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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 1,657 records · Page 92
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Predicting hot electron generation in inertial confinement fusion with particle-in-cell simulations

A series of two-dimensional particle-in-cell simulations with speckled laser drivers was carried out to study hot electron generation in direct-drive inertial confinement fusion on OMEGA. Scaling laws were obtained for hot electron fraction and temperature as functions of laser/plasma conditions in the quarter-critical region. Using these scalings and conditions from hydro simulations, the temporal history of hot electron generation can be predicted. The scalings can be further improved to predict hard x-rays for a collection of OMEGA warm target implosions within experimental error bars. Furthermore, these scalings can be readily implemented into inertial confinement fusion design codes.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Stokesian dynamics with odd viscosity

Stokesian dynamics is a well-established computational method for simulating dynamics of many particles suspended in a conventional passive fluid medium. Active fluids composed of self-driving particles with broken time-reversal symmetry permit the emergence of a so-called odd viscosity. Here, in this work, we extended the conventional Stokesian dynamics formalism to incorporate the additional hydrodynamic effects due to odd viscosity, which enables simulating collective behavior of many particles suspended in an active fluid medium with both even viscosity and odd viscosity.

42 ENGINEERING↗
DOE OSTI2020

Measurement of Kinetic-Scale Current Filamentation Dynamics and Associated Magnetic Fields in Interpenetrating Plasmas

Here, we present the first local, quantitative measurements of ion current filamentation and magnetic field amplification in interpenetrating plasmas, characterizing the dynamics of the ion Weibel instability. The interaction of a pair of laser-generated, counterpropagating, collisionless, supersonic plasma flows is probed using optical Thomson scattering (TS). Analysis of the TS ion-feature revealed anticorrelated modulations in the density of the two ion streams at the spatial scale of the ion skin depth c/ω pi = 120 μm, and a correlated modulation in the plasma current. The inferred current profile implies a magnetic field amplitude ~30 ± 6 T , corresponding to ~1% of the flow kinetic energy, indicating that magnetic trapping is the dominant saturation mechanism.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Signature of Collective Plasma Effects in Beam-Driven QED Cascades

QED cascades play an important role in extreme astrophysical environments like magnetars. Furthermore, they can also be produced by passing a relativistic electron beam through an intense laser field. Signatures of collective pair plasma effects in these QED cascades are shown to appear, in exquisite detail, through plasma-induced frequency upshifts in the laser spectrum. Remarkably, these signatures can be detected even in small plasma volumes moving at relativistic speeds. Strong-field quantum and collective pair plasma effects can thus be explored with existing technology, provided that ultradense electron beams are colocated with multipetawatt lasers.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Stable Positron Acceleration in Thin, Warm, Hollow Plasma Channels

Hollow plasma channels are attractive for lepton acceleration for providing intrinsic emittance preservation regimes. However, beam breakup instabilities dominate the dynamics. Here, we show that thin, warm hollow channels can sustain large-amplitude plasma waves ready for high-quality positron acceleration. We verify that the combination of warm electrons and thin hollow channels enables positron focusing structures. Such focusing wakefields unlock beam breakup damping mechanisms. We demonstrate that such channels emerge self-consistently during the long-term plasma dynamics in the blowout's regime aftermath, allowing for experimental demonstration.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Probing Strong-Field QED with Doppler-Boosted Petawatt-Class Lasers

In this work, we propose a scheme to explore regimes of strong-field quantum electrodynamics (SF QED) otherwise unattainable with the currently available laser technology. The scheme relies on relativistic plasma mirrors curved by radiation pressure to boost the intensity of petawatt-class laser pulses by Doppler effect and focus them to extreme field intensities. We show that very clear SF QED signatures could be observed by placing a secondary target where the boosted beam is focused.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Holographic Plasma Lenses

We report a hologram fully encodes a three-dimensional light field by imprinting the interference between the field and a reference beam in a recording medium. Here we show that two collinear pump lasers with different foci overlapped in a gas jet produce a holographic plasma lens capable of focusing or collimating a probe laser at intensities several orders-of-magnitude higher than the limits of a nonionized optic. We outline the theory of these diffractive plasma lenses and present simulations for two plasma mechanisms that allow their construction: spatially varying ionization and ponderomotively driven ion-density fluctuations. Damage-resistant plasma optics are necessary for manipulating high-intensity light, and divergence control of high-intensity pulses—provided by holographic plasma lenses—will be a critical component of high-power plasma-based lasers.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Bohm Criterion of Plasma Sheaths away from Asymptotic Limits

The plasma exit flow speed at the sheath entrance is constrained by the Bohm criterion. The so-called Bohm speed regulates the plasma particle and power exhaust fluxes to the wall, and it is commonly deployed as a boundary condition to exclude the sheath region in quasineutral plasma modeling. In this work, the Bohm criterion analysis is performed in the intermediate plasma regime away from the previously known limiting cases of adiabatic laws and the asymptotic limit of infinitesimal Debye length in a finite-size system, using the transport equations of an anisotropic plasma. The resulting Bohm speed has explicit dependence on local plasma heat flux, temperature isotropization, and thermal force. Comparison with kinetic simulations demonstrates its accuracy over the plasma-sheath transition region in which quasineutrality is weakly perturbed and the Bohm criterion applies.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Higher Harmonics in Multipactor Induced Plasma Ionization Breakdown near a Dielectric Surface

In this Letter, the novel physics of higher harmonic (HH) generation of the normal electric field near a dielectric surface is reported in multipactor induced plasma ionization breakdown, as determined by kinetic particle-in-cell simulations. The observed HH frequency is around ten times the fundamental rf driving frequency, but lower than the electron plasma frequency. A theory is constructed which indicates that stream plasma interaction-induced instability is the mechanism of HH generation in the collisional regime. The HH frequency and its corresponding growth rate of the HH oscillation amplitude from the theory are in good agreement with kinetic particle-in-cell simulations.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2024

Light-Matter Interaction near the Schwinger Limit Using Tightly Focused Doppler-Boosted Lasers

Strong-field quantum electrodynamics (SF QED) is a burgeoning research topic dealing with electromagnetic fields comparable to the Schwinger field (≈1.32×10 18 V/m). While most past and proposed experiments rely on reaching this field in the rest frame of relativistic particles, the Schwinger limit could also be approached in the laboratory frame by focusing to its diffraction limit the light reflected by a plasma mirror irradiated by a multipetawatt laser. Here, we explore the interaction between such intense light and matter with particle-in-cell simulations. We find that the collision with a relativistic electron beam would enable the study of the nonperturbative regime of SF QED, while the interaction with a solid target leads to a profusion of SF QED effects that retroact on the interaction. In both cases, relativistic attosecond pair jets with high densities are formed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Broadening of the Divertor Heat Flux Profile in High Confinement Tokamak Fusion Plasmas with Edge Pedestals Limited by Turbulence in DIII-D

Multimachine empirical scaling predicts an extremely narrow heat exhaust layer in future high magnetic field tokamaks, producing high power densities that require mitigation. Here, in the experiments presented, the width of this exhaust layer is nearly doubled using actuators to increase turbulent transport in the plasma edge. This is achieved in low collisionality, high confinement edge pedestals with their gradients limited by turbulent transport instead of large-scale, coherent instabilities. The exhaust heat flux profile width and divertor leg diffusive spreading both double as a high frequency band of turbulent fluctuations propagating in the electron diamagnetic direction doubles in amplitude. The results are quantitatively reproduced in electromagnetic XGC particle-in-cell simulations which show the heat flux carried by electrons emerges to broaden the heat flux profile, directly supported by Langmuir probe measurements.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Intrinsic Toroidal Rotation Driven by Turbulent and Neoclassical Processes in Tokamak Plasmas from Global Gyrokinetic Simulations

Gyrokinetic tokamak plasmas can exhibit intrinsic toroidal rotation driven by the residual stress. While most studies have attributed the residual stress to the parallel-momentum flux from the turbulent E × B motion, the parallel-momentum flux from the drift-orbit motion (denoted $Π^D_\parallel$) and the E × B-momentum flux from the E × B motion (denoted $Π_{E×B}$) are often neglected. Here, we use the global total-f gyrokinetic code XGC to study the residual stress in the core and the edge of a DIII-D H-mode plasma. Numerical results show that both $Π^D_\parallel$ and $Π_{E×B}$ make up a significant portion of the residual stress. In particular, $Π^D_\parallel$ in the core is higher than the collisional neoclassical level in the presence of turbulence, while in the edge it represents an outflux of countercurrent momentum even without turbulence. Using a recently developed “orbit-flux” formulation, we show that the higher-than-neoclassical-level $Π^D_\parallel$ in the core is driven by turbulence, while the outflux of countercurrent momentum from the edge is mainly due to collisional ion orbit loss. In conclusion, these results suggest that $Π^D_\parallel$ and $Π_{E×B}$ can be important for the study of intrinsic toroidal rotation.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Laboratory Demonstration of Collisionless Blob Formation via Laser-Produced Plasma Self-Focusing

Strongly localized, propagating plasma density structures that are capable of crossing magnetic field lines are known as “blobs.” Here we demonstrate a novel mechanism for the formation and propagation of an ion gyroradius-scale blob-cavity structure at the interface between a super-Alfvénic laser-produced plasma (LPP) and an ambient magnetized plasma. The LPP self-focuses along the edge of the diamagnetic cavity which results in a dense, jetlike structure as compared to ballistic motion. This collimated flow couples momentum to the ambient plasma through a collisionless process known as Larmor coupling. The Larmor electric fields locally displace the ambient ions forming a blob above the LPP flow. In the region between a gyrating blob and collimated LPP flow, a secondary cavity of expelled magnetic field forms. In conclusion, these findings are supported by particle-in-cell simulations that replicate the blob formation mechanism and provide insight to similar processes in space, astrophysical, and laboratory settings characterized by ion kinetic scales.

Fluorescence spectroscopy↗
DOE OSTI2025

Biermann-Battery-Driven Magnetized Collisionless Shock Precursors in Laser-Produced Plasmas

This Letter reports the first complete observation of magnetized collisionless shock precursors formed through the compression of Biermann-battery magnetic fields in laser produced plasmas. At OMEGA, lasers produce a supersonic CH plasma flow which is magnetized with Biermann-battery magnetic fields. The plasma flow collides with an unmagnetized hydrogen gas jet plasma to create a magnetized shock precursor. The situation where the flowing plasma carries the magnetic field is similar to the Venusian bow shock. Imaging 2⁢𝜔 Thomson scattering confirms that the interaction is collisionless and shows density and temperature jumps. Proton radiographs have regions of strong deflections and FLASH magnetohydrodynamic (MHD) simulations show the presence of Biermann fields in the Thomson scattering region. Electrons are accelerated to energies of up to 100 keV in a power-law spectrum. Here, OSIRIS particle-in-cell (PIC) simulations, initialized with measured parameters, show the formation of a magnetized shock precursor and corroborate the experimental observables.

High-energy-density plasmas↗