Amplitude insensitive microwave phase measurement system.
Microwave phase measurement system proportional only to phase and independent of amplitude fluctuations for determining lossy plasma phase change
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Microscale Alfven waves in the solar wind at 1 AU
Analysis of IMP 1 (Explorer 43) plasma and magnetic field fluctuations on a scale of one hour revealed that linearly and circularly polarized Alfven waves are rarely present in the solar wind at 1 AU. The most prevalent microscale fluctuations appeared to be large-amplitude Alfven waves with small but non-zero fluctuations in the magnetic field intensity. These waves are present about 40% of the time and are predominantly propagating away from the sun.
Burlaga, L. F.↗
Pulsed electromagnetic gas acceleration
Terminal voltage measurements with various cathodes and anodes in a high power, quasi-steady magnetoplasmadynamic (MPD) are discussed. The magnitude of the current at the onset of voltage fluctuations is shown to be an increasing function of cathode area and a weaker decreasing function of anode area. Tests with a fluted cathode indicated that the fluctuations originate in the plasma adjacent to the cathode rather than at the cathode surface. Measurements of radiative output from an optical cavity aligned to examine the current-carrying portion of a two-dimensional, 56 kA magnetoplasmadynamic discharge reveal no lasing in that region, consistent with calculations of electron excitation and resonance radiation trapping. A voltage-swept double probe technique allows single-shot determination of electron temperature and electron number density in the recombining MPD exhaust flow. Current distributions within the cavity of MPD hollow cathodes for various static prefills with no injected mass flow are examined.
Jahn, R. G.↗
Statistical properties of the interplanetary microscale fluctuations
Results are reported for a statistical study of short-period fluctuations in the interplanetary plasma velocity and magnetic field. The data base used consists of measurements of the interplanetary plasma and magnetic field by Pioneer 6 with a time resolution of 72 sec and by Mariner 5 with a resolution of 5 min. The analysis is conducted to characterize the parent population from which all individual microscale events on these time scales are drawn. The microscale changes are grouped according to their energy densities relative to the energy density of the background magnetic field, and it is found that each grouping exhibits certain statistical properties within the limits of observational uncertainty. It is noted that these statistical properties are purely observational and independent of any physical model which may be used to interpret them. The results are discussed in the context of MHD discontinuity theory for a thermally anisotropic plasma.
Belcher, J. W.↗
Pitch-angle diffusion by whistler mode waves near the Io plasma torus
As Voyager 1 traversed the inner radiation belt of Jupiter, wave-particle interactions involving energetic electrons and whistler mode turbulence were strongly affected by the presence of the Io plasma torus. Within the high density torus the resonant electron energy was low and the associated high index of refraction yielded high B-to-E ratios for the wave fields, leading to very strong pitch-angle scattering. It is shown that significant spatial and temporal variations in plasma conditions produced large fluctuations in local scattering times, and the problems associated with the evaluation of precipitation lifetime are discussed.
Scarf, F. L.↗
Infrared heterodyne receivers with IF responses approaching 5 GHz
Specialized coherent 10.6 micrometer infrared receivers were developed with infrared frequency responses approaching 5 GHz. Carbon dioxide lasers were employed for these applications because of their availability, stability, and high average power levels. Heterodyne receivers which employ extrinsic photoconductive Ge:Cu(Sb) mixers were developed for measurements of carbon dioxide laser scattering to determine: (1) the drive lower hybrid wave density fluctuations; and (2) the plasma ion temperature of the dense Tokamak plasmas.
Wolczok, J. M.↗
Constance mirror program: Progress and plans
The current state of the mechanics of the Constance II experiment, the physics results gathered, the motivation background, and future plans for the Constance II experiment are reviewed. Several improvements have been made and several experimental investigations have been completed. These include the construction/installation/testing of: (1) liquid-nitrogen cooled, Ioffe bars installed, (2) a diverter coil (3) the 100 kW ICRF generator, (4) the data acquisition system, and (5) the optimum hot-iron operation of the machine with Titanium and pulsed-gas plasma guns. Measurements were made of the density, temperature, and radius of the plasma. Ion-cyclotron fluctuations were observed, their bandwidth measured, and data collected demonstrating resonance heating. New X-ray diagnostics were designed and purchased, and progress on the Thomson scattering was made. Finally, a new hot cathode gun was designed and constructed.
Klinkowstein, R. E.↗
Anomalous resistivity on auroral field lines
Consideration is given to a possible explanation for the one-dimensional anomalous resistivity and breakdown of runaway acceleration observed in the auroral zones. It is shown that under conditions existing along auroral field lines, where the cyclotron frequency is greater than the plasma frequency and density fluctuations exceed 0.25, trapping of a major portion of the electron distribution function by large-amplitude ion cyclotron waves can inhibit the free acceleration of runaways and act to violate the conservation of the first adiabatic invariant for electrons above a certain threshold velocity. Particle simulations combining the effects of finite ion cavities and pitch angle scattering at the anomalous Doppler resonance are then presented which demonstrate the formation of a runaway distribution upon the application of a constant dc field and the effects of the instability at the anomalous Doppler resonance in preventing it. The necessity for further large-scale macrophysics simulations to gain a fuller understanding of the total system dynamics is pointed out.
Rowland, H. L.↗
Submilliarcsecond VLBI Using Compact Close Pairs of Radio Sources: Error Analysis
The potential accuracy attainable for (delta) VLBI positional measurements (submilliarc second level) is reached by simultaneously observing pairs of compact radio sources whose angular separation are smaller than the beamwidth of each antenna. Simultaneous (delta) VLBI (SVLBI) enables significant cancellation of measurement errors. Solar plasma is the dominant fluctuating error source in SVLBI positional measurements since there is enhanced cancellation of the troposphere and ionosphere, and complete cancellation of oscillator instabilities. Of the nonfluctuating error sources, errors due to universal time predominate. By performing SVLBI experiments over several years with many different close pairs of radio sources, limits can be placed on reference frame stability. Intrinsic properties of the sources, such as source structure and proper motion, will limit measurements. The SVLBI differential phase and corruptive noise sources will be discussed here along with estimated results.
Morabito, D. D.↗
Quenching of the beam-plasma instability by 3-D spectra of large scale density fluctuations
A model is presented to explain the highly variable yet low level of Langmuir waves measured in situ by spacecraft when electron beams associated with Type III solar bursts are passing by; the low level of excited waves allows the propagation of such streams from the Sun to well past 1 AU without catastrophic energy losses. The model is based, first, on the existence of large scale density fluctuations that are able to efficiently diffuse small k beam unstable Langmuir waves in phase space, and, second, on the presence of a significantly isotropic nonthermal tail in the distribution function of the background electron population, which is capable of stabilizing larger k modes. The strength of the model lies in its ability to predict various levels of Langmuir waves depending on the parameters. This feature is consistent with the high variability actually observed in the measurements.
Muschietti, L.↗
Detailed examination of a plasmoid in the distant magnetotail with ISEE 3
Details of an investigation of a lone plasmoid encountered by the ISEE-3 spacecraft in February 1983 are reported. ISEE-3 was then at 217 earth radii distance, in the magnetosheath, and had entered the magnetotail. Intense energetic particle, plasma and magnetic field fluctuations were detected, indicating a large electron flux moving tailward, a suprathermal proton flux, a jump in electron temperature, and inverse signatures of an increasing magnetic field. Closed magnetic field lines were also detected as were IMF field lines around the plasmoid and open field lines connecting the earth with space. The hot particles in the plasmoid are concluded to have been magnetically confined in a boundary one earth radius thick. An earthward directed beam was also detected and was found to balance the tailward flux. The origin and characteristics of the beam were not discerned.
Hones, E. W., Jr.↗
Thermal fluctuations from an artificial ion beam injection into the ionosphere
Simulations of argon beam experiments flown on two sounding rocket flights (ARCS 1, 2) reveal two bands of electrostatic wave emissions, one at high frequencies around the upper hybrid mode, the other at low frequencies around the lower hybrid mode. The latter is significantly enhanced by the argon beam in the simulations, and the enhancement was clearly observed on ARCS 2. This enhancement at phase velocities greater than the beam velocity is suggested to be due to an increase in the thermal fluctuation level of the plasma when the argon beam is present. Inclusion of electron dynamics and oblique angles of wave propagation with respect to B allows investigation of electron heating. Electron tail heating is observed parallel to B for k-parallel/k-perpendicular proportional to the square root of m(e)/m(0), while background ions are heated perpendicular to B.
Hudson, M. K.↗
Clumpy Langmuir waves in type III solar radio bursts
A model is developed for type III radio emission in the interplanetary medium based on recent data on Langmuir waves, associated with ion sound waves, density fluctuations in the interplanetary plasma, streaming electrons and radio emission. In this model, Langmuir wave growth is suppressed by refraction in field-aligned density irregularities except near density minima where clumps of Langmuir waves form. Quasi-linear relaxation limits the growth of the Langmuir waves in the clumps. The radio emission, which is attributed to coalescence of the Langmuir waves with associated ion sound waves, saturates at a brightness temperature equal to the effective temperature of the Langmuir waves, estimated to be between 10 to the 15th and 10 to the 16th K from obserrvational data. The model is consistent with all the relevant data on type III events. In particular, it accounts naturally for observed brightness temperatures of type III bursts.
Melrose, D. B.↗
Interstellar Optics
We discuss the effects of finite source size on the diffraction pattern produced by scattering in a thin screen, particularly as applied to radio-wave scattering, by density fluctuations in the interstellar plasma.
Interstellar Optics Scattering techniques telescop↗
Correlation of ISS Electric Potential Variations with Mission Operations
Orbiting approximately 400 km above the Earth, the International Space Station (ISS) is a unique research laboratory used to conduct ground-breaking science experiments in space. The ISS has eight Solar Array Wings (SAW), and each wing is 11.7 meters wide and 35.1 meters long. The SAWs are controlled individually to maximize power output, minimize stress to the ISS structure, and minimize interference with other ISS operations such as vehicle dockings and Extra-Vehicular Activities (EVA). The Solar Arrays are designed to operate at 160 Volts. These large, high power solar arrays are negatively grounded to the ISS and collect charged particles (predominately electrons) as they travel through the space plasma in the Earth's ionosphere. If not controlled, this collected charge causes floating potential variations which can result in arcing, causing injury to the crew during an EVA or damage to hardware [1]. The environmental catalysts for ISS floating potential variations include plasma density and temperature fluctuations and magnetic induction from the Earth's magnetic field. These alone are not enough to cause concern for ISS, but when they are coupled with the large positive potential on the solar arrays, floating potentials up to negative 95 Volts have been observed. Our goal is to differentiate the operationally induced fluctuations in floating potentials from the environmental causes. Differentiating will help to determine what charging can be controlled, and we can then design the proper operations controls for charge collection mitigation. Additionally, the knowledge of how high power solar arrays interact with the environment and what regulations or design techniques can be employed to minimize charging impacts can be applied to future programs.
Willis, Emily M.↗
Self-Organized Criticality, Multifractals, and Intermittent Turbulence in Earth's Magnetotail
We have achieved all the goals stated in our grant proposal in collaboration with Dr. C.C. Wu of the University of California at Los Angeles. Specifically, these include: The understanding of the complexity induced nonlinear spatiotemporal structures and the coexisting propagating modes. The development of plasma resonances and coherent structures in space plasmas. The study of fluctuation-induced nonlinear instabilities and their role in the reconfiguration of magnetic topologies in the magnetotail. The development of "anisotropic three-dimensional complexity" in the plasma sheet due to localized merging and interactions of the magnetic coherent structures and associated topological phase transitions. The understanding of the intermittent turbulence and energization process of the observed Bursty Bulk Flows (BBF's) in the Earth s magnetotail. The acceleration of ions due to the intermittent turbulence of propagating arid nonpropagating fluctuations In the following, we include lists of our published papers, invited talks, and professional activities. A detailed description of our accomplished research results is given in Section IV.
Chang, Tom↗
Time domain reflectometry in time variant plasmas
The effects of time-dependent electron density fluctuations on a synthesized time domain reflectometry response of a one-dimensional cold plasma sheath are considered. Numerical solutions of the Helmholtz wave equation, which describes the electric field of a normally incident plane wave in a specified static electron density profile, are used. A study of the effects of Doppler shifts resulting from moving density fluctuations in the electron density profile of the sheath is included. Varying electron density levels corrupt time domain and distance measurements. Reducing or modulating the electron density levels of a given electron density profile affects the time domain response of a plasma and results in motion of the turning point, and the effective motion has a significant effect on measuring electron density locations.
Scherner, Michael J.↗
Field line motion in the presence of finite conductivity.
The relation of plasma motion to field line motion is determined in the case where the conductivity is imperfect. The imperfect conductivity may result from collisions between plasma particles and neutrals, as in the case of the earth's ionosphere, or from the scattering of charged particles by the enhanced field fluctuations which characterize a turbulent plasma. A magnetic field is assumed which is a given, known function of space and time, and it is further assumed that all field lines intersect an ideally conducting surface and are identified by their points of intersection. It is shown that the relative displacement between drifting particles and moving field lines has significance only when compared with some other pertinent length such as the total particle drift distance. In such a comparison, when the latter quantity is much larger than the first, the particles can be followed by tracing field lines.
Birmingham, T. J.↗