Seeding the Electrothermal Instability through a Three-Dimensional, Nonlinear Perturbation.

Electrothermal instability plays an important role in applications of current-driven metal, creating striations (which seed the magneto-Rayleigh-Taylor instability) and filaments (which provide a more rapid path to plasma formation). However, the initial formation of both structures is not well understood. Simulations show for the first time how a commonly occurring isolated defect transforms into the larger striation and filament, through a feedback loop connecting current and electrical conductivity. Simulations have been experimentally validated using defect-driven self-emission patterns.

Harmonic Generation and Inverse Cascade in the z-Pinch Driven, Preseeded Multimode, Magneto-Rayleigh-Taylor Instability.

The magneto-Rayleigh-Taylor instability (MRTI) plays an essential role in astrophysical systems and in magneto-inertial fusion, where it is known to be an important degradation mechanism of confinement and target performance. In this Letter, we show for the first time experimental evidence of mode mixing and the onset of an inverse-cascade process resulting from the nonlinear coupling of two discrete preseeded axial modes (400- and 550-µm wavelengths) on an Al liner that is magnetically imploded using the 20-MA, 100-ns rise-time Z Machine at Sandia National Laboratories. Four radiographs captured the temporal evolution of the MRTI. We introduce a novel unfold technique to analyze the experimental radiographs and compare the results to simulations and to a weakly nonlinear model. We find good quantitative agreement with simulations using the radiation magnetohydrodynamics code hydra. Spectral analysis of the MRTI time evolution obtained from the simulations shows evidence of harmonic generation, mode coupling, and the onset of an inverse-cascade process. The experiments provide a benchmark for future work on the MRTI and motivate the development of new analytical theories to better understand this instability.

Performance Scaling in Magnetized Liner Inertial Fusion Experiments.

We present experimental results from the first systematic study of performance scaling with drive parameters for a magnetoinertial fusion concept. In magnetized liner inertial fusion experiments, the burn-averaged ion temperature doubles to 3.1 keV and the primary deuterium-deuterium neutron yield increases by more than an order of magnitude to 1.1×10^{13} (2 kJ deuterium-tritium equivalent) through a simultaneous increase in the applied magnetic field (from 10.4 to 15.9 T), laser preheat energy (from 0.46 to 1.2 kJ), and current coupling (from 16 to 20 MA). Individual parametric scans of the initial magnetic field and laser preheat energy show the expected trends, demonstrating the importance of magnetic insulation and the impact of the Nernst effect for this concept. A drive-current scan shows that present experiments operate close to the point where implosion stability is a limiting factor in performance, demonstrating the need to raise fuel pressure as drive current is increased. Simulations that capture these experimental trends indicate that another order of magnitude increase in yield on the Z facility is possible with additional increases of input parameters.

Experimental Demonstration of the Stabilizing Effect of Dielectric Coatings on Magnetically Accelerated Imploding Metallic Liners.

Enhanced implosion stability has been experimentally demonstrated for magnetically accelerated liners that are coated with 70 µm of dielectric. The dielectric tamps liner-mass redistribution from electrothermal instabilities and also buffers coupling of the drive magnetic field to the magneto-Rayleigh-Taylor instability. A dielectric-coated and axially premagnetized beryllium liner was radiographed at a convergence ratio [CR=Rin,0/Rin(z,t)] of 20, which is the highest CR ever directly observed for a strengthless magnetically driven liner. The inner-wall radius Rin(z,t) displayed unprecedented uniformity, varying from 95 to 130 µm over the 4.0 mm axial height captured by the radiograph.

Experimental demonstration of fusion-relevant conditions in magnetized liner inertial fusion.

This Letter presents results from the first fully integrated experiments testing the magnetized liner inertial fusion concept [S. A. Slutz et al., Phys. Plasmas 17, 056303 (2010)], in which a cylinder of deuterium gas with a preimposed 10 Taxial magnetic field is heated by Z beamlet, a 2.5 kJ, 1 TW laser, and magnetically imploded by a 19 MA, 100 ns rise time current on the Z facility. Despite a predicted peak implosion velocity of only 70 km = s, the fuel reaches a stagnation temperature of approximately 3 keV, with T(e) ≈ T(i), and produces up to 2 x 10(12) thermonuclear deuterium-deuterium neutrons. X-ray emission indicates a hot fuel region with full width at half maximum ranging from 60 to 120 µm over a 6 mm height and lasting approximately 2 ns. Greater than 10(10) secondary deuterium-tritium neutrons were observed, indicating significant fuel magnetization given that the estimated radial areal density of the plasma is only 2 mg = cm(2).

Understanding fuel magnetization and mix using secondary nuclear reactions in magneto-inertial fusion.

Magnetizing the fuel in inertial confinement fusion relaxes ignition requirements by reducing thermal conductivity and changing the physics of burn product confinement. Diagnosing the level of fuel magnetization during burn is critical to understanding target performance in magneto-inertial fusion (MIF) implosions. In pure deuterium fusion plasma, 1.01 MeV tritons are emitted during deuterium-deuterium fusion and can undergo secondary deuterium-tritium reactions before exiting the fuel. Increasing the fuel magnetization elongates the path lengths through the fuel of some of the tritons, enhancing their probability of reaction. Based on this feature, a method to diagnose fuel magnetization using the ratio of overall deuterium-tritium to deuterium-deuterium neutron yields is developed. Analysis of anisotropies in the secondary neutron energy spectra further constrain the measurement. Secondary reactions also are shown to provide an upper bound for the volumetric fuel-pusher mix in MIF. The analysis is applied to recent MIF experiments [M. R. Gomez et al., Phys. Rev. Lett. 113, 155003 (2014)] on the Z Pulsed Power Facility, indicating that significant magnetic confinement of charged burn products was achieved and suggesting a relatively low-mix environment. Both of these are essential features of future ignition-scale MIF designs.

Three-dimensional feedback processes in current-driven metal.

Using three-dimensional (3D) magnetohydrodynamic simulations, we study how a pit on a metal surface evolves when driven by intense electrical current density j. Redistribution of j around the pit initiates a feedback loop: j both reacts to and alters the electrical conductivity σ, through Joule heating and hydrodynamic expansion, so that j and σ are constantly in flux. Thus, the pit transforms into larger striation and filament structures predicted by the electrothermal instability theory. Both structures are important in applications of current-driven metal: The striation constitutes a density perturbation that can seed the magneto-Rayleigh-Taylor instability, while the filament provides a more rapid path to plasma formation, through 3D j redistribution. Simulations predict distinctive self-emission patterns, thus allowing for experimental observation and comparison.

Demonstration of improved laser preheat with a cryogenically cooled magnetized liner inertial fusion platform.

We report on progress implementing and testing cryogenically cooled platforms for Magnetized Liner Inertial Fusion (MagLIF) experiments. Two cryogenically cooled experimental platforms were developed: an integrated platform fielded on the Z pulsed power generator that combines magnetization, laser preheat, and pulsed-power-driven fuel compression and a laser-only platform in a separate chamber that enables measurements of the laser preheat energy using shadowgraphy measurements. The laser-only experiments suggest that ∼89% ± 10% of the incident energy is coupled to the fuel in cooled targets across the energy range tested, significantly higher than previous warm experiments that achieved at most 67% coupling and in line with simulation predictions. The laser preheat configuration was applied to a cryogenically cooled integrated experiment that used a novel cryostat configuration that cooled the MagLIF liner from both ends. The integrated experiment, z3576, coupled 2.32 ± 0.25 kJ preheat energy to the fuel, the highest to-date, demonstrated excellent temperature control and nominal current delivery, and produced one of the highest pressure stagnations as determined by a Bayesian analysis of the data.

Penetrating radiography of imploding and stagnating beryllium liners on the Z accelerator.

The implosions of initially solid beryllium liners (tubes) have been imaged with penetrating radiography through to stagnation. These novel radiographic data reveal a high degree of azimuthal correlation in the evolving magneto-Rayleigh-Taylor structure at times just prior to (and during) stagnation, providing stringent constraints on the simulation tools used by the broader high energy density physics and inertial confinement fusion communities. To emphasize this point, comparisons to 2D and 3D radiation magnetohydrodynamics simulations are also presented. Both agreement and substantial disagreement have been found, depending on how the liner's initial outer surface finish was modeled. The various models tested, and the physical implications of these models are discussed. These comparisons exemplify the importance of the experimental data obtained.

Measurements of magneto-Rayleigh-Taylor instability growth during the implosion of initially solid Al tubes driven by the 20-MA, 100-ns Z facility.

The first controlled experiments measuring the growth of the magneto-Rayleigh-Taylor instability in fast (∼100 ns) Z-pinch plasmas are reported. Sinusoidal perturbations on the surface of an initially solid Al tube (liner) with wavelengths of 25-400 µm were used to seed the instability. Radiographs with 15 µm resolution captured the evolution of the outer liner surface. Comparisons with numerical radiation magnetohydrodynamic simulations show remarkably good agreement down to 50 µm wavelengths.

Temperature distributions and gradients in laser-heated plasmas relevant to magnetized liner inertial fusion.

We present two-dimensional temperature measurements of magnetized and unmagnetized plasma experiments performed at Z relevant to the preheat stage in magnetized liner inertial fusion. The deuterium gas fill was doped with a trace amount of argon for spectroscopy purposes, and time-integrated spatially resolved spectra and narrow-band images were collected in both experiments. The spectrum and image data were included in two separate multiobjective analysis methods to extract the electron temperature spatial distribution T_{e}(r,z). The results indicate that the magnetic field increases T_{e}, the axial extent of the laser heating, and the magnitude of the radial temperature gradients. Comparisons with simulations reveal that the simulations overpredict the extent of the laser heating and underpredict the temperature. Temperature gradient scale lengths extracted from the measurements also permit an assessment of the importance of nonlocal heat transport.

Origin of bilaterian body plans: evolution of developmental regulatory mechanisms.

An argument is proposed to explain the origin of large metazoans, based on the regulatory processes that underlie the morphogenetic organization of pattern in modern animals. Genetic regulatory systems similar to those used in modern, indirectly developing marine invertebrates are considered to indicate the Precambrian regulatory platform on which were erected innovations that underlie the development of macroscopic body plans. Those systems are genetic regulatory programs that produce groups of unspecified "set-aside cells" and hierarchical regulatory programs that initially define regions of morphogenetic space in terms of domains of transcription factor expression. These ideas affect interpretation of the development of arthropods and chordates as well as interpretation of the role of the genes of the homeotic complex in embryogenesis.

Laser propagation measurements in long-scale-length underdense plasmas relevant to magnetized liner inertial fusion.

We report experimental results and simulations showing efficient laser energy coupling into plasmas at conditions relevant to the magnetized liner inertial fusion (MagLIF) concept. In MagLIF, to limit convergence and increase the hydrodynamic stability of the implosion, the fuel must be efficiently preheated. To determine the efficiency and physics of preheating by a laser, an Ar plasma with n_{e}/n_{crit}∼0.04 is irradiated by a multi-ns, multi-kJ, 0.35-µm, phase-plate-smoothed laser at spot-averaged intensities ranging from 1.0×10^{14} to 2.5×10^{14}W/cm^{2} and pulse widths from 2 to 10 ns. Time-resolved x-ray images of the laser-heated plasma are compared to two-dimensional radiation-hydrodynamic simulations that show agreement with the propagating emission front, a comparison that constrains laser energy deposition to the plasma. The experiments show that long-pulse, modest-intensity (I=1.5×10^{14}W/cm^{2}) beams can efficiently couple energy (∼82% of the incident energy) to MagLIF-relevant long-length (9.5 mm) underdense plasmas. The demonstrated heating efficiency is significantly higher than is thought to have been achieved in early integrated MagLIF experiments [A. B. Sefkow et al., Phys. Plasmas 21, 072711 (2014)10.1063/1.4890298].

Spatial expression of a forkhead homologue in the sea urchin embryo.

Echinoderms are the sister group of the chordates and hemichordates within the deuterostomes. They lack a notochord or any structures obviously homologous with it. To gain insight into developmental mechanisms important in the origin and early evolution of chordates, we investigated sea urchin homologues of chordate genes that are implicated in notochord formation, viz. Brachyury and HNF-3 beta. Here we report the pattern of expression of a sea urchin orthologue of forkhead, Hphnf3 which is present as a single copy per haploid genome. An Hphnf3 transcript of 3.0 kb was first detected at the swimming blastula stage, accumulated maximally at the gastrula and prism-embryo stages, and decreased at the pluteus-larva stage. In situ hybridization signals were found in cells of the vegetal plate of the swimming blastula. During gastrulation, intense staining was evident in the cells surrounding the blastopore, whereas weak staining was detected in the invaginating archenteron. At the prism-embryo stage, the entire archenteron stained intensely; then, at pluteus stage, the larva staining decreased in intensity. The forkhead and Brachyury genes begin to be expressed almost simultaneously in sea urchin embryos, in the vegetal plate at the late blastula stage. After the onset of gastrulation, however, Hphnf3 is expressed in the posterior part of the archenteron, whereas the Brachyury orthologue, HpTa, is expressed in the secondary mesenchyme founder cells, which occupy the anterior tip of archenteron. Hphnf3 may contribute to specification of embryonic cells as archenteron, and the role of HpTa may be directed towards specification of mesodermal founder cells. Except for the basal character of expression in endoderm and endomesoderm, these transcription factors are clearly utilized differently in chordates.

Depression and anxiety in cancer patients: evidence for different causes.

Fifty-seven cancer patients currently receiving treatment were classified into three groups: (1) those who stated they were depressed/anxious for reasons other than cancer at any time in the past, including the interview day, (2) those who stated they were depressed/anxious solely related to cancer during the past or currently, (3) those who stated they were not depressed/anxious at anytime either in the past or currently, or had only 'normal' symptoms. Patients who were depressed for reasons other than cancer scored higher on self-rated anxiety, depression, and somatization. Patients who were depressed solely due to cancer were not significantly different from those with 'normal' symptoms. The findings suggest the importance of adequate differential diagnosis. The use of anti-depressant treatment with a subset of depressed cancer patients is also suggested.

Bovine anaplasmosis transmission studies conducted under controlled natural exposure in a Dermacentor andersoni = (venustus) indigenous area of eastern Oregon.

In Anaplasma marginale transmission studies conducted on the high semi-arid range of eastern Oregon during the 1974 and 1975 vector season, A marginale-susceptible calves (principals) were maintained on 2 raised tick-proof platforms. Anaplasmosis-susceptible control calves of approximately the same age and latent-infected cows grazed the area surrounding the platforms. One latent-infected steer spent the entire 1975 vector season on a platform with the principals. The 28 principals did not develop anaplasmosis, whereas 15 of 30 (50%) controls became infected. The disease was not transmitted from the latent-infected cattle to the principals exposed only to flying hematophagous insects, whereas 50% of the controls exposed to the Rocky Mountain wood tick Dermacentor andersoni) = (venustus) developed the disease. Dermacentor andersoni appears to be the principal vector on this range.

Absence of Anaplasma marginale infection in American Bison raised in an anaplasmosis endemic area.

Blood was collected at slaughter from 132 adult American bison (Bison bison) raised in an anaplasmosis endemic area where the vector Dermacentor andersoni (equals venustus) is indigenous. Hematologic studies revealed no indication of clinical anaplasmosis. Card agglutination and complement-fixation tests on all bison serums were negative. Eleven anaplasmosis-susceptible calves each inoculated with 204 ml of blood pooled from 12 bison did not develop anaplasmosis. Results of this study indicate American bison have resistance to natural A. marginale infection.

Magnetic field measurements via visible spectroscopy on the Z machine.

Sandia's Z Machine uses its high current to magnetically implode targets relevant to inertial confinement fusion. Since target performance is highly dependent on the applied drive field, measuring magnetic field at the target is essential for accurate simulations. Recently, the magnetic field at the target was measured through splitting of the sodium 3s-3p doublet at 5890 and 5896 Å. Spectroscopic dopants were applied to the exterior of the target, and spectral lines were observed in absorption. Magnetic fields in excess of 200 T were measured, corresponding to drive currents of approximately 5 MA early in the pulse.

Rangeomorphs, Thectardis (Porifera?) and dissolved organic carbon in the Ediacaran oceans.

The mid-Ediacaran Mistaken Point biota of Newfoundland represents the first morphologically complex organisms in the fossil record. At the classic Mistaken Point localities the biota is dominated by the enigmatic group of "fractally" branching organisms called rangeomorphs. One of the few exceptions to the rangeomorph body plan is the fossil Thectardis avalonensis, which has been reconstructed as an upright, open cone with its apex in the sediment. No biological affinity has been suggested for this fossil, but here we show that its body plan is consistent with the hydrodynamics of the sponge water-canal system. Further, given the habitat of Thectardis beneath the photic zone, and the apparent absence of an archenteron, movement, or a fractally designed body plan, we suggest that it is a sponge. The recognition of sponges in the Mistaken Point biota provides some of the earliest body fossil evidence for this group, which must have ranged through the Ediacaran based on biomarkers, molecular clocks, and their position on the metazoan tree of life, in spite of their sparse macroscopic fossil record. Should our interpretation be correct, it would imply that the paleoecology of the Mistaken Point biota was dominated by sponges and rangeomorphs, organisms that are either known or hypothesized to feed in large part on dissolved organic carbon (DOC). The biology of these two clades gives insight into the structure of the Ediacaran ocean, and indicates that a non-uniformitarian mechanism delivered labile DOC to the Mistaken Point seafloor.

Where's the glass? Biomarkers, molecular clocks, and microRNAs suggest a 200-Myr missing Precambrian fossil record of siliceous sponge spicules.

The earliest evidence for animal life comes from the fossil record of 24-isopropylcholestane, a sterane found in Cryogenian deposits, and whose precursors are found in modern demosponges, but not choanoflagellates, calcareans, hexactinellids, or eumetazoans. However, many modern demosponges are also characterized by the presence of siliceous spicules, and there are no convincing demosponge spicules in strata older than the Cambrian. This temporal disparity highlights a problem with our understanding of the Precambrian fossil record--either these supposed demosponge-specific biomarkers were derived from the sterols of some other organism and are simply retained in modern demosponges, or spicules do not primitively characterize crown-group demosponges. Resolving this issue requires resolving the phylogenetic placement of another group of sponges, the hexactinellids, which not only make a spicule thought to be homologous to the spicules of demosponges, but also make their first appearance near the Precambrian/Cambrian boundary. Using two independent analytical approaches and data sets--traditional molecular phylogenetic analyses and the presence or absence of specific microRNA genes--we show that demosponges are monophyletic, and that hexactinellids are their sister group (together forming the Silicea). Thus, spicules must have evolved before the last common ancestor of all living siliceans, suggesting the presence of a significant gap in the silicean spicule fossil record. Molecular divergence estimates date the origin of this last common ancestor well within the Cryogenian, consistent with the biomarker record, and strongly suggests that siliceous spicules were present during the Precambrian but were not preserved.