Eun-jin Kim ,  University of California, San Diego

Release of magnetic energy and change of magnetic topology via
`fast reconnection' processes are crucial to the understanding
of a number of natural phenomena, the heating of the solar corona being one
prominent example. However, classical MHD reconnection rates are
pathetically slow, and are not predicted to be dramatically
enhanced by turbulent spatial diffusion and transport of magnetic
fields, on account of the severe topological constraints imposed on the
dynamics of those of processes [1]. Thus, one is powerfully motivated
to explore other mechanisms for fast reconnection. One such mechanism
particularly relevant to low collisionality regimes, is the enhancement
of electron-ion momentum exchange via kinetic processes and turbulence [2].
Note this contributes a TRUE `anomalous resistivity', and not merely
the course-grained transport of magnetic field lines which are still
individually constrained by the frozen-in condition of MHD. In practice,
such resistivity anomalies are usually linked to the current-driven
ion-acoustic instability, driven by inverse Landau resonance on a
shifted Maxwellian distribution function.
In this paper, we present a novel theory of anomalous resistivity
based upon the exchange of parallel momentum between ions and electron
phase density holes. Special emphasis is placed upon the interplay between
phase space dynamics and macroscopic physics, such as reconnection-layer
structure. Phase space density holes are self-bound, rather like Jeans
equilibria (NB: The `depletion' is due to the sign of the background
dielectric screening constant). Holes do not require linear instability
for their formation, and can, in fact, extract free energy from the mean
distribution function in the absence of linear waves [3]! Thus, this theory is
not heavily tied to the details of the linear theory of
current driven ion-acoustic instability,
as are most previous theories of anomalous resistivity. Also,
the hole growth mechanism is intrinsically nonlinear.
Holes formation has been observed in recent numerical simulations [4].

The research work performed is concerned with three issues:

i) calculation of the acceleration and growth of an electron hole via
scattering off ions
ii) the implications of (i) for non-collisional momentum and energy
exchange between species, for a given parallel electric field
(iii) the implications of (i) and (ii) for the macroscopic reconnection
and heating rates in simple configurations. Special attention is given
to reconciling the cross-field hole size with reconnection layer
width, and to the possibility of bursty reconnection.

[1] E. Kim and P.H. Diamond, Astrophys. J., {\bf 556}, 1052 (2001)
[2] T.H. Dupree, Phys. of Fluids, {\bf 25}, 277 (1982)
[3] R.H. Berman, et al, Phys. Rev. Lett., {\bf 48}, 1249 (1982)
[4] J.F. Drake, Science, {\bf 299}, 873 (2003)