Non-contact optical three dimensional liner metrology
We optically captured the "as-built" liner geometry of NTLX (near term liner experiments) for Shiva Star using ultra-precision ranging lasers. We subsequently verified the resulting digitized geometry against the 3D CAD model of the part. The results confirmed that the Liner contours are within designed tolerances but revealed subtle fabrication artifacts that would typically go undetected. These features included centimeters long waviness and saddle and bulge regions of 1 micron or less in magnitude. The laser technology typically provided 10 micron spatial resolution with /spl plusmn/12 nanometer ranging precision. Atlas liners in the future may have to be diamond turned and will have the centimeter wavelength and 100 angstrom amplitude requirements. The advantages of using laser technology are (1) it avoids surface damage that may occur with conventional contact probes and (2) dramatically improves spatial resolution over CMM, capacitance and inductance type probes. Our work is the result of a perceived future need to develop precision, non-contact, liner inspection techniques to verify geometry, characterize machining artifacts and map wall thickness on delicate diamond turned surfaces. Capturing "as-built" geometry in a non-contact way coupled with part-to-CAD verification software tools creates a new metrology competency for MST-7.
Rayleigh-Taylor instability growth enigma: liner studies on Pegasus
The goal of the RTMIX series on Pegasus is to study Rayleigh-Taylor instability growth and mixing in a convergent geometry, at a metal-foam interface, as a function of material strength and initial perturbation amplitude. Results of three experiments are presented. The first experiment, reported in the previous Pulsed Power Conference, involved a solid Z-pinch liner driven by a Pegasus current of /spl sim/5.5 MA onto a high-density foam target. The inside diameter of the liner was smooth for the first experiment. No instability growth or mixing was observed at the resolution limit of the diagnostics, as expected. In the second experiment, azimuthally symmetric sine-wave perturbations were machined onto the inner diameter with a wavelength of 1.0 mm and amplitudes of 12.5 /spl mu/m and 50 /spl mu/m. Growth of the large amplitude perturbations was predicted, but growth of the small amplitude perturbations was expected to be inhibited by the material strength of the Cu. Neither amplitude perturbation grew. The third experiment was a repeat of the second with a low-strength Sn/In alloy (in place of the Cu) that should have melted early in the implosion. The Sn/In layer was mass-matched to the Cu layer that it replaced. Since the Sn/In layer was expected to be liquid during the unstable deceleration phase, no material strength stabilization should have occurred, and both amplitude perturbations should have shown dramatic growth. Preliminary inspection of radiographs from this experiment indicates no Rayleigh-Taylor instability growth.
One-and-Two-Dimensional Simulations of Liner Performance at Atlas Parameters
The authors report results of one-and-two-dimensional MHD simulations of an imploding heavy liner in Z-pinch geometry. The driving current has a pulse shape and peak current characteristic of the Atlas pulsed-power facility being constructed at Los Alamos National Laboratory. One-dimensional simulations of heavy composite liners driven by 30 MA currents can achieve velocities on the order of 14 km/sec. Used to impact a tungsten target, the liner produces shock pressures of approximately fourteen megabars. The first 2-D simulations of imploding liners driven at Atlas current parameters are also described. These simulations have focused on the interaction of the liner with the glide planes, and the effect of realistic surface perturbations on the dynamics of the pinch. It is found that the former interaction does not seriously affect the inner liner surface. Results from the second problem indicate that a surface perturbation having amplitude as small as 0.2 {micro}m can have a significant effect on the implosion dynamics.