Threshold for Thermal Ionization of an Aluminum Surface by Pulsed Megagauss Magnetic Field

The first measurement of the threshold for thermal ionization of the surface of thick metal by pulsed magnetic field (B) is reported. Thick aluminum-with depth greater than the magnetic skin layer-was pulsed with partial derivative B/partial derivative t from 30-80 MG/mu s. Novel loads avoided nonthermal plasma (from electron avalanche, or energetic particles or photons from arcs). Thermal plasma forms from 6061-alloy aluminum when the surface magnetic field reaches 2.2 MG, in qualitative agreement with numerical simulation results by Garanin et al. [J. Appl. Mech. Tech. Phys. 46, 153 (2005)].