Radiative and Electrical Properties of Exploding Silver Wires

Abstract

The radiative properties of silver wires exploded by capacitive discharge are studied using time-integrated and time-resolved spectroscopy. Discharge current measurements are obtained from a calibrated current shunt and are correlated with time-resolved spectra to obtain a model for the current conduction processes during wire explosions. Two basic explosion mechanisms are described, both of which begin with the conversion of the wire from a conducting solid to a rapidly expanding dielectric cylinder of metal vapor. This results in a rapid reduction of discharge current. Current then may resume in one of two ways. In He at atmospheric and reduced pressure and in air at reduced pressure dielectric breakdown of the gas surrounding the wire occurs with current conduction peripheral to the expanding metal vapor cylinder. In air at atmospheric pressure, dielectric breakdown occurs through the metal vapor. This results in current conduction along the vapor cylinder axis. The advantages of peripheral current conduction for the analysis of metals electroplated on the surface of silver wires are discussed. Parametric studies with Cd-plated silver wires indicate that the intensity of the background continuum can be reduced by nearly 2 orders of magnitude with little effect on Cd line intensities by reducing the pressure from 730 Torr to 50 Torr in He where peripheral current conduction occurs.