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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 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Magnetic field signatures of substorms on high-latitude field lines in the nighttime magnetosphere.

Two types of magnetic field changes are repeatedly observed in the high-latitude nightside magnetosphere in association with magnetic substorms. One type of field change occurs on field lines associated with the high-latitude part of the auroral oval and is characterized by a sudden decrease in the field strength accompanied by an abrupt perturbation in the field declination angle. These changes are attributed to field-aligned sheet currents flowing on the high-latitude boundary of an expanding plasma sheet following substorms. A second type of field change observed on polar cap field lines is a decrease in field inclination during substorms. This type of change is regarded as a further manifestation of the changing field configuration during substorms and can be described in terms of azimuthal currents.

Fairfield, D. H.↗
NASA NTRS1986

Electrodynamic interactions

The electrodynamic interaction of long metallic tethers with the ionosphere is introduced. Due to the tether's motion across the Earth's field, a polarization electric field is generated along the tether. In a system like the Tethered Satellite System (TSS) where the tether is coated with dielectric and the electrical contact is between its two terminations and the ionosphere, the upper end termination will collect electrons and, in a passive system, the lower end termination will collect ions. Space charge regions will develop around the two terminations of the system, which can be at considerable potential with respect to the unperturbed ionospheric plasma and the current in the tether will be most significantly determined by local processes in such space charge regions. A qualitative view of the global perturbation induced by TSS in the ionosphere is outlined. One of the applications of electrodynamic tethers is that of using them as low frequency wave generators to communicate to the Earth. This application is briefly discussed. An equivalent circuit of the tether system is described. The basic equation of the circuit is given.

Dobrowolny, M.↗
NASA NTRS2014

The Situational Awareness Sensor Suite for the ISS (SASSI): A Mission Concept to Investigate ISS Charging and Wake Effects

The complex interaction between the International Space Station (ISS) and the surrounding plasma environment often generates unpredictable environmental situations that affect operations. Examples of affected systems include extravehicular activity (EVA) safety, solar panel efficiency, and scientific instrument integrity. Models and heuristically‐derived best practices are well‐suited for routine operations, but when it comes to unusual or anomalous events or situations, especially those driven by space weather, there is no substitute for real‐time monitoring. Space environment data collected in real‐time (or near‐real time) can be used operationally for both real‐time alarms and data sources in assimilative models to predict environmental conditions important for operational planning. Fixed space weather instruments mounted to the ISS can be used for monitoring the ambient space environment, but knowing whether or not (or to what extent) the ISS affects the measurements themselves requires adequate space situational awareness (SSA) local to the ISS. This paper presents a mission concept to use a suite of plasma instruments mounted at the end of the ISS robotic arm to systematically explore the interaction between the Space Station structure and its surrounding environment. The Situational Awareness Sensor Suite for the ISS (SASSI) would be deployed and operated on the ISS Express Logistics Carrier (ELC) for long‐term "survey mode" observations and the Space Station Remote Manipulator System (SSRMS) for short‐term "campaign mode" observations. Specific areas of investigation include: 1) ISS frame and surface charging during perturbations of the local ISS space environment, 2) calibration of the ISS Floating Point Measurement Unit (FPMU), 3) long baseline measurements of ambient ionospheric electric potential structures, 4) electromotive force-induced currents within large structures moving through a magnetized plasma, and 5) wake‐induced ion waves in both electrostatic (i.e. particles) and electromagnetic modes. SASSI will advance the understanding of plasma‐boundary interaction phenomena, demonstrate a suite a sensors acting in concert to provide effective SSA, and validate and/or calibrate existing ISS space environment instruments and models.

Krause, L. Habash↗
NASA NTRS1982

Existence of a component corotating with the earth in high-latitude disturbance magnetic fields

A study of the data from the high-latitude North American IMS network of magnetic stations suggests that there is a component in substorm perturbations that corotates with the earth. It is as yet not certain whether the existence of this component stems from the corotation of a part of the magnetospheric plasma involved in the substorm mechanism or if it is a 'phase change' resulting from the control of the substorm manifestations by the earth's main magnetic field which is not axially symmetric. There are other geophysical phenomena showing a persistence of longitudinal variations corotating with the earth. These phenomena are of significance for a better understanding of ionosphere-magnetosphere coupling.

Suzuki, A.↗
NASA NTRS1985

Science Applications, Part 1

The tethered satellite system mission can allow direct observation of the structure and the dynamics of the lower atmosphere; as well as answer some basic questions on the chemical composition of the atmosphere; the coupling mechanisms between small and large scale motions; the global wind field of the lower atmosphere, and how it is influenced by waves and tides; the mass, momentum, and energy fluxes in the lower thermosphere; how the above are affected by externally perturbed conditions (for example by magnetic storms, solar wind and its variability, etc.); and the pattern of electric current circulation and its relationship with the magnetospheric environment. Fundamental plasma processes can also be studied. Similarity of conditions in other plasmas in space makes it possible to get information on the magnetospheres of the giant planets or more generally on the solar system. The electrodynamic phenomena associated with the Jovian satellite Io (radioemission, UV emission, energetic electron precipitation) can be examined by simple scaling to the terrestrial case.

Mariani, F.↗
DOE OSTI2024

EFIT‐AI: Machine Learning and Artificial Intelligence Assisted Equilibrium Reconstruction for Tokamak Experiments and Burning Plasmas (Final Report)

The EFIT-AI project is creating a modern advanced equilibrium reconstruction code suitable for tokamak experiments of burning plasmas. EFIT [1,2] was the first and is the most extensively used equilibrium reconstruction code in the world. This project builds on the production-level experience and adds key elements as follows. 1. A Model Order Reduction (MOR) version of the two-dimensional (2D) Grad-Shafranov equation solver (EFIT-MORNN) using physics-informed neural networks. 2. Improved optimization and data analysis capabilities using a Bayesian framework enhanced with machine learning. 3. A MOR version of the three-dimensional (3D) perturbed equilibrium reconstruction tool.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1975

Effects of plasma microfields on radiative transitions from atomic levels above the ionization threshold

The effects of plasma electric microfields on line-like optical features arising from atomic levels above the ionization threshold are investigated within the framework of the quasi-static and single-frequency dynamic-field theories of spectral-line broadening. The 2p(23)P to 1s2p(3)P and 2s2p(3)P to 1s2s(3)S transitions in helium and helium-like ions are treated as examples. The mixing of the doubly excited levels in the perturbing microfields produces Stark broadening of the emission lines and induces autoionization of the 2p(23)P level, which, unlike the 2s2p(3)P level, is metastable against autoionization in the field-free environment. Determination of the complete Stark-broadening profiles in thermal plasmas is complicated by the need to include the effects of both the (quasi-static) ion and the (dynamic) electron fields. Under nonequilibrium conditions, where electric fields from either electron or ion plasma waves can far exceed nearby particle fields, the calculation and interpretation of the line shapes may be simplified and could provide a diagnostic probe of the wave-field properties.

Davis, J.↗
DOE OSTI2024

Generation of shear flows induced by AE / EPM in LHD plasma

The generation of shear flows (SFs) by Alfven Eigenmodes (AEs) and energetic particle modes (EPMs) have important effects on the operation of future nuclear fusion reactors, because SFs regulate the saturation of the AEs/EPMs, the transport of EPs and thermal plasma, as well as the formation of transport barriers among other consequences. The aim of this study is the analysis of SFs generation during the saturation phase of AEs and EPMs in LHD plasma. Experiments performed in the 23rd and 24th LHD experimental campaigns are dedicated to explore the destabilization of AEs/EPMs in discharges with different heating patterns, thermal plasma and magnetic field configurations. In particular, the shots 176490 and 179697 show the destabilization of MHD bursts and energetic-ion-driven resistive interchange modes (EIC), respectively. Charge exchange spectroscopy measurements in both discharges indicate that the generation of SFs by AE/EPM is uncorrelated with the perturbation induced by the neutral beam injector (NBI). Nonlinear simulations performed using the gyro-fluid code FAR3d show the generation of zonal structures, especially SFs, induced during the saturation phase of Toroidal Alfven Eigenmodes (TAEs) triggered in the MHD burst as well as by the 1/1 EIC in the bursting phase. The simulations indicate that SFs are caused by the radial electric fields powered by energy transfers from the unstable AE/EPM towards the thermal plasma. The strongest SFs are measured during the EIC bursting phase once the 1/1 EPM overlaps with nearby resonances at the plasma periphery. Likewise, the largest SFs during the MHD burst are observed once TAEs radially overlap in the inner-middle plasma region.

AE↗
NASA NTRS1988

The diamagnetic effect during AMPTE's tail releases - Initial results

A series of four plasma injection experiments were performed by the AMPTE-IRM spacecraft in the nighttime magnetosphere between 12 and 18 earth radii geocentric distance during spring 1985. The most prominent effect of these tail releases is the creation of magnetic cavities. The lifetime of the cavities ranged from a few seconds to some minutes, depending mainly on the ion species and secondly on the ambient field strength. Due to the subsonic and sub-Alfvenic environment, the interaction between the plasma cloud and the ambient plasma flow played only a minor role in these cases (in contrast to the releases in the solar wind), and thus the diamagnetic effect could be studied extensively. The perturbation of the exterior field and fine structures in the current-carrying shell were observed. The thickness of the shell and the current distribution in this layer were deduced from the magnetic recordings each time IRM entered the cavity.

Luehr, H.↗
NASA NTRS1991

The finite-amplitude behavior of the Joule mode under astrophysical conditions

Magnetized astrophysical plasmas reveal a great deal of structure when spatially resolved. One possible explanation for this structuring is based on the existence of filamenting instabilities driven by radiation. In this paper, previous linear calculations are extended by considering the weakly nonlinear (finite-amplitude) development of such filamenting instabilities in magnetized unstratified plasmas. It is shown that under most conditions these instabilities (in particular, the Jouse model) are unstable at finite amplitude; in particular, in the temperature and plasma-beta domains characteristic of, for example, much of the solar transition region, these modes - which can be linearly stable under these conditions - become unstable to finite-amplitude perturbations. The relevance of this to the problem of heating the solar low transition region by current dissipation is discussed.

Bodo, G.↗
NASA NTRS1992

Staircase ion signature in the polar cusp - A case study

On 15 October, 1981 Dynamics Explorer 2 crossed the polar cusp at 1015 MLT and observed three distinct ion populations as it was moving poleward. These three populations had peak-flux energy around 2.7 keV, 850 eV, and 360 eV. At the time of observation, the IMF was southward. The first step coincided with a rotation of the flow from westward to poleward and then eastward. The second and third steps showed a flow directed principally poleward. Furthermore, the magnetic and electric perturbations in the first step are well fitted by an elongated flux tube footprint model. These results suggest that three consecutive Flux Transfer Events (FTEs) have injected solar wind plasma into the ionosphere forming the polar cusp. The individual FTE signatures can only be identified by the jumps in the precipitation pattern. The newest reconnected FTE footprint was crossed near the edge of the event while the two oldest ones were crossed around the event center. The small latitudinal size of these FTE footprints (40 km) and their short recurrence rate (3, 6 min) is consistent with an intermittent reconnection taking place at the subsolar point on a short time scale.

Escoubet, C. P.↗
NASA NTRS1992

Distinct ion population in the polar cusp: Possible signature of transient reconnection

Observations of ion energy dispersion, a common feature of the polar cusp, are discussed. Normally these dispersions show a continuous decrease in energy. However, they occasionally show steplike features in the dispersion. On 15 Oct. 1981, Dynamics Explorer 2 (DE 2) crossed the polar cusp at 1015 MLT and observed three distinct ion populations as the spacecraft moved poleward. These three populations had peak flux energy around 2.7 keV, 850 eV, and 360 eV. The first step coincided with a rotation of the flow; the flow being directed westward on the equatorward edge, poleward in the center, and eastward on the poleward edge. The second and third stems showed a flow directed principally poleward. Furthermore, the magnetic and electric perturbations in the first step are well fitted by an elongated Flux Transfer Event (FTE) footprint model. These results suggest that three consecutive FTE's have injected solar wind plasma into the ionosphere forming the polar cusp. The small latitudinal size of these FTE footprints (approximately 40 km) and their short recurrence rate (3 and 6 min) would be consistent with an intermittent reconnection taking place at the subsolar point in a short time scale.

Escoubet, C. P.↗
NASA NTRS1994

Characterization of the association of nitrate reductase with barley (Hordeum vulgare L.) root membranes

The nature of the association between nitrate reductase (NR) and membranes was examined. Nitrate reductase activity (NRA) associated with the microsomal fraction of barley (Hordeum vulgare L.) roots amounted to 0.6 to 0.8% of soluble NRA following sonication in the presence of 250 mM KI and repeated osmotic shock. This treatment removed all contaminating soluble NRA from microsomes of uninduced barley roots that had been homogenized in a soluble extract from roots of NO3(-)-induced plants. On continuous sucrose gradients, NRA co-migrated specifically with VO4(-)-sensitive ATPase activity, a plasma membrane (PM) marker; activity of glucose-6-phosphate dehydrogenase, assayed as cytosolic marker, co-migrated with NRA. Microsomal NRA was absent in barley deficient in soluble NR. Perturbation and trypsinolysis experiments with PM vesicles isolated by aqueous two-phase partitioning indicated that NR is associated with the periphery of the cytoplasmic face of the bilayer. These results demonstrate that PM and soluble NRs are essentially the same protein but that the membrane-associated form is tightly bound. Although it is possible that PM-associated NR exists in vivo, unequivocal evidence for this has yet to be shown. However, PM NR is definitely present in vitro.

Non-NASA Center↗
DOE OSTI2025

Demonstration of Super-X divertor exhaust control for transient heat load management in compact fusion reactors

Nuclear fusion could offer clean, abundant energy. However, managing the power exhausted from the core fusion plasma towards the reactor wall remains a major challenge. This is compounded in emerging compact reactor designs promising more cost-effective pathways towards commercial fusion energy. Alternative Divertor Configurations (ADCs) are a potential solution. In this work, we demonstrate exhaust control in ADCs, employing a novel method to diagnose the neutral gas buffer, which shields the target. Our work on the Mega Ampere Spherical Tokamak Upgrade shows that ADCs tackle key risks and uncertainties for fusion energy. Their highly reduced sensitivity to perturbations enables active exhaust control in otherwise unfeasible situations and facilitates an increased passive absorption of transients, which would otherwise damage the divertor. We observe a strong decoupling of each divertor from other reactor regions, enabling near-independent control of the divertors and core plasma. Our work showcases the real-world benefits of ADCs for effective heat load management in fusion power reactors.

Imaging techniques↗
NASA NTRS1983

Spiky ion acoustic waves in collisionless auroral plasma

A theory of spiky electric fields in 'inverted V' precipitation regions is elaborated and compared with recent spacecraft observations of solitary waves and double layers. A prediction from the theory is that the electric fields propagate along the magnetic field as perturbed ion acoustic solitons that intensify by exchanging momentum with reflected particles. The solitons have minimum scale lengths of approximately 100 m and maximum electric potential and field amplitudes of 1-10 V and 1-10 mV/m. They propagate at the local ion acoustic speed and are Doppler-shifted by the drift speed of upward flowing cold ions. Both rarefactive and compressive solitons with, respectively, negative and positive electric potentials are possible. It is noted that upward propagating compressive modes intensify when the upward flow of ionospheric ions exceeds approximately 10 times the local ion acoustic speed. The kinematic and dynamic properties of rarefactive solitons are found to be consistent with recent observations.

Lotko, W.↗
DOE OSTI2024

Non-equilibrium Dynamics of the Quark Gluon Plasma (Final Report)

During this funding period I continued my work on far-from-equilibrium formulations of hydrodynamics and bottomonium suppression in the quark-gluon plasma. I published 23 peer-reviewed articles and 9 proceedings contributions. The publications produced during this period have thus far received 705 citations. I delivered 22 talks, seminars, and colloquia about my work, most of which were invited. In addition to the work on hydrodynamics and heavy quarkonia, I also worked on high-order perturbative calculations of N=4 supersymmetric Yang-Mills thermodynamics and contributed to the efforts of the MUSES collaboration whose focus is developing a modular equation-of-state framework for use in modeling neutron stars and neutron star mergers.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1991

Two-dimensional model of a slow-mode expansion fan at Io

A 2D model for the standing slow-mode expansion fan that is expected to exist downstream of the Jovian moon Io is developed. The leading edge of the expansion fan makes an angle of 45 deg with the upstream magnetic field direction, and the fan width is about 114 deg. The plasma flow returns to its upstream direction by way of a slow-mode shock behind Io where the MHD parameters return asymptotically to their upstream conditions. The magnetic field perturbation within the fan is much smaller than that associated with the Alfven wing, which lies farther upstream.

Krisko, P. H.↗
NASA NTRS2008

Scalability of Localized Arc Filament Plasma Actuators

Temporal flow control of a jet has been widely studied in the past to enhance jet mixing or reduce jet noise. Most of this research, however, has been done using small diameter low Reynolds number jets that often have little resemblance to the much larger jets common in real world applications because the flow actuators available lacked either the power or bandwidth to sufficiently impact these larger higher energy jets. The Localized Arc Filament Plasma Actuators (LAFPA), developed at the Ohio State University (OSU), have demonstrated the ability to impact a small high speed jet in experiments conducted at OSU and the power to perturb a larger high Reynolds number jet in experiments conducted at the NASA Glenn Research Center. However, the response measured in the large-scale experiments was significantly reduced for the same number of actuators compared to the jet response found in the small-scale experiments. A computational study has been initiated to simulate the LAFPA system with additional actuators on a large-scale jet to determine the number of actuators required to achieve the same desired response for a given jet diameter. Central to this computational study is a model for the LAFPA that both accurately represents the physics of the actuator and can be implemented into a computational fluid dynamics solver. One possible model, based on pressure waves created by the rapid localized heating that occurs at the actuator, is investigated using simplified axisymmetric simulations. The results of these simulations will be used to determine the validity of the model before more realistic and time consuming three-dimensional simulations are conducted to ultimately determine the scalability of the LAFPA system.

Brown, Clifford A.↗