Three-dimensional solutions of magnetohydrodynamic equations for prominence magnetic support: Twisted magnetic flux rope

The search for a background magnetic configuration favorable for prominence support has been given a great deal of attention for several decades. The most recent theoretical studies seem to agree that a promising candidate for the support of the dense and cooler prominence material, which fulfills several of the theoretical and observational requirements such as twist, shear along the neutral line, and dips, is a magnetic flux rope. The most convincing models take an infinitely long periodic configuration that consists of a linear constant-α force-free magnetic field. These models, however, assume values of α that are close to its maximum possible value. In this Letter, we report our recent results, which show that it is indeed possible to produce a configuration that consists of a twisted magnetic flux tube embedded in an overlaying, almost potential, arcade such that high electric currents (and therefore values of α) are confined to the inner twisted magnetic flux rope. We present two MHD processes - corresponding to two different types of boundary conditions - that produce such a configuration. Our results show that the process associated variations of B_z at the photospheric level by applying an electric field involving diffusion is much more efficient for creating a structure with more twist and dips.