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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Influences of δB contribution and parallel inertial term of energetic particles on MHD-kinetic hybrid simulations: a case study of the 1/1 internal kink mode

The magnetohydrodynamic-kinetic (MHD-kinetic) hybrid model (Park et al 1992 Phys. Fluids B 4 2033–7) has been widely applied in studying energetic particles (EPs) problems in fusion plasmas for past decades. The pressure-coupling scheme or the current-coupling scheme is adopted in this model. However, two noteworthy issues arise in the model application: firstly, the coupled term introduced in the pressure-coupling scheme, (∇•P h ) ⟂ , is often simplified by ∇•P h , which is equivalent to neglecting the parallel inertial term of EPs; secondly, besides the $δf$ contribution caused by changing in the EP distribution function, the magnetic field perturbation (the $δB$ contribution) generated during development of the instabilities should also be considered, but it is often ignored in existing hybrid simulations. In this paper, we derive the analytical formulations under these two coupling schemes and then numerically study the representative case of the linear stability of the $m/n$ = $1/1$ internal kink mode (IKM) (Fu et al 2006 Phys. Plasmas 13 052517) by using the CLT-K code. Further, it is found that the approximated models can still yield reasonable results when EPs are isotopically distributed. But it fails completely in cases with anisotropic EP distributions. In addition, we further investigate the influence of EP's orbit width on the stability of IKM and verify the equivalence between pressure-coupling scheme and the current-coupling scheme.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Hybrid simulation of Alfvén wave parametric decay instability in a laboratory relevant plasma

Large-amplitude Alfvén waves are subject to parametric decays, which can have important consequences in space, astrophysical, and fusion plasmas. Although the Alfvén wave parametric decay instability (PDI) was predicted decades ago, observational evidence is limited, stimulating considerable interest in laboratory demonstration of the instability and associated numerical modeling. Here, we report an important step toward direct hybrid simulation of the Alfvén wave PDI in a laboratory plasma, using antenna-like wave injection of a circularly polarized wave and realistic wave-plasma parameters. Considering collisionless damping, we identify the threshold Alfvén wave amplitudes and frequencies required for triggering the instability. These threshold behaviors are corroborated by simple theoretical analysis, considering the balance between PDI growth and ion Landau damping and PDI development in a bounded plasma. Other effects not included in the present model such as finite transverse wave scale and ion–neutral collisions are briefly discussed. These hybrid simulations promise to be a useful tool for investigating laboratory Alfvén wave dynamics and may provide guidance for future laboratory demonstration of the PDI process.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1995

Investigation of intrinsic variability in one-dimensional parallel shocks using steady state hybrid simulations

We have developed a means of producing a steady state hybrid simulation of a collisionless shock. The shock is stopped in the simulation box by transforming into the shock frame and by modifying the downstream boundary conditions to allow the plasma to flow through the simulation box. Once the shock is stationary in the box frame, the simulation can be run for an arbitrary time with a fixed box size and a fixed number of simulation particles. Using this technique, we have shown that certain gross properties associated with the shock, such as the particle distribution function (including energetic particles produced by Fermi acceleration) and the flow speed profile, are constant (except for statistical variations) over hundreds of gyroperiods when averaged over times short compared to the average residence time of energetic particles. Our results imply that any microphysical processes responsible for particle heating and/or injection into the Fermi mechanism can be viewed as smooth and continuous on timescales longer than a few gyroperiods.

Bennett, Lee↗
NASA NTRS2019

Hybrid Simulation of Solar-Wind-Like Turbulence

We present 2.5D hybrid simulations of the spectral and thermodynamic evolution of an initial state of magnetic field and plasma variables that in many ways represents solar wind fluctuations. In accordance with Helios near-Sun high-speed stream observations, we start with Alfvénic fluctuations along a mean magnetic field in which the fluctuations in the magnitude of the magnetic field are minimized. Since fluctuations in the radial flow speed are the dominant free energy in the observed fluctuations, we include a field-aligned v∥(k⊥) with an k(exp −1) spectrum of velocity fluctuations to drive the turbulent evolution. The flow rapidly distorts the Alfvénic fluctuations, yielding spectra (determined by spacecraft-like cuts) transverse to the field that become comparable to the k∥ fluctuations, as in spacecraft observations. The initial near constancy of the magnetic field is lost during the evolution; we show this also takes place observationally. We find some evolution in the anisotropy of the thermal fluctuations, consistent with expectations based on Helios data. We present 2D spectra of the fluctuations, showing the evolution of the power spectrum and cross-helicity. Despite simplifying assumptions, many aspects of simulations and observations agree. The greatly faster evolution in the simulations is at least in part due to the small scales being simulated, but also to the non-equilibrium initial conditions and the relatively low overall Alfvénicity of the initial fluctuations.

Roberts, D. Aaron↗
NASA NTRS2013

Spontaneous Hot Flow Anomalies at Quasi-Parallel Shocks: 2. Hybrid Simulations

Motivated by recent THEMIS observations, this paper uses 2.5-D electromagnetic hybrid simulations to investigate the formation of Spontaneous Hot Flow Anomalies (SHFA) upstream of quasi-parallel bow shocks during steady solar wind conditions and in the absence of discontinuities. The results show the formation of a large number of structures along and upstream of the quasi-parallel bow shock. Their outer edges exhibit density and magnetic field enhancements, while their cores exhibit drops in density, magnetic field, solar wind velocity and enhancements in ion temperature. Using virtual spacecraft in the simulation, we show that the signatures of these structures in the time series data are very similar to those of SHFAs seen in THEMIS data and conclude that they correspond to SHFAs. Examination of the simulation data shows that SHFAs form as the result of foreshock cavitons interacting with the bow shock. Foreshock cavitons in turn form due to the nonlinear evolution of ULF waves generated by the interaction of the solar wind with the backstreaming ions. Because foreshock cavitons are an inherent part of the shock dissipation process, the formation of SHFAs is also an inherent part of the dissipation process leading to a highly non-uniform plasma in the quasi-parallel magnetosheath including large scale density and magnetic field cavities.

Quasi-Parallel↗
NASA NTRS1985

Hybrid simulation techniques applied to the earth's bow shock

The application of a hybrid simulation model, in which the ions are treated as discrete particles and the electrons as a massless charge-neutralizing fluid, to the study of the earth's bow shock is discussed. The essentials of the numerical methods are described in detail; movement of the ions, solution of the electromagnetic fields and electron fluid equations, and imposition of appropriate boundary and initial conditions. Examples of results of calculations for perpendicular shocks are presented which demonstrate the need for a kinetic treatment of the ions to reproduce the correct ion dynamics and the corresponding shock structure. Results for oblique shocks are also presented to show how the magnetic field and ion motion differ from the perpendicular case.

Winske, D.↗
NASA NTRS1990

Two-dimensional hybrid simulation of a curved bow shock

Results are presented from two-dimensional hybrid simulations of curved collisionless supercritical shocks, retaining both quasi-perpendicular and quasi-parallel sections of the shock in order to study the character and origin of the foreshock ion population. The simulations demonstrate that the foreshock ion population is dominated by ions impinging upon the quasi-parallel side of the shock, while nonlocal transport from the quasi-perpendicular side of the shock into the foreshock region is minimal. Further, it is shown that the ions gain energy by drifting significantly in the direction of the convection electric field through multiple shock encounters.

Thomas, V. A.↗
NASA NTRS1994

A hybrid simulation of contact discontinuity

Contact discontinuities in a collisionless plasma are studied by hybrid simulations, in which ions are treated as particles and electrons are considered as a fluid. It is demonstrated that contact discontinuity with a stable density ramp can exist in cases with a finite electron temperature. An electron pressure gradient is present across the contact discontinuity, leading to the presence of a parallel electric field and hence field-aligned potential increase (Delta Phi (sub parallel)) in the transition region. By reflecting ions at the discontinuity, this parallel electric potential peak reduces the interpenetration between hot and cold ions and maintains a stable density ramp across the contact discontinuity. The ratio of the field-aligned electric potential energy to ion thermal energy, e(Delta) Phi(sub parallel)/kT(sub i), is found to be an increasing function of T(sub e)/T(sub i), where T(sub e) and T(sub i) are respectively the electron and ion temperature.

Wu, B. H.↗
NASA NTRS2010

The Interaction of the Solar Wind with Solar Probe Plus - 3D Hybrid Simulation: The Study for the Distance 4.5Rs - Report 1

Our report devotes a 3D numerical hybrid model of the interaction of the solar wind with the Solar Probe spacecraft. The SPP model includes 3 main parts, namely, a non-conducting heat shield, a support system, and cylindrical section or spacecraft bus that contains the particle analysis devices and antenna. One observes an excitation of the low frequency Alfven and whistler type wave directed by the magnetic field with an amplitude of about (0.06-0.6) V/m. The compression waves and the jumps in an electric field with an amplitude of about (0.15-0.7) V/m were also observed. The wave amplitudes are comparable to or greater than previously estimated max wave amplitudes that SPP is expected to measure. The results of our hybrid simulation will be useful for understanding the plasma environment near the SPP spacecraft at the distance 4.5 Rs. Future simulation will take into account the charging of the spacecraft, the charge separation effects, an outgassing from heat shield, a photoionization and an electron impact ionization effects near the spacecraft.

Lipatov, Alexander S.↗
NASA NTRS2010

The Interaction of the Solar Wind with Solar Probe Plus - 3D Hybrid Simulation: The Study for the Distance 4.5Rs - Report 1

Our report devotes a 3D numerical hybrid model of the interaction of the solar wind with the Solar Probe spacecraft. The Solar Probe Plus (SPP) model includes 3 main parts, namely, a non-conducting heat shield, a support system, and cylindrical section or spacecraft bus that contains the particle analysis devices and antenna. One observes an excitation of the low frequency Alfven and whistler type wave directed by the magnetic field with an amplitude of about (0.06-0.6) V/m. The compression waves and the jumps in an electric field with an amplitude of about (0.15-0.7) V/m were also observed. The wave amplitudes are comparable to or greater than previously estimated max wave amplitudes that SPP is expected to measure. The results of our hybrid simulation will be useful for understanding the plasma environment near the SPP spacecraft at the distance 4.5 Rs. Future simulation will take into account the charging of the spacecraft, the charge separation effects, an outgassing from heat shield, a photoionization and an electron impact ionization effects near the spacecraft.

Lipatov, Alexander S.↗
NASA NTRS2012

Hybrid Simulation of the Shock Wave Trailing the Moon

A standing shock wave behind the Moon was predicted by Michel (1967) but never observed nor simulated. We use 1D hybrid code in order to simulate the collapse of the plasma-free cavity behind the Moon and for the first time to model the formation of this shock. Starting immediately downstream of the obstacle we consider the evolution of plasma expansion into the cavity in the frame of reference moving along with the solar wind. Well-known effects as electric charging of the cavity affecting the plasma flow and counterstreaming ion beams in the wake are reproduced. Near the apex of the inner Mach cone where the plasma flows from the opposite sides of the obstacle meet, a shock wave arises. We expect the shock to be produced at periods of high electron temperature solar wind streams (T(sub i) much less than T(sub e) approximately 100 eV). The shock is produced by the interaction of oppositely directed proton beams in the plane containing solar wind velocity and interplanetary magnetic field vectors. In the direction across the magnetic field and the solar wind velocity, the shock results from the interaction of the plasma flow with the region of the enhanced magnetic field inside the cavity that plays the role of the magnetic barrier. The appearance of the standing shock wave is expected at the distance of approximately 7R(sub M) downstream of the Moon.

Moon↗
NASA NTRS2023

Soft X-Ray Imaging of Earth's Dayside Magnetosheath and Cusps Using Hybrid Simulations

Interactions between solar wind ions and neutral hydrogen atoms in Earth's exosphere can lead to the emission of soft X-rays. Upcoming missions such as SMILE and LEXI aim to use soft X-ray imaging to study the global structure of the magnetosphere. Although the magnetosheath and dayside magnetopause can often be driven by kinetic physics, it has typically been omitted from fluid simulations used to predict X-ray emissions. We study the possible results of soft X-ray imaging using hybrid simulations under quasi-radial interplanetary magnetic fields, where ion-ion instabilities drive ultra-low frequency foreshock waves, leading to turbulence in the magnetosheath, affecting the dynamics of the cusp and magnetopause. We simulate soft X-ray emission to determine what may be seen by missions such as LEXI, and evaluate the possibility of identifying kinetic structures. While kinetic structures are visible in high-cadence imaging, current instruments may not have the time resolution to discern kinetic signals.

J Ng↗
DOE OSTI2024

A Study of Slow-mode Shocks in the Near-Earth Magnetotail with MMS Observations and Hybrid Simulations

The structure of the magnetic reconnection boundary, particularly the presence of slow-mode shocks in the near-Earth magnetotail was studied by using magnetospheric multiscale (MMS) observations and 2.5D hybrid simulations. A total of 51 crossings of MMS from 2017 to 2021 were analyzed. We found that the detection percentage of slow-mode shocks in the near-Earth magnetotail is 41%–55%. Previous studies have only reported one slow-mode shock event in the near-Earth magnetotail and a slow-mode shock detection percentage of 10% or lower in the mid-to-distant magnetotail. It was observed that if the high-energy beam region data is removed from the slow-mode shock downstream observations then the detection of slow-mode shocks reduces, implying that the kinetic effects play an important role in the detection of slow-mode shocks. For the crossings where the interface was not identified as a slow-mode shock, it was found that the turbulence in those crossings can change the mass flux values and disrupt the detection of slow-mode shock. However, the macroscopic slow-mode shock-like structure stably exists around the magnetic reconnection interface, as most of the conditions for slow-mode shocks were satisfied. This result suggests that slow-mode shocks are a general feature of magnetic reconnection geometry. We find that the lack of detection of slow-mode shocks in previous observations and simulations can be explained by taking into account the kinetic structure of slow-mode shocks and the presence of turbulence.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Hybrid RANS-LES of the Atmospheric Boundary Layer for Wind Farm Simulations: Preprint

Wind farm simulations often do not accurately represent wake-atmospheric boundary layer (ABL) interactions, blade boundary layer (BL) dynamics, and turbine-turbine interactions. In this work, we use Active Model Split (AMS), a new hybrid Reynolds-Averaged Navier Stokes (RANS)-large eddy simulation (LES) model, which is well suited to capture these effects because the model can (i) accurately simulate the ABL with the Coriolis effect, (ii) is accurate in adverse pressure gradients such as those near wind turbine blades, and (iii) has sufficiently low computational cost to simulate multiple turbines while resolving the blade BL. For simplicity and consistency we develop AMS to be used throughout the domain rather than in a zonal method. We implement our work in the massively parallel flow solver, Nalu-Wind, so that our model can access the compute resources needed for blade-resolved simulations of multiple wind turbines. To accomplish these aims, we modify the baseline AMS by changing the RANS contribution to SST k - omega with a length scale limiter, adding the Coriolis effect, and developing an appropriate wall treatment. We show that AMS of the ABL with the Coriolis effect matches LES reference results better than those obtained with RANS. We describe our plans to add buoyancy effects and wind turbines to our AMS simulations.

atmospheric boundary layer↗
NASA NTRS1995

Hybrid simulations of the saturated Farley-Buneman instability in the ionosphere

Numerical simulations of the Farley-Buneman instability in 2-1/2 dimensions using particle ions and fluid electrons show the growth, saturation and nonlinear behavior of two-stream waves. This hybrid technique models the saturated state of the instability for a much longer period of time than the pure particle codes that preceded it. While focusing principally on modeling the topside E region equatorial electrojet, many of these results apply to the auroral two-stream instability as well. The following features are seen in all our hybrid simulations: (1) wave growth at an angle offset from the electron drift direction where the angle depends on the strength of the driving electric field, (2) nonlinear coupling to waves traveling perpendicular to the propagation direction of the principal two-stream waves, (3) a saturated wave phase velocity at or above the sound speed but well below the velocity predicted by linear theory and (4) phase velocities which remain almost constant as a simulated radar sweeps from a horizontal direction to nearly vertical. The nonlinear electron motion dominates the behavior of these waves. Further, these simulations indicate that ion kinetic effects are not essential for the saturation of the instability and that electron temperature effects have a minor impact on the final saturated state.

Oppenheim, Meers↗