Numerical investigations on the nanosecond electrical explosion of single aluminum wire in vacuum

Summary form only given. The nanosecond electrical explosion of aluminum (Al) wire in vacuum is investigated using a one-dimensional magnetohydrodynamic model with the “cold start” conditions, which describes the severe phase transition from solid state into exploding plasma. Thomas-Fermi equation of state with quantum and exchange corrections, which allows the phase transition from solid to plasma state to be approximately simulated, is adoptted¹. The Lee-More conductivity model with Dasjarlais´s correction is used as well. The ion charge state is determined by Saha equation with electron degeneracy and ion excited state taken into consideration. The hydrodynamic equations are solved using the NND method proposed by Zhang. Four stages are suggested in this model according to the temperature and phases, namely, the solid stage, the transition stage from solid to liquid, the liquid stage and the plasma formation stage. Thermodynamical calculation is carried out during the solid state of Al wire. When the temperature is above the melting point, the dense core, gaseous metal, and the plasma are treated as fluid. The grid is labeled as vacuum when the density is lower than 10^-4 kg/m³. The evolution of the liquid core into gaseous and plasma state is clearly illustrated without taking into consideration the complexity of instability. It is demonstrated that increasing the current rate leads to the increased energy deposited in the wire before voltage collapse, at which the condensed core along with low density plasma structure is formed. Then the current moves from the high-density cold core to the low-density hot plasma rapidly. Simulation results indicate that the radial velocity of low-density plasma reaches ~70 km/s, and the expansion velocity of dense core is ~2.5 km/s, which are in accordance with relevant experimental data².