Transverse irregularities and thermal instabilities in the cores of wires electrically exploded in air

Summary form only given. The causes of the transverse irregularities (breaks and narrow regions) and thermal instabilities in the dense cores of exploding single wires observed in experiment are discussed. A series of shots was performed with 25-μπι and 50-μπι diameter copper, nickel, and tungsten wires electrically exploded in air by using high-power current pulses of up to 8 kA short-circuit peak and about 400 ns rise time. The velocity of propagation of the shock wave front and the velocity of expansion of the core were estimated by processing laser shadowgraphs taken at a probe radiation wavelength of 532 nm with an exposure time of 70 ps. It has been found that the core either breaks up or becomes narrow depending on the nature of the initial defect of the wire. Breaks appeared at the sites where the wire initially had defects related to the irregularity of the crystal structure (bends, residual tensile strains, etc.) responsible for an increase in deposited energy in the respective regions. The difference between the energy deposited in the wire material at the site of a break and the specific energy averaged over the wire length was estimated. It has also been revealed that contaminants present on the wire surface can reduce the energy deposited in the wire at the resistive stage, resulting in a narrowing of the core around the contaminated region.