THE DYNAMICS OF BIFURCATING BRIGHT-SPOTS IN FIBER Z-PINCH PLASMAS

Results are presented from the diagnosis of the optical and x-ray emis sion from ''bright-spots'' in carbon fiber Z-pinch experiments using t he MAGPIE (Mega-Ampere Generator for Plasma Implosion Experiments) gen erator [I. H. Mitchell et al., Rev. Sci. Instrum. 67, 1533 (1996)]. In homogeneities evolve very rapidly within the plasma with bright-spots becoming detectable after 15-20 ns. After a short (similar to 4 ns) du ration formation phase, these bright-spots exhibit highly dynamic beha vior. Bifurcation of the bright-spots is observed giving rise to rapid axial motion at 1-3 x 10(5) ms(-1). The post-bifurcation bright-spots persist for up to 49 ns. Analysis of cross-filtered, time integrated, x-ray pinhole images yield bright-spot parameters during the formatio n phase (diameter similar to 80 mu m, temperature 250-300 eV, ion numb er densities similar to 2 x 10(26) m(-3)). With a Spatial resolution o f 175 mu m, the strong temperature and density gradients within the po st-bifurcation spots can be resolved in gated x-ray images with 2 ns e xposure times. After the dynamic phase of bright-spot evolution, the p inch enters a quiescent phase where the time scale for evolution is mu ch longer. (C) 1997 American Institute of Physics.