The physics of partially ionized gas with applications to processes in the interstellar medium

E. J. Greenfield, J. R. Jokipii, Joe Giacalone

Research output: Chapter in Book/Report/Conference proceedingConference contribution

2 Scopus citations

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 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.

Original languageEnglish (US)
Title of host publicationPartially Ionized Plasmas Throughout the Cosmos - Proceedings of the 2010 Huntsville Workshop
Pages115-121
Number of pages7
DOIs
StatePublished - Oct 20 2011
Event2010 Huntsville Workshop on Partially Ionized Plasmas Throughout the Cosmos - Nashville, TN, United States
Duration: Oct 3 2011Oct 8 2011

Publication series

NameAIP Conference Proceedings
Volume1366
ISSN (Print)0094-243X
ISSN (Electronic)1551-7616

Other

Other2010 Huntsville Workshop on Partially Ionized Plasmas Throughout the Cosmos
CountryUnited States
CityNashville, TN
Period10/3/1110/8/11

Keywords

  • Alfvén waves
  • Conductivity
  • Interstellar medium
  • MHD
  • Magnetic fields
  • Partially ionized plasma
  • Turbulence

ASJC Scopus subject areas

  • Physics and Astronomy(all)

Fingerprint Dive into the research topics of 'The physics of partially ionized gas with applications to processes in the interstellar medium'. Together they form a unique fingerprint.

  • Cite this

    Greenfield, E. J., Jokipii, J. R., & Giacalone, J. (2011). The physics of partially ionized gas with applications to processes in the interstellar medium. In Partially Ionized Plasmas Throughout the Cosmos - Proceedings of the 2010 Huntsville Workshop (pp. 115-121). (AIP Conference Proceedings; Vol. 1366). https://doi.org/10.1063/1.3625595