Dynamo threshold detection in the von Kármán sodium experiment

Area of Science:

• Plasma Physics
• Fluid Dynamics
• Magnetohydrodynamics

Background:

• Predicting dynamo self-generation in liquid metal experiments remains challenging due to high turbulent fluctuations (kinetic Reynolds numbers > 10^6).
• Existing methods for simple dynamical systems are insufficient for complex fluid flows in experimental settings.

Purpose of the Study:

• To develop and apply reliable techniques for predicting dynamo capacity in liquid metal flows.
• To estimate the critical magnetic Reynolds number for dynamo instability in turbulent flows.
• To quantify dynamo capacity in configurations that have not previously exhibited self-generation.

Main Methods:

• Utilizing the von Kármán sodium experiment to study responses to an externally applied magnetic field.
• Applying critical slowing down analysis to identify dynamo thresholds.
• Employing susceptibility divergence analysis to estimate critical parameters.
• Quantifying dynamo capacity in non-generating flow configurations.

Main Results:

• A dynamo threshold can be reliably estimated using critical slowing down and susceptibility divergence in configurations exhibiting dynamo action.
• These analytical approaches were successfully applied to flow configurations that did not self-generate magnetic fields.
• The dynamo capacity of previously non-generating configurations was successfully quantified.

Conclusions:

• Critical slowing down and susceptibility divergence provide effective methods for predicting dynamo thresholds in liquid metal experiments.
• These techniques enable the quantification of dynamo capacity, advancing the understanding of magnetic field self-generation in turbulent flows.
• The study offers a pathway to better predict and understand dynamo phenomena in complex experimental setups.