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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 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Temporal features of the outflow of heavy ionospheric ions in response to a high altitude plasma cavity

Using a hydrodynamic model for the plasma, it is demonstrated that the auroral plasma cavity is capable of drawing an appreciably large flux of oxygen ions, which are normally gravitationally bound. This escape mechanism of O(+) does not involve any additional heating or acceleration of the plasma in the ionosphere. The temporal evolution of the outflow shows that it starts near the cavity and penetrates into the ionosphere with a flux front moving down with the ion-acoustic speed. A steady outflow is reached in a few hours for a cavity at a height of one R(e) if the cavity is maintained. This time reduces to less than 1 hour for cavity heights less than 3000 km. During the transient state the outflux can appreciably exceed that in the steady state. In view of the horizontal convection, the transient outflow is of special significance. As the cavity descends, the ionospheric flux of O(+) increases; for the lower edge of the cavity in the altitude range 3000-10,000 km, the steady flux is found to be in the range 10 to the 7th to 10 to the 9th. An analysis for the steady state shows that outflow is controlled by the density scale height in the cavity.

Singh, Nagendra↗
NASA NTRS1991

Computer simulation of astrophysical plasmas

The role of sophisticated numerical models and simulations in the field of plasma astrophysics is discussed. The need for an iteration between microphysics and macrophysics in order for astrophysical plasma physics to produce quantitative results that can be related to astronomical data is stressed. A discussion on computational requirements for simulations of astrophysical plasmas contrasts microscopic plasma simulations with macroscopic system models. An overview of particle-in-cell simulations (PICS) is given and two examples of PICS of astrophysical plasma are discussed including particle acceleration by collisionless shocks in relativistic plasmas and magnetic field reconnection in astrophysical plasmas.

Max, Claire E.↗
NASA NTRS1975

Magnetospheric and auroral plasmas - A short survey of progress

Important milestones in our researches of auroral and magnetospheric plasmas for the past quadrennium 1971-1975 are reviewed. Many exciting findings, including those of the polar cusp, the polar wind, the explosive disruptions of the magnetotail, the interactions of hot plasmas with the plasmapause, the auroral field-aligned currents, and the striking inverted V electron precipitation events, were reported during this period. Solutions to major questions concerning the origins and acceleration of these plasmas appear possible in the near future. A comprehensive bibliography of current research is appended to this brief survey of auroral and magnetospheric plasmas.

Frank, L. A.↗
NASA NTRS1980

Observations of waves artificially stimulated by an electron beam inside a region with auroral precipitation

Observations of waves stimulated by artificial injection inside an auroral arc by an electron accelerator mounted on the POLAR 5 sounding rocket are presented. The accelerator produced a pulsed electron beam with currents up to 130 mA and energies up to 10 keV; emissions after the end of beam injection were generated by perturbations in the ambient plasma near the accelerator during beam injection. These emissions were independent of the electron beam direction along the geomagnetic field. The high frequency emission observed after beam injection correlated with the passage through an auroral arc; the low frequency emissions after beam injection were concentrated in two bands below the lower hybrid frequency.

Grandal, B.↗
NASA NTRS1992

Scientific objectives of a Solar Probe mission

The Solar Probe is a mission of exploration and discovery in an uninvestigated region near the sun. The Solar Probe can enhance general understanding of the corona and the solar wind. The first in situ measurements of coronal particles and fields are expected to provide definitive discriminators among many currently proposed models of processes that shape the structure and dynamics of the outer corona and solar wind. In addition, observations of the development of turbulence, nonlinear wave processes, plasma heating, and particle acceleration in the corona can advance these areas of plasma physics in a regime neither duplicated by earth-based laboratories nor by previous space exploration. It also fills the last gap between knowledge of the terrestrial response to solar output as well as provide insight for interpreting observations of general stellar envelopes.

Feldman, W.↗
NASA NTRS2001

Experimental Investigation of Current Sheet Instabilities

Configuration space instabilities of propagating current sheets were studied in order to better understand acceleration mechanisms in pulsed plasma thrusters. Experiments were carried out in a parallel plate accelerator with argon as propellant. Propagating current sheets were visualized using fast framing cameras with inter-frame delays ranging between 0.05 - 2 microsecond. Schlieren photography using a pulse-burst Nd:YAG laser was used to image electron density gradients in the discharge. Magnetic field probes were used to map the magnetic field topology during the evolution of the discharge. Pressure probes were used to monitor axial pressure gradients. Emission spectroscopy was used to estimate the electron temperature in the arc. The motivation for applying all of these diagnostics was to gain an understanding of what parameters influence the macroscopic stability of a propagating current sheet. Since a stable current sheet is required for any effective snowplow-type of accelerator, an understanding of the processes which can cause current sheets to break apart into filaments is essential for the design of future pulsed plasma thrusters.

Markusic, Thomas E.↗
NASA NTRS1972

Observations of the solar plasma using radio scattering and scintillation methods

Observations of the solar plasma using the interplanetary scintillation technique have been made at radial distances of 0.03 to 1.2 AU. The solar wind is found to be independent of ecliptic latitude and radial distance, except close to the sun where acceleration is observed. Plasma density irregularities on a scale near the proton gyro radius, which modulate the mean density by about 1 percent, are present throughout the observed range of radial distance.

Hewish, A.↗
DOE OSTI2023

Improved melt model for power flow

Accelerators that drive z-pinch experiments transport current densities in excess of 1 MA/cm 2 in order to melt or ionize the target and implode it on axis. These high current densities stress the transmission lines upstream from the target, where rapid electrode heating causes plasma formation, melt, and possibly vaporization. These plasmas negatively impact accelerator efficiency by diverting some portion of the current away from the target, referred to as “current loss”. Simulations that are able to reproduce this behavior may be applied to improving the efficiency of existing accelerators and to designing systems operating at ever higher current densities. The relativistic particle-in-cell code CHICAGO ® is the primary code for modeling power flow on Sandia National Laboratories’ Z accelerator. We report here on new algorithms that incorporate vaporization and melt into the standard power-flow simulation framework. Taking a hybrid approach, the CHICAGO® kinetic/multi-fluid treatment has been expanded to include vaporization while the quasi-neutral equation-of-motion has been updated for melt at high current-densities. For vaporization, a new one-dimensional substrate model provides a more accurate calculation of electrode thermal, mass, and magnetic field diffusion as well as a means of emitting absorbed contaminants and vaporized metal ions. A quasi-fluid model has been implemented expressly to mimic the motion of imploding liners for accurate inductance histories. For melt, a multi-ion Hall-MHD option has been implemented and benchmarked against Alegra MHD. This new model is described with sufficient detail to reproduce these algorithms in any hybrid kinetic code. Physics results from the new code are also presented. A CHICAGO ® Hall-MHD simulation of a radial transmission line demonstrates that Hall physics, not included in Alegra, has no significant impact on the diffusion of electrode material. When surface contaminant desorption is mocked in as a hydrogen surface plasma, both the surface and bulk-material plasmas largely compress under the influence of the j × B force. Similar results are seen in Alegra, which also shows magnetic and material diffusion scaling with peak current. Test vaporization simulations using MagLIF and a power-flow experimental geometry show Fe + ions diffuse only a few hundred µm from the electrodes, so present models of Z power flow remain valid.

43 PARTICLE ACCELERATORS↗
DOE OSTI2020

Plasma Processing of SRF Cavities for the Next Generation of Particle Accelerators

What are the major goals of the project? Goal 1: Optimize interactively processing of the single-cell cavity by combining plasma treatment and vertical cold bath testing. Continue using single cell cavity as the test bed for new applications. Goal 2: Work on upgrading the plasma etching technology for multi-cell SRF cavities. Goal 3: Develop and adapt discharge configurations to critical cavity regions including the electron beam weld (EBW) and iris areas. Goal 4: Develop tailored methods to prepare surface properties for a specific function prior to any additional modification, such as (but not limited to) surface passivation in preparation of other superconducting materials and structures.

43 PARTICLE ACCELERATORS↗
DOE OSTI2026

Vidyut3d: A GPU accelerated fluid solver for non-equilibrium plasmas on adaptive grids

We present the numerical methods, programming methodology, verification, and performance assessment of a non-equilibrium plasma fluid solver that can effectively utilize current and upcoming central processing and graphics processing unit (CPU+GPU) architectures, in this work. Our plasma fluid model solves the coupled conservation equations for species transport, electrostatic Poisson and electron temperature on adaptive Cartesian grids. Our solver is written using performance portable adaptive-grid/particle management library, AMReX, and is portable over widely available vendor specific GPU architectures. We present verification of our solver using method of manufactured solutions that indicate formal second order accuracy with central diffusion and fifth-order weighted-essentially-non-oscillatory (WENO) advection scheme. We also verify our solver with published literature on capacitive discharges and atmospheric pressure streamer propagation. We demonstrate the use of our solver on two 3D simulation cases: an atmospheric streamer propagation in Ar-H2 mixtures and a low pressure three-electrode radio frequency reactor. Our performance studies on three different CPU+GPU architectures indicate ~ 150-400X speed-up using AMD and NVIDIA GPUs per time step compared to a single CPU core for a 4 million cell simulation with 15 species.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

Vidyut3d: A Gpu Accelerated Fluid Solver for Non-Equilibrium Plasmas on Adaptive Grids

We present the numerical methods, programming methodology, verification, and performance assessment of a non-equilibrium plasma fluid solver that can effectively utilize current and upcoming central processing and graphics processing unit (CPU+GPU) architectures, in this work. Our plasma fluid model solves the coupled conservation equations for species transport, electrostatic Poisson and electron temperature on adaptive Cartesian grids. Our solver is written using performance portable adaptive-grid/particle management library, AMReX, and is portable over widely available vendor specific GPU architectures. We present verification of our solver using method of manufactured solutions that indicate formal second order accuracy with central diffusion and fifth-order weighted-essentially-non-oscillatory (WENO) advection scheme. We also verify our solver with published literature on capacitive discharges and atmospheric pressure streamer propagation. We demonstrate the use of our solver on two 3D simulation cases: an atmospheric streamer propagation in Ar-H2 mixtures and a low pressure twin electrode radio frequency reactor. Our performance studies on three different CPU+GPU architectures indicate approximately 150-400X speed-up using AMD and NVIDIA GPUs per time step compared to a single CPU core for a 4 million cell simulation with 15 species.

Sitaraman, Hariswaran↗
NASA NTRS2004

Unified Models of Turbulence and Nonlinear Wave Evolution in the Extended Solar Corona and Solar Wind

The PI (Cranmer) and Co-I (A. van Ballegooijen) made substantial progress toward the goal of producing a unified model of the basic physical processes responsible for solar wind acceleration. The approach outlined in the original proposal comprised two complementary pieces: (1) to further investigate individual physical processes under realistic coronal and solar wind conditions, and (2) to extract the dominant physical effects from simulations and apply them to a 1D model of plasma heating and acceleration. The accomplishments in Year 2 are divided into these two categories: 1a. Focused Study of Kinetic Magnetohydrodynamic (MHD) Turbulence. lb. Focused Study of Non - WKB Alfven Wave Rejection. and 2. The Unified Model Code. We have continued the development of the computational model of a time-study open flux tube in the extended corona. The proton-electron Monte Carlo model is being tested, and collisionless wave-particle interactions are being included. In order to better understand how to easily incorporate various kinds of wave-particle processes into the code, the PI performed a detailed study of the so-called "Ito Calculus", i.e., the mathematical theory of how to update the positions of particles in a probabilistic manner when their motions are governed by diffusion in velocity space.

Cranmer, Steven R.↗
DOE OSTI2021

Characterizing the acceleration time of laser-driven ion acceleration with data-informed neural networks

Peak ion energy is an important figure-of-merit in short-pulse, laser-driven ion acceleration and is dependent on an associated acceleration time. Standard metrics for these quantities depend on analytical results such as the self-similar fluid model or empirical models based on relatively small experimental and simulation datasets. In this work we attempt to use a data-informed neural network (NN) as a surrogate model for a large ensemble of PIC simulations to investigate an effective acceleration time. We explore the application of a stacked convolutional and recurrent NN architecture for improved regression by incorporating the time dependencies of the data into the training process. Of particular note is how pretraining a network on lower fidelity data, e.g. 1D analytical results, greatly improves the network's ability to learn more complex, higher fidelity data. Finally, the dependency of the acceleration time on various laser and plasma parameters is explored.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗