Dynamo threshold detection in the von Kármán sodium experiment.
Predicting dynamo self-generation in liquid metal experiments has been an ongoing question for many years. In contrast to simple dynamical systems for which reliable techniques have been developed, the ability to predict the dynamo capacity of a flow and the estimate of the corresponding critical value of the magnetic Reynolds number (the control parameter of the instability) has been elusive, partly due to the high level of turbulent fluctuations of flows in such experiments (with kinetic Reynolds numbers in excess of 10(6)). We address these issues here, using the von Kármán sodium experiment and studying its response to an externally applied magnetic field. We first show that a dynamo threshold can be estimated from analysis related to critical slowing down and susceptibility divergence, in configurations for which dynamo action is indeed observed. These approaches are then applied to flow configurations that have failed to self-generate magnetic fields within operational limits, and we quantify the dynamo capacity of these configurations.
Laboratoire de Physique, École Normale Supérieure de Lyon, CNRS & Université de Lyon, 46 allée d'Italie, 69364 Lyon Cedex 07, France.
Sophie
S
Miralles
Nicolas
N
Bonnefoy
Mickael
M
Bourgoin
Philippe
P
Odier
Jean-François
JF
Pinton
Nicolas
N
Plihon
Gautier
G
Verhille
Jean
J
Boisson
François
F
Daviaud
Bérengère
B
Dubrulle