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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
DOE OSTI2020

Expanded capabilities of the CarMa code in modeling resistive wall mode dynamics with 3-D conductors

In this work, an improved version of the CarMa code is presented, called CarMa-D, for the analysis of resistive wall modes (RWMs) in fusion devices, simultaneously considering the effects of volumetric three-dimensional conducting structures, plasma dynamics, toroidal rotation or drift-kinetic damping. Unlike static CarMa, CarMa-D does not rely on the simplifying assumptions such as neglecting the plasma mass, toroidal rotation and kinetic damping. The new coupling strategy is based on matrix-based Padé rational functions approximation of plasma a response. The arising mathematical model is formally equivalent to the original CarMa model, but with a higher number of degrees of freedom to model the dynamics of the plasma. CarMa-D overcomes the main limitations of the original CarMa, in particular: (i) the massless assumption for the plasma is removed, allowing modeling of global modes growing both on ideal kink time scales and in the typical RWM growth rate regime, with a suitable treatment of the model; (ii) the effects of toroidal plasma flow and drift kinetic damping can be included into the new model, providing a powerful tool to study macroscopic phenomena where both plasma dynamics and 3-D conducting structures play important roles.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1985

IMF B(y)-dependent plasma flow and Birkeland currents in the dayside magnetosphere. II - A global model for northward and southward IMF

The qualitative convection pattern presented by Burch et al. (1984) is extended here to all interplanetary magnetic field orientations. The model of Burch et al. is based on the antiparallel merging hypothesis of Crooker (1979) with the addition of small but finite cells driven by quasi-viscous processes on the dawn and dusk edges of the polar cap. Although the treatment presented here is only qualitative, interesting predictions are made about newly observed phenomena, such as theta auroras.

Reiff, P. H.↗
NASA NTRS1999

Beta in Streamers

Streamers are often described as regions of the corona in which the density is higher than in coronal holes because the plasma is trapped by closed loops of magnetic flux. In contrast, Magnetohydrodynamics (MHD) models of the global corona show that the plasma beta identically equal to 8(pi)p/B(exp 2) > 1 in streamers above approximately 1.2Rs heliocentric height (p=pressure, B=magnetic field strength). There are three recent contributions to this topic. The first is that heating near the cusp further drives Beta up and can result in release of new slow solar wind from the top of the streamer. The second is SOHO/UVCS observations, in combination with a potential field/source surface model of the magnetic field, show beta > 1 above 1.2Rs in a streamer observed near solar sunspot minimum. The third is a magnetic field reconstruction technique (using field deforming algorithms) which was applied both to an isolated active region (AR 7999) and to the Pneuman & Kopp global MHD model. In the active region, beta becomes larger than unity at approximately 1.2Rs. In the Pneuman & Kopp model, beta = 1.0 at the base of the streamer and rises with increasing height, becoming 15-20 at 1.6Rs and 35-55 at 1.7RS. The collective implication of these three results is that beta > 1 everywhere in streamers above approximately 1.2 Rs. Global simulations go on to show that the reason streamers do not simply explode under such high beta conditions is that they are held down by pressure from the sides due to the magnetic fields (and low beta) in adjacent coronal holes. The main role of the closed magnetic loops near the cusp is to keep the streamer from continuously leaking plasma, as otherwise happens in a magnetic pinch which is similar but has no closed loops. The purpose of this note is to summarize the results implying that beta > 1 is a general property of streamers above 1.2 Rs.

Suess, Steven T.↗
DOE OSTI2020

Benchmark of the KGMf with a coupled Boltzmann equation solver

The Kinetic Global Model framework (KGMf) is an open-source general-purpose global model (spatially averaged) simulation code developed to explore the reaction kinetics and pathways in plasma discharge systems. It contains species continuity and electron energy balance equations, with a time-dependent evaluated electron energy distribution function (EEDF) for electron impact reactions. The EEDF is utilized to determine the rate coefficients for electron impact reactions, which can have profound impact on the temporal evolutions of plasma parameters. Previously, the EEDF was commonly assumed as Maxwellian or an analytical function of the effective electron temperature. In this work, the KGMf is coupled with a Boltzmann equation (BE) solver to self-consistently compute the EEDF. The EEDF evolution frequency is determined based on relative changes of the reduced electric field. The KGMf is benchmarked with the ZDPlasKin code based on high-pressure low-temperature argon plasma discharge cases. Additionally, the temporal evolutions of reduced electric field, electron temperature, EEDF, reaction rates, and species densities, are obtained and compared under different discharge conditions, showing good agreement between the KGMf and the ZDPlasKin simulations. The application of the KGMf for predicting breakdown times in high power microwave discharges is also presented, which shows qualitative agreement with particle-in-cell simulations. The KGMf can be further applied for more complicated plasma discharge systems, where the reaction kinetics are more intricate (e.g., plasma-assisted combustion systems).

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS2014

Titan's Plasma Environment : 3D Hybrid Kinetic Modeling of the TA Flyby and Comparison with CAPS-ELS and RPWS LP Observations

In this report we discuss the global plasma environment of the TA flyby from the perspective of 3D hybrid modeling. In our model the background, pickup, and ionospheric ions are considered as particles, whereas the electrons are described as a fluid. In homogeneous photoionization, electron-impact ionization and charge exchange are included in our model. We also take into account the collisions between the ions and neutrals. Our modeling shows that mass loading of the background plasma (H(+), O(+)) by pick up ions H2(+), CH4(+) and N2(+) differs from theT9 encounter simulations when O(+) ions are not introduced into the background plasma. In our hybrid-modeling we use Chamberlain profiles for the atmospheric components. We also include a simple ionosphere model with average mass M=28 amu ions that were generated inside the ionosphere. Titan's interior is considered as a weakly conducting body. Special attention has been paid to comparing the simulated pickup ion density distribution with CAPS-ELS and with RPWS LP observations by the Cassini-Huygens spacecraft along theta trajectory. Our modeling shows an asymmetry of the ion density distribution and the magnetic field, including the formation of Alfven wing-like structures.

induced magnetospheres↗
DOE OSTI2025

Optimization of simulated high-field side lower hybrid current drive coupling using machine learning predictions of scrape-off layer density

Lower hybrid current drive (LHCD) is a potential source of non-inductive off-axis current drive (CD) for tokamaks. Although LHCD has been successfully deployed on a number of tokamaks, it is highly sensitive to the scrape-off layer (SOL) conditions local to the LHCD launcher. Large gaps between the launcher and plasma core, SOL turbulence, or edge density perturbations due to edge-localized modes can hamper CD or cause large reflected power. These coupling issues in part motivated the installation of an LHCD launcher on the high-field side (HFS) of DIII-D. On the HFS, the SOL is less turbulent and more controllable compared to the low-field side. This quiescence may result in more predictable edge conditions and thus a more predictable CD. Here, in this work, HFS SOL reflectometry measurements are predicted from global plasma parameters using machine learning models. The SOL predictions coupled with the full-wave simulation of the LHCD launcher allow for the prediction of reflected power, directivity, and arcing risk before the discharge. Launcher performance is then optimized using multi-objective Bayesian optimization, finding the shot parameters that result in an optimal SOL density that maximizes CD while minimizing the risk of arcing. The predictions and optimizations of LHCD performance are then accelerated using a surrogate model of the full-wave LHCD simulation.

Bayesian optimization↗
NASA NTRS1988

Possible explanations of north-south plasma flow in the outer heliosphere and meridional transport of magnetic flux

Observed meridional plasma flow and its connection with other plasma parameters in the outer heliosphere are discussed. The dynamics of the flow are examined locally and compared with observed plasma parameters and a global flow model which predicts such flows in a steady solar wind. The observational evidence supports stream dynamics and associated pressure gradients as responsible for driving the flow. Such a meridional flow may result in a net transport of magnetic flux from regions near the heliographic equator. The amplitude of the observed meridional component of solar wind flow is consistent with observed magnetic flux deficits in the outer heliosphere. The limited coverage of heliographic latitude by Voyager 2 precludes a direct measurement of the full flow pattern; however, the magnitude of reported magnetic flux deficits and the unambiguous, regular variations in the meridional flow suggest that the stream interactions do produce a net movement of magnetic flux away from the heliographic equator.

Mcnutt, R. L., Jr.↗
DOE OSTI2025

Global Gyrokinetic Simulations of Isotope Effects under Ambipolar Electric Fields and Advances Toward Whole-Volume Modeling

We review global gyrokinetic simulation studies on plasma transport in the Large Helical Device using XGC-S. XGC-S is an extended version of X-point Gyrokinetic Code for stellarators and has been progressively verified throughout the code development process. Verification tests of neoclassical transport successfully demonstrate the generation of an ambipolar electric field due to ripple-trapped particles. We perform quasi-linear analyses of the ion temperature gradient mode under the influence of the ambipolar electric field. The results reveal that the ambipolar electric field and the heavy hydrogen component in mixed isotope plasmas can lead to the favorable isotope effect observed in recent deuterium experiments. We also present recent efforts in code development toward whole-volume simulations, including the helical divertor region. A mesh generation scheme based on field-line tracing and the construction of curved surfaces perpendicular to the magnetic field would be promising for global field calculations in the whole-volume simulations.

Basic Plasma Phenomena and Gas Discharges↗
NASA NTRS1993

Shaping of the magnetotail from the mantle - Global and local structuring

Kinetic modeling of the properties of magnetotail formation from a plasma mantle source are discussed, and a unified view of the structure of the central part of the magnetotail plasma sheet as well as the structure of its boundary layer is developed. The Tsyganenko magnetic field model for quiet periods of magnetospheric activity is used to trace trajectories of mantle protons in the presence of a uniform dawn-dusk electric field. The present model shows the evolution of the global structure of the tail with a clearly defined central plasma sheet and plasma sheet boundary layer developing from its beginnings as a plasma 'nucleus' in the distant tail current sheet. This large-scale restructuring is accompanied by the creation of small-scale features in the particle distribution functions. It is also shown that complementary ring distribution structures should also exist in the central plasma sheet. The ion distribution functions in the central plasma sheet should take a rather specific form in velocity space with loss regions oriented predominantly orthogonal to the magnetic field.

Ashour-Abdalla, Maha↗
DOE OSTI2024

Verification of the kinetic electron role in the microinstabilities in a negative triangularity model equilibrium

Effect of kinetic electrons on negative triangularity plasmas has been investigated and compared against the corresponding positive triangularity plasmas, using the global gyrokinetic code X-point Gyrokinetic Code with scale-separated delta-f option without Coulomb collisions. Our model magnetic equilibria have strong positive and negative triangularities and weak magnetic shear. However, unusually large ρ i > a and low density plasmas are chosen to maximize the nonlocal effect to investigate the finite ρ i effect and to be clearly away from kinetic ballooning modes. Similar conclusions to previous flux tube and global simulations have been obtained in this highly nonlocal model plasma: it is essential to include kinetic electrons in the micro-instability study of negative triangularity plasmas. Most physics findings agree with existing reports, with some disagreement. We offer a new “effective trapping fraction” concept that can add to the explanation of the growth rate difference between NT and PT plasmas, pointing to the significant variation in trapped particle fractions that have turning points in the mode growth regions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1988

Magnetohydrodynamic boundary conditions for global models

Boundary conditions in the ionosphere and the upstream solar wind are important in determining the dynamics of global magnetohydrodynamic models of the magnetosphere. It is generally recognized that the orientation of the magnetic field in the upstream solar wind strongly modulates the rate of energy input into the magnetosphere by magnetic reconnection. However, other aspects of the upstream boundary conditions may determine whether the reconnection occurs in a patchy manner, as in flux transfer events, or in a global manner, as in the Paschmann et al. (1979) events. Ionospheric boundary conditions should also affect the reconnection process. For example, ionospheric line-tying can cause x-line motion in the outer magnetosphere. If it is assumed that auroras occur on field lines mapping to x-lines, then auroral motions are different than the local convective motion of the plasma in which they occur. Global magnetohydrodynamic models which incorporate both magnetospheric reconnection and ionospheric convection could be used to investigate the effect of reconnection and convection upon dayside and nightside auroral motions during the course of a magnetic substorm.

Forbes, T. G.↗
NASA NTRS1989

Features of terrestrial plasma transport

Research concerning the transport and distribution of ionospheric plasma in the magnetosphere are reviewed, stressing the dichotomy in explanations given for the low plasma densities outside the plasmasphere. The convection/hot solar plasma model and the convection/loss model are considered. Observations of global ionospheric outflows are compared with theoretical studies. It is suggested that there is a need for a hybrid model of magnetospheric plasma in which terrestrial plasma is both lost into the solar wind and energized and trapped within the magnetosphere, inflating the geomagnetic field and excluding cold plasma from conjugate regions.

Moore, T. E.↗
DOE OSTI2026

Detecting shearless phase-space transport barriers in global gyrokinetic turbulence simulations with test particle map models

In magnetically confined fusion plasmas, the role played by zonal 𝐸 x 𝐵 flow shear layers in the suppression of turbulent transport is relatively well understood. However, less is understood about the role played by the weak shear regions that arise in the non-monotonic radial electric field profiles often associated with these shear layers. In electrostatic simulations from the global total-𝑓 gyrokinetic particle-in-cell code XGC, we demonstrate how shearless regions with non-zero flow curvature form zonal ‘jets’ that, in conjunction with neighbouring regions of shear, can act as robust barriers to particle transport and turbulence spreading. By isolating quasi-coherent fluctuations radially localised to the zonal jets, we construct a map model for the Lagrangian dynamics of gyrokinetic test particles in the presence of drift waves. We identify the presence of shearless invariant tori in this model and verify that these tori act as partial phase-space transport barriers in the simulations. We also demonstrate how avalanches impinging on these shearless tori cause eddy detachment events that form ‘cold/warm core ring’ structures analogous to those found in oceanic jets, facilitating transport across the barriers without destroying them completely. We discuss how shearless tori may generically arise from tertiary instabilities or other types of discrete eigenmodes, suggesting their potential relevance to broader classes of turbulent fluctuations.

fusion plasma↗
DOE OSTI2022

COMPASS-U Global Heat Balance Calculations

COMPASS-U is a medium size, high magnetic field experimental tokamak (R = 0.9 m, B t = 5 T, and I p = 2 MA), built at the Institute of Plasma Physics, Czech Academy of Sciences (IPP-CAS). This global heat balance calculation for COMPASS-U was done at Princeton Plasma Physics Laboratory (PPPL). Based on our previous experience of building global thermal model for National Spherical Torus Experiment-Upgrade (NSTX-U) at PPPL, this 2-D global thermal model geometry represents a typical cross section of COMPASS-U machine. The model includes thermal radiation, conduction, and convection among components and also between the machine and outer environment. Helium gas heating/cooling was modeled with fluid element and surface element. This model was used to calculate component temperatures and heat distribution during heat up, cryogenic cool down, normal operation, and fault operation scenarios. Definition of 14 main thermal scenarios was provided by IPP-CAS. First nine are normal operation scenarios. Scenarios #10–#14 are fault scenarios. Results of thermal scenario #5 will be given and discussed in this article, including peak temperatures, temperature ratcheting, energy distribution, and required cooling power.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1991

Low latitude electrodynamic plasma drifts - A review

The characteristics and driving mechanisms of low latitude ExB plasma drifts and electric fields particularly at F-region heights are reviewed. It is concluded that the general characteristics of the quiet-time plasma can be explained as resulting from E- and F-region dynamo and interhemispheric coupling processes. The disturbance dynamo effects are found to be responsible for the drift perturbations following the periods of enhanced magnetic activity. The prompt penetration of high-latitude electric fields to lower latitudes produces large perturbations on the upward/poleward drifts, but has no significant effect on the low-latitude and the equatorial zonal drifts. Detailed low-latitude and global numerical models for studying the characteristics of plasma drifts are capable of reproducing the latitudinal variation of the perturbation electric fields and their diurnal variations.

Fejer, B. G.↗
DOE OSTI2021

A boundary value “reservoir problem” and boundary conditions for multi-moment multifluid simulations of sheaths

Multifluid simulations of plasma sheaths are increasingly used to model a wide variety of problems in plasma physics ranging from global magnetospheric flows around celestial bodies to plasma–wall interactions in thrusters and fusion devices. For multifluid problems, accurate boundary conditions to model an absorbing wall that resolves a classical sheath remain an open research area. This work justifies the use of vacuum boundary conditions for absorbing walls to show comparable accuracy between a multifluid sheath and lower moments of a continuum-kinetic sheath.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1987

Characteristics of cometary picked-up ions in a global model of Giacobini-Zinner

Energetic ions observed during the International Cometary Explorer (ICE) spacecraft flyby of comet Giacobini-Zinner provide information about both the constitution of comets and the plasma physical processes associated with their interaction with the solar wind. In this investigation the details of ion 'pickup,' in the limit where small-scale fluctuations in the plasma and magnetic field are neglected, are modeled by following the motion of a large number of initially cold, heavy (mass 18) ions in a global magnetohydrodynamic model of the local plasma and magnetic field. The results indicate how the background or macroscopic velocity and magnetic field structure of the comet can affect the average spatial and spectral characteristics of the observed cometary ions. These effects, which occur by virtue of forces associated with the compression and the curvature of the magnetic field in the presence of the stagnating plasma flow, can explain the double maxima in the time series of the energetic ion flux observed along the ICE trajectory.

Kimmel, C. D.↗
NASA NTRS1984

Nightward ion flow in the Venus ionosphere - Implications of momentum balance

Using global empirical models of Venus ionospheric conditions, the plasma flow field consistent with the horizontal momentum equation in both viscid and inviscid forms is solved for. It is found that plasma viscosity is negligible except at low altitudes and that the observed plasma flows are consistent with the inviscid solution above 300 km but are larger than the calculated flows at lower altitudes. This is probably due to downward momentum advection. The strong vertical shear in the calculated and observed flows just beyond the terminator may produce turbulence there, manifested as the observed transterminator waves in plasma density and magnetic field. The implications of ionospheric superrotation are discussed.

Elphic, R. C.↗