[Previous] | [Session 54] | [Next]
M. Opher, S. Cowley, A. Schekochihin, R.M. Kinney, B. Chandran, J. Maron, J.C. McWilliams (UCLA)
The origin of the magnetic field in the universe is one of the great problems in astrophysics. The observed magnetic fields in spiral galaxies, for example, are of the order of microgauss and are coherent over galactic scales. Its is usually assumed that turbulent fluid motions will enhance a seed field. In the present work we invetigate the growth of the magnetic field in plasmas with high magnetic Prandtl number (the ratio of viscosity to resistivity). This growth occur initially at scales below the viscous scale [1]. Kinney et al. [2] showed that in 2D the field saturates at an amplitude independent of the mean scale of the field. We discuss the initial growth in the three dimensional case where the dynamics of the field on scales less than the viscosity scale [3]. At low initial field, the field grows and the scale decreases until the resistive scale is reached. The field then grows at a reduced rate until it reaches an equilibrium with the mean scale at a resistive scale. At higher initial amplitude, the field saturates before the mean scale has decreased to the resistive scale. The subsequent evolution is a slow decrease of the scale to the resistive scale, at which point it reaches equilibrium and stops evolving. To explain the large scale coherence of galactic fields, an inverse cascade is necessary. There is no evidence of an inverse cascade. We will present results for extended physics models including tensor viscosity and ambipular diffusion.
[1] R. Kulsrud, and S. Anderson, Astrophys. J., 396, 606 (1992); A. Gruzinov, S. Cowley, and R. Sudan, Phys.Rev.Lett., 77, 4342 (1996).
[2] R. M. Kinney, B. Chandran, S. Cowley, J. C. McWilliams, Astrophys. J., accepted to publication (2000).
[3] M. Opher, S. Cowley, A. Schekochihin, R. M. Kinney, B. Chandran, J. Maron and J.C. McWilliams, in preparation (2001).