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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 1,099 records · Page 61
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Effect of nonuniform radial density distribution on the space charge dominated beam bunching

Beam dynamics of a space charge dominated beam during the bunch compression is studied self consistently for the case of fixed shape non-uniform bell shape and hollow shape density distributions in the transverse direction. We have used thick slices at different parts of the beam to account for variation in the beam radius in the study of the transverse dynamics. The longitudinal dynamics has been studied using the disc model. The axial variation of the radius of the slices and emittance growth arising from the phase dependence of the transverse rf forces are also included in the simulation. We have modified the beam envelope equation to take into account the longitudinal space charge effect on the transverse motion which arises due to the finite bunch size. To demonstrate the application of the theoretical formulations developed, we have studied a sinusoidal beam bunching system and presented detailed numerical results.

43 PARTICLE ACCELERATORS↗
DOE OSTI2026

Decomposition of methane diluted with inert gas in an RF discharge cell

Decomposition of methane using non-thermal plasmas is an attractive route for producing hydrogen-rich gases and valuable carbon nanomaterials. Understanding how plasma discharge modes influence methane decomposition in optimizing plasma-assisted chemical conversion remains unexplored. This study explores the coupling between the discharge structure and product selectivity in RF capacitively coupled discharges operating in methane/inert gas mixtures in the pressure range of 2–3 torr. Under our experimental conditions the discharge exhibits mode transitions from uniform to striated in Ar and Kr and from diffuse to contracted in Ar and Kr with <5% CH 4 . The discharges in He and Ne remained uniform under our operating conditions, and their mixtures with CH 4 remained diffuse. A 0-d model for Ar/CH 4 discharge established a threshold for contraction while also asserting the importance of Ar$^{*}_{\textrm{m}}$ in the dissociation and ionization processes. The highest degree of methane decomposition, >99.7% with the main products of acetylene and graphitized solid carbon was achieved in the contracted discharge mode for both Kr or Ar with ⩽5% CH 4 . We demonstrate that contraction can play a crucial role in the effective decomposition of methane with value-added products and that both the electronic and thermal properties of plasma gas are responsible for this effect.

RF plasma↗
NASA NTRS2002

Robe Development for Electrical Conductivity Analysis in an Electron Gun Produced Helium Plasma

The use of magnetohydrodynamic (MHD) power conversion systems, potentially coupled with a fission power source, is currently being investigated as a driver for an advanced propulsion system, such as a plasma thruster. The efficiency of a MHD generator is strongly dependent on the electrical conductivity of the fluid that passes through the generator; power density increases as fluid conductivity increases. Although traditional MHD flows depend on thermal ionization to enhance the electrical conductivity, ionization due to nuclear interactions may achieve a comparable or improved conductivity enhancement while avoiding many of the limitations inherent to thermal ionization. Calculations suggest that nuclear-enhanced electrical conductivity increases as the neutron flux increases; conductivity of pure He-3 greater than 10 mho/m may be achievable if exposed to a flux greater than 10(exp 12) neutrons/cm2/s.) However, this remains to be demonstrated experimentally. An experimental facility has been constructed at the Propulsion Research Center at the NASA Marshall Space Flight Center, using helium as the test fluid. High energy electrons will be used to simulate the effects of neutron-induced ionization of helium gas to produce a plasma. These experiments will be focused on diagnosis of the plasma in a virtually static system; results will be applied to future tests with a MHD system. Initial experiments will utilize a 50 keV electron gun that can operate at up to a current of 200 micro A. Spreading the electron beam over a four inch diameter window results in an electron flux of 1.5x 10(exp 13) e/sq cm/s. The equivalent neutron flux that would produce the same ionization fraction in helium is 1x10(exp 12) n/sq cm/s. Experiments will simulate the neutron generated plasma modeled by Bitteker, which takes into account the products of thermal neutron absorption in He-3, and includes various ion species in estimating the conductivity of the resulting plasma. Several different probes will be designed and implemented to verify the plasma kinetics model. System parameters and estimated operating ranges are summarized. The predicted ionization fraction, electron density, and conductivity levels are provided in for an equivalent neutron flux of 1x10(exp 12) n/cm2/s. Understanding the complex plasma kinetics throughout a MHD channel is necessary to design an optimal power conversion system for space propulsion applications. The proposed experiments seek to fully characterize the helium plasma and to determine the reliability of each measurement technique, such that they may be applied to more advanced MHD studies. The expected value of each plasma parameter determined from theoretical models will be verified experimentally by several independent techniques to determine the most reliable method of obtaining each parameter. The results of these experiments will be presented in the final paper.

Bragg-Sitton, Shannon M.↗
DOE OSTI2016

DE-SC0001605 Final Report

The aim of the original proposal was a basic plasma study to experimentally investigate the fundamental physics of how dense, fast-flowing, and field-aligned jets of plasma couple energy and momentum to a much larger, ambient, magnetized plasma. Coupling channels that were explored included bulk plasma heating and flow generation; shock wave production; and wave radiation, particularly in the form of shear and compressional Alfvén waves. The wave radiation, particularly to shear Alfvén waves was successfully modeled using the 3D Particle-In-Cell code, OSIRIS. Experimentally, these jets were produced via pulsed Nd:YAG laser ablation of solid carbon (graphite) rods, which were immersed in the main plasma column of the Large Plasma Device (LaPD) at UCLA’s Basic Plasma Science Facility (BaPSF.) The axial expansion of the laser-produced plasma (LPP) was supersonic and with parallel expansion speeds approximately equal to the Alfvén speed. The project was renewed and refocused efforts to then utilize the laser-produced plasmas as a tool for the disruption and reconnection of current sheets in magnetized plasmas

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Pseudospectral Maxwell solvers for an accurate modeling of Doppler harmonic generation on plasma mirrors with particle-in-cell codes

With the advent of petawatt class lasers, the very large laser intensities attainable on target should enable the production of intense high-order Doppler harmonics from relativistic laser-plasma mirror interactions. At present, the modeling of these harmonics with particle-in-cell (PIC) codes is extremely challenging as it implies an accurate description of tens to hundreds of harmonic orders on a broad range of angles. In particular, we show here that due to the numerical dispersion of waves they induce in vacuum, standard finite difference time domain (FDTD) Maxwell solvers employed in most PIC codes can induce a spurious angular deviation of harmonic beams potentially degrading simulation results. This effect was extensively studied and a simple toy model based on the Snell-Descartes law was developed that allows us to finely predict the angular deviation of harmonics depending on the spatiotemporal resolution and the Maxwell solver used in the simulations. Our model demonstrates that the mitigation of this numerical artifact with FDTD solvers mandates very high spatiotemporal resolution preventing realistic three-dimensional (3D) simulations even on the largest computers available at the time of writing. Finally, we finally show that nondispersive pseudospectral analytical time domain solvers can considerably reduce the spatiotemporal resolution required to mitigate this spurious deviation and should enable in the near future 3D accurate modeling on supercomputers in a realistic time to solution.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Pre-equilibrium photons from the early stages of heavy-ion collisions

Abstract We use QCD kinetic theory to compute photon production in the chemically equilibrating Quark-Gluon Plasma created in the early stages of high-energy heavy-ion collisions. We do a detailed comparison of pre-equilibrium photon rates to the thermal photon production. We show that the photon spectrum radiated from a hydrodynamic attractor evolution satisfies a simple scaling form in terms of the specific shear viscosityη/sand entropy densitydS/dζ∼ (Tτ 1/3 ) 3/2 ∞ . We confirm the analytical predictions with numerical kinetic theory simulations. We use the extracted scaling function to compute the pre-equilibrium photon contribution in$$ \sqrt{s_{NN}} $$ s NN = 2.76 TeV 0–20% PbPb collisions. We demonstrate that our matching procedure allows for a smooth switching from pre-equilibrium kinetic to thermal hydrodynamic photon production. Finally, our publicly available implementation can be straightforwardly added to existing heavy ion models.

Physics↗
DOE OSTI2024

Unraveling Nonequilibrium Generation of Atomic Nitrogen and Hydrogen in Plasma-Aided Ammonia Synthesis

In this study, nonequilibrium generation of atomic nitrogen and hydrogen governing ammonia production both in the gas phase and on the catalyst surface is critical to plasma-aided ammonia synthesis. Here, this work studies the nonequilibrium generation of atomic nitrogen and hydrogen with a focus on the kinetic role of vibrational energy transfer of hydrogen molecules in plasma-aided ammonia synthesis. By combining two-photon absorption laser-induced fluorescence measurements and plasma kinetic modeling, we found that plasma not only generates ammonia but also produces critical H, N, and NH radicals via both electron impact and vibrational energy transfer excitations. The vibrational energy transfer from the excited hydrogen H 2 (v = 1) to higher vibrational levels H 2 (v = 2–3) via the V–V exchange (H 2 (v)–H 2 (v)) and V–V' exchange (N 2 (v)–H 2 (v)) significantly enhances the H and NH production and then promotes the coupling between N and NH for ammonia synthesis both in the gas phase and on the catalyst surface.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Multidimensional modeling of non-equilibrium plasma generated by a radio-frequency corona discharge

Low-temperature plasma (LTP) ignition concepts rely on the production of radical and charged species to speed up the onset of combustion in spark-ignition engines. These features are responsible for the superior performance of LTP igniters under extremely dilute combustion operation that is not achievable by conventional spark igniters. Additionally, LTP discharges extend the lifetime of the igniters, due to the avoidance of spark processes. For these reasons, the engine research community and the automotive industry have shown growing interest in this technology in the recent years. As of today, computational fluid-dynamics (CFD) codes typically used by the multi-dimensional engine modeling community do not have reliable models to describe LTP ignition processes. One key missing piece of information is the physical and chemical properties of the plasma and their effect on combustion ignition. Most non-equilibrium plasma simulations reported in literature are based on simplified, canonical geometries, with simple discharge excitation schemes. Here we conduct multi-dimensional modeling of the non-equilibrium plasma generated by an application-relevant radio-frequency (RF) corona discharge in air. Three test cases are simulated, characterized by different environmental pressure levels and peak electrode voltage values at room temperature. Streamer penetration, electron number density, atomic oxygen production, and bulk gas temperature distribution in the first 10 sinusoidal pulses are presented and discussed. This model can be used as a key tool for an in-depth understanding of RF-corona discharge for automotive applications and provides the basis for future implementations of dedicated LTP ignition models in CFD codes.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Kinetic modeling of hot tail runaway electron generation during plasma disruptions using the JOREK code

The generation of runaway electrons (REs) during disruptions poses a significant challenge for the operation of tokamaks. The production of these high-energy electrons can cause substantial damage, particularly when the plasma current is high, making it a critical concern for ITER. For the high-temperature plasmas anticipated in ITER, the primary generation of REs may be dominated by the hot tail mechanism, which consists of the acceleration of hot electrons from the pre-disruption population which have not yet thermalized with the bulk following the rapid cooling of the plasma. To account for the significant 3D effects on RE production, a hot tail modeling framework has been developed within the non-linear 3D extended MHD code JOREK. This paper presents the structure of this framework, which is based on test electrons evolving in MHD fields. The verification of the method shows good agreement with the reference DREAM code for 0D test cases, as well as for axisymmetric simulations of 15 MA ITER H-mode disruption scenarios. Furthermore, a proof-of-principle application to a DIII-D case demonstrates the framework’s capability to capture for the first time the hot tail generation in 3D MHD simulations in realistic geometry. Preliminary results suggest that the production of REs is significantly reduced by stochastic losses.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Microwave ECR plasma electron flood for low pressure wafer charge neutralization

Modern ion implanters typically use dc arc discharge Plasma Electron Floods (PEFs) to neutralize wafer charge. The arc discharge requires using at least some refractory metal hardware, e.g. a thermionically emitting filament, which can be undesirable in applications where no metallic contamination is critical. rf discharge PEFs have been proposed to mitigate contamination risks but the gas flows required can result in high process chamber pressures. Axcelis has developed a microwave electron cyclotron resonance (ECR) PEF to provide refractory metals contamination-free wafer neutralization with low gas flow requirement. Our PEF uses a custom, reentrant cusp magnet field providing ECR and superior electron confinement. Stable PEF operation with extraction slits sized for 300 mm wafers can be attained at Xe gas flows lower than 0.2 sccm. Electron extraction currents can be as high as 20 mA at absorbed microwave powers < 70 W. On Axcelis' new medium current implanter, plasma generation has proven robust against pressure transients caused by, for example, photoresist outgassing by high power ion beams. Charge monitor and floating potential measurements along the wafer surface corroborate adequate wafer charge neutralization for low energy, high current ion beams.

43 PARTICLE ACCELERATORS↗
DOE OSTI2019

A ten-inch manipulator (TIM) based fast-electron spectrometer with multiple viewing angles (OU-ESM)

The measurement of angularly resolved energy distributions of MeV electrons is vital for gaining a better understanding of the interaction of ultra-intense laser pulses with plasma, especially for fast-ignition laser-fusion research. It is also important when evaluating the production of suprathermal (several 10-keV) electrons through laser-plasma instabilities in conventional hot-spot-ignition and shock-ignition research. For these purposes, we developed a ten-inch manipulator-based multichannel electron spectrometer — the Osaka University electron spectrometer (OU-ESM) — that combines angular resolution with high-energy resolution. The OU-ESM consists of five small electron spectrometers set at every 5°, with an energy range from ~40 keV to ~40 MeV. A low-magnetic-field option provides a higher spectral resolution for an energy range of up to ~5 MeV. We successfully gained angularly resolved electron spectra for various experiments on the OMEGA and OMEGA EP Laser Systems.

47 OTHER INSTRUMENTATION↗
DOE OSTI2011

Origin of extracted negative ions by 3D PIC-MCC modeling. Surface vs Volume comparison

The development of a high performance negative ion (NI) source constitutes a crucial step in the construction of Neutral Beam Injector (NBI) of the future fusion reactor ITER. NI source should deliver 40 A of H{sup -}(or D{sup -}), which is a technical and scientific challenge, and requires a deeper understanding of the underlying physics of the source and its magnetic filter. The present knowledge of the ion extraction mechanism from the negative ion source is limited and concerns magnetized plasma sheaths used to avoid electrons being co-extracted from the plasma together with the NI. Moreover, due to the asymmetry induced by the ITER crossed magnetic configuration used to filter the electrons, any realistic study of this problem must consider the three spatial dimensions. To address this problem, a 3D Particles-in-Cell electrostatic collisional code was developed, specifically designed for this system. Binary collisions between the particles are introduced using Monte Carlo Collision scheme. The complex orthogonal magnetic field that is applied to deflect electrons is also taken into account. This code, called ONIX (Orsay Negative Ion eXtraction), was used to investigate the plasma properties and the transport of the charged particles close to a typical extraction aperture [1]. This contribution focuses on the limits for the extracted NI current from both, plasma volume and aperture wall. Results of production, destruction, and transport of H{sup -} in the extraction region are presented. The extraction efficiency of H{sup -} from the volume is compared to the one of H{sup -} coming from the wall.

43 PARTICLE ACCELERATORS↗
DOE OSTI2019

Rapid activation product separations from fission products and soil matrixes

We report that a rapid method for the separation and qualitative analysis of several neutron activation products ( 198 Au, 192 Ir, 72 Ga, 51 Cr, 191/195m/197 Pt, 54 Mn, 57 Co, and 59 Fe) from fission products and soil matrixes has been developed. Analytes were isolated within 20 h using ion exchange chromatography. After separation, the activation products were characterized by γ-spectroscopy and inductively coupled plasma-optical emission spectroscopy. Validation experiments demonstrated versatility of the method, showing that the activation products could be isolated from fresh fission products and other contaminants associated with complex soil matrixes.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2019

Support for the 2018 Advanced Accelerator Concepts Workshop (Final Report)

We organized the 18th Advanced Accelerator Concepts (AAC18) Workshop at the Beaver Run Resort and Conference Center in Breckenridge, Colorado on August 12–17, 2018. AAC18 was organized under the sponsorship of the IEEE Council on Superconductivity and managed under the supervision of IEEE 2018 Advanced Accelerator Conference Committee. Workshop day-to-day management, including financial, was handled by a qualified conference management company. The 2018 meeting was devoted to cross-disciplinary discussions of advanced accelerator concepts, including progress in various plasma acceleration methods, new methods of particle acceleration and high energy photon generation, techniques for production of ultra-high accelerating gradients in media other than plasmas, diagnostics and control of particle and photon beams and various associated particle beam, RF and energy sources. The Workshop had 278 attendees, including a record 96 students. Attendees came from 12 countries representing a wide range of institutions. The workshop format consisted of plenary sessions in the morning with topical leaders from around the world presenting the latest breakthroughs to the entire workshop. In the late morning and afternoons attendees broke out into eight different Working Groups for more detailed presentations and discussions that were summarized on the final day of the workshop. In addition, there were student tutorial presentations on two afternoons to provide in depth education and training for the next generation of accelerator scientists, as well as a poster session one evening.

43 PARTICLE ACCELERATORS↗
NASA NTRSDate not supplied

Plasma for the Space Environment: An Overview of the Research at NASA's Kennedy Space Center

Human life amongst other planets requires vast technological advancements to sustain nutritional, environmental, and logistical needs. Plasma systems allow for advanced chemical processing while mitigating consumable needs or reliance on industrial infrastructure. Scientists at NASA’s Kennedy Space Center are attempting to close technology gaps with research into plasmas and their applications. Some such work includes the use of plasma for waste gasification, water activation, nutrient recovery techniques, lunar regolith reduction for oxygen extraction, and space crop production support. Here we report on the needs, success criteria, and results of plasma efforts for crewed transit and planetary habitation.

Plasma↗
DOE OSTI2014

Synchrotron radiation, pair production, and longitudinal electron motion during 10-100 PW laser solid interactions

At laser intensities above 10{sup 23} W/cm{sup 2}, the interaction of a laser with a plasma is qualitatively different to the interactions at lower intensities. In this intensity regime, solid targets start to become relativistically underdense, gamma-ray production by synchrotron emission starts to become an important feature of the dynamics and, at even higher intensities, electron-positron pair production by the non-linear Breit-Wheeler process starts to occur. In this paper, an analysis is presented of the effects of target density, laser intensity, target preplasma properties, and other parameters on the conversion efficiency, spectrum, and angular distribution of gamma-rays by synchrotron emission. An analysis of the importance of Breit-Wheeler pair production is also presented. Target electron densities between 10{sup 22} cm{sup −3} and 5 × 10{sup 24} cm{sup −3} and laser intensities covering the range between 10{sup 21} W/cm{sup 2} (available with current generation laser facilities) and 10{sup 24} W/cm{sup 2} (upper intensity range expected from the ELI facility are considered. Results are explained in terms of the behaviour of the head of the laser pulse as it interacts with the target.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS2013

Investigating Titan's Atmospheric Chemistry at Low Temperature in Support of the NASA Cassini Mission

Titan's atmosphere, composed mainly of N2 and CH4, is the siege of a complex chemistry induced by solar UV radiation and electron bombardment from Saturn's magnetosphere. This organic chemistry occurs at temperatures lower than 200 K and leads to the production of heavy molecules and subsequently solid aerosols that form the orange haze surrounding Titan. The Titan Haze Simulation (THS) experiment has been developed on the COSMIC simulation chamber at NASA Ames in order to study the different steps of Titan's atmospheric chemistry at low temperature and to provide laboratory data in support for Cassini data analysis. The chemistry is simulated by plasma in the stream of a supersonic expansion. With this unique design, the gas mixture is adiabatically cooled to Titan-like temperature (approx. 150 K) before inducing the chemistry by plasma discharge. Different gas mixtures containing N2, CH4, and the first products of the N2,-CH4 chemistry (C2H2, C2H4, C6H6...) but also heavier molecules such as PAHs or nitrogen containing PAHs can be injected. Both the gas phase and solid phase products resulting from the plasma-induced chemistry can be monitored and analyzed. Here we present the results of recent gas phase and solid phase studies that highlight the chemical growth evolution when injecting heavier hydrocarbon trace elements in the initial N2-CH4 mixture. Due to the short residence time of the gas in the plasma discharge, only the first steps of the chemistry have time to occur in a N2-CH4 discharge. However by adding acetylene and benzene to the initial N2-CH4 mixture, we can study the intermediate steps of Titan's atmospheric chemistry as well as specific chemical pathways. These results show the uniqueness of the THS experiment to help understand the first and intermediate steps of Titan fs atmospheric chemistry as well as specific chemical pathways leading to Titan fs haze formation.

Sciamma-O'Brien, Ella↗
DOE OSTI2024

Origin of deactivation of aqueous Na–CO 2 battery and mitigation for long-duration energy storage

Here, the development of long-duration energy storage technology is crucial to facilitate the efficient utilization of renewable energy sources while mitigating carbon dioxide production. In this study, we investigate the deactivation and reactivation mechanisms of the aqueous Na–CO 2 battery during extended cycling. We have designed the cathode to include non-precious intermetallic catalysts. As the cell undergoes repeated cycles, the voltage polarization during discharge progressively rises, eventually leading to the cell's deactivation and formation of decomposition products clogging the electrode surface. Results obtained from comprehensive characterization techniques, including conductive atomic force microscopy (cAFM), Raman spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and inductively coupled plasma-mass spectrometry provide insight into the decomposition products. We also showcase an electrochemical approach for regeneration of these aqueous cells. Our findings, along with the insights we have gained, provide a path toward creating long-duration systems with self-healing properties.

25 ENERGY STORAGE↗