Revisiting the role of helicity in MHD dynamos

P.D. MININNI

Princeton

Workshop; Workshop "The dynamo effect in astrophysical and laboratory plasmas"; 2015

Princeton Center for Theoretical Science

Symmetry properties of physical systems govern their behavior, and are associated with conservation of physical quantities in the ideal case. In magnetohydrodynamics, the absence of mirror symmetry in the flow (i.e., the presence of mechanical helicity) results in the growth of large scale magnetic fields through dynamo action. The importance of helicity for the dynamo is well understood, although its possible origins and its impact in other properties of the flow is still under debate. In this talk I will discuss possible sources of helicity in astrophysical flows, and the effect of mechanical helicity in the partition of energy among modes, and in the emergence of coherent structures that can be beneficial for dynamo action. Then, I will revisit the transfer of helicity among scales as a result of dynamo action, and the impact mechanical helicity has on long-term statistical properties of magnetohydrodynamic flows.