Decay of turbulent energy in a collisionless plasma: Hall MHD

Details Decay of turbulent energy in a collisionless plasma: Hall MHD Decay of turbulent energy in a collisionless plasma: Hall MHD

Dec 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufmsh12a0416m&link_type=abstract

American Geophysical Union, Fall Meeting 2002, abstract #SH12A-0416

Other

2149 Mhd Waves And Turbulence, 2159 Plasma Waves And Turbulence, 7827 Kinetic And Mhd Theory, 7835 Magnetic Reconnection, 7863 Turbulence

Scientific paper

Low frequency plasma turbulence such as that observed in the solar wind, is typically studied in a magnetohydrodynamic (MHD) limit. The usual expectation in MHD turbulence (as in hydrodynamic turbulence) is that the energetic large scale fluctuations, or "energy-containing eddies" regulate the dynamics of the cascade process, including the rate of decay of fluctuation energy. In this view the specific nature of small dissipative processes are not important in regulating decay rates. One might then expect that addition of small scale modifications appropriate to a low-collisionality plasma would have no effect on turbulence decay rates. On the other hand, recent studies of spontaneous magnetic reconnection indicate that collisionless effects can be very important, increasing the rate of reconnection, and that the Hall effect correction to Ohm's Law is perhaps the most crucial modification to MHD results. In the latter perspective one might expect that Hall effect facilitates the small scale reconnection events that typify MHD turbulence cascade and dissipation. The question naturally arises then as to whether Hall effect indeed does modify turbulent decay rates, and whether control of decay by large scale eddies remains relevant in collisonless plasma turbulence. We address this issue by comparison of direct high resolution simulations of ordinary compressible resistive MHD and Hall-modified MHD (HMHD) equations. We conclude, for low cross helicity turbulence over a substantial range of plasma beta, that Hall effect has no substantial effect on turbulent decay rates, which remain well described by a cascade theory controlled by large scale fluctuations. This research supported in part by NSF grants ATM-0105254, ATM-9977692 and ATM-0096324.

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