Controlled seeding of perturbations is employed to study the evolution of wire array z-pinch implosion instabilities which strongly impact x-ray production when the 3D plasma stagnates on axis. Wires modulated in radius exhibit locally enhanced magnetic field and imploding bubble formation at discontinuities in wire radius due to the perturbed current path. Wires coated with localized spectroscopic dopants are used to track turbulent material flow. Experiments and MHD modeling offer insight into the behavior of z-pinch instabilities.
Experiments to study the implosion dynamics and radiation characteristics of copper z-pinches have been fielded at the 1 MA Zebra facility and the 20 MA Z facility. The impact of initial load mass, initial load diameter, and nesting of wire arrays on the precursor and the stagnated plasma has been evaluated through spectroscopy, shadowgraphy, and fluence measurements. Plasma parameters extracted from modeling of the time-integrated L-shell spectra indicate the presence of more than one plasma source contributing to the radiation, likely due to non-uniform hot spot x-ray emission or temporal gradients.
Three-dimensional hybrid simulation of a plasma current-carrying column reveal two different regimes of sausage and kink instability development. In the first regime, with small Hall parameter, development of instabilities leads to the appearance of large-scale axial perturbations and eventually to bending of the plasma column. In the second regime, with a four-times-larger Hall parameter, small-scale perturbations dominate and no bending of the plasma column is observed. Simulation results are compared with laser probing experimental data obtained during wire array implosions on the Zebra pulse power generator at the Nevada Terawatt Facility.
The conclusions of this report are: (1) 1D and 2D RMHD simulations indicate feasibility of producing high thermonuclear neutron yields in deuterium and DT gas-puff Z-pinches -- (a) Z 1.7 x 10{sup 13} DD neutrons at 70 kV, 13 MA (Z1384); (b) (3 to 6) x 10{sup 14} at 90 kV, 17 MA (Z1422); (c) Predicted for ZR 2 x 10{sup 15} DD and 6 x 10{sup 16} DT neutrons; (2) Theory and modeling issues -- collisionless ions, nonthermal ions; (3) Experimental data on the origin of the neutrons not yet conclusive, need more shots; and (4) Applications -- (a) Fusion 2.5 and 14 MeV neutron source; (b) Pulsed subcritical neutron source with uranium blanket for {approx}10x neutron and {approx}1000x energy multiplication (Smirnov, Feoktistov and Klimov); and (c) Fusion-assisted keV x-ray plasma radiation source.