Characteristics and scaling of tungsten-wire-array z -pinch implosion dynamics at 20 MA.

We present observations for 20-MA wire-array z pinches of an extended wire ablation period of 57%+/-3% of the stagnation time of the array and non-thin-shell implosion trajectories. These experiments were performed with 20-mm-diam wire arrays used for the double- z -pinch inertial confinement fusion experiments [M. E. Cuneo, Phys. Rev. Lett. 88, 215004 (2002)] on the Z accelerator [R. B. Spielman, Phys. Plasmas 5, 2105 (1998)]. This array has the smallest wire-wire gaps typically used at 20 MA (209 microm ). The extended ablation period for this array indicates that two-dimensional (r-z) thin-shell implosion models that implicitly assume wire ablation and wire-to-wire merger into a shell on a rapid time scale compared to wire acceleration are fundamentally incorrect or incomplete for high-wire-number, massive (>2 mg/cm) , single, tungsten wire arrays. In contrast to earlier work where the wire array accelerated from its initial position at approximately 80% of the stagnation time, our results show that very late acceleration is not a universal aspect of wire array implosions. We also varied the ablation period between 46%+/-2% and 71%+/-3% of the stagnation time, for the first time, by scaling the array diameter between 40 mm (at a wire-wire gap of 524 mum ) and 12 mm (at a wire-wire gap of 209 microm ), at a constant stagnation time of 100+/-6 ns . The deviation of the wire-array trajectory from that of a thin shell scales inversely with the ablation rate per unit mass: f(m) proportional[dm(ablate)/dt]/m(array). The convergence ratio of the effective position of the current at peak x-ray power is approximately 3.6+/-0.6:1 , much less than the > or = 10:1 typically inferred from x-ray pinhole camera measurements of the brightest emitting regions on axis, at peak x-ray power. The trailing mass at the array edge early in the implosion appears to produce wings on the pinch mass profile at stagnation that reduces the rate of compression of the pinch. The observation of precursor pinch formation, trailing mass, and trailing current indicates that all the mass and current do not assemble simultaneously on axis. Precursor and trailing implosions appear to impact the efficiency of the conversion of current (driver energy) to x rays. An instability with the character of an m = 0 sausage grows rapidly on axis at stagnation, during the rise time of pinch power. Just after peak power, a mild m = 1 kink instability of the pinch occurs which is correlated with the higher compression ratio of the pinch after peak power and the decrease of the power pulse. Understanding these three-dimensional, discrete-wire implosion characteristics is critical in order to efficiently scale wire arrays to higher currents and powers for fusion applications.

Effect of platelet-derived growth factor on tibial osteotomies in rabbits.

The effect of exogenous platelet-derived growth factor (PDGF) BB on bone healing was tested in a pilot study using a unilateral tibial osteotomy in rabbits. Each osteotomy was injected with collagen or collagen containing 80 micrograms of PDGF. At 28 days, both tibiae from each rabbit were harvested and subjected to three-point bending to failure. The effect upon bone healing was tested by comparing the healing rates of PDGF-treated and -nontreated osteotomies with their respective normal contralateral bones. Three animals died before 28 days. The remaining 6 experimental and 5 control animals were available for assessment. Radiographically, at 2 weeks and 4 weeks, there was a clear increase in callus density and volume around the PDGF-treated osteotomies compared with the control rabbits' osteotomies. Osteotomies treated with PDGF were not statistically different in strength from their nonoperated contralateral bones. In the control group, however, the osteotomies were statistically weaker than their nonoperated (contralateral) bones. Microscopically, it was generally observed that PDGF-treated tibiae displayed a more florid and advanced state of osteogenic differentiation, both endosteally and periosteally, than the control osteotomies. Radiographic, mechanical, and histopathological data suggest that exogenous PDGF has a stimulatory effect on fracture healing.

X-ray absorption spectroscopy measurements of thin foil heating by Z-pinch radiation.

Absorption spectroscopy measurements of the time-dependent heating of thin foils exposed to intense z-pinch radiation sources are presented. These measurements and their analysis provide valuable benchmarks for, and insights into, the radiative heating of matter by x-ray sources. Z-pinch radiation sources with peak powers of up to 160 TW radiatively heated thin plastic-tamped aluminum foils to temperatures approximately 60 eV. The foils were located in open slots at the boundary of z-pinch hohlraums surrounding the pinch. Time-resolved Kalpha satellite absorption spectroscopy was used to measure the evolution of the Al ionization distribution, using a geometry in which the pinch served as the backlighter. The time-dependent pinch radius and x-ray power were monitored using framing camera, x-ray diode array, and bolometer measurements. A three-dimensional view factor code, within which one-dimensional (1D) radiation-hydrodynamics calculations were performed for each surface element in the view factor grid, was used to compute the incident and reemitted radiation flux distribution throughout the hohlraum and across the foil surface. Simulated absorption spectra were then generated by postprocessing radiation-hydrodynamics results for the foil heating using a 1D collisional-radiative code. Our simulated results were found to be in good general agreement with experimental x-ray spectra, indicating that the spectral measurements are consistent with independent measurements of the pinch power. We also discuss the sensitivity of our results to the spectrum of the radiation field incident on the foil, and the role of nonlocal thermodynamic equilibrium atomic kinetics in affecting the spectra.

Design of dynamic Hohlraum opacity samples to increase measured sample density on Z.

We are attempting to measure the transmission of iron on Z at plasma temperatures and densities relevant to the solar radiation and convection zone boundary. The opacity data published by us to date has been taken at an electron density about a factor of 10 below the 9×10(22)/cm(3) electron density of this boundary. We present results of two-dimensional (2D) simulations of the heating and expansion of an opacity sample driven by the dynamic Hohlraum radiation source on Z. The aim of the simulations is to design foil samples that provide opacity data at increased density. The inputs or source terms for the simulations are spatially and temporally varying radiation temperatures with a Lambertian angular distribution. These temperature profiles were inferred on Z with on-axis time-resolved pinhole cameras, x-ray diodes, and bolometers. A typical sample is 0.3 µm of magnesium and 0.078 µm of iron sandwiched between 10 µm layers of plastic. The 2D LASNEX simulations indicate that to increase the density of the sample one should increase the thickness of the plastic backing.

Diagnosis of x-ray heated Mg/Fe opacity research plasmas.

Understanding stellar interiors, inertial confinement fusion, and Z pinches depends on opacity models for mid-Z plasmas in the 100-300 eV temperature range. These models are complex and experimental validation is crucial. In this paper we describe the diagnosis of the first experiments to measure iron plasma opacity at a temperature high enough to produce the charge states and electron configurations that exist in the solar interior. The dynamic Hohlraum x-ray source at Sandia National Laboratories' Z facility was used to both heat and backlight Mg/Fe CH tamped foils. The backlighter equivalent brightness temperature was estimated to be T(r) approximately 314 eV+/-8% using time-resolved x-ray power and imaging diagnostics. This high brightness is significant because it overwhelms the sample self-emission. The sample transmission in the 7-15.5 A range was measured using two convex potassium acid phthalate crystal spectrometers that view the backlighter through the sample. The average spectral resolution over this range was estimated to be lambda/deltalambda approximately 700 by comparing theoretical crystal resolution calculations with measurements at 7.126, 8.340, and 12.254 A. The electron density was determined to be n(e)=6.9+/-1.7 x 10(21) cm(-3) using the Stark-broadened Mg Hebeta, Hegamma, and Hedelta lines. The temperature inferred from the H-like to He-like Mg line ratios was T(e)=156+/-6 eV. Comparisons with three different spectral synthesis models all have normalized chi(2) that is close to unity, indicating quantitative consistency in the inferred plasma conditions. This supports the reliability of the results and implies the experiments are suitable for testing iron opacity models.

Wire initiation critical for radiation symmetry in z-pinch-driven dynamic hohlraums.

Axial symmetry in x-ray radiation of wire-array z pinches is important for the creation of dynamic hohlraums used to compress inertial-confinement-fusion capsules. We present the first evidence that this symmetry is directly correlated with the magnitude of the negative radial electric field along the wire surface. This field (in turn) is inferred to control the initial energy deposition into the wire cores, as well as any current shorting to the return conductor.

Blunt needles in fascial closure.

Blunt needles have been developed that are easily used in fascial closures while limiting penetrating cutaneous injury to the surgeon and the operating staff. These needles offer the surgeon further protection from inadvertent exposure to blood borne pathogens.

In vivo evaluation of a collagenous membrane as an absorbable adhesion barrier.

An absorbable membrane made from purified, pepsin-soluble collagen was compared to Interceed, an absorbable cellulose-based product, and to a control group for effectiveness in inhibiting the formation of adhesions between peritoneal surface injuries in adult rats. An adhesion scoring system was used to evaluate and compare the performance of the test materials with the control group in regard to the extent, tenacity, and type of any adhesions evident at 28 days following surgery. The collagen group performed significantly better (p < 0.05) than either the Interceed or control groups, showing fewer, less extensive adhesions. The collagen membranes resulted in either no or weak adhesions between the body wall and caecum. Adhesions in the Interceed group were quite variable and characterized by a marked peritoneal reaction in the caecal and body walls adjacent to adhesions. Control samples were characterized by close, dense fibrotic adhesions between the caecum and body wall. Both of the test materials showed some deficiencies in respect to their physical and handling properties that could be further improved for this indication.

Mass-profile and instability-growth measurements for 300-wire Z-pinch implosions driven by 14-18 MA.

We present the first comprehensive study of high wire-number, wire-array Z-pinch dynamics at 14-18 MA using x-ray backlighting and optical shadowgraphy diagnostics. The cylindrical arrays retain slowly expanding, dense wire cores at the initial position up to 60% of the total implosion time. Azimuthally correlated instabilities at the array edge appear during this stage which continue to grow in amplitude and wavelength after the start of bulk motion, resulting in measurable trailing mass that does not arrive on axis before peak x-ray emission.

Hot dense capsule-implosion cores produced by Z-pinch dynamic Hohlraum radiation.

Hot dense capsule implosions driven by Z-pinch x rays have been measured using a approximately 220 eV dynamic Hohlraum to implode 1.7-2.1 mm diameter gas-filled CH capsules. The capsules absorbed up to approximately 20 kJ of x rays. Argon tracer atom spectra were used to measure the T(e) approximately 1 keV electron temperature and the n(e) approximately 1-4 x 10(23) cm(-3) electron density. Spectra from multiple directions provide core symmetry estimates. Computer simulations agree well with the peak emission values of T(e), n(e), and symmetry, indicating reasonable understanding of the Hohlraum and implosion physics.

X-ray imaging measurements of capsule implosions driven by a Z-pinch dynamic hohlraum.

The radiation and shock generated by impact of an annular tungsten Z-pinch plasma on a 10-mm diam 5-mg/cc CH(2) foam are diagnosed with x-ray imaging and power measurements. The radiative shock was virtually unaffected by Z-pinch plasma instabilities. The 5-ns-duration approximately 135-eV radiation field imploded a 2.1-mm-diam CH capsule. The measured radiation temperature, shock radius, and capsule radius agreed well with computer simulations, indicating understanding of the main features of a Z-pinch dynamic-hohlraum-driven capsule implosion.