Numerical simulation predicts several m/s liquid-metal velocities in fusion ducts from 100 T/s magnetic field decay

The study solves the coupled induction and momentum equations for a channel flow matching typical fusion blanket parameters under a rapidly decaying longitudinal field superimposed on a steady wall-normal field. Eddy currents induced by the 100 T/s decay interact with the steady field to produce the driving Lorentz force, resulting in large-amplitude, gradually decaying velocity and magnetic oscillations identified as standing Alfvén waves. Parametric sweeps across Hartmann numbers, interaction parameters, and decay rates yield power-law scalings for maximum velocity and force; the most severe responses occur at the highest decay rates and strongest transverse fields. Compressibility and acoustic wave effects were tested separately and produced only minor modifications to the early-time evolution. Prior analytic work on MHD duct flows under steady fields had not captured the transient wave dynamics that dominate here. The present results imply that existing blanket designs may require additional structural margins or active mitigation to withstand disruption-induced loads, a point not addressed in most steady-state blanket studies. Future three-dimensional simulations with realistic geometry and two-way fluid-structure coupling will be needed to quantify local stress concentrations and validate the one-dimensional approximation against potential secondary flows.