Time resolved visible spectroscopy characterizations of single wire aluminum plasmas

Abstract

The conditions within plasmas generated by current-driven explosions of single 15–50µm aluminum (Al) wires are being investigated using time-resolved emission spectroscopy at visible wavelengths. The experiments are being carried out at Cornell University on the 10kA, 500ns rise time Low Current Pulser 3 (LCP3). The plasma parameters being determined as a function of time and radial position include electron temperature and density, ionization state and magnetic field. To determine the magnetic field, a new diagnostic method is being developed which makes use of Zeeman-effect-produced differences in the line shapes of two fine structure components of a multiplet that are equally broadened by both Stark effect and Doppler broadening. This method has been demonstrated at the Weizmann Institute of Science (WSI) in laser-produced plasmas [1] with lower energy densities than are being studied here. As in the work at WSI, we use the Al III [4s–4p] transitions at 5696Å and 5722Å to determine the magnitude of the magnetic field. In the experimental plasmas generated by LCP3, electron number densities are in the range 1017–1018cm−3 while electron temperatures are between 2 and 5eV. Under these conditions, seen close to peak current 300 µm away from the wire, the line broadening due to a magnetic field of 6.5 T is calculated to be 3.0 Å while the Stark broadening at 1018/cm3 is calculated to be 3.5 Å; the Doppler broadening is negligible. The total FWHM difference of the doublet lines resulting from these mechanisms is estimated to be 10%. We are setting up a new spectroscopic system capable of clearly detecting this difference after carrying out preliminary experiments on a lower resolution system. Initial high-resolution data will be presented.