Numerical investigation on plasma formation and current transfer in electrical explosion of single wire

Abstract

The electrical explosion of single wire is widely used to understand the physics of the early stage of wire-array Z pinch. When the current pulse passes through the thin metallic wire, the wire heats, melts, vaporizes and ionizes. The metallic wire is exploded to two-object structure, the dense cold core surrounded by a conductive corona. Initially, the voltage across and the current through the wire increase until the voltage collapse occurs. The formation of plasma around the core and the transfer of current to the conducting plasma are responsible for the voltage collapse. In the first stage, a one-dimensional MHD model is constructed to simulate the formation of the initial corona plasma with the “cold start” condition. The initial density, current, temperature distribution and expanding velocity of core and corona are derived. Those data are then used as the initial conditions of the second stage, in which a simplified MHD model is adopted to describe the expansion of core and corona. The semi-empirical equation of state, in which the contribution of electron is calculated by Thomas-Fermi model with quantum and exchange corrections, and the ion is treated as perfect gas, makes it possible to approximately simulate the phase transition of metallic wire. The plasma transport coefficients are calculated by the well-known Lee-More-Desjarlais model. Using the proposed model, simulation are carried out with wire material of aluminum and copper. The simulation results of aluminum wire are compared with our previous experiments1. In Ref.2, the current transfer and plasma formation have been experimentally observed with a specially designed electrode in the electrical explosion of copper wire. The simulation of exploding copper wire is conducted in accordance with the experimental configurations, and the process of current transfer is compared with the experimental data as well.