## 2. The loop modelThe cylindrical flux tube as well as the numerical procedure used in this study are described in details in Paper I. However, we briefly recall here the main features of the coronal loop model. An initially axisymmetric equilibrium with a force-free magnetic
field and a vanishing plasma pressure is assumed. The twist, that has
been numerically calculated, is a decreasing function of the radial
coordinate with a maximum value of on
the axis (see Fig. 2 in Paper I). As one can see in
Fig. 1, an internal twisted flux tube of length
Therefore, as the starting point of the present work, a constant and uniform resistivity coefficient (in our dimensionless units) is introduced at a given time ( being the radial Alfvén crossing time defined in Paper I) corresponding to a kinked state that gives a (maximum) current density amplitude of two times the initial equilibrium one. This resistivity value is an optimal one as higher values would lead to the unrealistic diffusion of the whole equilibrium while smaller values lead to a considerable amount of time of cpu computation (Paper I). A viscosity coefficient equal to the resistivity one is also used. We have then completed the time evolution of the system until a relaxed state of lower magnetic energy was obtained. As explained in Paper I and by Arber et al. (1999), this final state is characterized by the dissipation of the current concentration that is representative of the available free magnetic energy. © European Southern Observatory (ESO) 2000 Online publication: July 27, 2000 |