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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Apparatus and process for the separation of gases using supersonic expansion and oblique wave compression

The disclosure provides an apparatus and method for gas separation through the supersonic expansion and subsequent deceleration of a gaseous stream. The gaseous constituent changes phase from the gaseous state by desublimation or condensation during the acceleration producing a collectible constituent, and an oblique shock diffuser decelerates the gaseous stream to a subsonic velocity while maintain the collectible constituent in the non-gaseous state. Following deceleration, the carrier gas and the collectible constituent at the subsonic velocity are separated by a separation means, such as a centrifugal, electrostatic, or impingement separator. In an embodiment, the gaseous stream issues from a combustion process and is comprised of N.sub.2 and CO.sub.2.

42 ENGINEERING↗
DOE OSTI2016

Stable Adaptive Inertial Control of a Doubly-Fed Induction Generator

This paper proposes a stable adaptive inertial control scheme of a doubly-fed induction generator. The proposed power reference is defined in two sections: the deceleration period and the acceleration period. The power reference in the deceleration period consists of a constant and the reference for maximum power point tracking (MPPT) operation. The latter contributes to preventing a second frequency dip (SFD) in this period because its reduction rate is large at the early stage of an event but quickly decreases with time. To improve the frequency nadir (FN), the constant value is set to be proportional to the rotor speed prior to an event. The reference ensures that the rotor speed converges to a stable operating region. To accelerate the rotor speed while causing a small SFD, when the rotor speed converges, the power reference is reduced by a small amount and maintained until it meets the MPPT reference. The results show that the scheme causes a small SFD while improving the FN and the rate of change of frequency in any wind conditions, even in a grid that has a high penetration of wind power.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2018

Evaporation of Cu, Sn, and S from Fe-C-Cu-Sn-S Liquid Alloys in the Temperature Range from 1513 K to 1873 K (1240 °C to 1600 °C)

Evaporation of Cu or Sn from liquid iron alloys containing C and S was experimentally investigated. The initial C concentration, [pct C] 0 , in the liquid alloy was varied from zero to C saturation, and the evaporation temperature was varied from 1513 K to 1773 K (1240 °C to 1500 °C). Along with the report by one of the present authors, the evaporation mechanism of Cu and Sn from liquid Fe-C-S alloy is proposed, after a modification from the previous mechanism. It was proposed that Cu and Sn evaporate as Cu(g) and Sn(g) and also evaporate as CuS(g) and SnS(g), which are more volatile species. Therefore, availability of S in the alloy affects the overall evaporation rate of Cu and Sn. At the same time, C in the alloy also forms volatile carbosulfides CS(g) and CS 2 (g), thereby competing with Cu and Sn. Moreover, C increases the activity coefficients of Cu, Sn, and S. This increases the thermodynamic driving force for the formation of CuS(g) and SnS(g). Therefore, increasing [pct C] partly accelerates the evaporation rate of Cu and Sn by increasing the activity coefficient but partly decelerates the evaporation rate by lowering the available S content. S partly accelerates the evaporation rate by increasing the available S for the sulfide gas species but partly decelerates the evaporation rate due to the surface poisoning effect. Increasing the reaction temperature increases the overall evaporation rate. All these facts were taken into account in order to develop an evaporation rate model. This model was extended from the present authors’ previous one by taking into account (1) CS(g), S(g), and CS{ 2 (g) (therefore, the following species were considered as dominant evaporating species: Cu(g), CuS(g), Sn(g), SnS(g), S(g), CS(g), and CS 2 (g)); (2) the effect of C and temperature on the activity coefficients of Cu, Sn, and S; (3) the effect of C and temperature on the density of the liquid alloy; and (4) the effect of temperature on the S adsorption coefficient. This revised evaporation model was used in order to explain the experimental data, and it showed good agreement. In particular, it was found that the temperature showed a significant effect on the evaporation rate, and the effect of temperature and C content on the activity coefficients of Cu, Sn, and S also significantly affected the evaporation rate. The chemical reaction rate constant of the individual evaporation reaction (k i } R ) and residual rate constant (k i r ) could be obtained as a function of temperature. The activation energy of each evaporation reaction was derived and discussed. The evaporation rate model can be applied in order to predict the content of Cu and Sn remaining in liquid iron under various conditions of temperature and [pct C].

36 MATERIALS SCIENCE↗
DOE OSTI2017

A reduced order model to analytically infer atmospheric CO 2 concentration from stomatal and climate data

To address questions related to the acceleration or deceleration of the global hydrological cycle or links between the carbon and water cycles over land, reliable data for past climatic conditions based on proxies are required. In particular, the reconstruction of palaeoatmospheric CO 2 content (C a ) is needed to assist the separation of natural from anthropogenic C a variability and to explore phase relations between C a and air temperature T a time series. Both T a and C a are needed to fingerprint anthropogenic signatures in vapor pressure deficit, a major driver used to explain acceleration or deceleration phases in the global hydrological cycle. Current approaches to C a reconstruction rely on a robust inverse correlation between measured stomatal density in leaves (ν) of many plant taxa and C a . There are two methods that exploit this correlation: The first uses calibration curves obtained from extant species assumed to represent the fossil taxa, thereby restricting the suitable taxa to those existing today. The second is a hybrid eco-hydrological/physiological approach that determines C a with the aid of systems of equations based on quasi-instantaneous leaf-gas exchange theories and fossil stomatal data collected along with other measured leaf anatomical traits and parameters. In this contribution, a reduced order model (ROM) is proposed that derives C a from a single equation incorporating the aforementioned stomatal data, basic climate (e.g. temperature), estimated biochemical parameters of assimilation and isotope data. The usage of the ROM is then illustrated by applying it to isotopic and anatomical measurements from three extant species. The ROM derivation is based on a balance between the biochemical demand and atmospheric supply of CO 2 that leads to an explicit expression linking stomatal conductance to internal CO 2 concentration (C i ) and C a . The resulting expression of stomatal conductance from the carbon economy of the leaf is then equated to another expression derived from water vapor gas diffusion that includes anatomical traits. When combined with isotopic measurements for long-term C i /C a , C a can be analytically determined and is interpreted as the time-averaged C a that existed over the life-span of the leaf. Key advantages of the proposed ROM are: 1) the usage of isotopic data provides constraints on the reconstructed atmospheric CO 2 concentration from ν, 2) the analytical form of this approach permits direct links between parameter uncertainties and reconstructed C a , and 3) the time-scale mismatch between the application of instantaneous leaf-gas exchange expressions constrained with longer-term isotopic data is reconciled through averaging rules and sensitivity analysis. The latter point was rarely considered in prior reconstruction studies that combined models of leaf-gas exchange and isotopic data to reconstruct C a from ν. The proposed ROM is not without its limitations given the need to a priori assume a parameter related to the control on photosynthetic rate. Our work here further explores immanent constraints for the aforementioned photosynthetic parameter.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2015

A cosmological study in massive gravity theory

A detailed study of the various cosmological aspects in massive gravity theory has been presented in the present work. For the homogeneous and isotropic FLRW model, the deceleration parameter has been evaluated, and, it has been examined whether there is any transition from deceleration to acceleration in recent past, or not. With the proper choice of the free parameters, it has been shown that the massive gravity theory is equivalent to Einstein gravity with a modified Newtonian gravitational constant together with a negative cosmological constant. Also, in this context, it has been examined whether the emergent scenario is possible, or not, in massive gravity theory. Finally, we have done a cosmographic analysis in massive gravity theory.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Inflationary universe in deformed phase space scenario

We consider a noncommutative (NC) inflationary model with a homogeneous scalar field minimally coupled to gravity. The particular NC inflationary setting herein proposed, produces entirely new consequences as summarized in what follows. We first analyze the free field case and subsequently examine the situation where the scalar field is subjected to a polynomial and exponential potentials. We propose to use a canonical deformation between momenta, in a spatially flat Friedmann–Lemaî tre–Robertson–Walker (FLRW) universe, and while the Friedmann equation (Hamiltonian constraint) remains unaffected the Friedmann acceleration equation (and thus the Klein–Gordon equation) is modified by an extra term linear in the NC parameter. This concrete noncommutativity on the momenta allows interesting dynamics that other NC models seem not to allow. Let us be more precise. This extra term behaves as the sole explicit pressure that under the right circumstances implies a period of accelerated expansion of the universe. We find that in the absence of the scalar field potential, and in contrast with the commutative case, in which the scale factor always decelerates, we obtain an inflationary phase for small negative values of the NC parameter. Subsequently, the period of accelerated expansion is smoothly replaced by an appropriate deceleration phase providing an interesting model regarding the graceful exit problem in inflationary models. This last property is present either in the free field case or under the influence of the scalar field potentials considered here. Moreover, in the case of the free scalar field, we show that not only the horizon problem is solved but also there is some resemblance between the evolution equation of the scale factor associated to our model and that for the R{sup 2} (Starobinsky) inflationary model. Therefore, our herein NC model not only can be taken as an appropriate scenario to get a successful kinetic inflation, but also is a convenient setting to obtain inflationary universe possessing the graceful exit when scalar field potentials are present.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

Advances in understanding vacuum break dynamics in liquid helium-cooled tubes for accelerator beamline applications

Understanding air propagation and condensation following a catastrophic vacuum break in particle accelerator beamlines cooled by liquid helium is essential for ensuring operational safety. This review summarizes experimental and theoretical work conducted in our cryogenics lab to address this issue. Systematic measurements were performed to study nitrogen gas propagation in uniform copper tubes cooled by both normal liquid helium (He I) and superfluid helium (He II). These experiments revealed a nearly exponential deceleration of the gas front, with stronger deceleration observed in He II-cooled tubes. To interpret these results, a one-dimensional (1D) theoretical model was developed, incorporating gas dynamics, heat transfer, and condensation mechanisms. The model successfully reproduced key experimental observations in the uniform tube system. However, recent experiments involving a bulky copper cavity designed to mimic the geometry of a superconducting radiofrequency (SRF) cavity revealed strong anisotropic flow patterns of nitrogen gas within the cavity, highlighting limitations in extrapolating results from simplified tube geometries to real accelerator beamlines. To address these complexities, we outline plans for systematic studies using tubes with multiple bulky cavities and the development of a two-dimensional (2D) model to simulate gas dynamics in these more intricate configurations. As a result, these efforts aim to provide a comprehensive understanding of vacuum breaks in particle accelerators and improve predictive capabilities for their operational safety.

Beamline tube↗
DOE OSTI2025

Osmotic control of the spacing of parallel shear cracks in shale growing subcritically in geologic past

The geological genesis of natural cracks in sedimentary rocks such as shale is a problem that needs to be understood to improve the technology of hydraulic fracturing as well as deep sequestration of harmful fluids. Why are the vertical natural cracks roughly parallel and equidistant, and why is the spacing roughly 10 cm rather than 1 cm or 100 cm? Fracture mechanics of critical cracks cannot answer this question. Neither can the material heterogeneity. The growth of critical parallel cracks is impossible because the relative crack face displacements would immediately localize into one crack, leading to an earthquake. The cracks must have formed, on the tectonic time scale, by a slow growth of subcritical shear cracks governed by the Charles-Evans law. The idea advanced here is that what controls the crack spacing is the balance between the reduction, due to shear dilatancy, of the concentration of ions such as Na + and Cl - in each fracture process zone (PFZ), which decelerates the cracks, and the restoration of ion concentration by diffusion of ions from the space between the cracks into the FPZ. This diffusion of water is driven mainly by the osmotic pressure gradient, which offsets the deceleration and depends strongly on the crack spacing. A simple analytical solution of the steady state is rendered possible by approximating the ion concentration profiles between adjacent cracks by parabolic arcs. Applying this theory to Woodford shale yields the approximate crack spacing of 10 cm, which is realistic. Furthermore, the stability of unlimited parallel mode II frictional crack growth is proven by examining the second variation of the free energy. Water concentration drop in the FPZ due to shear dilatancy and its restoration by water diffusion from the inter-crack space have similar effect, although probably much weaker.

42 ENGINEERING↗
DOE OSTI2018

Seasonal Evolution of the Subglacial Hydrologic System Modified by Supraglacial Lake Drainage in Western Greenland

The impact of summer surface melt on Greenland Ice Sheet dynamics is modulated by the state of the subglacial hydrologic system. Studies of ice motion indicate that efficiency of the subglacial system increases over the melt season, decreasing the sensitivity of ice motion to surface melt inputs. However, the behavior of the subglacial hydrologic system is complex and some characteristics are still poorly constrained. Here we investigate the coevolution of subglacial hydrology and ice motion in the Pâkitsoq region of western Greenland during the 2011 melt season. We analyze measurements from 11 Global Positioning System stations, from which we derive ice velocity, longitudinal strain rates, and basal uplift, alongside observations of surface ablation and supraglacial lake drainages. We observe ice acceleration after the onset of local surface melting, followed by gradual ice deceleration, consistent with increasing subglacial efficiency. In the study area, supraglacial lake drainages cooccur with a change in regional strain rate patterns and ice deceleration, suggesting that lake drainages contribute to rapid subglacial reorganization. At lower ice surface elevations (below ~900 m above sea level), ice motion is correlated with both total basal uplift and its rate of change, while at higher elevations (~900–1,100 m above sea level), ice motion correlated only with the basal uplift rate. This pattern suggests that continued cavity growth or subglacial sediment dynamics may be important in the apparent increase in subglacial drainage efficiency at higher elevations in the ablation zone. Furthermore, our results further suggest that transient subglacial behavior is important in the seasonal evolution of ice motion.

58 GEOSCIENCES↗
DOE OSTI2020

A Case Study of Nonresonant Mode 3-s ULF Waves Observed by MMS

The nature of the 3-s ultralow frequency (ULF) wave in the Earth's foreshock region and the associated wave-particle interaction are not yet well understood. In this work, we investigate the 3-s ULF waves using Magnetospheric Multiscale (MMS) observations. By combining the plasma rest frame wave properties obtained from multiple methods with the instability analysis based on the velocity distribution in the linear wave stage, the ULF wave is determined to be due to the ion/ion nonresonant mode instability. The interaction between the wave and ions is analyzed using the phase relationship between the transverse wave fields and ion velocities and using the longitudinal momentum equation. During the stage when ULF waves have sinusoidal waveforms up to |dB|/|B 0 | ~ 3, where dB is the wave magnetic field and B0 is the background magnetic field, the wave electric fields perpendicular to B 0 do negative work to solar wind ions; along B 0 , a longitudinal electric field develops, but the V × B force is stronger and leads to solar wind ion deceleration. During the same wave stage, the backstreaming beam ions gain energy from the transverse wave fields and get deceleration along B 0 by the longitudinal electric field. The ULF wave leads to electron heating, preferentially in the direction perpendicular to the local magnetic field. Secondary waves are generated within the ULF waveforms, including whistler waves near half of the electron cyclotron frequency, high-frequency electrostatic waves, and magnetosonic whistler waves. The work improves the understanding of the nature of 3-s ULF waves and the associated wave-particle interaction.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Schizophrenia-related microdeletion causes defective ciliary motility and brain ventricle enlargement via microRNA-dependent mechanisms in mice

Progressive ventricular enlargement, a key feature of several neurologic and psychiatric diseases, is mediated by unknown mechanisms. Here, using murine models of 22q11-deletion syndrome (22q11DS), which is associated with schizophrenia in humans, we found progressive enlargement of lateral and third ventricles and deceleration of ciliary beating on ependymal cells lining the ventricular walls. The cilia-beating deficit observed in brain slices and in vivo is caused by elevated levels of dopamine receptors (Drd1), which are expressed in motile cilia. Haploinsufficiency of the microRNA-processing gene Dgcr8 results in Drd1 elevation, which is brought about by a reduction in Drd1-targeting microRNAs miR-382-3p and miR-674-3p. Replenishing either microRNA in 22q11DS mice normalizes ciliary beating and ventricular size. Knocking down the microRNAs or deleting their seed sites on Drd1 mimicked the cilia-beating and ventricular deficits. These results suggest that the Dgcr8–miR-382-3p/miR-674-3p–Drd1 mechanism contributes to deceleration of ciliary motility and age-dependent ventricular enlargement in 22q11DS.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2015

Tuning the reactivity of mononuclear nonheme manganese( iv )-oxo complexes by triflic acid

Triflic acid (HOTf)-bound nonheme Mn( IV )-oxo complexes, [(L)Mn IV (O)] 2+ –(HOTf) 2 (L = N4Py and Bn-TPEN; N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine and Bn-TPEN = N-benzyl-N,N',N'-tris(2-pyridylmethyl)ethane-1,2-diamine), were synthesized by adding HOTf to the solutions of the [(L)Mn IV (O)] 2+ complexes and were characterized by various spectroscopies. The one-electron reduction potentials of the Mn IV (O) complexes exhibited a significant positive shift upon binding of HOTf. The driving force dependences of electron transfer (ET) from electron donors to the Mn IV (O) and Mn IV (O)–(HOTf) 2 complexes were examined and evaluated in light of the Marcus theory of ET to determine the reorganization energies of ET. The smaller reorganization energies and much more positive reduction potentials of the [(L)Mn IV (O)] 2+ –(HOTf) 2 complexes resulted in greatly enhanced oxidation capacity towards one-electron reductants and para-X-substituted-thioanisoles. The reactivities of the Mn(IV)-oxo complexes were markedly enhanced by binding of HOTf, such as a 6.4 × 10 5 -fold increase in the oxygen atom transfer (OAT) reaction (i.e., sulfoxidation). Such a remarkable acceleration in the OAT reaction results from the enhancement of ET from para-X-substituted-thioanisoles to the MnIV(O) complexes as revealed by the unified ET driving force dependence of the rate constants of OAT and ET reactions of [(L)Mn IV (O)] 2+ –(HOTf) 2 . In contrast, deceleration was observed in the rate of H-atom transfer (HAT) reaction of [(L)Mn IV (O)] 2+ –(HOTf) 2 complexes with 1,4-cyclohexadiene as compared with those of the [(L)Mn IV (O)] 2+ complexes. Thus, the binding of two HOTf molecules to the Mn IV (O) moiety resulted in remarkable acceleration of the ET rate when the ET is thermodynamically feasible. When the ET reaction is highly endergonic, the rate of the HAT reaction is decelerated due to the steric effect of the counter anion of HOTf.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Baryon acoustic oscillations in the Ly α forest of BOSS quasars

In this paper, we report a detection of the baryon acoustic oscillation (BAO) feature in the three-dimensional correlation function of the transmitted flux fraction in the Lyα forest of high-redshift quasars. The study uses 48,640 quasars in the redshift range $2.1\le z \le 3.5$ from the Baryon Oscillation Spectroscopic Survey (BOSS) of the third generation of the Sloan Digital Sky Survey (SDSS-III). At a mean redshift $z=2.3$, we measure the monopole and quadrupole components of the correlation function for separations in the range 20 h -1 Mpc < r < 200 h -1 . A peak in the correlation function is seen at a separation equal to $(1.01\pm0.03)$ times the distance expected for the BAO peak within a concordance $\Lambda$CDM cosmology. This first detection of the BAO peak at high redshift, when the universe was strongly matter dominated, results in constraints on the angular diameter distance D A and the expansion rate $H$ at $z=2.3$ that, combined with priors on $H_0$ and the baryon density, require the existence of dark energy. Combined with constraints derived from Cosmic Microwave Background (CMB) observations, this result implies $H(z=2.3)=(224\pm8){\rm km\,s^{-1}Mpc^{-1}}$, indicating that the time derivative of the cosmological scale parameter $\dot{a}=H(z=2.3)/(1+z)$ is significantly greater than that measured with BAO at $z\sim0.5$. This demonstrates that the expansion was decelerating in the range 0.7 < z < 2.3 , as expected from the matter domination during this epoch. Finally, combined with measurements of H 0 , one sees the pattern of deceleration followed by acceleration characteristic of a dark-energy dominated universe.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

A simple model of universe describing the early inflation and the late accelerated expansion in a symmetric manner

We construct a simple model of universe which 'unifies' vacuum energy and radiation on the one hand, and matter and dark energy on the other hand in the spirit of a generalized Chaplygin gas model. Specifically, the phases of early inflation and late accelerated expansion are described by a generalized equation of state p/c{sup 2} = αρ+kρ{sup 1+1/n} having a linear component p = αρc{sup 2} and a polytropic component p = kρ{sup 1+1/n}c{sup 2}. For α= 1/3, n= 1 and k=−4/(3ρ{sub P}), where ρ{sub P}= 5.1610{sup 99} g/m{sup 3} is the Planck density, this equation of state describes the transition between the vacuum energy era and the radiation era. For t≥ 0, the universe undergoes an inflationary expansion that brings it from the Planck size l{sub P}= 1.6210{sup −35} m to a size a{sub 1}= 2.6110{sup −6} m on a timescale of about 23.3 Planck times t{sub P}= 5.3910{sup −44} s (early inflation). When t > t{sub 1}= 23.3t{sub P}, the universe decelerates and enters in the radiation era. We interpret the transition from the vacuum energy era to the radiation era as a second order phase transition where the Planck constant ℏ plays the role of finite size effects (the standard Big Bang theory is recovered for ℏ= 0). For α= 0, n=−1 and k=−ρ{sub Λ}, where ρ{sub Λ}= 7.0210{sup −24} g/m{sup 3} is the cosmological density, the equation of state p/c{sup 2} = αρ+kρ{sup 1+1/n} describes the transition from a decelerating universe dominated by pressureless matter (baryonic and dark matter) to an accelerating universe dominated by dark energy (late inflation). This transition takes place at a size a{sub 2}= 0.204l{sub Λ}. corresponding to a time t{sub 2}= 0.203t{sub Λ} where l{sub Λ}= 4.38 10{sup 26} m is the cosmological length and t{sub Λ}= 1.46 10{sup 18} s the cosmological time. The present universe turns out to be just at the transition between these two periods (t{sub 0}∼t{sub 2}). Our model gives the same results as the standard ΛCDM model for t≫t{sub P} and completes it by incorporating a phase of early inflation for t < 23.3t{sub P} in a very natural manner. Furthermore, it reveals a nice 'symmetry' between the early and the late evolution of the universe. The early universe is modeled by a polytrope n=+ 1 and the late universe by a polytrope n=−1. Furthermore, the cosmological constant Λ in the late universe plays a role similar to the Planck constant ℏ in the early universe. The mathematical formulae in the early and in the late universe are then strikingly symmetric. We interpret the cosmological constant as a fundamental constant of Nature describing the 'cosmophysics' just like the Planck constant describes the 'microphysics'. The Planck density and the cosmological density represent fundamental upper and lower bounds differing by 122 orders of magnitude. The cosmological constant 'problem' may be a false problem. Finally, we show that our model admits a scalar field interpretation based on a quintessence field or a tachyon field.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Synthesis of endohedral iron-fullerenes by ion implantation

In this paper, we discuss the results of our study of the synthesis of endohedral iron-fullerenes. A low energy Fe{sup +} ion beam was irradiated to C{sub 60} thin film by using a deceleration system. Fe{sup +}-irradiated C{sub 60} thin film was analyzed by high performance liquid chromatography and laser desorption/ ionization time-of-flight mass spectrometry. We investigated the performance of the deceleration system for using a Fe{sup +} beam with low energy. In addition, we attempted to isolate the synthesized material from a Fe{sup +}-irradiated C{sub 60} thin film by high performance liquid chromatography.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Hydrodynamic instability growth and mix experiments at the National Ignition Facility

Hydrodynamic instability growth and its effects on implosion performance were studied at the National Ignition Facility [G. H. Miller, E. I. Moses, and C. R. Wuest, Opt. Eng. 443, 2841 (2004)]. Implosion performance and mix have been measured at peak compression using plastic shells filled with tritium gas and containing embedded localized carbon-deuterium diagnostic layers in various locations in the ablator. Neutron yield and ion temperature of the deuterium-tritium fusion reactions were used as a measure of shell-gas mix, while neutron yield of the tritium-tritium fusion reaction was used as a measure of implosion performance. The results have indicated that the low-mode hydrodynamic instabilities due to surface roughness were the primary culprits for yield degradation, with atomic ablator-gas mix playing a secondary role. In addition, spherical shells with pre-imposed 2D modulations were used to measure instability growth in the acceleration phase of the implosions. The capsules were imploded using ignition-relevant laser pulses, and ablation-front modulation growth was measured using x-ray radiography for a shell convergence ratio of ∼2. The measured growth was in good agreement with that predicted, thus validating simulations for the fastest growing modulations with mode numbers up to 90 in the acceleration phase. Future experiments will be focused on measurements at higher convergence, higher-mode number modulations, and growth occurring during the deceleration phase.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Time-resolved characterization and energy balance analysis of implosion core in shock-ignition experiments at OMEGA

Time-resolved temperature and density conditions in the core of shock-ignition implosions have been determined for the first time. The diagnostic method relies on the observation, with a streaked crystal spectrometer, of the signature of an Ar tracer added to the deuterium gas fill. The data analysis confirms the importance of the shell attenuation effect previously noted on time-integrated spectroscopic measurements of thick-wall targets [R. Florido et al., Phys. Rev. E 83, 066408 (2011)]. This effect must be taken into account in order to obtain reliable results. The extracted temperature and density time-histories are representative of the state of the core during the implosion deceleration and burning phases. As a consequence of the ignitor shock launched by the sharp intensity spike at the end of the laser pulse, observed average core electron temperature and mass density reach T ~ 1100 eV and ρ ~ 2 g/cm 3 ; then temperature drops to T ~ 920 eV while density rises to ρ ~ 3.4 g/cm 3 about the time of peak compression. Compared to 1D hydrodynamic simulations, the experiment shows similar maximum temperatures and smaller densities. Simulations do not reproduce all observations. Differences are noted in the heating dynamics driven by the ignitor shock and the optical depth time-history of the compressed shell. Time-histories of core conditions extracted from spectroscopy show that the implosion can be interpreted as a two-stage polytropic process. Furthermore, an energy balance analysis of implosion core suggests an increase in total energy greater than what 1D hydrodynamic simulations predict. This new methodology can be implemented in other ICF experiments to look into implosion dynamics and help to understand the underlying physics.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

The effect of shock dynamics on compressibility of ignition-scale National Ignition Facility implosions

The effects of shock dynamics on compressibility of indirect-drive ignition-scale surrogate implosions, CH shells filled with D{sup 3}He gas, have been studied using charged-particle spectroscopy. Spectral measurements of D{sup 3}He protons produced at the shock-bang time probe the shock dynamics and in-flight characteristics of an implosion. The proton shock yield is found to vary by over an order of magnitude. A simple model relates the observed yield to incipient hot-spot adiabat, suggesting that implosions with rapid radiation-power increase during the main drive pulse may have a 2× higher hot-spot adiabat, potentially reducing compressibility. A self-consistent 1-D implosion model was used to infer the areal density (ρR) and the shell center-of-mass radius (R{sub cm}) from the downshift of the shock-produced D{sup 3}He protons. The observed ρR at shock-bang time is substantially higher for implosions, where the laser drive is on until near the compression bang time (“short-coast”), while longer-coasting implosions have lower ρR. This corresponds to a much larger temporal difference between the shock- and compression-bang time in the long-coast implosions (∼800 ps) than in the short-coast (∼400 ps); this will be verified with a future direct bang-time diagnostic. This model-inferred differential bang time contradicts radiation-hydrodynamic simulations, which predict constant 700–800 ps differential independent of coasting time; this result is potentially explained by uncertainties in modeling late-time ablation drive on the capsule. In an ignition experiment, an earlier shock-bang time resulting in an earlier onset of shell deceleration, potentially reducing compression and, thus, fuel ρR.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗