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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 1,549 records · Page 86
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Liner implosion experiments driven by a dynamic screw pinch

This paper expands upon recent experimental results [Campbell et al., Phys. Rev. Lett. 125, 035001 (2020)], where thin-foil liner implosions were driven by a dynamic screw pinch (DSP) and found to have magneto-Rayleigh–Taylor instability (MRTI) amplitudes up to three times smaller than in implosions driven by a standard z-pinch (SZP). Here, the expanded discussion presented herein includes: (1) a detailed comparison of the MRTI growth measured in the experiment with that calculated from theory; (2) measurements of axial magnetic field injection into the liner interior prior to the implosion, as well as the subsequent compression of this field during the implosion; (3) an in-depth description of how the helical geometry of the DSP can result in earlier implosion and stagnation times relative to the SZP; and (4) particle-in-cell simulations showing different electron drift behavior in the anode–cathode gap of the DSP relative to the SZP, and how this difference may be related to the different current waveforms recorded during the experiments.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Current polarity effects on laboratory plasma jets

Plasma jets produced by a pulsed power machine were investigated using Thomson scattering and other diagnostics in order to make detailed comparisons to simulations. These jets were produced from a 15 μm thick disc of Al foil on a 1.2 MA, 100 ns rise time, pulsed power machine. Experiments were performed with both a radially inward and a radially outward current ow in the Al foil to investigate the effects of voltage polarity in the experiments and determine how extended magnetohydrodynamic (XMHD) effects, such as the Hall effect, change the formation of the jet. We recorded Thomson scattering spectra with a low enough laser energy to not perturb the plasma, while providing a high enough signal to noise ratio to resolve the scattered features. This enabled the measurement of the electron temperature in the jet region of the plasma, 15.5±4 eV for both current polarities. Jets with a radially outward current ow were heated more from inverse bremsstrahlung when 10 J of laser energy was used, implying that these jets are denser than the ones with a radially inward current. This higher density was con rmed by interferometry measurements. Experimental results were compared with XMHD computer simulations, which predicted electron temperatures 1.5 to 3 σ above those measured, and significantly higher density than experiments in both polarities. In this paper, possible sources of this discrepancy are discussed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Constraining physical models at gigabar pressures

High-energy-density (HED) experiments in convergent geometry are able to test physical models at pressures beyond hundreds of millions of atmospheres. The measurements from these experiments are generally highly integrated and require unique analysis techniques to procure quantitative infor mation. This work describes a methodology to constrain the physics in convergent HED experiments by adapting the methods common to many other fields of physics. As an example, a mechanical model of an imploding shell is constrained by data from a thin-shelled direct-drive exploding-pusher experiment on the OMEGA Laser System using Bayesian inference, resulting in the reconstruction of the shell dynamics and energy transfer during the implosion. The model is tested by analyzing synthetic data from a 1-D hydrodynamics code and is sampled using a Markov chain Monte Carlo to generate the posterior distributions of the model parameters. As a result, the goal of this work is to demonstrate a general methodology that can be used to draw conclusions from a wide variety of HED experiments.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Ion Number Density Quantification Utilizing Pulsing Frequency in Negative Differential Resistance (NDR) Regime of Microplasma Operation

A mathematical model is presented for quantifying the ion number density over a range of discharge current in microplasma discharges. The ion number density is determined from measured discharge voltage, current, pulsing frequency, and trace impurity that is injected into the system deliberately. Experiments are conducted in pure helium with nitrogen being introduced as the trace species. The ion number density is estimated over a range of discharge current and is compared with multidimensional simulation results.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Scalar Power Spectra and Scalar Structure Function Evolution in the Richtmyer–Meshkov Instability Upon Reshock

The Richtmyer–Meshkov instability of a twice-shocked gas interface is studied using high-speed planar laser-induced fluorescence in the Wisconsin Shock Tube Laboratory's vertical shock tube. The initial condition is a shear layer with broadband diffuse perturbations at the interface between a helium–acetone mixture and argon. Furthermore, this initial condition is accelerated by a shock of nominal strength M = 1.9, and then accelerated again by the transmitted shock that reflects off the end wall of the tube. Three individual experiments are analyzed, the energy spectrum and the structure functions of the light gas mole fraction field are calculated and compared.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Measurement of accreted helium ion velocity using Doppler spectroscopy in the CTIX compact-toroid plasma accelerator

A compact-toroid (CT) accelerator is a device for the production of plasma bodies which contain a relatively strong internal magnetic field, which permits the plasma body to withstand large forces of acceleration while retaining its magnetic field structure. Typically, the CT occupies an annular region between inner and outer radii, defined by coaxial inner and outer electrodes, across which a large electric potential is applied. The internal magnetic fields of the CT contain both a toroidal and poloidal component, as shown in Fig. 1(a). These fields are typically of comparable magnitude. Because of the effective rigidity provided by internal magnetic fields, the CT can be accelerated to high velocities in short distances. Since internal fields increase in proportion to accelerating magnetic field, there is no strength at which the accelerating magnetic fields overcome the internal field (blow-by). Because of this, the kinetic energy density of CTs can be made to exceed the energy density of magnetic fields typical of plasma containment devices such as tokamaks. CTs have the potential to be launched into the interior of such devices for either delivering fuel (typically deuterium or hydrogen), or to deliver particles of high atomic number (high-Z). An important application of high-Z CT injection into tokamaks is to aid in plasma quenching by radiation, to mitigate the effects of plasma disruptions and prevent damage to the plasma confinement device. In addition, high-Z CTs may be used as sources of kinetic energy density for plasma-compression experiments. In this case, the use of plasma species of high atomic number is also desirable, since kinetic energy density is proportional to atomic number for given CT velocity and electron density gas puffing.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Final Technical Report - Rapid Surface Microanalysis using a Low Temperature Plasma

This project focused on improving our current understanding and scientific knowledge in the area of plasma-surface interactions and plasma assisted material synthesis related to advanced microelectronics and nanotechnology. Current challenges include: controlling the interaction of Low Temperature Plasma (LTP) with a single layer of atoms to manufacture integrated circuits, continued miniaturization of integrated circuits, LTP processing of material surfaces and thin films to enable industrial scale fabrication of advanced microelectronics, synthesis of new materials, nanomaterials, nanotubes, and complex materials, Technology developed in this subtopic is of value to either (i) enable scans of surfaces (~1 sq. cm area) using various microscopies (electron, optical, other) at high resolution (micron or sub-micron resolution) rapidly (hours or days rather than years to complete a high-resolution scan of such a large surface area), or (ii) enable scans of surfaces (~1 sq. cm area) using various microscopies (electron, optical, other) at relatively low resolution rapidly, then apply algorithms to select spots for micron-scale imaging. Sputtering occurs when particles of a solid material are ejected from its surface by energetic particles from a plasma. While the degradation of the solid material and the subsequent deposition of the ejected material onto vulnerable surfaces are the usual subjects of sputtering studies, plasma science has yet to be combined with sputtering to create new diagnostics devices and systems. Small changes in the design of the plasma discharge device make it possible to create broad plasma beams for rapid scanning or small plasma beams to obtain the distribution of ejected elements with micron resolution. In the high-resolution use, the ion flux is extracted from the gas-discharge plasma and focused by a spherical emission surface to micron sizes onto the target specimen, providing very local sputtering and local elemental analysis. We call this “self-focusing”. The radiation from the excited and ionized sputtered atoms is recorded by a spectrometer through a window and fiberglass cable and analyzed with standard software packages used for optical glow discharge spectroscopy. Computer simulations of beam formation were used to verify and optimize the designs to be tested. A prototype was designed, constructed, and used to start experiments of beam formation.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS2001

The effect of acute microgravity on mechanically-induced membrane damage and membrane-membrane fusion events

Although it is unclear how a living cell senses gravitational forces there is no doubt that perturbation of the gravitational environment results in profound alterations in cellular function. In the present study, we have focused our attention on how acute microgravity exposure during parabolic flight affects the skeletal muscle cell plasma membrane (i.e. sarcolemma), with specific reference to a mechanically-reactive signaling mechanism known as mechanically-induced membrane disruption or "wounding". Both membrane rupture and membrane resealing events mediated by membrane-membrane fusion characterize this response. We here present experimental evidence that acute microgravity exposure can inhibit membrane-membrane fusion events essential for the resealing of sarcolemmal wounds in individual human myoblasts. Additional evidence to support this contention comes from experimental studies that demonstrate acute microgravity exposure also inhibits secretagogue-stimulated intracellular vesicle fusion with the plasma membrane in HL-60 cells. Based on our own observations and those of other investigators in a variety of ground-based models of membrane wounding and membrane-membrane fusion, we suggest that the disruption in the membrane resealing process observed during acute microgravity is consistent with a microgravity-induced decrease in membrane order.

Parabolic Flight↗
DOE OSTI2025

Estimating ionization states and continuum lowering from ab initio path integral Monte Carlo simulations for warm dense hydrogen

Warm dense matter (WDM) is an active field of research, with applications ranging from astrophysics to inertial confinement fusion. Ionization degree and continuum lowering are important quantities to understand how materials behave under these conditions, but can be difficult to diagnose since experimental campaigns are limited and often require model-dependent analysis. This is especially true for hydrogen, which has a comparably low scattering cross section, making high-quality data particularly difficult to obtain. Consequently, building equation of state tables often relies on simulations in combination with untested approximations to extract properties from experiments. Here, we investigate an approach for extracting the ionization potential depression and ionization degree—quantities which are otherwise not directly accessible from the physical model—from first-principles path integral Monte Carlo (PIMC) simulations utilizing a chemical model. In contrast to experimental measurements, where noise and nonequilibrium effects add to the uncertainty of the inferred parameters, PIMC simulations provide a clean signal with well-defined thermodynamic conditions. Comparisons against commonly used models show a qualitative agreement, but we find deviations primarily for the high-density and high-temperature cases. We also demonstrate the decreasing sensitivity of the dynamic structure factor with respect to both ionization and continuum lowering for increasing scattering angles in x-ray Thomson scattering experiments. Our work has important implications for the design of future experiments, but also offers qualitative understanding of structure factors and the imaginary-time correlation function obtained from first-principles quantum Monte Carlo simulations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Unraveling electronic correlations in warm dense quantum plasmas

The study of matter at extreme densities and temperatures has emerged as a highly active frontier at the interface of plasma physics, material science and quantum chemistry with relevance for planetary modeling and inertial confinement fusion. A particular feature of such warm dense matter is the complex interplay of Coulomb interactions, quantum effects, and thermal excitations, making its rigorous theoretical description challenging. Here, we demonstrate how ab initio path integral Monte Carlo simulations allow us to unravel this intricate interplay for the example of strongly compressed beryllium, focusing on two X-ray Thomson scattering data sets obtained at the National Ignition Facility. We find excellent agreement between simulation and experiment with a very high level of consistency between independent observations without the need for any empirical input parameters. Our results call into question previously used chemical models, with important implications for the interpretation of scattering experiments and radiation hydrodynamics simulations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS2004

Magnetohydrodynamic Instabilities in a Simple Gasdynamic Mirror Propulsion System

The gasdynamic mirror has been proposed as a concept which could form the basis of a highly efficient fusion rocket engine. Gasdynamic mirrors differ from most other mirror type plasma confinement schemes in that they have much larger aspect ratios and operate at somewhat higher plasma densities. To evaluate whether a gasdynamic mirror could indeed confine plasmas in a stable manner for long periods of time, a small scale experimental gasdynamic mirror was built and tested. The objective of this experiment was to determine ranges of mirror ratios and plasma densities over which gasdynamic mirror could maintain stable plasmas. Theoretical analyses indicated that plasma magnetohydrodynamic instabilities were likely to occur during subsonic to supersonic flow transitions in the mirror throat region of the gasdynamic mirror. The experimental evidence based upon data derived from the Langmuir probe measurements seems to confirm this analysis. The assumption that a gasdynamic mirror using a simple mirror geometry could be used as a propulsion system, therefore, appears questionable. Modifications to the simple mirror concept are presented which could mitigate these MHD instabilities.

Emrich, William J., Jr.↗
NASA NTRSDate not supplied

Plasma-Induced Electron Screening at the Bragg Peak

Over 36 years of laboratory astrophysics experiments employing accelerated hydrogen isotope beams have demonstrated the role of electron screened, enhanced nuclear reactions. The astrophysical role of weak and strong electron screening was first discussed by Saltpeter in 1954 and later by Hagino and Balantekin in 2002. Assenbaum, et al., Czerski, et al., and Schenkel, et al., have used accelerated deuteron beams on various metal targets and observed increased fusion rates over the expected Astrophysical, S(E), and Gamow Factors for bare deuteron-deuteron fusion rates. The Pines calculated both electron screened direct and asymptotic enhancement factors, f(E). Arguably, electron screening makes LENR possible.

plasma↗
DOE OSTI2023

Density limits as disruption forecasters for spherical tokamaks

Fusion power output from spherical tokamaks would benefit from increased confined plasma density, but there exists a limit on the density before confinement is lost and the plasma current is disrupted. This density limit has long been characterized by a simple, global Greenwald limit proportional to the plasma current and inversely proportional to the cross sectional area of the plasma. It is shown that in the database of discharges from the National Spherical Tokamak Experiment (NSTX) and Mega Ampere Spherical Tokamak (MAST) spherical tokamaks, the likelihood of disruption does increase above the Greenwald limit, and especially in the plasma current rampdown phase. The physics of the density limit has been recently theoretically explored through local criteria. Several of these are tested using the disruption event characterization and forecasting (DECAF TM ) code for their potential effectiveness as disruption warning signals. For a limited set of NSTX discharges, a local island power balance criteria was found to be less reliable, presently, than the Greenwald limit. For this work, an empirical critical edge line density and a boundary turbulent transport limit were both tested for MAST-U, which has an electron density profile measurement with high spatial resolution in the outer part of the plasma. Both were found to have similar dependencies on key plasma parameters. In a limited set of MAST-U discharges that appear to disrupt due to rising density at values under the Greenwald limit, crossing of the boundary turbulent transport limit occurred close to the time of disruption. Finally, these limits were evaluated for their potential use in real-time, and it was found that with the necessary real-time inputs and with refinement through further testing, these limits could be implemented in a real-time disruption forecasting system.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Fast electron transport dynamics and energy deposition in magnetized, imploded cylindrical plasma

Inertial confinement fusion approaches involve the creation of high-energy-density states through compression. High gain scenarios may be enabled by the beneficial heating from fast electrons produced with an intense laser and by energy containment with a high-strength magnetic field. Here, we report experimental measurements from a configuration integrating a magnetized, imploded cylindrical plasma and intense laser-driven electrons as well as multi-stage simulations that show fast electrons transport pathways at different times during the implosion and quantify their energy deposition contribution. The experiment consisted of a CH foam cylinder, inside an external coaxial magnetic field of 5 T, that was imploded using 36 OMEGA laser beams. Two-dimensional (2D) hydrodynamic modelling predicts the CH density reaches 9.0 g cm − 3 , the temperature reaches 920 eV and the external B-field is amplified at maximum compression to 580 T. At pre-determined times during the compression, the intense OMEGA EP laser irradiated one end of the cylinder to accelerate relativistic electrons into the dense imploded plasma providing additional heating. The relativistic electron beam generation was simulated using a 2D particle-in-cell (PIC) code. Finally, three-dimensional hybrid-PIC simulations calculated the electron propagation and energy deposition inside the target and revealed the roles the compressed and self-generated B-fields play in transport. During a time window before the maximum compression time, the self-generated B-field on the compression front confines the injected electrons inside the target, increasing the temperature through Joule heating. For a stronger B-field seed of 20 T, the electrons are predicted to be guided into the compressed target and provide additional collisional heating. This article is part of a discussion meeting issue ‘Prospects for high gain inertial fusion energy (part 2)’.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Investigating radiatively driven, magnetized plasmas with a university scale pulsed-power generator

We present first results from a novel experimental platform that is able to access physics relevant to topics including indirect-drive magnetized inertial confinement fusion, laser energy deposition, various topics in atomic physics, and laboratory astrophysics (for example, the penetration of B-fields into high energy density plasmas). This platform uses the x rays from a wire array Z-pinch to irradiate a silicon target, producing an outflow of ablated plasma. The ablated plasma expands into ambient, dynamically significant B-fields (∼5 T), which are supported by the current flowing through the Z-pinch. The outflows have a well-defined (quasi-1D) morphology, enabling the study of fundamental processes typically only available in more complex, integrated schemes. Experiments were fielded on the MAGPIE pulsed-power generator (1.4 MA, 240 ns rise time). On this machine, a wire array Z-pinch produces an x-ray pulse carrying a total energy of ∼15 kJ over ∼30 ns. This equates to an average brightness temperature of around 10 eV on-target.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

A Gaussian Process-Based extended Goldak heat source model for finite element simulation of laser powder bed fusion additive manufacturing process

In this study, laser powder bed fusion (L-PBF) additive manufacturing (AM) is a key enabling technology to manufacture highly complex and integrated metallic structures. In L-PBF AM process, the melting of the metal powders and the layers underneath can be governed by either “conduction mode” or “keyhole mode”, with the keyhole mode reportedly leading to porosity and decreased strength and ductility by many studies. In part scale simulations, finite element (FE) model is often used to study the temperature distribution during printing and to predict the residual stress, where a volumetric heat flux with a Gaussian or a double ellipsoidal (Goldak) distribution is often applied as the laser heat source. However, the above heat source models can only capture the melt pool shape in the conduction mode, and fail to capture the transition to keyhole melting mode when the process parameters change. To overcome this inaccuracy, an extended Goldak heat source model is proposed by introducing a laser penetration term as a function of laser parameters obtained from a Gaussian-Process (GP) model. The model is validated by “2D pad” AlSi10Mg L-PBF experiments under a wide range of laser power, scan speed, and laser focus offset, and the results show the model successfully captures the measured melt pool shape in all conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Digital Twins for Nuclear Power Plants and Facilities

The nuclear digital twin (DT) is the virtual representation of a nuclear energy system across its lifecycle. The nuclear DT uses real-time information and other data sources to improve the process of design, licensing, construction, security, O&M, decommissioning, and waste disposal. By leveraging the knowledge base and experience from the past 40 years of LWR operation, the nuclear DT is helping to accelerate the development and deployment of advanced nuclear technology in areas of passive safety, new fuel forms, instrumentation, and reactor control. For the currently operating nuclear fleet, DTs are reducing the operational risks, increasing plant availability, increasing energy capability, and reducing electricity production costs. For advanced fission and fusion reactors, DTs are being used to design for passive safety and built-in security-by-design. Rapidly deployable small modular reactor (SMR) and microreactor designs compatible with modular construction techniques and advanced manufacturing will be the new normal, reducing the need for large capital expenditures and compressing construction schedules. In addition, lower operational and maintenance costs will be realized by reducing the complexity of operations, staffing needs, and maintenance-related activities.

Kropaczek, Dave↗
DOE OSTI2021

Laboratory measurements of the physics of auroral electron acceleration by Alfvén waves

While the aurora has attracted attention for millennia, important questions remain unanswered. Foremost is how auroral electrons are accelerated before colliding with the ionosphere and producing auroral light. Powerful Alfvén waves are often found traveling Earthward above auroras with sufficient energy to generate auroras, but there has been no direct measurement of the processes by which Alfvén waves transfer their energy to auroral electrons. Here, we show laboratory measurements of the resonant transfer of energy from Alfvén waves to electrons under conditions relevant to the auroral zone. Experiments are performed by launching Alfvén waves and simultaneously recording the electron velocity distribution. Numerical simulations and analytical theory support that the measured energy transfer process produces accelerated electrons capable of reaching auroral energies. The experiments, theory, and simulations demonstrate a clear causal relationship between Alfvén waves and accelerated electrons that directly cause auroras.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗