species and/or between electrons and ions are large enough to drive lower hybrid waves, which could cause transverse accelerations of ions and parallel accelerations of electrons. This mechanism is being further studied by means of kinetic simulations using 2.5- and 3-D particle-in-cell codes. The ongoing modeling efforts on space weather require quantitative estimates of energy inputs of various kinds, including the electromagnetic energy. Our studies described here contribute to the methods of determining the estimates of the input from ubiquitous Alfven waves.

Singh, Nagendra↗

NASA NTRS2022

Revolutionizing Our Understanding of Particle Energization in Space Plasmas Using on-Board Wave-Particle Correlator Instrumentation

A leap forward in our understanding of particle energization in plasmas throughout the heliosphere is essential to answer longstanding questions in heliophysics, including the heating of the solar corona, acceleration of the solar wind, and energization of particles that lead to observable phenomena, such as the Earth’s aurora. The low densities and high temperatures of typical heliospheric environments lead to weakly collisional plasma conditions. Under these conditions, the energization of particles occurs primarily through collisionless interactions between the electromagnetic fields and the individual plasma particles with energies characteristic of a particular interaction. To understand how the plasma heating and particle acceleration impacts the macroscopic evolution of the heliosphere, impacting phenomena such as extreme space weather, it is critical to understand these collisionless wave-particle interactions on the characteristic ion and electron kinetic timescales. Such understanding requires high-cadence measurements of both the electromagnetic fields and the three-dimensional particle velocity distributions. Although existing instrument technology enables these measurements, a major challenge to maximize the scientific return from these measurements is the limited amount of data that can be transmitted to the ground due to telemetry constraints. A valuable, but underutilized, approach to overcome this limitation is to compute on-board correlations of the maximum-cadence field and particle measurements to improve the sampling time by several orders of magnitude. Here we review the fundamentals of the innovative field-particle correlation technique, present a formulation of the technique that can be implemented as an on-board wave-particle correlator, and estimate results that can be achieved with existing instrumental capabilities for particle velocity distribution measurements.

plasma heating↗

NASA NTRS1989

Space plasma contractor research, 1988

Results of experiments conducted on hollow cathode-based plasma contractors are reported. Specific tests in which attempts were made to vary plasma conditions in the simulated ionospheric plasma are described. Experimental results showing the effects of contractor flowrate and ion collecting surface size on contactor performance and contactor plasma plume geometry are presented. In addition to this work, one-dimensional solutions to spherical and cylindircal space-charge limited double-sheath problems are developed. A technique is proposed that can be used to apply these solutions to the problem of current flow through elongated double-sheaths that separate two cold plasmas. Two conference papers which describe the essential features of the plasma contacting process and present data that should facilitate calibration of comprehensive numerical models of the plasma contacting process are also included.

Williams, John D.↗

NASA NTRS1984

Space plasma high-voltage drainage experiment (A0054)

The objectives of this experiment are to place large numbers of dielectric samples under electric stress in space; to determine their in-space current drainage behavior; to recover, inspect, and further test these samples in laboratory facilities; and finally to specify allowable electric stress levels for these materials as applied to solar-array and thermal control coatings for prolonged exposure in space. These findings, in turn, will pace the design of encapsulated, lightweight, high-voltage solar arrays as well as the development of coating materials for spacecraft operation in energetic charged-particle environments such as that experienced at geosynchronous altitudes during magnetic substorms.

Taylor, W. W. L.↗

NASA NTRS1992

Recent results from studies of electron beam phenomena in space plasmas

The paper examines selected results from experiments, performed in 1980s, involving the ejection of beams of electrons from spacecraft. Special attention is given to the basic processes associated with the spacecraft charging, passive current collection, beam-atmosphere interactions, beam-plasma interactions, and neutral gas emission. Consideration is also given to future experiments on active electron beam ejections in space.

Neubert, Torsten↗

NASA NTRS1992

Techniques for the remote sensing of space plasma in the heliosphere via energetic neutral atoms - A review

A survey is conducted for state-of-the-art techniques for detecting energetic neutral atoms (ENAs) in the 100-300 keV range, in regions from the heliospheric boundary to the auroral zones where the solar wind plays a crucial role. While ENA spectrometry allows sampling of the mass and energy distributions of a distant plasma, ENA imaging gives a global view of the structures and dynamics of an extended plasma. The ENA instrument designs discussed share many components which exhibit excellent flight performance as elements in charged-particle analyzers for space missions.

Hsieh, K. C.↗

NASA NTRS1994

Operating in the space plasma environment: A spacecraft charging study of the Solar X-ray Imager

This study presents the results of a spacecraft charging effects protection study conducted on the Solar X-ray Imager (SXI). The SXI is being developed by NASA Marshall Space Flight Center for NOAA's Space Environment Laboratory, and will be used to aid in forecasting energetic particle events and geomagnetic storms. Images will provide information on the intensity and location of solar flares, coronal mass ejections, and high speed solar streams. The SXI will be flown on a next-generation GOES sometime in the mid to late 1990's. Charging due to the encounter with a worst-case magnetic substorm environment is modeled using the NASCAP/GEO computer code. Charging levels of exterior surfaces and the floating potential of the spacecraft relative to plasma are determined as a function of spacecraft design, operational configuration, and orbital conditions. Areas where large surface voltage gradients exist on or near the SXI are identified as possible arc-discharge sites. Results of the charging analysis are then used to develop design recommendations that will limit the effects of spacecraft charging on the SXI operation.

Herr, Joel L.↗