Nonlinear magnetic diffussion and the surface explosion of metals in fast rising megagauss magnetic field

Abstract

The behavior of metals in fast rising high (∼100 ns, >1 MG) magnetic fields have attracted attention in connection with designing laboratory-scale superpower pulse generators capable of producing currents of amplitude 50 MA and rise time 100–200 ns. The interaction of a magnetic field with a metal features an extremely fast penetration of the field into the metal in the form of a nonlinear diffusion wave and the formation of surface plasma due to Joule heating. The paper presents results of an experimental study of the propagation of a nonlinear magnetic diffusion wave and its relation to the formation of thermal plasma at the metal surface. The experiment was performed using metal rods and tubes of outer diameter 1–3 mm subject to 2–2.5 MA pulsed currents. The MIG pulse power generator1 (2.5 MA, 100 ns) was used as a driver. With these parameters, the azimuthal magnetic field induction could reach 8 MGs within 100 ns. Surface plasma was detected using VUV detectors and an optical framing camera. The velocity of magnetic field diffusion was measured with a voltage probe inserted axially into the tube.2 Copper, aluminum, titanium, steel, and stainless steel rods were used to prepare test samples.