A W Klemmer, S E Kreher, T M Hutchinson, E P Yu, T J Awe, C L Rousculp, D H Dolan, B T Hutsel, K C Yates, K J Swanson, J J Iratcabal, A Dahal, B S Bauer
In current-driven metal loads, a nonlinear magnetic-diffusion wave carries current and Joule heating inward from the electrical skin-depth layer, coupling the electromagnetic drive to material compression, melting, and expansion. Photon Doppler velocimetry of electrically thick aluminum measures premelt radial magnetic compression of 34.8±2.1 nm and an acceleration transition during surface melting. Interpreted with one-dimensional magnetohydrodynamic calculations, the measured velocity history gives a model-assisted solid-liquid transition duration of 4.5±0.7ns. The result is a validation-relevant surface-motion constraint for integrated current-driven material models, complementary to direct pressure-density-temperature measurements of aluminum.