Physics and Astronomy Colloquium

Cary Forest

The self-generation of magnetic fields in planets and
stars--the dynamo effect--is a long-standing problem of magnetohydrodynamics and plasma physics. Until recently, research on the self-excitation process has been primarily theoretical. This talk will address how dynamo experiments, using high speed flows of liquid sodium, have been investigating the key processes of the geodynamo and solar dynamo. I will begin with a brief tutorial on how magnetic fields are generated in planets and stars, describing the "Standard Model" of self-exciting dynamos known as the alpha-omega dynamo. In this model, axisymmetric differential rotation can produce the majority of the magnetic field, but some non-axisymmetric, turbulence driven currents are also necessary. Understanding the conversion of turbulent kinetic energy in the fluid motion into electrical currents and thus magnetic fields, is the biggest challenge for both experiments and theory at this time. Experimental evidence for these currents has recently been discovered in a 1 meter diameter, spherical, liquid sodium dynamo experiment at the University of Wisconsin. These experiments will be described and future directions will be discussed.