The Heavy-Ion Approximation for Ambipolar Diffusion Calculations for Weakly Ionized Plasmas

Details The Heavy-Ion Approximation for Ambipolar Diffusion Calculations for Weakly Ionized Plasmas The Heavy-Ion Approximation for Ambipolar Diffusion Calculations for Weakly Ionized Plasmas

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006apj...653.1280l&link_type=abstract

The Astrophysical Journal, Volume 653, Issue 2, pp. 1280-1291.

Astronomy and Astrophysics

Astronomy

12

Ism: Kinematics And Dynamics, Ism: Magnetic Fields, Magnetic Fields, Magnetohydrodynamics: Mhd, Stars: Formation

Scientific paper

Ambipolar diffusion redistributes magnetic flux in weakly ionized plasmas and plays a critical role in star formation. Simulations of ambipolar diffusion using explicit MHD codes are prohibitively expensive for the level of ionization observed in molecular clouds (<~10-6), since an enormous number of time steps is required to represent the dynamics of the dominant neutral component with a time step determined by the trace ion component. Here, we show that ambipolar diffusion calculations can be significantly accelerated by the ``heavy-ion approximation,'' in which the mass density of the ions is increased and the collisional coupling constant with the neutrals decreased such that the product remains constant. In this approximation the ambipolar diffusion time and the ambipolar magnetic Reynolds number remain unchanged. We present three tests of the heavy-ion approximation: C-type shocks, the Wardle instability, and the one-dimensional collapse of a magnetized slab. We show that this approximation is quite accurate provided that (1) the square of the Alfvén Mach number is small compared to the ambipolar diffusion Reynolds number for dynamical problems, and that (2) the ion mass density is negligible for quasi-static problems; a specific criterion is given for the magnetized slab problem. The first condition can be very stringent for turbulent flows with large density fluctuations.

Affiliated with

Also associated with

No associations

Rating

The Heavy-Ion Approximation for Ambipolar Diffusion Calculations for Weakly Ionized Plasmas does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with The Heavy-Ion Approximation for Ambipolar Diffusion Calculations for Weakly Ionized Plasmas, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and The Heavy-Ion Approximation for Ambipolar Diffusion Calculations for Weakly Ionized Plasmas will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-1239562