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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Development of optical diagnostics for performance evaluation of arcjet thrusters

Laser and optical emission-based measurements have been developed and implemented for use on low-power hydrogen arcjet thrusters and xenon-propelled electric thrusters. In the case of low power hydrogen arcjets, these laser induce fluorescence measurements constitute the first complete set of data that characterize the velocity and temperature field of such a device. The research performed under the auspices of this NASA grant includes laser-based measurements of atomic hydrogen velocity and translational temperature, ultraviolet absorption measurements of ground state atomic hydrogen, Raman scattering measurements of the electronic ground state of molecular hydrogen, and optical emission based measurements of electronically excited atomic hydrogen, electron number density, and electron temperature. In addition, we have developed a collisional-radiative model of atomic hydrogen for use in conjunction with magnetohydrodynamic models to predict the plasma radiative spectrum, and near-electrode plasma models to better understand current transfer from the electrodes to the plasma. In the final year of the grant, a new program aimed at developing diagnostics for xenon plasma thrusters was initiated, and results on the use of diode lasers for interrogating Hall accelerator plasmas has been presented at recent conferences.

Cappelli, Mark A.↗
DOE OSTI2023

MRT 7365: Power flow physics and key physics phenomena

The Z accelerator at Sandia National Laboratories conducts z-pinch experiments at 26 MA in support of DOE missions in stockpile stewardship, dynamic materials, fusion, and other basic sciences. Increasing the current delivered to the z-pinch would extend our reach in each of these disciplines. To achieve increases in current and accelerator efficiency, a fraction of Z’s shots are set aside for research into transmission-line power flow. These shots, with supporting simulations and theory, are incorporated into this Advanced Diagnostics milestone report. The efficiency of Z is reduced as some portion of the total current is shunted across the transmission-line gaps prior to the load. This is referred to as “current loss”. Electrode plasmas have long been implicated in this process, so the bulk of dedicated power-flow experiments are designed to measure the plasma environment. The experimental analyses are enhanced by simulations conducted using realistic hardware and Z voltage pulses. In the same way that diagnostics are continually being improved for sensitivity and resolution, the modeling capability is continually being improved to provide faster and more realistic simulations. The specifics of the experimental hardware, diagnostics, simulations, and algorithm developments are provided in this report. The combined analysis of simulation and data confirms that electrode plasmas have the most detrimental impact on current delivery. Experiments over the last three years have tested the theoretical current-loss mechanisms of enhanced ion current, plasma gap closure, and Hall-related current. These mechanisms are not mutually exclusive and may be coincident in the final feed as well as in upstream transmission lines. The final-feed geometries tested here, however, observe lower-density plasmas without dominant ion currents which is consistent with a Hall-related current. The picture of plasma formation and transport formed from experiment and simulation is informing hardware designs being fielded on Z now and being proposed for the Next-Generation Pulsed Power (NGPP) facility. In this picture, the strong magnetic fields that heat the electrodes above particle emission thresholds also confine the charged particles near the surface. Some portion of the plasmas thus formed is transported into the transmission-line gap under the force of the electric field, with aid from plasma instabilities. The gap plasmas are then transported towards the load by a cross-field drift, where they accumulate and contribute to a likely Hall-related cross-gap current. The achievements in experimental execution, model validation, and physical analysis presented in this report set the stage for continued progress in power flow and load diagnostics on Z. The planned shot schedule for Z and Mykonos will provide data for extrapolation to higher current to ensure the predicted performance and efficiency of a NGPP facility.

43 PARTICLE ACCELERATORS↗
DOE OSTI2015

The impact of plasma dynamics on the self-magnetic-pinch diode impedance

In this study, the self-magnetic-pinch diode is being developed as an intense electron beam source for pulsed-power-driven x-ray radiography. The basic operation of this diode has long been understood in the context of pinched diodes, including the dynamic effect that the diode impedance decreases during the pulse due to electrode plasma formation and expansion. Experiments being conducted at Sandia National Laboratories' RITS-6 accelerator are helping to characterize these plasmas using time-resolved and time-integrated camera systems in the x-ray and visible. These diagnostics are analyzed in conjunction with particle-in-cell simulations of anode plasma formation and evolution. The results confirm the long-standing theory of critical-current operation with the addition of a time-dependent anode-cathode gap length. The results may suggest that anomalous impedance collapse is driven by increased plasma radial drift, leading to larger-than-average ion v r × B θ acceleration into the gap.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Additively manufactured electrodes for plasma and power-flow studies in high-power transmission lines on the 1-MA MAIZE facility

Power-flow studies on the 30-MA, 100-ns Z facility at Sandia National Laboratories have shown that plasmas in the facility’s magnetically insulated transmission lines (MITLs) and double post-hole convolute can result in a loss of current delivered to the load. To study power-flow physics on the 1-MA, 100-ns MAIZE facility at the University of Michigan, planar MITL loads and planar post-hole convolute loads have been developed that extend into the lines of sight for various imaging diagnostics on MAIZE. These loads use 3D-printed dielectric support structures lined with thin foils of either aluminum or stainless steel. Here, the metal foils serve as the current-carrying power-flow surfaces, which generate plasma during the current pulse. The foil thickness (50 µm) and widths (11.5–16 mm) are selected to ensure a sufficient linear current density (0.5–0.7 MA/cm) for plasma formation. Laser backlighting (532 nm) and visible-light self-emission imaging capture the overall plasma evolution in the anode–cathode gaps, including the gap closure velocities (1–4 cm/μs).

47 OTHER INSTRUMENTATION↗
DOE OSTI2013

On the magnetic field signal radiated by an atmospheric pressure room temperature plasma jet

In this paper, the magnetic field signal radiated from an atmospheric pressure room temperature plasma plume is measured. It's found that the magnetic field signal has similar waveform as the current carried by the plasma plume. By calibration of the magnetic field signal, the plasma plume current is obtained by measuring the magnetic field signal radiated by the plasma plume. In addition, it is found that, when gas flow modes changes from laminar regime to turbulence regime, the magnetic field signal waveforms appears different, it changes from a smooth curve to a curve with multiple spikes. Furthermore, it is confirmed that the plasma plume generated by a single electrode (without ground electrode) plasma jet device carries higher current than that with ground electrode.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Effect of a floating electrode on a plasma jet

Two kinds of floating electrode, floating dielectric barrier covered electrode (FDBCE) and floating pin electrode (FPE), which can enhance the performance of plasma jet are reported. The intense discharge between the floating electrode and power electrode decreased the voltage to trigger the plasma jet substantially. The transition of plasma bullet from ring shape to disk shape in the high helium concentration region happened when the floating electrode was totally inside the powered ring electrode. The enhanced electric field between propagating plasma bullet and ground electrode is the reason for this transition. The double plasma bullets happened when part of the FDBCE was outside the powered ring electrode, which is attributed to the structure and surface charge of FDBCE. As part of the FPE was outside the powered ring electrode, the return stroke resulted in a single intensified plasma channel between FPE and ground electrode.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

3D numerical investigation of a free-burning argon arc with metal electrodes using a novel sheath coupling procedure

In this study, a novel coupling procedure describing the complicated plasma-electrode interaction process has been developed and applied into the 3D finite volume simulation of a direct current tungsten inert gas (TIG) welding system. This is achieved by making the space charge layer (sheath) incorporated into the computation domain and interact with both bulk plasma and cathode through the effective electrical conductivity. Both chemical and thermal nonequilibrium phenomena as well as the self-induced magnetic fields have been taken into consideration by the model to ensure a realistic numerical description of a non-thermal arc. The applicability of this coupling procedure is further improved by calculating the real electric potential, which is capable of accounting for the effects of the complicated drift and diffusion processes. Numerical results of both 100 and 200A discharge currents are presented, field reversal is obtained at near-anode regions in both cases, which is followed by the negative anode sheath potential drop. The region of the strongest electron overpopulation appears at the intersection of plasma fringes and electrode surface. Finally, numerical results of plasma temperature and voltage show good agreement with experimental measurements.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Design of the new extraction grid for the NIO1 negative ion source

NIO1 is a compact source of negative ions jointly developed by RFX and INFN, to study the physics of production and acceleration of H{sup −} beams. Negative ions, up to 120 mA of current, are extracted from a radiofrequency driven plasma, by means of a gridded electrode (plasma grid, PG) featuring 9 apertures arranged in a 3x3 square lattice. The same aperture pattern is replicated in the following electrodes, allowing ion acceleration up to 60 keV. All electrodes are realized in copper, by electro-deposition technique, leaving empty slots in the metal to place magnets and to flow water for the grid cooling. The first set of electrodes was completed, installed in the source and tested. At the same time, an upgrade of the extraction system was carried out, in order to optimize the beam optics and to explore alternative electrostatic configurations. In particular, the accelerator will be modified by completely replacing the EG grid, exploiting the modularity of NIO1. The new electrode will feature other slots in between apertures, to place additional magnets. This allows testing different magnetic configurations, to optimize electron filtering and residual ion deflection. The present paper describes the theoretical activities driving the design of these new extractors, carried out with most updated numerical codes, and exploiting the synergy with the refined modeling of the 40 A ITER negative ion sources, under development at Consorzio RFX. Beam simulations are performed both with tracing codes (SLACCAD and OPERA) and with particle in cell codes (ACCPIC)

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Plasma spark discharge reactor and durable electrode

A plasma spark discharge reactor for treating water. The plasma spark discharge reactor comprises a HV electrode with a head and ground electrode that surrounds at least a portion of the HV electrode. A passage for gas may pass through the reactor to a location proximate to the head to provide controlled formation of gas bubbles in order to facilitate the plasma spark discharge in a liquid environment.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2012

Study of the near-electrode processes in quasi-steady plasma accelerators with impenetrable electrodes

Near-electrode processes in a coaxial plasma accelerator with equipotential impenetrable electrodes are simulated using a two-dimensional (generally, time-dependent) two-fluid MHD model with allowance for the Hall effect and the plasma conductivity tensor. The simulations confirm the theoretically predicted mechanism of the so-called 'crisis of current' caused by the Hall effect. The simulation results are compared with available experimental data. The influence of both the method of plasma supply to the channel and an additional longitudinal magnetic field on the development of near-electrode instabilities preceding the crisis of current is studied.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Development and Benchmarking of a Hybrid PIC Code For Dense Plasmas and Fast Ignition (Final Report)

Radiation processes play an important role in the study of both fast ignition and other inertial confinement schemes, such as plasma jet driven magneto-inertial fusion, both in their effect on energy balance, and in generating diagnostic signals. In the latter case, warm and hot dense matter may be produced by the convergence of a plasma shell formed by the merging of an assembly of high Mach number plasma jets. This innovative approach has the potential advantage of creating matter of high energy densities in voluminous amount compared with high power lasers or particle beams. An important application of this technology is as a plasma liner for the flux compression of magnetized plasma to create ultra-high magnetic fields and burning plasmas. HyperV Technologies Corp. has been developing plasma jet accelerator technology in both coaxial and linear railgun geometries to produce plasma jets of sufficient mass, density, and velocity to create such imploding plasma liners. An enabling tool for the development of this technology is the ability to model the plasma dynamics, not only in the accelerators themselves, but also in the resulting magnetized target plasma and within the merging/interacting plasma jets during transport to the target. Welch pioneered numerical modeling of such plasmas (including for fast ignition) using the LSP simulation code. Lsp is an electromagnetic, parallelized, plasma simulation code under development since 1995. It has a number of innovative features making it uniquely suitable for modeling high energy density plasmas including a hybrid fluid model for electrons that allows electrons in dense plasmas to be modeled with a kinetic or fluid treatment as appropriate. In addition to in-house use at Voss Scientific, several groups carrying out research in Fast Ignition (LLNL, SNL, UCSD, AWE (UK), and Imperial College (UK)) also use LSP. A collaborative team consisting of HyperV Technologies Corp., Voss Scientific LLC, FAR-TECH, Inc., Prism Computational Sciences, Inc. and Advanced Energy Systems Inc. joined efforts to develop new physics and numerical models for LSP in several key areas to enhance the ability of LSP to model high energy density plasmas (HEDP). This final report details those efforts. Areas addressed in this research effort include: adding radiation transport to LSP, first in 2D and then fully 3D, extending the EMHD model to 3D, implementing more advanced radiation and electrode plasma boundary conditions, and installing more efficient implicit numerical algorithms to speed complex 2-D and 3-D computations. The new capabilities allow modeling of the dominant processes in high energy density plasmas, and further assist the development and optimization of plasma jet accelerators, with particular attention to MHD instabilities and plasma/wall interaction (based on physical models for ion drag friction and ablation/erosion of the electrodes). In the first funding cycle we implemented a solver for the radiation diffusion equation. To solve this equation in 2-D, we used finite-differencing and applied the parallelized sparse-matrix solvers in the PETSc library (Argonne National Laboratory) to the resulting system of equations. A database of the necessary coefficients for materials of interest was assembled using the PROPACEOS and ATBASE codes from Prism. The model was benchmarked against Prism's 1-D radiation hydrodynamics code HELIOS, and against experimental data obtained from HyperV's separately funded plasma jet accelerator development program. Work in the second funding cycle focused on extending the radiation diffusion model to full 3-D, continued development of the EMHD model, optimizing the direct-implicit model to speed up calculations, add in multiply ionized atoms, and improved the way boundary conditions are handled in LSP. These new LSP capabilities were then used, along with analytic calculations and Mach2 runs, to investigate plasma jet merging, plasma detachment and transport, restrike and advanced jet accelerator design. In addition, a strong linkage to diagnostic measurements was made by modeling plasma jet experiments on PLX to support benchmarking of the code. A large number of upgrades and improvements advancing hybrid PIC algorithms were implemented in LSP during the second funding cycle. These include development of fully 3D radiation transport algorithms, new boundary conditions for plasma-electrode interactions, and a charge conserving equation of state that permits multiply ionized high-Z ions. The final funding cycle focused on 1) mitigating the effects of a slow-growing grid instability which is most pronounced in plasma jet frame expansion problems using the two-fluid Eulerian remap algorithm, 2) extension of the Eulerian Smoothing Algorithm to allow EOS/Radiation modeling, 3) simulations of collisionless shocks formed by jet merging, 4) simulations of merging jets using high-Z gases, 5) generation of PROPACEOS EOS/Opacity databases, 6) simulations of plasma jet transport experiments, 7) simulations of plasma jet penetration through transverse magnetic fields, and 8) GPU PIC code development. The tools developed during this project are applicable not only to the study of plasma jets, but also to a wide variety of HEDP plasmas of interest to DOE, including plasmas created in short-pulse laser experiments performed to study fast ignition concepts for inertial confinement fusion.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

The augmented saddle field discharge characteristics and its applications for plasma enhanced chemical vapour deposition

A high ion flux parallel electrode plasma is proposed and studied in its DC configuration. By cascading a diode source region which supplies electrons and a saddle field region where these seed electrons are energized and amplified, the energy of ion bombardment on the substrate can be decoupled from the plasma density. The sufficiently large density of electrons and holes in the vicinity of the substrate raises the possibility to perform plasma enhanced chemical vapour deposition on insulating materials, at low sheath voltages (around 40 V in the configuration studied), at low temperatures in which the surface mobility of film growth species may be provided by the bombardment of moderate energy ions. As a benchmarking exercise, experiments are carried out on silane discharge characteristics and deposition of hydrogenated amorphous silicon (a-Si:H) on both silicon wafer and glass. The films grown at low anode voltages have excellent microstructures with predominantly monohydride bonds, sharp band tails, but relatively high integrated defect density in the mid 10{sup 16}/cm{sup 3} range for the particular substrate temperature of 180 Degree-Sign C, indicating that further optimizations are necessary if the electrode configuration is to be used to create a-Si:H devices.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Impact of electrode porosity architecture on electrochemical performances of 1 mm-thick LiFePO4 binder-free Li-ion electrodes fabricated by Spark Plasma Sintering

Thick electrodes with high active material loadings have been intensively studied over the last couple of decades in pursuit of achieving high energy density systems. To optimize and enhance the electrochemical performance of such electrodes, one has to control the pore morphology by, for example, varying the pore size and shape, and the level of porosity. In the present work, the fabrication of thick binder-free LiFePO4 (LFP) electrodes with two different pore sizes (12 and 20 mu m) and porosities (21 vol% and 44 vol%) using Spark Plasma Sintering (SPS) and templating approach is reported. The well-controlled porous architecture inside the thick electrodes is realized by fine-tuning experimental parameters. The impact of porosity architecture on electrochemical performance is quantified and correlated with the 3D tortuosity values determined from both micro-computed tomography and electrochemical impedance-based experimental methods. Based on the micro-computed tomography data analysis, estimated tortuosity values along X, Y, and Z axes reveal an anisotropic effect perpendicularly to the SPS compression axis (Z-direction). This is particularly profoundly observed in the samples with larger pores (20 mu m). The correlation between morphological properties and the rate capability performance is established indicating that the capacity loss happens mainly due to the Li-ion diffusion limitations.

Cathode material↗