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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 919 records · Page 51
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Ion acceleration - A phenomenon characteristic of the 'expansion of plasma into a vacuum'

The physics of the complex process by which plasma expands across a strong density gradient is briefly discussed with particular emphasis on the resulting ion acceleration. The results from a laboratory experiment that addresses the steady-state expansion of a collisionless, streaming plasma into the wake of a body are presented. The experimental results are in good qualitative agreement with theoretical predictions, thereby demonstrating the equivalence of expansion with distance in the flow direction to time in the one-dimensional theory. On this basis, the potential application of the plasma process in space plasma physics is mentioned.

Samir, Uri↗
DOE OSTI2021

Adaptive complex nanocomposite alloys for burning plasma-material interface tunability (Final Report)

The focus of this program is discovery and development of novel self-healing and adaptive materials for the PMI (plasma-material interface) envisioned for future plasma-burning extreme environments in thermonuclear fusion reactors that can provide enhanced radiation-tolerance or resistance. This program was conceived and stems from the PI’s DOE Early Career Award work on harnessing nanotechnology and mesoscale materials design in refractory metals to address gaps in PMI research. These gaps pertain to the lack of understanding of multi-scale interactions at the plasma-material interface and the development of novel material interfaces that can be designed to adapt to extreme fusion reactor conditions. The final report is separated into two primary sections: The first section consists of the program’s first two years (FY16-FY17) performance period. The second section consists of FY18 to FY19 period, where the FY19 period was a supplemental addition to support the completion of a PhD thesis and continuation of another. This work consists of an excellent team consisting of a co-PI, one postdoctoral researcher, two graduate students, two undergraduate students and collaborators both domestic and abroad.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Quadruple Langmuir probe characterization of different fuel gases in a plasma deflagration accelerator

Astrophysical flows may be studied by reproducing similar conditions using a coaxial plasma accelerator operating in the deflagration regime (or plasma deflagration accelerator). This allows for the recreation and investigation of dynamics present in complex highly coupled plasma systems at the laboratory scale. Here we report on measurements of the plasma density, temperature, plasma potential and velocity found using a quadruple Langmuir probe (QLP) on such a deflagration accelerator in the form of the Stanford Coaxial High ENerGy (CHENG) device operating with multiple gases – specifically argon, nitrogen and hydrogen. Experiments show a general decrease in bulk plasma velocity with gas atomic mass from upwards of 120 km s –1 with hydrogen to less than 30 km s –1 with argon. There was an accompanying increase in peak plasma density with increasing atomic mass from ~3 × 10 20 m –3 with hydrogen to ~1.5 × 10 21 m –3 with argon. It was found that the momentum flux and internal energy density also generally increase with atomic mass while the particle flux is constant between shots. Further investigation is needed to understand these correlations and the underlying physics. Lastly, comparisons with scaling laws show that while the CHENG device may be operated in such a way as to simulate the effects of bulk solar wind movement, it may not properly capture the thermal effects.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Quantification of complex protective surface oxide layer formed during plasma jet exposure of multicomponent ultra-high temperature carbides

Multicomponent ultra-high temperature ceramics (MC-UHTCs) has garnered attention due to their improved thermo-mechanical and oxidation properties. MC-UHTC was progressively formed by adding a UHTC component at each step, producing binary, ternary and quaternary UHTC systems, processed by spark plasma sintering (SPS). Here, we investigate the role of multi-elements and thermochemical stability of the surface oxide layer formed during plasma arc jet exposure (T > 2500 °C) of MC-UHTCs using core-level X-ray photoelectron spectroscopy (XPS) correlated with the structural investigation. The results indicate that adding a UHTC component improves oxidation resistance due to the assemblage of refractory phases forming complex mixed oxides via preferential oxidation. XPS spectra of Ta4f, Nb3d, Ti1p, and Hf4f showed that the nature of the chemical bonds switched from metal carbides to metal oxides (metal oxy-carbides) in the binary system with retained metal carbides in ternary and quaternary UHTCs. The absence of a metal carbide peak in the high-resolution C1s scan of the binary system also supports this finding. The principal complex mixed oxide phases emanate in the exiguous oxidation of MC-UHTCs are quantified using Rietveld analysis. Overall, this study suggests that MC-UHTC is a promising material for possible application in thermal protection systems (TPS).

36 MATERIALS SCIENCE↗
DOE OSTI2021

Perspectives on Machine Learning-assisted Plasma Medicine: Towards Automated Plasma Treatment

Cold atmospheric plasmas (CAPs) have shown great promise for medical applications through their synergistic chemical, electrical, and thermal effects, which can induce therapeutic outcomes. However, safe and reproducible plasma treatment of complex biological surfaces poses a major hurdle to the widespread adoption of CAPs for medical applications. Predictive modeling of the mutual interactions between the plasma and biological surfaces and, thus, systematic approaches to quantify and predict plasma treatment outcomes remain largely elusive due to the lack of mechanistic understanding of plasma-surface interactions that can span across vastly different length-and time-scales. In addition, real-time sensing capabilities in biomedical CAP devices are often limited, which can be detrimental to plasma treatment due to the intrinsic plasma and surface variability during the treatment, as well as sensitivity to external perturbations. All of these challenges can make reproducible and effective plasma treatment of biological surfaces difficult to realize, which is further compounded by errors due to human operation of hand-held CAP devices. Machine learning and data-driven approaches can be particularly useful in addressing these challenges in three major ways: (i) data-driven modeling of hard-to-model plasma-surface interactions and plasma treatment outcomes; (ii) learning data analytics for plasma and surface diagnostics in real-time; and (iii) developing predictive controllers that enable reliable and effective CAP treatments. Furthermore, this paper discusses the promise of machine learning to accelerate plasma medicine research in these areas, toward machine learning-assisted and automated CAP treatment of complex biological surfaces.

60 APPLIED LIFE SCIENCES↗
NASA NTRSDate not supplied

Plasma for Crewed Transit and Planetary Habitation

As human exploration moves beyond low Earth orbit, innovative life support and resource production systems become forerunners for human colonization. Plasma systems allow for complex chemical processes while mitigating consumable needs. Plasma technology and applications can redefine the space environment. With this, scientists at NASA are looking to close known space technology gaps and create a paradigm shift in space-based applications. NASA’s Kennedy Space Center is exploring the use of low-temperature plasma for applications in agriculture, sanitation ,regolith reduction, waste gasification, water activation, and nutrient recovery techniques. Using low temperature plasmas, we report on the success criteria and experimental results for plasma applications for crewed transit and planetary habitation.

Plasma↗
NASA NTRSDate not supplied

Plasma for Crewed Transit and Planetary Habitation

As human exploration moves beyond low Earth orbit, innovative life support and resource production systems become forerunners for human colonization. Plasma systems allow for complex chemical processes while mitigating consumable needs. Plasma technology and applications can redefine the space environment. With this, scientists at NASA are looking to close known space technology gaps and create a paradigm shift in space-based applications. NASA’s Kennedy Space Center is exploring the use of low-temperature plasma for applications in agriculture, sanitation, regolith reduction, waste gasification, water activation, and nutrient recovery techniques. Using low temperature plasmas, we report on the success criteria and experimental results for plasma applications for crewed transit and planetary habitation.

Waste management↗
NASA NTRS1989

Causality of plasma permittivity with loss and restoring terms

The causality of the complex permittivity for a plasma model in which both loss and restoring terms are included is shown. Discussions as to what occurs in this causality property when the loss and restoring terms vanish are presented. Results are shown to agree with earlier work.

Cockrell, C. R.↗
NASA NTRS2010

Modeling of the Convection and Interaction of Ring Current, Plasmaspheric and Plasma Sheet Plasmas in the Inner Magnetosphere

Distinctive sources of ions reside in the plasmasphere, plasmasheet, and ring current regions at discrete energies constitute the major plasma populations in the inner/middle magnetosphere. They contribute to the electrodynamics of the ionosphere-magnetosphere system as important carriers of the global current system, in triggering; geomagnetic storm and substorms, as well as critical components of plasma instabilities such as reconnection and Kelvin-Helmholtz instability at the magnetospheric boundaries. Our preliminary analysis of in-situ measurements shoves the complexity of the plasmas pitch angle distributions at particularly the cold and warm plasmas, vary dramatically at different local times and radial distances from the Earth in response to changes in solar wind condition and Dst index. Using an MHD-ring current coupled code, we model the convection and interaction of cold, warm and energetic ions of plasmaspheric, plasmasheet, and ring current origins in the inner magnetosphere. We compare our simulation results with in-situ and remotely sensed measurements from recent instrumentation on Geotail, Cluster, THEMIS, and TWINS spacecraft.

Fok, Mei-Ching↗
DOE OSTI2022

Influence of temporal variations in plasma conditions on the electric potential near self-organized dust chains

Self-organization of dust grains into stable filamentary dust structures (or “chains”) largely depends on dynamic interactions between individual charged dust grains and complex electric potential arising from the distribution of charges within a local plasma environment. Recent studies have shown that the positive column of the gas discharge plasma in the Plasmakristall-4 (PK-4) experiment at the International Space Station supports the presence of fast-moving ionization waves, which lead to variations of plasma parameters by up to an order of magnitude from the average background values. The highly variable environment resulting from ionization waves may have interesting implications for the dynamics and self-organization of dust particles, particularly concerning the formation and stability of dust chains. Here, we investigate the electric potential surrounding dust chains in the PK-4 experiment by employing a molecular dynamics model of the dust and ions with boundary conditions supplied by a particle-in-cell with Monte Carlo collision simulation of the ionization waves. The model is used to examine the effects of the plasma conditions within different regions of the ionization wave and compare the resulting dust structure to that obtained by employing the time-averaged plasma conditions. Here, the comparison between simulated dust chains and experimental data from the PK-4 experiment shows that the time-averaged plasma conditions do not accurately reproduce observed results for dust behavior, indicating that more careful treatment of plasma conditions in the presence of ionization waves is required. It is further shown that commonly used analytic forms of the electric potential do not accurately describe the electric potential near charged dust grains under these plasma conditions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Kinetic effects of self-organization in low-temperature magnetized plasmas (Final Report for DE-SC0019045: 9/1/2018-8/31/2019)

The research goal of this Early Career Research Program project is to advance the science of low temperature magnetized plasmas using first-principles kinetic, e.g., solving the Boltzmann equation, models. A better understanding of the plasma transport properties, such as electrical resistivity and thermal conductivity must be obtained to better control and design magnetized plasma sources. A key physical phenomenon in low-temperature magnetized plasmas is the self-organization of plasma flows, e.g., coherent plasma structures and transition between different discharge modes. Understanding the physics of coherent plasma structures has been identified as one of the four important frontier topics in a recent workshop by the Office of Fusion Energy Science. These self-emerging plasma patterns results from the nonlinear coupling between plasma constituents (ions, electrons, and neutral atoms), electromagnetic fields, and materials. The physics of low-temperature magnetized plasmas is particularly complex because (i) the collisionless instabilities affect collisional phenomena (ionization, transport, etc.) and vice versa and (ii) the presence of materials (sheath, electron injection, etc.) influences the bulk plasma properties in low-temperature plasma (LTP) devices. Computational models of these plasma flows remain challenging because the plasma density can vary several orders of magnitudes, a wide range of temporal and spatial scales must be resolved, the phenomena are inherently three-dimensional, and various physical processes, such as wall interaction, instabilities, inelastic collisions, etc., must be simultaneously and self-consistently taken into account. Understanding the fundamental transport mechanisms in cross-field configurations enables additional controllability of plasma properties and electron energy distribution functions (EEDFs).

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Experimental and computational investigation into the hydrodynamics and chemical dynamics of laser ablation aluminum plasmas

Laser ablation plasma chemistry is governed by a complex interplay between hydrodynamic plasma-gas mixing processes, thermodynamics, and rapid high-temperature chemical reactions. Here, in this work, we investigate the gas-phase oxidation chemistry of ns-laser ablation aluminum plasmas in air using optical spectroscopy combined with advanced multi-physics modeling. Experimental measurements demonstrate the formation of AlO in the plasma plume as early as 1 μs while computational results reveal that several Al x O y species are distributed in the periphery of the plume at even earlier times (<20 ns) in the presence of large temperature gradients and strong shockwaves. Interactions with the ablation crater during rapid plume expansion are shown to initiate vortex formation, followed by mixing dynamics that work to pull AlO into the vortices to react with gas-phase Al to form Al 2 O. Oxygen and several aluminum oxides are simultaneously pulled up through the stem of the fireball, encouraging further intermixing between reacting species and enhanced molecular formation. This work concludes that chemical dynamics in laser ablation plasmas is driven by diffusion processes, concentration gradients, and plume hydrodynamics while strong shockwaves generated during laser ablation do not impede chemical reactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

hPIC2: A hardware-accelerated, hybrid particle-in-cell code for dynamic plasma-material interactions

The exascale era of high performance computing promises to bring the field of computational plasma physics ever closer to the goal of accurate multiscale modeling. Such computers will rely on hardware acceleration to offload work to dedicated components, notably general-purpose graphics processing units (GPUs). However, devices from different manufacturers require software to be written with different parallel programming models, greatly increasing the code maintenance burden of applications designed to perform on more than one such device. hPIC2 is a hybrid plasma simulation code developed with the Kokkos performance portability framework to target the architectures that will drive exascale computing for the foreseeable future. As a hybrid simulation code, hPIC2 investigates the simultaneous use of various plasma models on the same domain, at the same time. hPIC2 also optionally couples to RustBCA, which accurately models ion-material interactions using the binary collision approximation (BCA) method. In conclusion, hPIC2 therefore achieves scalable performance on a variety of computing architectures when simulating complex and diverse plasmas, particularly near plasma-material interfaces.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS2011

Variability of Thermosphere and Ionosphere Responses to Solar Flares

We investigated how the rise rate and decay rate of solar flares affect the thermosphere and ionosphere responses to them. Model simulations and data analysis were conducted for two flares of similar magnitude (X6.2 and X5.4) that had the same location on the solar limb, but the X6.2 flare had longer rise and decay times. Simulated total electron content (TEC) enhancements from the X6.2 and X5.4 flares were 6 total electron content units (TECU) and approximately 2 TECU, and the simulated neutral density enhancements were approximately 15% -20% and approximately 5%, respectively, in reasonable agreement with observations. Additional model simulations showed that for idealized flares with the same magnitude and location, the thermosphere and ionosphere responses changed significantly as a function of rise and decay rates. The Neupert Effect, which predicts that a faster flare rise rate leads to a larger EUV enhancement during the impulsive phase, caused a larger maximum ion production enhancement. In addition, model simulations showed that increased E x B plasma transport due to conductivity increases during the flares caused a significant equatorial anomaly feature in the electron density enhancement in the F region but a relatively weaker equatorial anomaly feature in TEC enhancement, owing to dominant contributions by photochemical production and loss processes. The latitude dependence of the thermosphere response correlated well with the solar zenith angle effect, whereas the latitude dependence of the ionosphere response was more complex, owing to plasma transport and the winter anomaly.

Qian, Liying↗
DOE OSTI2025

Diagnostics: Chapter 8 of the special issue: on the path to tokamak burning plasma operation

This chapter presents the activity conducted by the ITPA topical group (TG) on Diagnostics over about the last 15 years. Following a general introduction of the ITER Diagnostics led by their measurement roles, the document is organized in several subchapters detailing the design support, research and development activity conducted by each of the specialist working groups (WGs) of the TG. Please note that the magnetic diagnostics were supported at the TG without a specific WG. Their status is included in the general introduction. In the following some highlights of the subchapter’s contents are provided. Recent advances in ITER first wall (FW) diagnostics for the measurements of plasma-metallic wall interaction in support of the ITER research plan are reported. An InfraRed imaging Video Bolometer for ITER has been developed and tested on several tokamaks to measure the radiated power loss. A laser-induced breakdown spectroscopy (LIBS) technique which utilizes a pulsed laser beam to ablate locally by forming a crater, will measure local tritium inventory in the FW material. Real-time Residual Gas Analyzers will measure the neutral gas composition in a divertor port and an equatorial port during plasma operation. Due to the full metallic FW environment, the plasma-wall interaction in ITER will face several challenges such as the compromised radiated power and divertor heat flux measurements by reflection. Ray tracing and analysis codes have been developed to eliminate and correct the effects of reflection in the measurements. The characteristics of the reflecting surfaces depending on the roughness and angle of the incidence have been measured by dedicated experiments, and the results were applied to the reflection elimination. For the measurement of the metallic impurity radiation induced by eroded metallic atoms, a vacuum ultraviolet spectrometer has been developed and tested. An extensive thermonuclear diagnostic suite will be required to support the operation of ITER and the planned experimental program for future burning plasma experiments. Due to the harsh environmental conditions, the implementation of diagnostic systems in ITER is a major challenge. These conditions include high levels of neutron and gamma fluxes, neutron heating, particle bombardment. Therefore, the selection and design of diagnostic systems must take into account a number of phenomena previously unseen in diagnostic design. For this reason, the measurement of neutrons and confined or lost fast ions, with particular emphasis on alpha particles, is critical to ITER. The diagnostics associated with these measurements will be important for future plasma-burning experiments at ITER. The high neutron emission and very large plasma size in ITER make neutron diagnostics the main diagnostic method used to measure plasma parameters such as fusion power, fusion power density, ion temperature, energy of fast ions and their spatial distributions in the plasma core. Active spectroscopy techniques are methods where a neutral particle beam is injected into the plasma and information on plasma parameters is extracted from the measurement of line emission resulting from the beam-plasma interaction, either by plasma ions or by beam atoms. Spatial localization is achieved by crossing the beamline and multiple observation lines. The ITER plasma will be a high temperature, moderately dense, fully ionized collisional plasma. The plasma facing surfaces are principally metallic being fashioned from beryllium or tungsten but many other elements, arising from either structural or from operational needs, may enter this plasma. The energy range of the emitted photons range from meV (infra-red) to multi keV (x-rays) and originate from all areas of the plasma volume. The primary role of passive emission diagnostics is to identify what is in the plasma from spectral signatures. Extracting quantitative information from these measurements such as impurity content, ion temperature, rotation, degree of detachment and radiated power depends on calibrated instruments, a physics model of the atomic and molecular processes and plasma transport and an analysis workflow that takes into account environmental effects such as reflections. The particular needs for ITER have prompted a multi-machine, many-year effort to address all these aspects and this chapter reviews the work on diagnostic design, experiments and new analysis techniques. An overview of the laser diagnostics to be implemented on ITER is also provided in this paper. This includes descriptions of the Thomson scattering in the core, edge and divertor regions, polarimetry and interferometry diagnostics used for measuring plasma density and also measurements of helium density in the divertor using Laser Induced Flourescence. Techniques which can allow improvements on current measurements are also addressed in particular expanding poloidal polarimetry measurements to measure field fluctuations and proposed use of dispersion interferometery which has a number of advantages over existing methods. This paper identifies particular areas where further research and testing on existing tokamaks is useful even at this advanced stage to inform the design of diagnostics for ITER. Outstanding areas of concern for the implementation of laser diagnostics, in particular with a view to reliable operation are identified. An overview of the latest developments of microwave diagnostic systems and techniques is given. The primary focus is the contributions for ITER—the next step burning plasma experiment—which is supplemented by describing recent progress of techniques applicable for fusion experiments beyond ITER. The contributions are intentionally kept concise, and are being supplemented by a rich list of references for further studies. Radiation induced effects are receiving continuous and well-deserved attention of the ITER diagnostic community and they are in many cases one of the primary design drivers of the ITER diagnostic systems. The paper summarizes recent progress in this area focusing primarily on the ITER diagnostics but in some cases provides also outlook for the possible solutions for even more demanding radiation environment of fusion reactors beyond ITER. Despite advancements in the area of modeling and simulation of various radiation induced effects, experimental testing in a nuclear environment as close as possible to the target one is still seen as unavoidable for proper qualification of particular diagnostic functional elements. Recent advancement within three diagnostic areas: optical diagnostics, magnetics and bolometers is covered. Encouraging results on qualification of silica glass vacuum window assemblies are presented. In the area of magnetic sensors, progress of irradiation tests performed on ITER in-vessel LTCC inductive sensors is presented with outlook for novel technological approaches to inductive sensors utilizing thick printing and photolithography technologies being highlighted. Summary of advancements in the area of steady state magnetic field sensors based on Hall effect is given. New results of neutron irradiation test of the ITER borosilicate glass inserts for vacuum electrical feedthroughs are summarized finding negligible swelling at target level of neutron fluence. Off-line irradiation tests of fiber optic current sensors for plasma current measurement demonstrated that both for gamma doses up to 5 MGy and a total neutron fluence up to 10 15 cm −2 , radiation induced changes are still compatible with required measurement accuracy on ITER. The ITER bolometers are given as an example how considering radiation effects may influence the diagnostic design. Finally, outlook for future main R&D directions is outlined. All optical and laser-based diagnostics in ITER will be using mirrors to guide plasma radiation toward detectors, cameras and sensors. In the hostile plasma, radiation and particle environment the optical characteristics of diagnostic mirrors will degrade directly affecting the entire performance of involved diagnostic systems. An assessment of factors affecting mirror performance is provided. Among the prime adverse factors are deposition of plasma impurities, sputtering of mirror surface and steam ingress in the vicinity of mirrors. Within the International Tokamak Physics Activity with active support by ITER central team and domestic agencies, the structured research and development (R&D) program on mitigation of risks for diagnostic mirrors is underway. Within this program the mirror material development, the passive mitigation of mirror degradation by using diagnostic ducts and shutters along with an active mirror recovery program comprising the in-situ mirror cleaning and calibration is underway. Recent developments in diagnostic mirror R&D are described in this Chapter along with an example of their implementation of R&D solutions in ITER Infrared Thermography diagnostic. An assessment of still open engineering and physics questions, considerations on mirror risks during an early phase of ITER operation are given along with an overview of diagnostic mirror evolution in the late ITER operation stage toward the demonstration fusion power plant. Several crucial areas of diagnostic R&D outlined in ITER Research Plan are addressed. The basic control groups in a fusion reactor can be broken-down in five categories: (1) plasma position, magnetic configuration, and plasma current control, (2) profile control and confinement optimization, (3) MHD control and suppression, (4) edge dissipation control, radiation and plasma exhaust control and (5) break-down optimization. These categories are coupled via the physics (a control action in one domain will affect the other domains) and via shared actuators (e.g. ECRH for impurity accumulation avoidance, current density distribution control and MHD suppression). Consequently, a supervisory control system should determine the priority of the various control tasks, their couplings, and the interfaces with the safety and interlock system. For the systematic development of the various controllers taking the complexity of the plasma and the control system into account, a model-based approach is required. A short historical overview is given of the developments in systems and control theory and control engineering with special emphasis on those developments that are most relevant for Nuclear Fusion research and operation. An overview is given of the state of the field of fusion plasma control for the control categories. It will be shown how synthetic diagnostics are being developed in ITER and how they are used in diagnostic design and design validation and how they can be in model-based controller synthesis using relatively simple models. In modern control methods, multiple diagnostics are used to constrain relatively simple models. The constrained models provide an estimate for the state. This opens the route to state controllers, such as model predictive control. A major challenge in nuclear fusion research is the coherent combination of data from heterogeneous diagnostics and modeling codes for machine control and safety as well as physics studies. Measured data from different diagnostics often provide information about the same subset of physical parameters. Additionally, information provided by some diagnostics might be needed for the analysis of other diagnostics. A joint analysis of complementary and redundant data allows, e.g. to improve the reliability of parameter estimation, to increase the spatial and temporal resolution of profiles, to obtain synergistic effects, to consider diagnostics interdependencies and to find and resolve data inconsistencies. Physics-based modeling and parameter relationships provide additional information improving the treatment of ill-posed inversion problems. A coherent combination of all kind of available information within a probabilistic framework allows for improved data analysis results. The concept of integrated data analysis (IDA) in the framework of Bayesian probability theory is outlined and contrasted with conventional data analysis. Components of the probabilistic approach are summarized and specific ingredients beneficial for data analysis at fusion devices are discussed.

ITER↗
DOE OSTI2021

Coupled heat pulse propagation in two-fluid plasmas

Because of the large mass differences between electrons and ions, the heat diffusion in electron-ion plasmas exhibits more complex behavior than simple heat diffusion found in typical gas mixtures. In particular, heat is diffused in two distinct, but coupled, channels. Conventional single fluid models neglect the resulting complexity, and can often inaccurately interpret the results of heat pulse experiments. However, by recognizing the sensitivity of the electron temperature evolution to the ion diffusivity, not only can previous experiments be interpreted correctly, but informative simultaneous measurements can be made of both ion and electron heat channels.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1978

Development of a plasma sprayed ceramic gas path seal for high pressure turbine application

Development of the plasma sprayed graded, layered ZRO2/CoCrAlY seal system for gas turbine engine blade tip seal applications up to 1589 K (2400 F) surface temperature was continued. The effect of changing ZRO2/CoCrAlY ratios in the intermediate layers on thermal stresses was evaluated analytically with the goal of identifying the materials combinations which would minimize thermal stresses in the seal system. Three methods of inducing compressive residual stresses in the sprayed seal materials to offset tensile thermal stresses were analyzed. The most promising method, thermal prestraining, was selected based upon potential, feasibility and complexity considerations. The plasma spray equipment was modified to heat, control and monitor the substrate temperature during spraying. Specimens were fabricated and experimentally evaluated to: (1) substantiate the capability of the thermal prestrain method to develop compressive residual stresses in the sprayed structure and (2) define the effect of spraying on a heated substate on abradability, erosion and thermal shock characteristics of the seal system. Thermal stress analysis, including residual stresses and material properties variations, was performed and correlated with thermal shock test results. Seal system performance was assessed and recommendations for further development were made.

Shiembob, L. T.↗
NASA NTRS2014

On the Nature of the Hard X-Ray Sources SWIFT J1907.3-2050, IGR J12123-5802 and IGR J19552+0044

The INTEGRAL and Swift hard X-ray surveys have identified a large number of new sources, among which many are proposed as Cataclysmic Variables (CVs). Here we present the first detailed study of three X-ray selected CVs, Swift J1907.3-2050, IGRJ12123-5802, and IGRJ19552+0044 based on XMM-Newton, Suzaku, Swift observations and ground based optical and archival nIR/IR data. Swift J1907.3-2050 is highly variable from hours to monthsyears at all wavelengths. No coherent X-ray pulses are detected but rather transient features. The X-ray spectrum reveals a multi-temperature optically thin plasma absorbed by complex neutral material and a soft black body component arising from a small area. These characteristics are remarkably similar to those observed in magnetic CVs. A supra-solar abundance of nitrogen could arise from nuclear processed material from the donor star. Swift J1907.3-2050 could be a peculiar magnetic CV with the second longest (20.82 h) binary period. IGRJ12123-5802 is variable in the X-rays on a timescale of approximately or greater than 7.6 h. No coherent pulsations are detected, but its spectral characteristics suggest that it could be a magnetic CV of the Intermediate Polar (IP) type. IGRJ19552+0044 shows two X-ray periods, approximately 1.38 h and approximately 1.69 h and a X-ray spectrum characterized by a multi-temperature plasma with little absorption.We derive a low accretion rate, consistent with a CV below the orbital period gap. Its peculiar nIR/IR spectrum suggests a contribution from cyclotron emission. It could either be a pre-polar or an IP with the lowest degree of asynchronism.

X-ray Sources↗