Transport processes in a time-dependent chaotic magnetic-field configuration.

Grasso D., Di Giannatale G., Falessi M., Pegoraro F.
  Venerdì 30/09   09:00 - 12:00   Edificio Psicologia 2 - Aula 2B   II - Fisica della materia
Magnetic-field lines embedded in a plasma confinement system are often char-acterized by a chaotic motion, that can lead to the degradation of the confinement properties of the system. However, even in case of chaotic domains, magnetic bar- riers can emerge and limit the field line motion itself (D. Borgogno $et al.$ (2011)). In this paper we analyze the Lagrangian Coherent Structures (LCS) that determine the transport properties of magnetic-field lines in a chaotic magnetic field, generated by a reconnection event (D. Borgogno $et al.$ (2005)). Differently from what has been done (D. Borgogno $et al.$ (2005)), where the barriers have been found as ridges of the finite-time Lyapunov exponent field, here the LCS are determined as the most attracting and repelling material lines, according to G. Haller (2000). First, following the work of M.V.Falessi $$ (2015), we illustrate the method by a direct comparison of the LCS calculated according to the new defintion and the ones calculated adopting the approach of D. Borgogno $$ (2005), analyzing the Hamiltonian of magnetic-field lines at a fixed -time. Then, we will show how these LCS modify in time, assuming a time-dependent Hamiltonian.