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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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

HRTEM Imaging and Mechanistic Insights Into Carbon Nanotube Nucleation and Growth on Fe Nanocatalysts in a Thermal Plasma

Thermal plasma decomposition of natural gas is a scalable pathway for the production of hydrogen alongside high-value carbon nanotubes (CNTs). Metals evaporate from an electrode and condense to form seed nanoparticles that nucleate and grow CNTs. However, the lack of mechanistic understanding of the CNT nucleation and growth processes in thermal plasma makes control over CNT diameter, chirality, length, and yield difficult. We debundled and separated CNTs from soots produced using iron (Fe) nanocatalysts, and distributed them on monolayer graphene for high-resolution transmission electron microscopy (HRTEM) imaging to gain mechanistic insights. Full graphene encapsulation was found for relatively small Fe nanoparticles that were molten at high temperatures. Zigzag single-wall or double-wall CNTs (SWCNTs or DWCNTs) appeared to have grown out directly from the graphene covering on the conical or cylindrical bodies of small molten Fe nanodroplets with high curvature. Also, SWCNTs likely grew out from H- or O-atom etched single-wall carbon nanocones observed on conical Fe nanoparticles. A SWCNT/DWCNT could also be generated from the cracked opening of the graphene covering on a face-centered cubic (FCC) Fe nanoparticle. A simple, plausible pathway is proposed for the growth of an open, H-passivated, zigzag SWCNT involving reaction of CH 2 and CH radicals at high temperatures.

Fe nanocatalysts↗
DOE OSTI2025

DBD plasma-thermal tandem reactors for converting biogas to carbon nanofibers

Sequestering greenhouse gases (CO 2 and CH 4 ) in biogas into carbon nanofibers (CNF) offers a promising route to mitigate carbon emissions and create value-added solid carbon materials. Coupling non-thermal plasma with a thermocatalytic reactor in a tandem setup is a promising approach for tandem reactions of dry reforming of methane to synthesis gas and its subsequent conversion to CNF. Various parameters were studied to determine their effects on CNF growth. Decreasing the total flow rate resulted in an increase in CNF growth. Increasing the plasma power input or the plasma zone length also enhanced the production of CNF. These results illustrate that plasma-thermal tandem reactors can be used to synthesize CNF from biogas with tunable parameters that may be further optimized in future studies.

03 NATURAL GAS↗
DOE OSTI2024

MHD stability trends and improved performance of LHD inward-shifted configurations: The role of the neutral beam current drive and thermal plasma density

The aim of the present study is to analyze the effect of the neutral beam current drive (NBCD), thermal plasma density, and NBI operational regime on the stability of pressure gradient-driven modes (PGDM) and Alfvén eigenmodes (AE) in LHD inward-shifted configurations. The stabilization of n/m = 1/2 PGDM (n toroidal mode and m poloidal mode) is observed in the discharge 167 800 during the co-NBCD phase. The iota profile evolution measured by motional stark effect diagnostic may indicate the iota profile up-shift caused by the co-NBCD can induce a non-resonant transition of the rational surface 1/2 before the mode stabilization. The evolution of the iota profile and continuum gaps in the discharge 167 805 during the ctr-NBCD phase leads to the stabilization of the AE, caused by the narrowing of the continuum gap as the iota profile down-shift. Opposite stability trends are identified for PGDM and AE stability with respect to the thermal plasma density. A larger thermal plasma density (larger thermal β) further enhances PGDM although the continuum gaps are narrower leading to configurations with stable AEs. The linear stability of AEs is analyzed using the gyro-fluid FAR3d code to reproduce the AE stability trends observed in the experiments with respect to the NBCD and thermal plasma density. The analysis of hypothetical scenarios dedicated to study different NBI operational regimes with respect to EP energy, and β and radial density profiles indicate off-axis NBI operation shows a higher EP β threshold to destabilize AEs compared to on-axis configuration. This is explained by the presence of a TAE gap in the inner plasma region, easily destabilized by an on-axis NBI injection. The control of the NBCD and thermal plasma in the discharge 167 800 shows a transitory stabilization of PGDM and AEs, as well as an improved discharge performance identified by an increment of the neutron fluxes.

Varela, Jacobo↗
DOE OSTI2023

Inclusion of Biological Targets in the Analysis of Electrical Characteristics of Non-Thermal Plasma Discharge

In Plasma Medicine studies, the effect of non-thermal plasma (NTP) on biological targets is typically correlated with the amount of stable reactive oxygen and nitrogen species produced in a liquid medium. The effect of NTP and the response of the biological target on cellular redox mechanisms is overlooked in these investigations. Additionally, the influence of electrical properties of cells on the physical properties of NTP is neglected. Therefore, we used a floating electrode dielectric barrier discharge plasma to explore the impact of cell structure, size, and viability of the biological target on the physical properties of NTP. Lissajous figures were used to determine circuit capacitance and energy per cycle during NTP exposure of different cell suspensions. We show that both, structural integrity and active enzymic processes of cells change the electrical properties of NTP. Correlations were also drawn between NTP-produced hydrogen peroxide and nitrite with measured capacitance. Our studies indicate that the observed changes between different cell suspensions may be due to a feedback loop between the biological target and the NTP source. In future studies, a more detailed analysis is needed to improve the control of clinical NTP devices.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Cooling flow regime of a plasma thermal quench

A large class of Laboratory, Space, and Astrophysical plasmas is nearly collisionless. When a localized energy or particle sink, for example, in the form of a radiative cooling spot or a black hole, is introduced into such a plasma, it can trigger a plasma thermal collapse, also known as a thermal quench in tokamak fusion. Here we show that the electron thermal conduction in such a nearly collisionless plasma follows the convective energy transport scaling in itself or in its spatial gradient, due to the constraint of ambipolar transport. As a result, a robust cooling flow aggregates mass toward the cooling spot and the thermal collapse of the surrounding plasma takes the form of four propagating fronts that originate from the radiative cooling spot, along the magnetic field line in a magnetized plasma. The slowest one, which is responsible for deep cooling, is a shock front.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

On the interaction between non-thermal plasmas and small metallic particles: plasmonic plasmas

The overall objective of this project is to advance the understanding of the interaction between low-pressure plasmas and nanoparticles uniformly dispersed within them. In particular we aim at (OBJECTIVE 1) providing a Langmuir probe measurement of the electron energy distribution function in a dusty plasma and (OBJECTIVE 2) investigating the influence that plasmonic nanoparticles have on the properties of non-thermal plasmas. This work is well aligned with the DOE-FES “General Plasma Science Experiment and Theory” program and with topics such as “dusty, non-neutral and antimatter plasmas” and “advanced plasma diagnostic”. The proposed project, while based on the PI’s expertise in the non-thermal plasma processing of nanoparticles, will allow the PI to deepen his knowledge in the area of basic plasma physics and diagnostics, and will support the development of his research program, in line with the scope of the Early Career program.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Modeling nanoparticle charge distribution in the afterglow of non-thermal plasmas and comparison with measurements

Particle charging in the afterglows of non-thermal plasmas typically take place in a non-neutral space charge environment. We model the same by incorporating particle-ion collision rate constant models, developed in prior work by analyzing particle-ion trajectories calculated using Langevin Dynamics simulations, into species transport equations for ions, electrons and charged particles in the afterglow. A scaling analysis of particle charging and additional Langevin Dynamics calculations of the particle-ion collision rate constant are presented to extend the range of applicability to ion electrostatic to thermal energy ratios of 300 and diffusive Knudsen number (that scales inversely with gas pressure) up to 2000. The developed collision rate constant models are first validated by comparing predictions of particle charge against measured values in a stationary, non-thermal DC plasma from past PK-4 campaigns published in Phys. Rev. Lett. 93(8): 085001 and Phys. Rev. E 72(1): 016406). The comparisons reveal excellent agreement within ±35% for particles of radius 0.6,1.0,1.3 μm in the gas pressure range of ~20-150 Pa. The experiments to probe particle charge distributions by Sharma et al. (J. Physics D: Appl. Phys. 53(24): 245204) are modeled using the validated particle-ion collision rate constant models and the calculated charge fractions are compared with measurements. The comparisons reveal that the ion/electron concentration and gas temperature in the afterglow critically influence the particle charge and the predictions are generally in qualitative agreement with the measurements. Along with critical assessment of the modeling assumptions, several recommendations are presented for future experimental design to probe charging in afterglows.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Collaborative Research: Understanding Nanoparticle-Plasma Interactions in Dusty Non-Thermal Plasmas by Nanoparticle Probes and Online Aerosol Characterization

Research Objectives The goal of this research project is to understand the nature of charge interactions between plasmas and aerosol particles. Specifically, the project has the following objectives: 1) Study the effect of solid nanoparticles on properties of an atmospheric pressure plasma. 2) Study the influence of plasma density on the final charge of nanoparticles. 3) Develop a theoretical understanding of charge decay and charge dynamics in the spatial afterglow in support of experimental observations of the final charge of nanoparticles exiting a plasma.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Surface Heat Load Analysis Due to Plasma Thermal Radiation on Equatorial Port 09

This paper reports calculated surface heat load owing to plasma thermal radiation, which will be applied to the surfaces of Equatorial Port 09 (EP09) diagnostic shield modules (DSMs) for thermal analysis during normal operation. The calculation assumes that the thermal energy will deposit uniformly in all directions from the plasma to the adjacent components and environment (i.e. gray body radiation). Assuming the temperature for the plasma surface, calculated view factors are used to determine the allocation of thermal energy to each component. The analysis provides an initial assessment of the thermal radiation heat load on the DSMs to be checked in structural/thermal analyses to verify significance. In conclusion, the designs of the EP09 components are still in the early preliminary phase, and changes are expected in the future.

ANSYS↗
DOE OSTI2024

In Situ Monitoring of Non-Thermal Plasma Cleaning of Surfactant Encapsulated Nanoparticles

Surfactants are widely used in the synthesis of nanoparticles, as they have a remarkable ability to direct their growth to obtain well-defined shapes and sizes. However, their post-synthesis removal is a challenge, and the methods used often result in morphological changes that defeat the purpose of the initial controlled growth. Moreover, after the removal of surfactants, the highly active surfaces of nanomaterials may undergo structural reconstruction by exposure to a different environment. Thus, ex situ characterization after air exposure may not reflect the effect of the cleaning methods. Here, combining X-ray photoelectron spectroscopy, in situ infrared reflection absorption spectroscopy, and environmental transmission electron microscopy measurements with CO probe experiments, we investigated different surfactant-removal methods to produce clean metallic Pt nanoparticles from surfactant-encapsulated ones. It was demonstrated that both ultraviolet-ozone (UV-ozone) treatment and room temperature O2 plasma treatment led to the formation of Pt oxides on the surface after the removal of the surfactant. On the other hand, when H2 was used for plasma treatment, both the Pt0 oxidation state and nanoparticle size distribution were preserved. In addition, H2 plasma treatment can reduce Pt oxides after O2-based treatments, resulting in metallic nanoparticles with clean surfaces. These findings provide a better understanding of the various options for surfactant removal from metal nanoparticles and point toward non-thermal plasmas as the best route if the integrity of the nanoparticle needs to be preserved.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Novel soft x-ray multi-energy camera to study thermal plasmas on WEST

A multi-energy soft x-ray (SXR) pinhole camera has been built, calibrated and deployed on the WEST tokamak to aid the study of thermal plasmas. This novel imaging diagnostic technique employs a 2D pixelated x-ray detector in which the lower energy threshold for photon detection can be adjusted independently on each pixel. This innovation allows the simultaneous measurement of x-rays with space, time and energy resolution. Measurements at lower energy (2–6 keV) dominated by tungsten line emission are used to estimate the tungsten concentration and the plasma ΔZ eff . Measurements at higher energy (11–18 keV), where only continuum emission is present, are employed to infer the plasma electron temperature. Other applications of this powerful diagnostic include the determination of the plasma SXR centroid vertical position, characterization of tungsten UFOs and various real-time measurements.

electron temperature↗
DOE OSTI2021

Non-Thermal Plasma as a Novel Strategy for Treating or Preventing Viral Infection and Associated Disease

Pathogenic viruses cause many human, animal, and plant diseases that are associated with substantial morbidity, mortality and socio-economic impact. Although effective strategies for combatting virus transmission and associated disease are available, global outbreaks of viral pathogens such as the virus responsible for the COVID-19 pandemic demonstrate that there is still a critical need for new approaches that can be used to interrupt the chain of viral infection and mitigate virus-associated pathogenesis. Recent studies point to non-thermal plasma (NTP), a partly ionized gas comprised of a complex mixture of reactive oxygen and nitrogen species along with physical effectors, as the potential foundation for new antiviral approaches. A more thorough understanding of the antiviral properties and safety of NTP has stimulated explorations of NTP as the basis for treatments of viral diseases. The recently described immunomodulatory properties of NTP are also being evaluated for potential use in immunotherapies of viral diseases as well as in antiviral vaccination strategies. In this review, we present the current state-of-the-art in addition to compelling arguments that NTP merits further exploration for use in the prevention and management of viral infections and associated diseases.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2023

Electron heat flux and propagating fronts in plasma thermal quench via ambipolar transport

The thermal collapse of a nearly collisionless plasma interacting with a cooling spot, in which the electron parallel heat flux plays an essential role, is both theoretically and numerically investigated. Here, we show that such thermal collapse, which is known as thermal quench in tokamaks, comes about in the form of propagating fronts, originating from the cooling spot, along magnetic field lines. The slow fronts, propagating with local ion sound speed, limit the aggressive cooling of plasma, which is accompanied by a plasma cooling flow toward the cooling spot. The extraordinary physics underlying such a cooling flow is that the fundamental constraint of ambipolar transport along the field line limits the spatial gradient of electron thermal conduction flux to the much weaker convective scaling, as opposed to the free-streaming scaling, so that a large electron temperature and, hence, pressure gradient can be sustained. The last ion front for a radiative cooling spot is a shock front where cold but flowing ions meet hot ions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Jacobian-free Newton–Krylov method for the simulation of non-thermal plasma discharges with high-order time integration and physics-based preconditioning

A preconditioning framework for the numerical simulation of non-thermal streamer discharges is developed using the Jacobian-free Newton-Krylov (JFNK) method. A reduced plasma fluid model is considered, consisting of electrons, one positive ion, one negative ion, and the electrostatic potential. Here, the plasma kinetics model includes ionization, electron-ion recombination, electron attachment, electron detachment, and ion-ion recombination. The governing equations are made dimensionless, discretized in space with finite differences, and integrated in time with a fully implicit method based on high-order backward differentiation formulas. The preconditioning framework is based on a linearized form of the governing equations and physics-based operator splitting. The efficiency of the preconditioning strategy is assessed through two test cases: streamer propagation between parallel plates and an axisymmetric pin-to-pin discharge. The fully implicit approach overcomes traditional restrictions in the time step size due to processes such as electron drift, electron diffusion, and dielectric relaxation. Excellent performance is observed through relevant statistics of the JFNK solver, although the number of linear iterations increases for the pin-to-pin discharge when nonlinear numerical boundary conditions are imposed at the electrodes. Performance studies show scalability with O(100-1000) processors for O(10M) unknowns with ample room for optimization.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Plasma thermal transport with a generalized 8-moment distribution function

Moment equations that model plasma transport require an ansatz distribution function to close the system of equations. The resulting transport is sensitive to the specific closure used, and several options have been proposed in the literature. Two different 8-moment distribution functions can be generalized to form a single-parameter family of distribution functions. The transport coefficients resulting from this generalized distribution function can be expressed in terms of this free parameter. This provides the flexibility of matching the 8-moment model to some validating result at a given magnetization value, such as Braginskii’s transport, or the more recent results of Davies et al. [Physics of Plasma, 28, 012305 (2021)]. Here, this process can be thought of as solving for the 8-moment distribution function that matches the value of a transport coefficient given by a Chapman-Enskog expansion, while retaining the improved physical properties, such as finite propagation speeds and time dependence which belong to the hyperbolic moment models. Since the presented generalized distribution function only has a single free parameter, only a single transport coefficient can be matched at a time. However, this generalization process may be extended to provide multiple free parameters. The focus of this Brief Communication is on the dramatically improved thermal conductivity of the proposed model compared to the two base moment models.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2026

Verification of global gyrokinetic simulation of low frequency mode excited by thermal plasma in spherical tokamak

A low frequency Alfven eigenmode in the ST40 spherical tokamak (ST) is found to be resonantly excited by thermal ions from global gyrokinetic GTC simulations. The analyses of phase-space resonances and wave-particle energy exchanges show that the Beta-induced Alfvén-Acoustic Eigenmode (BAAE) is primarily driven unstable by thermal ions, but is stabilized by energetic particles (EPs). When all kinetic effects are artificially suppressed, GTC simulations in the ideal magnetohydrodynamic (MHD) limit confirm the existence of the MHD eigenmode with a frequency in the BAAEs gap, as previously found by the ideal MHD code NOVA. The kinetic effects of thermal ions induce a frequency downshift compared to the stable BAAE in the MHD simulations. These results support the verification for global gyrokinetic simulations of the BAAE in the ST. However, the simulations do not explain the experimental observations of the BAAE in the ST40, possibly owing to the limitation of the collisionless gyrokinetic Monte Carlo model for the EPs.

Alfvén eigenmode↗
DOE OSTI2024

Collisionless cooling of perpendicular electron temperature in the thermal quench of a magnetized plasma

Thermal quench of a nearly collisionless plasma against an isolated cooling boundary or region is an undesirable off-normal event in magnetic fusion experiments, but an ubiquitous process of cosmological importance in astrophysical plasmas. Parallel transport theory of ambipolar-constrained tail electron loss is known to predict rapid cooling of the parallel electron temperature $T_{e\Vert}$ although $T_{e\Vert}$ is difficult to diagnose in actual experiments. Instead direct experimental measurements can readily track the perpendicular electron temperature $T_{e\bot}$ via electron cyclotron emission. The physics underlying the observed fast drop in $T_{e\bot}$ requires a resolution. Here two collisionless mechanisms, dilutional cooling by infalling cold electrons and wave-particle interaction by two families of whistler instabilities, are shown to enable fast $T_{e\bot}$ cooling that closely tracks the mostly collisionless crash of $T_{e\Vert}$. These findings motivate both experimental validation and reexamination of a broad class of plasma cooling problems in laboratory, space, and astrophysical settings.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗