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Title: The Physics of Partially Ionized Gas with Applications to Processes in the Interstellar Medium

Abstract

The dynamical equations for a partially ionized plasma are a matter of some recent controversy. Understanding this problem is important in understanding the interaction of the interstellar medium with the heliosphere and for understanding the spectrum of interstellar turbulence. If collision scales are much smaller than the internal interaction scales such as the ion gyroradius, the fluid approximation may be used. The analysis then must deal with at least three fluids (protons, electrons, and neutrals) which are coupled to each other by collisions and/or electromagnetic fields. Often, the proton and electron gyro-radii are much smaller than the collision length scales, so the electric and magnetic fields dominate the motions of the electrons and protons. In this case, the only important particle-particle collisions are those of the electrons and protons with the neutral atoms. Since the three species have, in general, different velocities, it is not immediately clear which fluid velocity to use. This ambiguity in the choice of fluid velocity has led to recent confusion regarding the physics of partially ionized plasmas. If the neutrals have a significant fraction of the mass, working in the center-of-mass coordinate frame can result in dynamical equations that differ greatly from those of idealmore » MHD. This is because the magnetic field is not frozen into the frame moving at the center-of-mass velocity, which leads to additional effects on the magnetic field that can be difficult to understand intuitively. To the extent that the electron mass is negligible, the magnetic field is actually found to be frozen into the frame moving with the electron bulk velocity. If we then take U to be the bulk velocity of the proton fluid the resulting dynamical equations closely resemble those of ideal MHD with the exception of the Hall term in the induction equation. Similarly, the frequently used Cowling conductivity also depends on the choice of coordinate frame. These conclusions address directly the recent controversy regarding the interaction of the interstellar medium with the heliosphere and also impact our understanding of interstellar turbulence.« less

Authors:
 [1]; ;  [2]
  1. Department of Physics, University of Arizona, Tucson, AZ 85721 (United States)
  2. Department of Planetary Science, University of Arizona, Tucson, AZ 85721 (United States)
Publication Date:
OSTI Identifier:
21608317
Resource Type:
Journal Article
Journal Name:
AIP Conference Proceedings
Additional Journal Information:
Journal Volume: 1366; Journal Issue: 1; Conference: 2010 Huntsville workshop on partially ionized plasmas throughout the cosmos, Nashville, TN (United States), 3-8 Oct 2010; Other Information: DOI: 10.1063/1.3625596; (c) 2011 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0094-243X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; APPROXIMATIONS; ASTROPHYSICS; ATOMS; CENTER-OF-MASS SYSTEM; COORDINATES; COSMIC ELECTRONS; COSMIC PROTONS; ELECTROMAGNETIC FIELDS; ELECTRON COLLISIONS; HELIOSPHERE; HYDROMAGNETIC WAVES; INTERSTELLAR MAGNETIC FIELDS; IONIZATION; MAGNETOHYDRODYNAMICS; PLASMA; TURBULENCE; VELOCITY; ATMOSPHERES; BARYONS; CALCULATION METHODS; COLLISIONS; COSMIC RADIATION; ELECTRONS; ELEMENTARY PARTICLES; FERMIONS; FLUID MECHANICS; HADRONS; HYDRODYNAMICS; IONIZING RADIATIONS; LEPTONS; MAGNETIC FIELDS; MECHANICS; NUCLEONS; PHYSICS; PROTONS; RADIATIONS; SECONDARY COSMIC RADIATION; SOLAR ATMOSPHERE; STELLAR ATMOSPHERES

Citation Formats

Greenfield, E J, Jokipii, J R, and Giacalone, Joe. The Physics of Partially Ionized Gas with Applications to Processes in the Interstellar Medium. United States: N. p., 2011. Web. doi:10.1063/1.3625596.
Greenfield, E J, Jokipii, J R, & Giacalone, Joe. The Physics of Partially Ionized Gas with Applications to Processes in the Interstellar Medium. United States. https://doi.org/10.1063/1.3625596
Greenfield, E J, Jokipii, J R, and Giacalone, Joe. 2011. "The Physics of Partially Ionized Gas with Applications to Processes in the Interstellar Medium". United States. https://doi.org/10.1063/1.3625596.
@article{osti_21608317,
title = {The Physics of Partially Ionized Gas with Applications to Processes in the Interstellar Medium},
author = {Greenfield, E J and Jokipii, J R and Giacalone, Joe},
abstractNote = {The dynamical equations for a partially ionized plasma are a matter of some recent controversy. Understanding this problem is important in understanding the interaction of the interstellar medium with the heliosphere and for understanding the spectrum of interstellar turbulence. If collision scales are much smaller than the internal interaction scales such as the ion gyroradius, the fluid approximation may be used. The analysis then must deal with at least three fluids (protons, electrons, and neutrals) which are coupled to each other by collisions and/or electromagnetic fields. Often, the proton and electron gyro-radii are much smaller than the collision length scales, so the electric and magnetic fields dominate the motions of the electrons and protons. In this case, the only important particle-particle collisions are those of the electrons and protons with the neutral atoms. Since the three species have, in general, different velocities, it is not immediately clear which fluid velocity to use. This ambiguity in the choice of fluid velocity has led to recent confusion regarding the physics of partially ionized plasmas. If the neutrals have a significant fraction of the mass, working in the center-of-mass coordinate frame can result in dynamical equations that differ greatly from those of ideal MHD. This is because the magnetic field is not frozen into the frame moving at the center-of-mass velocity, which leads to additional effects on the magnetic field that can be difficult to understand intuitively. To the extent that the electron mass is negligible, the magnetic field is actually found to be frozen into the frame moving with the electron bulk velocity. If we then take U to be the bulk velocity of the proton fluid the resulting dynamical equations closely resemble those of ideal MHD with the exception of the Hall term in the induction equation. Similarly, the frequently used Cowling conductivity also depends on the choice of coordinate frame. These conclusions address directly the recent controversy regarding the interaction of the interstellar medium with the heliosphere and also impact our understanding of interstellar turbulence.},
doi = {10.1063/1.3625596},
url = {https://www.osti.gov/biblio/21608317}, journal = {AIP Conference Proceedings},
issn = {0094-243X},
number = 1,
volume = 1366,
place = {United States},
year = {Wed Sep 21 00:00:00 EDT 2011},
month = {Wed Sep 21 00:00:00 EDT 2011}
}