This award is made in response to a proposal submitted to and reviewed under the NSF/DOE Partnership in Basic Plasma Science and Engineering joint solicitation NSF 09-596. The award provides funds to support undergraduate participation in the overall research effort, which is being funded separately by the DOE under contract to University of Wisconsin (Grant DE-FG02-05ER54831).
This project would continue supporting magnetohydrodynamic (MHD) experiments addressing questions on the selfgeneration of magnetic fields (dynamos) from flows of liquid sodium and expand this line of research into studies of plasma dynamos. The experimental approach of this research complements more traditional analytical and computational approaches to understanding how magnetic fields can be generated in planets and stars.
Two experiments are part of this proposal: a liquid sodium experiment expected to be dynamo from theory, that is operational and making scientific discoveries, and a plasma based experiment under construction (with support from the NSF Major Research Instrumentation program) that will be operational in approximately three years. The goal of both experiments is to experimentally investigate fundamental processes related to self-generation of magnetic fields in naturally occurring dynamos. Both begin as unmagnetized, flowing conducting fluid with large magnetic Reynolds numbers (the key dimensionless number characterizing magnetic field evolution).
A central part of the dynamo research includes the training and mentoring of undergraduate and graduate students. Students are involved in all aspects of the project and are regularly sent to scientific meetings where they present their results and are exposed to the larger scientific community. Outreach activities include public lectures, press releases coordinated by the UW Media Relations and websites.
The NSF support of undergraduate participation adds a broader educational impact through the early-year training of students by introducing them to scientific research as a possible career path.
The Madison Dynamo Experiment has been investigating how magnetic fields are spontaneously generated by fast flowing, turbulent flows of liquid metal. The principle results from this award have been to show how the intrinsic fluctuating turbulence present in high Reynolds number flows can, on average, generate DC magnetic fields, even when the conductivity is not too large. Early on, the experiment provided the first ever evidence that such mean-field currents genereted from turbulence existed, and to some extent validated 50 year old theory the predicted the existence of these currents. The expeirment was designed to have a self-exciting dynamo by first demonstrating flows could be made, which were, on average predicted to self- excite, in a water version of the expeirment. Water and sodium have similar viscosities and so a dimensionally identical water experiment was constructed to demonstrate a working propellor design. The sodium experiment then followed. The device containes about 200 gallons of molten liquid sodium, stirred at speeds of greater than10 m/s. Eventually, the experiment showed that the role of the turbulence was primarily to enhance the effective resisitivity of the flowing liquid (when averaged over the fluctuations). Direct measurements of the turbulent EMF showed this. Ulimately, this turbulence was responsible for the lack of a self-exciting eigenmode in the device.
