Spectroscopic measurements in stagnating z-pinch plasmas are a powerful tool for investigating the complex physical processes taking place in high energy-density plasmas. In the present work, we measure the radial distribution of spectral line shapes emitted from a stagnating plasma to investigate both the current distribution and the plasma properties, through the determination of the contributions of both the Zeeman Effect and the Stark broadening to the shapes. In the experiment, we use an O₂ cylindrical plasma imploding from an initial radius of 22 mm to a stagnated column of ~3 mm radius and 18 mm length. To this end, a current pulse of ~500kA is driven into the plasma over ~500 ns. In the analysis, the line shapes are analyzed in detail, chord by chord, to obtain their distributions. A striking result obtained from the shape of O III – O VI ions is that the total current in the stagnated plasma is low, i.e., most of the current flows in the imploding compressing plasma. Another result is that accounting for all contributions to the line shape, including the Doppler broadening due to the ion thermal motion, indicates the existence of an additional source for the line broadening. A possible explanation is hydrodynamic turbulence in the plasma; in this case, our measurements provide a quantitative determination of the kinetic energy in the turbulence. Another possible explanation will also be discussed.

This work was supported in part by the Cornell Multi-University Center for High Energy-Density Science (USA), the Bi-National Israel-USA Science foundation, and the AFOSR (USA).