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NASA NTRS2014

Autonomous Method and System for Minimizing the Magnitude of Plasma Discharge Current Oscillations in a Hall Effect Plasma Device

An autonomous method for minimizing the magnitude of plasma discharge current oscillations in a Hall effect plasma device includes iteratively measuring plasma discharge current oscillations of the plasma device and iteratively adjusting the magnet current delivered to the plasma device in response to measured plasma discharge current oscillations to reduce the magnitude of the plasma discharge current oscillations.

Hruby, Vladimir↗

NASA NTRS2019

High-Frequency Density Oscillations from a Plasma Source Used for Simulating Low-Earth Orbit Plasma Environment

We present data from ground-based, vacuum-chamber tests demonstrating the ability to modulate the output of a plasma source capable of producing a low-Earth orbit (LEO) type plasma. We obtained plasma oscillations up to 2.5 kHz impingent on stationary test equipment, which corresponds to meter-level ionospheric structures in LEO. This plasma source is, therefore, suitable for developing scientific instruments that measure the LEO plasma environment, in situ, with meter-level spatial resolution. Measurements were made using a fixed-bias collector and an electrometer sampling at 40 kHz. A mechanical aperture was established at the output of the plasma source via two concentric grids. The outer grid was free to rotate in the azimuthal direction with respect to the fixed inner grid. An identical, alternating hole pattern in the two grids resulted in a variable aperture that cycles through 90 open/close cycles per revolution. The frequency of the plasma oscillations is limited by the mechanism used to spin the grids and the bearing assembly on which the grids rotate. Higher frequencies are obtainable by upgrading the drive mechanism, allowing the possibility of centimeter-level spatial resolution.

McTernan, Jesse K.↗

NASA NTRS2017

Performance of a Space-Based Wavelet Compressor for Plasma Count Data on the MMS Fast Plasma Investigation

Data compression has been a staple of imaging instruments for years. Recently, plasma measurements have utilized compression with relatively low compression ratios. The Fast Plasma Investigation (FPI) on board the Magnetospheric Multiscale (MMS) mission generates data roughly 100 times faster than previous plasma instruments, requiring a higher compression ratio to fit within the telemetry allocation. This study investigates the performance of a space-based compression standard employing a Discrete Wavelet Transform and a Bit Plane Encoder (DWT/BPE) in compressing FPI plasma count data. Data from the first 6 months of FPI operation are analyzed to explore the error modes evident in the data and how to adapt to them. While approximately half of the Dual Electron Spectrometer (DES) maps had some level of loss, it was found that there is little effect on the plasma moments and that errors present in individual sky maps are typically minor. The majority of Dual Ion Spectrometer burst sky maps compressed in a lossless fashion, with no error introduced during compression. Because of induced compression error, the size limit for DES burst images has been increased for Phase 1B. Additionally, it was found that the floating point compression mode yielded better results when images have significant compression error, leading to floating point mode being used for the fast survey mode of operation for Phase 1B. Despite the suggested tweaks, it was found that wavelet-based compression, and a DWT/BPE algorithm in particular, is highly suitable to data compression for plasma measurement instruments and can be recommended for future missions.

plasma↗

NASA NTRS1978

Microwave radiation measurements near the electron plasma frequency of the NASA Lewis bumpy torus plasma

Microwave emission near the electron plasma frequency was observed, and its relation to the average electron density and the dc toroidal magnetic field was examined. The emission was detected using a spectrum analyzer and a 50 omega miniature coaxial probe. The radiation appeared as a broad amplitude peak that shifted in frequency as the plasma parameters were varied. The observed radiation scanned an average plasma density ranging from 10 million/cu cm to 8 hundred million/cu cm. A linear relation was observed betweeen the density calculated from the emission frequency and the average plasma density measured with a microwave interferometer. With the aid of a relative density profile measurement of the plasma, it was determined that the emissions occurred from the outer periphery of the plasma.

Mallavarpu, R.↗

NASA NTRS1977

Systematic study of plasma flow during plasma sheet thinnings

On the basis of a study of Imp 6 measurements of plasma flow, it is concluded that there is no clear indication of a predominance of tailward plasma flow beyond about X = -15 R sub E in the midnight sector of the plasma sheet during the expansive phase of a substorm. In fact, it is shown statistically that sunward plasma flow is more frequently observed in the midnight sector within about 30 R sub E from the earth than in any other direction during plasma sheet thinning at the substorm expansion. This result supports the conclusion that there is no definite evidence for the formation of a reconnection neutral line in the near-earth plasma sheet during most substorms.

Lui, A. T. Y.↗

NASA NTRS1979

High temperature UF6 RF plasma experiments applicable to uranium plasma core reactors

An investigation was conducted using a 1.2 MW RF induction heater facility to aid in developing the technology necessary for designing a self critical fissioning uranium plasma core reactor. Pure, high temperature uranium hexafluoride (UF6) was injected into an argon fluid mechanically confined, steady state, RF heated plasma while employing different exhaust systems and diagnostic techniques to simulate and investigate some potential characteristics of uranium plasma core nuclear reactors. The development of techniques and equipment for fluid mechanical confinement of RF heated uranium plasmas with a high density of uranium vapor within the plasma, while simultaneously minimizing deposition of uranium and uranium compounds on the test chamber peripheral wall, endwall surfaces, and primary exhaust ducts, is discussed. The material tests and handling techniques suitable for use with high temperature, high pressure, gaseous UF6 are described and the development of complementary diagnostic instrumentation and measurement techniques to characterize the uranium plasma, effluent exhaust gases, and residue deposited on the test chamber and exhaust system components is reported.

Roman, W. C.↗

NASA NTRS1981

Substorm-related plasma sheet motions as determined from differential timing of plasma changes at the ISEE satellites

From an ISEE survey of substorm dropouts and recoveries during the period February 5 to May 25, 1978, 66 timing events observed by the Los Alamos Scientific Laboratory/Max-Planck-Institut Fast Plasma Experiments were studied in detail. Near substorm onset, both the average timing velocity and the bulk flow velocity at the edge of the plasma sheet are inward, toward the center. Measured normal to the surface of the plasma sheet, the timing velocity is 23 + or - 18 km/s and the proton flow velocity is 20 + or - 8 km/s. During substorm recovery, the plasma sheet reappears moving outward with an average timing velocity of 133 + or - 31 km/s; however, the corresponding proton flow velocity is only 3 + or - 7 km/s in the same direction. It is suggested that the difference between the average timing velocity for the expansion of the plasma sheet and the plasma bulk flow perpendicular to the surface of the sheet during substorm recovery is most likely the result of surface waves moving past the position of the satellites.

Forbes, T. G.↗

NASA NTRS1991

Production of organic compounds in plasmas: A comparison among electric sparks, laser-induced plasmas and UV light

In order to study the production of organic compounds in plasmas (and shocks), various mixtures of N2, CH4, and H2, modeling the atmosphere of Titan, were exposed to discrete sparks, laser-induced plasmas (LIP) and ultraviolet light. The yields of HCN and simple hydrocarbons were measured and compared to those calculated from a simple quenched thermodynamic equilibrium model. The agreement between experiment and theory was fair for HCN and C2H2. However, the yields of C2H6 and other hydrocarbons were much higher than those predicted by the model. Our experiments suggest that photolysis by ultraviolet light from the plasma is an important process in the synthesis. This was confirmed by the photolysis of gas samples exposed to the light, but not to the plasma or shock waves. The results of these experiments demonstrate that, in addition to the well-known efficient synthesis of organic compounds in plasmas, the yields of saturated species, e.g., ethane, may be higher than predicted by theory and that LIP provide a convenient and clean way of simulating planetary lightning and impact plasmas in the laboratory.

Scattergood, T. W.↗

NASA NTRS1991

A mysterious plasma wave emission and the determination of plasma densities in Neptune's inner magnetosphere

One of the strongest plasma wave signals observed during the Voyager 2 encounter with Neptune is a narrowband emission between 3.0 and 4.3 kHz that was detected over a period of roughly 2 hours around closest approach. The emission occurs below the electron cyclotron frequency and the low-frequency cutoff of the radio continuum radiation. Of the naturally occurring signals in the earth's auroral zone and in Jupiter's magnetosphere this emission most resembles trapped Z mode waves found near the left-hand cutoff frequency. Using this identification, a plasma density profile is obtained that is independent of the plasma temperature. These densities greatly exceed those measured by the plasma science instrument on Voyager but are lower than estimates based on other models of Neptunian plasma wave phenomenology. If this wave mode is not a natural emission, it might arise from an unusual interaction of the spacecraft with the cold, dense ambient plasma.

Moses, S. L.↗

NASA NTRS1999

Measurement of the Plasma Density Using the Intensification of z-Mode Waves at the Electron Plasma Frequency

A new method is proposed for measuring the number density of a plasma using spectral measurements of plasma wave. The method is based on predictions that the ratio electric to magnetic fields and the electric intensity is significantly enhanced in a narrow frequency band without the electron plasma frequency for z-mode waves propagating at small angles to the back-ground magnetic field in cold relatively strongly magnetized plasmas. The method is applied to emissions observed in space over Earth's polar cap, allowing identification of the plasma frequency and the mode consistent with the data available. This method should be useful for other cold, strongly magnetized plasmas in space and in the laboratory.

Cairns, Iver H.↗

NASA NTRS2001

MTF Driven by Plasma Liner Dynamically Formed by the Merging of Plasma Jets: An Overview

One approach for standoff delivery of the momentum flux for compressing the target in MTF consists of using a spherical array of plasma jets to form a spherical plasma shell imploding towards the center of a magnetized plasma, a compact toroid (Figure 1). A 3-year experiment (PLX-1) to explore the physics of forming a 2-D plasma liner (shell) by merging plasma jets is described. An overview showing how this 3-year project (PLX-1) fits into the program plan at the national and international level for realizing MTF for energy and propulsion is discussed. Assuming that there will be a parallel program in demonstrating and establishing the underlying physics principles of MTF using whatever liner is appropriate (e.g. a solid liner) with a goal of demonstrating breakeven by 2010, the current research effort at NASA MSFC attempts to complement such a program by addressing the issues of practical embodiment of MTF for propulsion. Successful conclusion of PLX-1 will be followed by a Physics Feasibility Experiment (PLX-2) for the Plasma Liner Driven MTF.

Thio, Y. C. Francis↗

NASA NTRS2001

Plasma Accelerator Development for Dynamic Formation of Plasma Liners: A Status Report

An experimental plasma accelerator for magnetic target fusion (MTF) applications under development at the NASA Marshall Space Flight Center is described. The accelerator is a pulsed plasma thruster and has been tested experimentally and plasma jet velocities of approximately 50 km/sec have been obtained. The plasma jet structure has been photographed with 10 ns exposure times to reveal a stable and repeatable plasma structure. Data for velocity profile information has been obtained using light pipes embedded in the gun walls to record the plasma transit at various barrel locations. Preliminary spatially resolved spectral data and magnetic field probe data are also presented. A high speed triggering system has been developed and tested as a means of reducing the gun "jitter". This jitter is being characterized and future work for second generation "ultra-low jitter" gun development is being identified.

Thio, Y. C. Francis↗

NASA NTRS2002

Progress In Plasma Accelerator Development for Dynamic Formation of Plasma Liners

An experimental plasma accelerator for magnetic target fusion (MTF) applications under development at the NASA Marshall Space Flight Center is described. The accelerator is a coaxial pulsed plasma thruster (Figure 1). It has been tested experimentally and plasma jet velocities of approx.50 km/sec have been obtained. The plasma jet has been photographed with 10-ns exposure times to reveal a stable and repeatable plasma structure (Figure 2). Data for velocity profile information has been obtained using light pipes and magnetic probes embedded in the gun walls to record the plasma and current transit respectively at various barrel locations. Preliminary spatially resolved spectral data and magnetic field probe data are also presented. A high speed triggering system has been developed and tested as a means of reducing the gun "jitter". This jitter is being characterized and future work for second generation "ultra-low jitter" gun development is being identified.

Thio, Y. C. Francis↗

NASA NTRS2003

Magnetized Plasma Expansion and its Interaction with a Plasma Stream

Expansion of magnetized plasma in the magnetic field of a solenoid is studied by means of simulations using a 3-dimensional hybrid code. The plasma expands against a high- density and slow plasma stream (PS). The expansion causes inflation of the magnetic field; near the solenoid the magnetic field variation with increasing distance (r) remains as B(alpha)r(sup -3), but at farther distances B(alpha)r(sup -p), where the exponent p is found in the range 0.5 approx. less than p approx. less than 1.2 forming a plateau in the magnetic field distribution B(r). At the start of injection of plasma from the ends of the solenoid, the PS interacts with the solenoid magnetic field and creates a bow shock at a distance where the Larmor radius (r(sub il)) of the PS ions in the solenoid magnetic field nearly equals the scale length (L) of B(r), that is, r(sub il) approx. L = (B(sup -1)dB L /dr)(sup -1). As the injected plasma accumulates in the solenoid magnetic field, it expands inflating the magnetic field and the bow shock moves outward. The speed of the expansion front and the shock progressively decreases and eventually a stand-off occurs when the PS dynamic pressure is eventually balanced by the magnetic and kinetic pressures of the expanding plasma and the inflating magnetic field. The inflating field shows wave-like behavior, with considerable structures in the field and current distributions.

Singh, Nagendra↗

NASA NTRS2011

VLF and HF Plasma Waves Associated with Spread-F Plasma Depletions Observed on the C/NOFS Satellite

The C/NOFS spacecraft frequently encounters structured plasma depletions associated with equatorial spread-F along its trajectory that varies between 401 km perigee and 867 km apogee in the low latitude ionosphere. We report two classes of plasma waves detected with the Vector Electric Field Investigation (VEFI) that appear when the plasma frequency is less than the electron gyro frequency, as is common in spread-F depletions where the plasma number density typically decreases below 10(exp 4)/cu cm. In these conditions, both broadband VLF waves with a clear cutoff at the lower hybrid frequency and broadband HF waves with a clear cutoff at the plasma frequency are observed. We interpret these waves as "hiss-type" emissions possibly associated with the flow of suprathermal electrons within the inter-hemispherical magnetic flux tubes. We also report evidence of enhanced wave "transients" sometimes embedded in the broader band emissions that are associated with lightning sferics detected within the depleted plasma regions that appear in both the VLF and HF data. Theoretical implications of these observations are discussed.

Pfaff, Robert↗

NASA NTRS2014

Ionosphere Plasma State Determination in Low Earth Orbit from International Space Station Plasma Monitor

A plasma diagnostic package is deployed on the International Space Station (ISS). The system - a Floating Potential Measurement Unit (FPMU) - is used by NASA to monitor the electrical floating potential of the vehicle to assure astronaut safety during extravehicular activity. However, data from the unit also reflects the ionosphere state and seems to represent an unutilized scientific resource in the form of an archive of scientific plasma state data. The unit comprises a Floating Potential probe and two Langmuir probes. There is also an unused but active plasma impedance probe. The data, at one second cadence, are collected, typically for a two week period surrounding extravehicular activity events. Data is also collected any time a visiting vehicle docks with ISS and also when any large solar events occur. The telemetry system is unusual because the package is mounted on a television camera stanchion and its data is impressed on a video signal that is transmitted to the ground and streamed by internet to two off center laboratory locations. The data quality has in the past been challenged by weaknesses in the integrated ground station and distribution systems. These issues, since mid‐2010, have been largely resolved and the ground stations have been upgraded. Downstream data reduction has been developed using physics based modeling of the electron and ion collecting character in the plasma. Recursive algorithms determine plasma density and temperature from the raw Langmuir probe current voltage sweeps and this is made available in real time for situational awareness. The purpose of this paper is to describe and record the algorithm for data reduction and to show that the Floating probe and Langmuir probes are capable of providing long term plasma state measurement in the ionosphere. Geophysical features such as the Appleton anomaly and high latitude modulation at the edge of the Auroral zones are regularly observed in the nearly circular, 51 deg inclined, 400 km altitude ISS orbit. Evidence of waves in the ion collection current data is seen in geographic zones known to exhibit the spread‐F phenomenon. An anomaly in the current collection characteristic of the cylindrical probe appears also too be organized by the geomagnetic field.

Kramer, Leonard↗

NASA NTRS2015

Performance of a Discrete Wavelet Transform for Compressing Plasma Count Data and its Application to the Fast Plasma Investigation on NASA's Magnetospheric Multiscale Mission

Plasma measurements in space are becoming increasingly faster, higher resolution, and distributed over multiple instruments. As raw data generation rates can exceed available data transfer bandwidth, data compression is becoming a critical design component. Data compression has been a staple of imaging instruments for years, but only recently have plasma measurement designers become interested in high performance data compression. Missions will often use a simple lossless compression technique yielding compression ratios of approximately 2:1, however future missions may require compression ratios upwards of 10:1. This study aims to explore how a Discrete Wavelet Transform combined with a Bit Plane Encoder (DWT/BPE), implemented via a CCSDS standard, can be used effectively to compress count information common to plasma measurements to high compression ratios while maintaining little or no compression error. The compression ASIC used for the Fast Plasma Investigation (FPI) on board the Magnetospheric Multiscale mission (MMS) is used for this study. Plasma count data from multiple sources is examined: resampled data from previous missions, randomly generated data from distribution functions, and simulations of expected regimes. These are run through the compression routines with various parameters to yield the greatest possible compression ratio while maintaining little or no error, the latter indicates that fully lossless compression is obtained. Finally, recommendations are made for future missions as to what can be achieved when compressing plasma count data and how best to do so.

Particles↗

NASA NTRS2016

Survey of Galileo Plasma Observations in Jupiter's Plasma Sheet

The plasma science (PLS) Instrument on the Galileo spacecraft (orbiting Jupiter from December 1995 to September 2003) measured properties of the ions that were trapped in the magnetic field. The PLS data provide a survey of the plasma properties between approx. 5 and 30 Jupiter radii [R(sub J)] in the equatorial region. We present plasma properties derived via two analysis methods: numerical moments and forward modeling. We find that the density decreases with radial distance by nearly 5 orders of magnitude from approx. 2 to 3000 cm(exp.-3) at 6R(sub j) to approx. 0.05cm(sub -3) at 30 R(sub j). The density profile did not show major changes from orbit to orbit, suggesting that the plasma production and transport remained constant within about a factor of 2. The radial profile of ion temperature increased with distance which implied that contrary to the concept of adiabatic cooling on expansion, the plasma heats up as it expands out from Io's orbit (where TI is approx.60-80 eV) at approx. 6R(sub j) to a few keV at 30R(sub j).There does not seem to be a long-term, systematic variation in ion temperature with either local time or longitude. This latter finding differs from earlier analysis of Galileo PLS data from a selection of orbits. Further examination of all data from all Galileo orbits suggests that System Ill variations are transitory on timescales of weeks, consistent with the modeling of Cassini Ultraviolet Imaging Spectrograph observations. The plasma flow is dominated by azimuthal flow that is between 80% and 100% of corotation out to 25 R(sub j).

Bagenal, Fran↗