The MHD dynamo is a process by which kinetic energy in flowing, conducting fluids can be spontaneously converted into magnetic energy. Although  this theory is well developed, there have been few laboratory models testing the key features of the dynamo theories. This grant supports studies of MHD phenomena in a new laboratory at the University of Wisconsin where key questions pertinent to the MHD dynamo will be investigated.

The main experiment supported by this award consists of a 300 gallon spherical tank filled with liquid sodium. Flows are driven in the liquid sodium by propellers at speeds up to 15 m/s.At these high speeds, magnetic field generation is expected to spontaneously occur.

To investigate and study magnetic field generation in the laboratory requires an ample volume of a sufficiently conducting liquid such as sodium, moving with a sufficiently high velocity to stretch and amplify magnetic fields.

The dimensionless number governing the transition to a dynamo is the magnetic Reynolds number Rm=m₀ s a V (a product of conductivity, scale length and velocity). For example, in spherical geometries self--generation of magnetic fields requires Rm>50; if using liquid sodium this requirement implies a vessel with a radius larger than 0.5 m and flows in excess of 10 m/s. Engineering analysis then shows that experiments addressing self-generation of magnetic fields require a minimum inventory of 300 gallons of liquid sodium, and more than 100 kW of mechanical energy for driving the required flows. Constructing such experiments introduces specialized engineering challenges (for example rugged mechanical seals capable of operating reliably with liquid sodium), requires development of new diagnostic tools, and also requires a safety infrastructure capable of dealing with liquid sodium hazards.

During the past three years, such a laboratory has been constructed at the University of Wisconsin. Funds from the NSF, the David and Lucille Packard Foundation, the University of Wisconsin, the Sloan Foundation, the Research Corporation, and DoE, have been used to assemble the laboratory and to construct a spherical dynamo experiment capable of self-generation of magnetic fields from flows in liquid sodium. The result of this labor and investment is a not only the experiment, but also a facility consisting of the liquid sodium reservoir, the sodium transfer  infrastructure, and motors for driving the flows.