Experimental Measurement of Compression and Acceleration on Metal Rods Driven by Intense Current

Complex plasma-material interactions are found in many fusion and high energy density experiments. These can dramatically alter the performance of a fusion device, as contaminated fusion fuel does not achieve as high of a temperature and thus fusion yield, due to radiative losses. Magneto-inertial fusion schemes, such as Sandia's MagLIF concept, have metal components that carry increasingly high current density in the vicinity of the plasma. Electrothermal instability of the metal can mix the metal into the plasma, both directly and by seeding magnetohydrodynamic (MHD) instabilities. Accurate numerical modeling of electrically driven conductors is currently challenging due to uncertainties in the equation of state (EOS) and electrical conductivity, especially during the metal-insulator transition. To supply data for comparison to MHD modeling, photonic Doppler velocimetry (PDV) was used to measure the surface motion of mm-diameter (6061 and 5N Al, 5N Cu, 4N Ni, and Ti) rods driven to 0.8 MA in 100 ns by the Sandia Mykonos generator. The high quality of the data permitted the initial magnetic compression of rods to be measured for the first time. Uncoated pure (5N) Al rods compressed 40 nm radially before expanding. Subsequently, the reflective surface experiences several changes in acceleration during the current rise. Last, taking advantage of PDV's sensitivity to multiple simultaneous velocities, the time dependence of the distribution of velocities in the reflective material is being investigated to compare with computer simulations of electrothermal and MHD instabilities. The experimental measurements are being used to benchmark MHD calculations, and thereby inform the choice of EOS and conductivity tables for modeling.