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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Optical Diagnostics of Discharges in and in Contact With Liquids

Discharges in liquids have been the subject of intensive investigations for a broad range of applications and involve highly coupled and complex phenomena with timescales ranging from picoseconds to seconds and length scales from micrometers to centimeters. This review focuses on some of the challenges in optical diagnostics of discharges in and in contact with liquids; this includes the interpretation of optical emission spectra, the inherently stochastic nature of many discharge phenomena including the initial stages of plasma ignition, and the large gradients in species and plasma properties interfacing with a dynamic liquid interface. We report recent notable advances, controversies in interpretations of diagnostics, and remaining opportunities.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Study of synchronous RF pulsing in dual frequency capacitively coupled plasma

Low-pressure multi-frequency capacitively coupled plasmas (CCPs) are used for numerous etch and deposition applications in the semiconductor industry. Pulsing of the radio-frequency (RF) sources enables control of neutral and charged species in the plasma on a millisecond timescale. The synchronous (i.e. simultaneous, in-phase) pulsing of both power sources in a dual frequency CCP is examined in this article. Due to the low gas pressure, modeling has been done using the electrostatic particle-in-cell/Monte Carlo collision method. Here, the objective of this work is to investigate the sensitivity of the plasma properties to small changes in timing during synchronous pulsing of the two RF sources. It is demonstrated that small deviations in the on and off times of the two RF sources can lead to major changes in the plasma characteristics. This high sensitivity is of concern for process repeatability but can be utilized to enable better control of the dynamics of plasma-surface interaction. In the simulations, the pulsing parameters (on and off times and ramp rates) are varied and the temporal evolution of plasma characteristics such as electron density (n e ), species current at the electrode, and electron temperature are examined. It is demonstrated that if the low-frequency (LF) source is turned off a few μs before (or after) the high-frequency source, n e during the off-state is significantly higher (or lower) due to the frequency coupling effect. Similarly, turning on the LF source with a small delay results in a sharp increase in the plasma density when the RF sources are turned on.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Data Needs for Modeling Low-Temperature Non-Equilibrium Plasmas: The LXCat Project, History, Perspectives and a Tutorial

Technologies based on non-equilibrium, low-temperature plasmas are ubiquitous in today’s society. Plasma modeling plays an essential role in their understanding, development and optimization. An accurate description of electron and ion collisions with neutrals and their transport is required to correctly describe plasma properties as a function of external parameters. LXCat is an open-access, web-based platform for storing, exchanging and manipulating data needed for modeling the electron and ion components of non-equilibrium, low-temperature plasmas. The data types supported by LXCat are electron- and ion-scattering cross-sections with neutrals (total and differential), interaction potentials, oscillator strengths, and electron- and ion-swarm/transport parameters. Online tools allow users to identify and compare the data through plotting routines, and use the data to generate swarm parameters and reaction rates with the integrated electron Boltzmann solver. In this review, the historical evolution of the project and some perspectives on its future are discussed together with a tutorial review for using data from LXCat.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1992

Ion-cyclotron waves at Jupiter - Possibility of detection by Ulysses

Recent thermal plasma data and a computer code by Horne (1989) are employed to evaluate the linear-path-integrated gain of waves propagating through the Io to predict the Jovian plasma-wave environment. Estimates of the nonlinear saturation amplitudes are utilized with the thermal plasma data from two frequency bands to study the convective growth of the ion-cyclotron (IC) waves. Strong cyclotron resonant damping is theorized to prevent wave propagation to the lower latitudes, and the thermal plasma and cyclotron resonant energetic ions are expected to further confine the IC waves. L-mode waves below the O(+) gyrofrequency in the equatorial region of the torus are shown to inhabit an unstable region. The IC waves probably achieve nonlinear amplitudes regardless of plasma properties due to the rapid amplification in this region. It is suggested that the Ulysses data complicate the identification of the waves because the magnetometer is not adequately sensitive and because of the low frequency of the plasma-wave detector.

Mei, YI↗
NASA NTRS2001

Etching in Chlorine Discharges Using an Integrated Feature Evolution-Plasma Model

Etching of semiconductor materials is reliant on plasma properties. Quantities such as ion and neutral fluxes, both in magnitude and in direction, are often determined by reactor geometry (height, radius, position of the coils, etc.) In order to obtain accurate etching profiles, one must also model the plasma as a whole to obtain local fluxes and distributions. We have developed a set of three models that simulates C12 plasmas for etching of silicon, ion and neutral trajectories in the plasma, and feature profile evolution. We have found that the location of the peak in the ion densities in the reactor plays a major role in determining etching uniformity across the wafer. For a stove top coil inductively coupled plasma (ICP), the ion density is peaked at the top of the reactor. This leads to nearly uniform neutral and ion fluxes across the wafer. A side coil configuration causes the ion density to peak near the sidewalls. Ion fluxes are thus greater toward the wall's and decrease toward the center. In addition, the ions bombard the wafer at a slight angle. This angle is sufficient to cause slanted profiles, which is highly undesirable.

Hwang, Helen H.↗
NASA NTRS1977

A simulation model of time-dependent plasma-spacecraft interactions

A plasma simulation code is presented that models the time-dependent plasma properties in the vicinity of a spherical, charged spacecraft. After showing agreement with analytic, steady-state theories and ATS-6 satellite data, the following three problems are treated: (1) transient pulses from photoemission at various emission temperatures and ambient plasma conditions, (2) spacecharge limited emission, and (3) simulated plasma oscillations in the long wavelength limit.

Rothwell, P. L.↗
DOE OSTI2022

Tomographic imaging of atmospheric pressure plasma on complex surfaces

Many plasma types and behaviors such as streamer, arcs, cathode spots, anode spots, ionization waves, and magnetic field interactions create non-symmetric, fully 3D plasma structures. The plasma distribution in 3D space is heavily influenced by complex surfaces and the coupling interactions between plasma properties and the interfacing material properties. For example, ionization waves propagate in directions where ionization rates are highest, leading to complex configurations that are not fully understood or well characterized. Recent advances in laser diagnostics and models have been able to investigate well-controlled idealized plasmas in 2D fashion, but the complex structure in actual plasmas requires a technique than can provide a more complete 3D picture. However, 3D plasma diagnostics do not currently exist. To address this limitation, this activity will leverage available equipment to build a new tomographic optical imaging capability and advance the state-of-the-art in plasma diagnostics to investigate 3D phenomena on complex surfaces.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1978

Acceleration and heating of the solar wind

Some of the competing theories of solar wind acceleration and heating are reviewed, and the observations that are required to distinguish among them are discussed. In most cases what is required is measurement of plasma velocity and temperature and magnetic field, as near the sun as possible and certainly inside 20 solar radii; another critical aspect of this question is determining whether a turbulent envelope exists in this inner region, and if so, defining its properties. Plasma and magnetic observations from the proposed Solar Probe mission would thus yield a quantum jump in our understanding of the dynamics of the solar wind.

Barnes, A.↗
DOE OSTI2024

The Role of Laser Wavelength on the Early-stage Electron Density Evolution in Laser-Produced Plasma

In this study, a laser-produced plasma (LPP) was generated by focusing fundamental (1064 nm), second (532nm), and fourth (266 nm) harmonic radiation from a 6 ns Nd:YAG laser at a laser intensity of 10 GW/cm2 onto a copper target placed in vacuum. The early time evolution of the plasma between 0-70 ns following laser ablation was then analyzed using Nomarski interferometry. The dependence of plasma properties such as the electron density distribution, plume velocity, and plume morphology on the laser wavelength are discussed.

(280.5395) Plasma Diagnostics, (140.3440) Laser-in↗
NASA NTRS1975

Numerical procedure for analyzing Langmuir probe data

A numerical procedure is proposed for analyzing Langmuir probe data in the presence of a two-group plasma containing both primary and Maxwellian electrons. The procedure is known as a least-squares differential-correction technique for determining the unknown coefficients of the governing equation. It is shown that for a given set of input data the results of the analysis are unique and independent of the initial estimate of electron temperature, that convergence is fastest when electron temperature is overestimated, that the results are sensitive to the region of the curve used as input and also to the voltage increment, and that plasma properties determined by the proposed numerical procedure are either consistent with those determined graphically or closer to expected values. With a suitable data acquisition system, the Fortran IV program worked out for this procedure could be used to provide real-time plasma diagnostic information for an operating ion thruster.

Beattie, J. R.↗
NASA NTRS2009

Coronal Holes

This paper reviews measurements of the plasma properties in coronal holes and how these measurements are used to reveal details about the physical processes that heat the solar corona and accelerate the solar wind. Evidence is presented for both heating and acceleration of the solar wind by open flux tubes energized by footpoint-driven wave-like fluctuations, and for intermittent energy deposition from closed loops into the open-field regions. Special emphasis is given to spectroscopic and coronagraphic measurements that allow the highly dynamic nonequilibrium evolution of the plasma to be followed as the asymptotic conditions in interplanetary space are established in the extended corona. For example, the importance of kinetic plasma physics and turbulence in coronal holes has been affirmed by surprising measurements from the UVCS instrument on SOHO that heavy ions are heated to hundreds of times the temperatures of protons and electrons. These observations point to specific kinds of collisionless Alfven wave damping (i.e., ion cyclotron resonance). Despite our incomplete knowledge of the complex multi-scale plasma physics, much progress has been made toward the goal of understanding the physical processes ultimately responsible for producing the observed properties of coronal holes.

Cranmer, Steven R.↗
DOE OSTI2024

Development of spatially and temporally resolved electron density measurements for the assessment of radiation hydrodynamics simulations of laboratory X-ray photoionized plasmas

The photoionized plasma gas cell experiment is an established platform we use to make at-parameter (ξ > > 1 ergs cm s –1 ) measurements of plasma properties with application to high-energy astrophysical systems. We model the experiments with 1D radiation hydrodynamics simulations using the HELIOS-CR code to inform our understanding and assist in the interpretation of results. The simulations predict that the bulk of the plasma is in a quasi-uniform and hydrodynamically unperturbed state throughout the duration of the experiment. To evaluate this prediction, we introduced a photonic Doppler velocimetry (PDV) diagnostic to measure spatially and temporally resolved plasma electron density. The initial measurements were successful but had limitations that made model-data comparisons challenging. To address this, we re-designed the gas cell PDV diagnostic and doubled the number of measurement locations to sample across two thirds of the depth of the cell. We also present a comparison of the results from the upgraded PDV diagnostic to the HELIOS-CR simulations for the first time. As a result, the experimental data confirms the prediction of an unperturbed region in the bulk of the plasma but reveals discrepancies in the time evolution and spatial distribution of the simulated electron density.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Characterization of an RF-driven argon plasma at atmospheric pressure using broadband absorption and optical emission spectroscopy

Atmospheric pressure plasmas in argon are of particular interest due to the production of highly excited and reactive species enabling numerous plasma-aided applications. In this contribution, we report on absolute optical emission and absorption spectroscopy of a radio frequency (RF) driven capacitively coupled argon glow discharge operated in a parallel-plate configuration. This enabled the study of all key parameters including electron density and temperature, gas temperature, and absolute densities of atoms in highly electronically excited states. The space and time-averaged electron density and temperature were determined from the measurement of the absolute intensity of the electron-atom bremsstrahlung in the visible range. Considering the non-Maxwellian electron energy distribution function, an electron temperature (T e ) of 2.1 eV and an electron density (n e ) of 1.1 × 10 19 m –3 were obtained. The time-averaged and spatially resolved absolute densities of atoms in the metastable (1s 5 and 1s 3 ) and resonant (1s 4 and 1s 2 ) states of argon in pure Ar and Ar/He mixture were obtained by broadband absorption spectroscopy. The 1s 5 metastable atoms had the largest density near the sheath region with a maximum value of 8 × 10 17 m –3 , while all other 1s states had densities of at most 2 × 10 17 m –3 . Here, the dominant production and loss mechanisms of these atoms were discussed, in particular, the role of radiation trapping. We conclude with a comparison of the plasma properties of the argon RF glow discharges with the more common He equivalent and highlight their differences.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS2021

Magnetosphere–Ionosphere Coupling of Precipitating Electrons and Ionospheric Conductance

Modeling of electrodynamic coupling between the magnetosphere and ionosphere depends on accurate specification of ionospheric conductances produced by auroral precipitation. Magnetospheric models determine the plasma properties on magnetic field lines connected to the auroral ionosphere, but the precipitation of energetic particles into the ionosphere is the result of a two-step process. The first step is the initiation of electron precipitation into both magnetically conjugate points from Earth’s plasma sheet via wave–particle interactions. The second step consists of the multiple atmospheric reflections of electrons at the two magnetically conjugate points.

George V Khazanov↗
NASA NTRS2023

Finding the magnetopause location using soft X-ray observations and a statistical inverse method

Variability in the location and shape of the dayside magnetopause is attributed to magnetic reconnection, a fundamental process that enables the transfer of mass, energy, and momentum from the solar wind into the magnetosphere. The spatial and temporal properties of the magnetopause, under varying solar and magnetospheric conditions, remain largely unknown because empirical studies using in-situ observations are challenging to interpret. Global wide field-of-view (FOV) imaging is the only means to simultaneously observe the spatial distribution of the plasma properties over the vast dayside magnetospheric region and, subsequently, quantify the energy transport from the interplanetary medium into the terrestrial magnetosphere. Two upcoming missions, ESA/CAS SMILE and NASA’s LEXI will provide wide-field imagery of the dayside magnetosheath in soft X-rays, an emission generated by charge exchange interactions between high charge-state heavy ions of solar wind origin and exospheric neutral atoms. High-cadence two-dimensional observations of the magnetosheath will allow the estimation of dynamic properties of its inner boundary, the magnetopause, and enable studies of its response to changes in the solar wind dynamic pressure and interplanetary magnetic field orientation. This work introduces a statistically-based estimation approach based on inverse theory to estimate the spatial distribution of magnetosheath soft X-ray emissivities and, with this, identify the location of the magnetopause over the Sun−Earth line. To do so, we simulate the magnetosheath structure using the MHD-based OpenGGCM model and generate synthetic soft X-ray images using LEXI’s orbit and attitude information. Our results show that 3-D estimations using the described statistically-based technique are robust against Poisson-distributed shot noise inherent to soft X-ray images. Also, our proposed methodology shows that the accuracy of both three-dimensional (3-D) estimation and the magnetopause standoff distance calculation highly depends on the observational point.

Gonzalo Cucho-Padin↗
NASA NTRS1985

Electrostatic ion-cyclotron waves in a nonuniform magnetic field

The properties of electrostatic ion-cyclotron waves excited in a single-ended cesium Q machine with a nonuniform magnetic field are described. The electrostatic ion-cyclotron waves are generated in the usual manner by drawing an electron current to a small exciter disk immersed in the plasma column. The parallel and perpendicular (to B) wavelengths and phase velocities are determined by mapping out two-dimensional wave phase contours. The wave frequency f depends on the location of the exciter disk in the nonuniform magnetic field, and propagating waves are only observed in the region where f is approximately greater than fci, where fci is the local ion-cyclotron frequency. The parallel phase velocity is in the direction of the electron drift. From measurements of the plasma properties along the axis, it is inferred that the electron drift velocity is not uniform along the entire current channel. The evidence suggests that the waves begin being excited at that axial position where the critical drift velocity is first exceeded, consistent with a current-driven excitation mechanism.

Cartier, S. L.↗
DOE OSTI2024

Observation of tantalum deposition and growth on TiB2 and ZrB2 from PISCES-RF deuterium and helium plasma exposures

Deuterium and helium plasma exposures on bulk TiB2 and ZrB2 samples were performed using the PISCES-RF linear plasma device. 40 and 90 eV deuterium ion plasma exposures were performed at 240 and 800 °C sample temperatures, and 80 eV helium ion plasma exposures were performed at 800 °C sample temperatures. Following plasma exposures, it was discovered that two plasma conditions (90 eV deuterium and 80 eV helium at 800 °C) resulted in thick (>200 nm) tantalum-rich (>10 at%) surface features on the targets, presumably from tantalum sourced from a tantalum adapter mask or cap used as part of the target holder. This work aims to characterize these tantalum-rich features and examine the mechanisms of impurity deposition.Plasma-induced surface morphology of the tantalum-rich surface layers depends on plasma properties and target temperature and chemistry. Greater titanium sputtering compared to zirconium resulted in more distinct surface features in the TiB2 samples compared to the ZrB2 samples via increased, prompt deposition onto tantalum surface impurities. There is still uncertainty as to why thick tantalum deposition only occurred under some plasma exposure conditions but not others; it is likely due to tantalum sputtering by a combination of boron molecules from the targets and carbon-impurities in the tantalum mask or targets. Impurity driven surface features are a well-documented phenomena in samples exposed to plasma from linear plasma device facilities—this work confirms the occurrence of this and emphasizes the need for chemistry characterization of isolated post-mortem surface features in plasma-exposed samples.

Nuckols, Lauren↗