Plasma Physical Processes Research Articles

Electromagnetic-wave absorption in highly collisional plasmas

An experimental and theoretical investigation of basic plasma-physics processes relating to the absorption of electromagnetic waves in collisional plasmas is described. One-way absorption of 63 dB at 4 GHz was demonstrated in a section of plasma-loaded rectangular C-band waveguide. The ultraviolet photoionization plasma-production technique employed permits independent variation of the plasma-density profile and electron-collision frequency. A theoretical model for the absorption and scattering processes, which includes scattering contributions from the plasma-vacuum interface, and partial reflections and collisional absorption in the bulk plasma, is in reasonable agreement with the experimental results.

Plasma wave profiles of Earth's bow shock at low Mach numbers: ISEE 3 observations on the far flankTtethered Satellite System

The Earth's bow shock is weak along its distant flanks where the projected component of solar wind velocity normal to the hyperboloidal surface is only a fraction of the total free stream velocity, severely reducing the local Mach number. We present a survey of selected crossings far downstream from the subsolar shock, delineating the overall plasma wave (pw) behavior of a selected set of nearly perpendicular crossings and another set of limited Mach number but broad geometry; we include their immediate upstream regions. The result is a generalizable pw signature, or signatures, of low Mach number shocks and some likely implications of those signatures for the weak shock's plasma physical processes on the flank. We find the data consistent with the presence of ion beam interactions producing noise ahead of the shock in the ion acoustic frequency range. One subcritical case was found whose pw noise was presumably related to a reflected ion population just as in stronger events. The presence or absence, and the amplitudes, of pw activity are explainable by the presence or absence of a population of upstream ions controlled by the component of interplanetary magnetic field normal to the solar wind flow.

Recent results from studies of electron beam phenomena in space plasmas

Experiments involving the ejection of beams of electrons from spacecraft have been performed for more than 2 decades in order to study fundamental plasma physical processes as well as for a range of diagnostic- and application-oriented purposes. This paper reviews some of the key issues that have been pursued in the past 10 years. These include questions regarding spacecraft charging and beam dynamics, the interaction of beams with neutral gas and plasmas, and the electromagnetic radiation generated by continuous and pulsed electron beams. It is shown how our understanding of these phenomena has matured, thereby providing a solid foundation for future experiments involving the use of electron beams.

Adhesion and corrosion behavior of Al-Zn and TiN/Ti/TiN coatings on a DU-0.75wt.% Ti alloy

Al-Zn alloy and multilayer TiN/Ti/TiN thin coatings were deposited on DU-0.75Ti alloy specimens by a cathodic arc plasma physical vapor deposition process. The quality, soundness and adhesion of the coatings to the substrate were evaluated by automatic scratch testing, in combination with optical and scanning electron microscopy examination of the scratch morphology. The galvanic corrosion behavior of DU-0.75Ti alloy coupled to the coated alloys and aluminum alloy 7075-T6 was also investigated by electrochemical tests in a 0.5 N NaCl aqueous solution.

Electrical Damage Due to Low Energy Plasma Processing of GaAs Structures

ABSTRACTThe effect of numerous plasma reative ion etch and physical milling processes on the electrical behavior of GaAs bulk substrates has been investigated by means of electric microwave absorption. It was seen that plasma treatments at quite low energies may significantly affect the electrical quality of the etched semiconductor. Predominantly physical plasma etchants (Ar) were seen to create significant damage at very low energies. Chemical processes (involving Cl or F), while somewhat less pernicious, also gave rise to electrical substrate damage, the effect greater for hydrogenic ambients. Whereas rapid thermal anneal treatments tend to worsen the electrical integrity, some substrates respond positively to long-time high temperature anneal steps.

Evaluation of adhesion of some metallic coatings on a depleted U-0.75Ti alloy

The adhesion, soundness and comparative quality of various coatings on a depleted uranium (DU-0.75Ti) alloy were evaluated with a CSEM Revetest automatic scratch tester. These coatings, namely aluminum, magnesium, zinc, titanium, Al-Zn, Al-Mg, TiN and Al/TiN, were deposited by a cathodic arc plasma physical vapor deposition process. During scratch testing the acoustic emission signal intensity, the frictional force and the friction coefficient were plotted vs. load. Scratch test results were correlated with coating microstructure characteristics as determined by optical and scanning electron microscopy. Al-Zn and Al-Mg coatings exhibit higher cohesive and adhesive (critical) loads and appear to be the best sacrificial coating materials for DU-0.75Ti.

Hydrodynamic cumulative processes in plasma physics

This review is devoted to cumulative hydrodynamic processes in a plasma and to the possibility of using them for controlled thermonuclear fusion. The cumulation of convergent shock waves and the mechanisms of their limitation are discussed in greatest detail. Results are presented of study of non-one-dimensional cumulative shock waves, which had practically not yielded to analysis until recently.

Plasma Density Fluctuations and the Physics of Short-pulse Laser-produced Plasmas

Abstract Laser-produced plasmas are studied for their relevance to laser fusion research, as bright pulsed sources of X-rays and fast particles, as well as for the fundamental plasma physics processes they reveal. The programme on laser-plasma-interaction physics at the Australian National University has gained prominence for elucidating the physics of plasmas generated using short laser pulses at very high intensity where complex nonlinear processes dominate behaviour. This review will discuss some of the results from that programme and in particular relate many of the observed phenomena to the existence of density fluctuations in the plasma.

Gidrodinamicheskie kumulyativnye protsessy v fizike plazmy

Gidrodinamicheskie kumulyativnye protsessy v fizike plazmy

Reconnection in space plasma: An international workshop

Reconnection is a process in plasma physics whereby released magnetic energy heats plasma and accelerates particles. The process is an important one in solar, solar‐terrestrial and magnetospheric physics. The concept of reconnection was originally introduced in 1946 by Giovanelli [Nature, 158, 81[ when he wrote, “During the growth of a sunspot there must be electric fields induced …” and “there will be places where actual neutral points exist …”Since that time our idea of reconnection has been refined and amplified. Today we no longer question that the process exists: there is little doubt that it plays a significant role in astrophysical and solar‐planetary plasma dynamics. During the past four decades theory, experiments and observations have made a great deal of progress in gaining an understanding of reconnection but have also posed a number of questions about the process.

The solar wind: Advances in our knowledge through two solar cycles

As the Pioneer and Voyager spacecraft have moved outward they have gradually unfolded a view of distant regions of the heliosphere. Information on the solar wind velocity, density and temperature as a function of distance out to more than 40 AU has been gathered. Meanwhile our description of the solar wind has evolved. Long-standing questions on the sources of the wind causing geomagnetic activity were clarified by the discovery of coronal holes and coronal mass ejections. The propagation of the resultant solar wind disturbances through the heliosphere has been studied using both observations and models. Plasma physical processes have been studied. This review focuses on the development of the concepts that have been used to describe the solar wind in the 3 dimensional heliosphere over the last two solar cycles. Collisionless shocks, transient disturbances in space, disturbance propagation and the distant solar wind are discussed.

Magnetosphere-ionosphere interactions —near-Earth manifestations of the plasma Universe

As the Universe consists almost entirely of plasma, the understanding of astrophysical phenomena must depend critically on our understanding of how matter behaves in the plasma state.In situ observations in the near-Earth cosmical plasma offer an excellent opportunity of gaining such understanding. The near-Earth cosmical plasma not only covers vast ranges of density and temperature, but is the site of a rich variety of complex plasma physical processes which are activated as a result of the interactions between the magnetosphere and the ionosphere. The geomagnetic field connects the ionosphere, tied by friction to the Earth, and the magnetosphere, dynamically coupled to the solar wind. This causes an exchange of energy and momentum between the two regions. The exchange is executed by magnetic-field aligned electric currents, the so-called Birkeland currents. Both directly and indirectly (through instabilities and particle acceleration) these also lead to an exchange of plasma, which is selective and therefore causes chemical separation. Another essential aspect of the coupling is the role of electric fields, especially magnetic-field aligned (‘parallel’) electric fields, which have important consequences both for the dynamics of the coupling and, especially, for energization of charged particles.

Characteristics of cometary picked‐up ions in a global model of Giacobini‐Zinner

Energetic ions observed during the International Cometary Explorer (ICE) spacecraft flyby of comet Giacobini‐Zinner provide information about both the constitution of comets and the plasma physical processes associated with their interaction with the solar wind. In this investigation the details of ion “pickup,” in the limit where small‐scale fluctuations in the plasma and magnetic field are neglected, are modeled by following the motion of a large number of initially cold, heavy (mass 18) ions in a global magnetohydrodynamic model of the local plasma and magnetic field. The results indicate how the background or macroscopic velocity and magnetic field structure of the comet can affect the average spatial and spectral characteristics of the observed cometary ions. These effects, which occur by virtue of forces associated with the compression and the curvature of the magnetic field in the presence of the stagnating plasma flow, can explain the double maxima in the time series of the energetic ion flux observed along the ICE trajectory.

Magnetosphere-Ionosphere Interactions-Near-Earth Manifestations of the Plasma Universe

As the universe consists almost entirely of plasma, the understanding of astrophysical phenomena must depend critically on our understanding of how matter behaves in the plasma state. In situ observations in the near-earth cosmical plasma offer an excellent opportunity for gaining such understanding. The near-earth cosmical plasma not only covers vast ranges of density and temperature, but is the site of a rich variety of complex plasma physical processes which are activated as a result of the interactions between the magnetosphere and the ionosphere. The geomagnetic field connects the ionosphere, tied by friction to the earth, and the magnetosphere, dynamically coupled to the solar wind. This causes an exchange of energy and momentum between the two regions. The exchange is executed by magnetic-field-aligned electric currents, the so-called Birkeland currents. Both directly and indirectly (through instabilities and particle acceleration) these also lead to an exchange of plasma, which is selective and therefore causes chemical separationi. Another essential aspect of the coupling is the role of electric fields, especially magnetic-field-aligned ("parallel") electric fields, which have important consequences both for the dynamics of the coupling and, especially, for energization of charged particles.

1985 James B. Macelwane Award

For his incisive, provocative, and pioneering work on the role of turbulent magnetohydrodynamical processes in space plasma physics, we honor William H. Matthaeus with the James B. Macelwane Award.An indefatigable worker—literally a ball of fire—Bill bubbles with ideas and enthusiasm. His interests and abilities are wide ranging. Although he could equally well have pursued a career in theoretical high‐energy physics,toward which he had been headed, it is our good fortune that, in a midcourse correction, he switched his field to theoretical plasma physics.

Physical processes in gamma-ray bursts

view Abstract Citations (73) References (32) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Physical processes in gamma-ray bursts Katz, J. I. Abstract Physical processes occurring in gamma-ray bursts are discussed, with special attention to the event of March 5, 1979 in the Large Magellanic Cloud. The source of that event's extraordinary intense line and continuum radiation has been explained as a pair plasma confined in a strong magnetic field, as in a neutron star magnetosphere, and some consequences of that model are studied. The magnetic field (approximately 10 to the 13th gauss) affects both plasma physical processes and annihilation, so that accurate measurements of the annihilation line shape may lead to quantitative field determinations. A simple model for gamma-gamma pair production and annihilation is calculated, implying that this process will not prevent escape of intense gamma-ray fluxes. Finally, energetic considerations suggest that the magnetospheric energy may be regenerated from internal sources, either during or between bursts. Publication: The Astrophysical Journal Pub Date: September 1982 DOI: 10.1086/160262 Bibcode: 1982ApJ...260..371K Keywords: Gamma Ray Bursts; Magellanic Clouds; Plasma Radiation; Astronomical Models; Continuous Radiation; Gamma Ray Astronomy; Magnetic Effects; Pair Production; Photons; Positron Annihilation; Astrophysics full text sources ADS | data products NED (1)

Gamma ray emission from interstellar clouds: a plasma physical process capable of enhancing electron fluxes

Gamma ray emission from interstellar clouds: a plasma physical process capable of enhancing electron fluxes

NASA program in solar‐terrestrial studies

As part of a continuing program open to participation by the academic community, NASA has announced new opportunities in the theoretical analysis and modeling of solar‐terrestrial phenomena. The program will be managed by the Solar Terrestrial Division of NASA's Office of Space Science. In fiscal year 1980 (October 1, 1979, to September 30,1980) the Solar Terrestrial Division will administer approximately $2.25 million explicitly designated for this program. One of the fundamental goals of the program is to obtain a theoretical understanding of the basic (predominantly plasma physical) processes that are important to solar physics and to the solar‐terrestrial environment.

Laboratory experiments of magnetospheric interest

Space-related laboratory experiments can play an important role as a complement to observations and active experiments in the magnetosphere. Excluding laboratory experiments for mere developing or testing of techniques for space experiments, we may distinguish between two major types: (1) partial scale model experiments and (2) experiments for clarifying basic plasma physical processes known or expected to be important in the magnetosphere (but without the ambition to simulate actual space configurations). The limitations and potentialities of both types are discussed and examples of experiments are given. It is concluded that there should be an increasing need for the experiments of the second type. In particular, they are needed for the clarification of the response of a thin plasma to electric fields and its ability to carry electric currents. This encompasses such key questions as the nature and role of ‘anomalous’ resistivity (and electron runaway in its presence), the possible formation of double layers (and the acceleration processes associated with them) and rapid dissipation of magnetic-field energy.