The characteristics of the electrical explosion of aluminum wire in a vacuum and in the air are investigated.The process of energy deposition is derived from the typical voltage and current waveforms.The energy deposited into the aluminum wire at the instant of voltage breakdown is very important for estimating the state of the metal wire.Energy of~2.8 eV/atom is deposited into the aluminum wire in a vacuum at the instant of voltage breakdown.However,the current flowing through the load for the electrical explosion of aluminum wire in the air decreases to zero gradually after the onset of the phase explosion,coming into the dwell stage.Energy of about 6 eV/atom is deposited into the wire at the instant of voltage breakdown for exploding aluminum wire in the air.Temperatures of 0.9 eV and 0.4 eV are estimated for exploding aluminum wires in a vacuum and in the air according to the experimental data combined with the transport coefficient model.The dwell stage is a significant feature for exploding aluminum wires in the air.The dependence of the dwell time on the initial charging voltage of the primary energy-storage capacitor is derived.The dwell time decreases from 95 ns to 17 ns with the increase of the initial voltage from 13 kV to 17 kV.The optical diagnostic equipment with high spatial and temporal resolution is constructed by a 532 nm,30 ps laser probe.The shadowgram demonstrates the expansion trajectories of the high-density products in different media.The expansion velocities of the high-density core for exploding aluminum wire in a vacuum and in the air are 1.9 km/s and 3 km/s,respectively.The energy deposition into the aluminum wire near the electrode region is slightly higher than in the middle region due to the polarity effect, which is analyzed by the distribution of the radial electric field on the wire surface.Because the explosive emission of the electrons is suppressed substantially by the air,the structure of the energy deposition for exploding aluminum wire in the air is more homogeneous.The structures of the energy deposition and the expansion trajectory of the shock wave are analyzed.The schlieren diagnostic is used to translate the exploding products with different refractivities.The schlieren images for exploding aluminum wire in a vacuum show that the metal wire is exploded into two-phase structure,i.e.,the low-density high-temperature corona plasma surrounding the high-density low-temperature core.However,the schlieren images for exploding aluminum wire in the air demonstrate that in addition to the core-corona structure,the channels of shock wave and compressed air layer are formed.The expansion trajectory of the shockwave front is derived according to the optical diagnostics.