Absorption of electrical energy provided to a metal wire in an exploding wire system is thought to be terminated or greatly diminished when the plasma is formed, after the joule heating of the metallic wire by the electrical current. Accordingly, it is common to account for the electrical energy delivered to the wire that the integration of current and voltage signals is halted when the voltage peak changes its slope. Usually, this moment is synchronized with the plasma appearance, as detected by optical sensors. In this work, experimental evidence of a two-step electrical energy absorption in an exploding wire surrounded by atmospheric air is presented. During the first step of the energy absorption the plasma is not formed, indicating that the delivered energy is not enough for ionizing the wire, giving place to a dark pause that lasts until a second energy absorption produces a plasma. The delay between the two steps can reach ≈2.2 µs for copper wires of 50 µm diameter charged at an initial voltage of 10 kV. Experimental investigation of variation of the delay between the two steps with different metals, charging voltages, and wire diameters are presented. A relation of the current density with the initial kinetic energy of the plasma and the electrical current rate is devised as a possible explanation of the observed phenomena.

The electrical behavior of exploding wires was obtained by numerically solving the nonlinear differential equation describing the discharge circuit. For metal wires of high conductivity and low sublimation heat, such as copper, aluminum, gold, and silver, the circuit simulation can be well performed based on the resistivity model developed by Tucker in which the resisitivity is expressed by the explicit functions of specific action, i.e., ρ = f(g). For metals such as titanium and zinc with anomalously changing resistivity, i.e., decreasing rather than increasing with the liquid heating, the circuit simulation of the exploding wires can be performed using the implicit relationship between ρ and g that is read out point by point from the experimentally measured curve. Using the circuit simulation, the rate of the energy deposition in the exploding wires before the explosion can be obtained, which is helpful to choose the right experimental conditions for possible overheating that is desirable for getting smaller nano-powders produced by exploding wires.