53rd Annual Meeting of the APS Division of Plasma Physics
Volume 56, Number 16
Monday–Friday, November 14–18, 2011;
Salt Lake City, Utah
Session GI3: Plasma Turbulence
9:30 AM–12:30 PM,
Tuesday, November 15, 2011
Room: Ballroom AC
Chair: Masaaki Yamada, Princeton Plasma Physics Laboratory
Abstract ID: BAPS.2011.DPP.GI3.6
Abstract: GI3.00006 : Reduction of Large-scale Turbulence and Optimization of Flows in the Madison Dynamo Experiment
12:00 PM–12:30 PM
Preview Abstract
Abstract
Author:
N.Z. Taylor
(University of Wisconsin-Madison)
The Madison Dynamo Experiment seeks to observe a magnetic field
grow at the
expense of kinetic energy in a flow of liquid sodium. The
enormous Reynolds
numbers of the experiment and its two vortex geometry creates strong
turbulence, which in turn leads to transport of magnetic flux
consistent
with an increase of the effective resistivity. The increased
effective
resistivity implies that faster flows are required for the dynamo to
operate. Three major results from the experiment will be reported
in this
talk. 1) A new probe technique has been developed for measuring
both the
fluctuating velocity and magnetic fields which has allowed a direct
measurement of the turbulent EMF from $<$ v x b $>$. 2) The scale
of the
largest eddies in the experiment has been reduced by an
equatorial baffle on
the vessel boundary. This modification of the flow at the
boundary results
in strong field generation and amplification by the mean velocity
of the
flow, and the role of turbulence in generating currents is
reduced. The
motor power required to drive a given flow speed is reduced by
20{\%}, the
effective Rm, as measured by the toroidal windup of the
field(omega effect),
increased by a factor of $\sim $2.4, and the turbulent EMF
(previously
measured to be as large as the induction by the mean flow) is
eliminated.
These results all indicate that the equatorial baffle has
eliminated the
largest-scale eddies in the flow. 3) Flow optimization is now
possible by
adjusting the pitch of vanes installed on the vessel wall. An
analysis of
the kinematic prediction for dynamo excitation reveals that the
threshold
for excitation is quite sensitive to the helical pitch of the flow.
Computational fluid dynamics simulations of the flow showed that by
adjusting the angle of the vanes on the vessel wall (which
control the
helical pitch of the flow) we should be able to minimize the
critical
velocity at which the dynamo onset occurs. Experiments are now
underway to
exploit this new capability in tailoring the large-scale flow.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2011.DPP.GI3.6