Scale-hierarchy and singular perturbation in astronomical plasmas

Z. Yoshida (University of Tokyo) and S. M. Mahajan

The cooperation of nonlinearity (producing collapsed characteristics) and 
dispersion (unfolding singularities) underlies a robust mechanism that imparts 
two distinct scales ("L" measuring the system size, and "d" being typically 
of the order of the ion skin depth) to the double Beltrami states of a 
two-fluid plasma.  The conventional single-fluid model (MHD), seemingly valid 
for a large system (d/L), fails to capture the small scale that is created by 
the singular perturbation of the two-fluid effect (dispersion).  The 
small-scale component plays an important role in various plasma phenomena, 
such as coronal heating.  The double Beltrami model is compared with Parker's 
model of current sheet --a different scenario of creation of small scales.