Physics of the interaction of pulsed magnetic fields with plasmas and relevance to applications

Summary form only given, as follows. Spatially and temporally resolved spectroscopic measurements of the ion velocities, electron density and temperature, non-thermal electric fields, and the magnetic field evolution in a current-carrying plasma, show that ion separation occurs in which a light-ion plasma is pushed ahead of a magnetic piston while a heavy-ion plasma lags behind the magnetic piston. The velocities of the heavier ions are determined from Doppler shifts and the proton velocity is obtained using charge-exchange spectroscopy. The width of the current channel, calculated from the spatial distribution of the magnetic field, determined from Zeeman splitting of doped helium lines, is significantly broader than expected from classical diffusion. A large electron and ion heating is observed during the field penetration, as predicted theoretically. Moreover, the formation of non-thermal fast electrons, associated with the field penetration is experimentally studied. Turbulent electric fields with a 10+-2 kV/cm amplitude are inferred from Stark broadening of hydrogen and helium lines. Explanations for the observed rapid magnetic field penetration into the heavy-ion plasma in the context of EMHD theory or turbulence-induced collisionality are discussed. It is shown that the presence of the light ions in the plasma significantly modifies the dissipated-magnetic-field-energy partitioning between electrons and ions. Furthermore, understanding the dynamics of different ion species allows for improving the switch opening and coupling to various loads. Relevance to astrophysics and magnetic fusion will also be discussed.