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

Summary form only given. 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.Using the measured current and the initial outer diameter of the rod, a threshold magnetic field has been determined at which surface plasma with brightness temperature 2 eV was generated. For Cu, Al, and steel samples, the threshold magnetic field was found to be a little higher than Bs Qs / 8 (Qs is the sublimation energy of the metal). The behavior of the metals of lower conductivity was observed to be more complicated. The experimental results and their discussion will be presented.