Nuno Loureiro ,   Imperial College

 
We study the nonlinear evolution of resistive tearing mode reconnection using the equations of reduced-MHD.
For island widths larger than the resistive scale,
existing theory predicts under certain assumptions that the linear (exponentially fast) stage
of the mode evolution is replaced by a nonlinear stage of algebraic island growth (the so-called Rutherford regime).
Numerical evidence of this regime's existence has been elusive
and it has been questioned that this regime is at all realized.
We show numerically that the Rutherford regime exists even at large values of the instability parameter D'.
It is further shown that for D' and island width above certain critical values,
the Rutherford stage gives way to a period of extremely fast growth (followed by saturation of the instability).
This speed-up is accompanied by a topological rearrangement of the region around the magnetic null,
from X to Y shape, i.e., the tearing-mode reconnection is replaced by Sweet-Parker reconnection.