Astrophysics Formal Seminars

Formal seminars take place every Monday during full term. For a complete list of talks please visited the talk.cam website.

Theoretical Foundation of 3D Alfven Resonances

The coupling of fast and Alfven magnetohydrodynamic (MHD) waves is of fundamental interest in astrophysical plasmas. Under certain conditions, Alfven waves can be resonantly excited by fast mode waves, resulting in a localised accumulation of energy in the plasma. In the solar community this is often referred to as resonant absorption, while in the magnetospheric community it’s known as field line resonance. These processes have applications in coronal heating and in magnetospheric dynamics.

Alfven resonances are well understood in 1D and 2D, but not so in 3D. We present a theoretical way of understanding the structure of Alfven resonances in 3D, which is corroborated by numerical simulations.

Title to be confirmed

Abstract not available

The effect of rotation on the dynamo threshold at the low Pm limit

In this seminar I will show that the critical magnetic Reynolds number Rm_c for a turbulent non-helical dynamo in the low magnetic Prandtl number Pm limit can be significantly reduced if the flow is submitted to global rotation. Even for moderate rotation rates the required energy injection rate can be reduced by a factor more than 10^3. This strong decrease of the onset is attributed to the reduction of the turbulent fluctuations that makes the flow to have a much larger cut-off length-scale compared to a non-rotating flow of the same Reynolds number. The dynamo thus behaves as if it is driven by laminar behaviour (i.e. high Pm behaviour) even at high values of the Reynolds number (i.e. at low values of Pm). Our finding thus points into a new paradigm for the design of new liquid metal dynamo experiments.

Title to be confirmed

Abstract not available

Title to be confirmed

Abstract not available