Henry M. Sze

Two-dimensional gas density and velocity distributions of a 12-cm-diameter, triple-nozzle argon Z-pinch load

We have developed a 12-cm-diameter Ar gas Z-pinch load, which produces two annular gas shells and a center gas jet. The two-dimensional (2-D) gas density profiles of the load, in r-/spl theta/ and r-z planes, were measured with submillimeter spatial resolutions using the planar-laser-induced fluorescence (PLIF) method, for conditions used in Z-pinch experiments. Due to interactions between the shells, the net gas density profile differs from the superposition of the individual shell profiles. Narrow density peaks are observed both at smaller and larger radii than the radius where the shells come in contact with each other. Two-dimensional flow velocity distributions are determined from the displacements between the fluorescence and later time phosphorescence images. The measured stream velocities of argon gas puffs are 650 /spl plusmn/ 20 m/s, higher than the ideal gas velocity due to the formation of clusters in the supersonic gas flow. Indeed, clusters were observed in earlier Rayleigh scattering experiments. The gas measurements of the initial phase using the PLIF will be combined with other density measurements of the implosion and pinch phases to better understand the implosion dynamics and to provide initial conditions for simulation codes.

K-shell radiation from nickel wire arrays at 18 MA

A series of nickel z pinch experiments was conducted at 18 MA current on the Z accelerator producing up to 13 kJ of K-shell radiation at 7.8 keV and above. Double-shell wire arrays were used, with the diameter of the outer array of the nested structure varied from 55 to 70 mm. By using Cr and Mn dopants in conjunction with a streak spectrograph, the interaction of the outer and inner array could be investigated. The radiation from the outer array E array started slightly after the inner array and lasted longer, producing comparable energy per atom at lower power. This indicates that the arrays were well mixed for most of the radiation pulse, in contrast to the observed behavior of a double-shell gas puff.

Mixed gas Z pinch experiments using a shell-on-shell nozzle on Double-EAGLE

A series of Z pinch experiments using argon and krypton was conducted on the Double-EAGLE pulse power driver at 3.5 to 4.0 MA peak current and 170-190 ns implosion time. A shell-on-shell nozzle provided the opportunity to separate the two gases and to control which was driven more strongly (by virtue of being in the inner plenum). With argon in the inner plenum, 12 to 16/spl plusmn/3 kJ krypton L-shell and 8 to 10/spl plusmn/3 kJ of argon K-shell radiation was produced. With krypton in the inner plenum, 23.6 /spl plusmn/2.5 kJ of krypton L-shell and 2.5/spl plusmn/2.3 kJ of argon K-shell radiation were produced. Since the optimum implosion times for the two gases were different, changing the mass of the z pinch varied the ratio of the yields. Using a streak spectrograph and PCDs with a Ross filter pair, the time history of the krypton and the argon radiation could be distinguished and seen to be simultaneous. Spectroscopic measurements of a chlorine dopant in the inner shell gas demonstrated that the implosions with krypton achieved lower density and electron temperature than with argon whether the krypton was in the inner or outer plenum.

Proof-of-principle laser-induced fluorescence measurements of gas distributions from supersonic nozzles

Summary form only given, as follows. We have applied the technique of acetone laser-induced fluorescence (LIF) to the measurement of gas distributions from axisymmetric, supersonic nozzles used to produce loads for z-pinch plasma radiation sources. Typical peak particle densities are /spl sim/1% of an atmosphere at standard temperature. A pulsed laser is used to obtain a snapshot along a chord through the center of the gas density distribution at 4.3 and 20.0 mm from the exit of the nozzle. We find good agreement between LIF and laser interferometer measurements. Strengths of the LIF approach include simplicity of implementation and high radial spatial resolution.

Interferometric measurement of physical phenomena during the implosion phase of a puff-on-puff Z-pinch load on Double-EAGLE

Theoretical studies have predicted that the disruptive role of the Rayleigh-Taylor (R-T) instability on the current conduction and implosion characteristics of annular Z-pinch loads will be mitigated by mass accretion if uniform fill or multiple annular shell loads are used. Holographic interferometry was used to study these physical processes during the implosion phase of puff-on-puff loads on a terawatt accelerator. Both axial (r-z) density perturbation and azimuthal (r-/spl theta/) filamentation modes of the R-T instability were observed. Significant ionization (Z/spl ap/3-10) of the inner gas puff atoms was observed below the anode grid before the outer puff had imploded to this radial position. Radiation hydrodynamic calculations indicate that photoionization by radiation from the outer current carrying shell could not account for this ionization. Current flowing on the inner gas puff could be the source of this ionization. The effect of these physical processes on the radiation yield from z-pinches warrants further investigation.