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At least 1,729 records · Page 96
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Laser-driven, ion-scale magnetospheres in laboratory plasmas. I. Experimental platform and first results

We report magnetospheres are a ubiquitous feature of magnetized bodies embedded in a plasma flow. While large planetary magnetospheres have been studied for decades by spacecraft, ion-scale “mini” magnetospheres can provide a unique environment to study kinetic-scale, collisionless plasma physics in the laboratory to help validate models of larger systems. In this work, we present preliminary experiments of ion-scale magnetospheres performed on a unique high-repetition-rate platform developed for the Large Plasma Device at the University of California, Los Angeles. The experiments utilize a high-repetition-rate laser to drive a fast plasma flow into a pulsed dipole magnetic field embedded in a uniform magnetized background plasma. 2D maps of the magnetic field with high spatial and temporal resolution are measured with magnetic flux probes to examine the evolution of magnetosphere and current density structures for a range of dipole and upstream parameters. The results are further compared to 2D particle-in-cell simulations to identify key observational signatures of the kinetic-scale structures and dynamics of the laser-driven plasma. We find that distinct 2D kinetic-scale magnetopause and diamagnetic current structures are formed at higher dipole moments, and their locations are consistent with predictions based on pressure balances and energy conservation.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

An efficient technique for magnetic equilibrium reconstruction with q profile constraints and its application on the EAST tokamak

An efficient technique for building plasma equilibria with preset or constrained q profiles by solving the nonlinear Grad–Shafranov equation iteratively is proposed. Here, the technique uses a set of dynamic virtual poloidal field probes in the plasma core region. Numerical examples are shown for monotonic q profiles and negative central magnetic shear equilibria which are obtained with this technique. As a proof of principle, the technique is applied on the EAST tokamak, to constrain the plasma equilibrium reconstruction with the experimental q = 1 surface information from the ECE diagnostic in addition to the external magnetic measurements.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1979

Global Aspects of the Earth's Magnetopause

Measurable characteristics of the magnetopause are discussed. The Earth's magnetopause is a thin magnetic discontinuity separating the shocked, magnetized plasma of the solar wind from a more tenuous plasma contained by the geomagnetic field. This external magnetosheath plasma flows around the magnetosphere with characteristics that are in approximate agreement with gas dynamic theory. The interplanetary magnetic field carried by this plasma becomes draped over the magnetosphere and its orientation relative to the local geomagnetic field determines the local magnetopause current. Solar wind pressure and interplanetary field direction control the geocentric distance to the magnetopause with high pressures and southware fields moving the equatorial magnetopause to a more earthward location. Evidence suggests that the magnetopause is Kelvin-Helmholtz unstable and surface waves are propagating toward the magnetotail.

Fairfield, D. H.↗
DOE OSTI2014

Shock-ignition relevant experiments with planar targets on OMEGA

We report on laser-driven, strong-shock generation and hot-electron production in planar targets in the presence of a pre-plasma at shock-ignition (SI) relevant laser and pre-plasma conditions. 2-D simulations reproduce the shock dynamics well, indicating ablator shocks of up to 75 Mbar have been generated. We observe hot-electron temperatures of ∼70 keV at intensities of 1.4 × 10{sup 15} W/cm{sup 2} with multiple overlapping beams driving the two-plasmon decay instability. When extrapolated to SI-relevant intensities of ∼10{sup 16} W/cm{sup 2}, the hot electron temperature will likely exceed 100 keV, suggesting that tightly focused beams without overlap are better suited for launching the ignitor shock.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

IMEX and exact sequence discretization of the multi-fluid plasma model

Multi-fluid plasma models, where an electron fluid is modeled in addition to multiple ion and neutral species as well as the full set of Maxwell's equations, are useful for representing physics beyond the scope of classic MHD. This advantage presents challenges in appropriately dealing with electron dynamics and electromagnetic behavior characterized by the plasma and cyclotron frequencies and the speed of light. For physical systems, such as those near the MHD asymptotic regime, this requirement drastically increases runtimes for explicit time integration even though resolving fast dynamics may not be critical for accuracy. Implicit time integration methods, with efficient solvers, can help to step over fast time-scales that constrain stability, but do not strongly influence accuracy. As an extension, Implicit-explicit (IMEX) schemes provide an additional mechanism to choose which dynamics are evolved using an expensive implicit solve or resolved using a fast explicit solve. In this study, in addition to IMEX methods we also consider a physics compatible exact sequence spatial discretization. Here, this combines nodal bases (H-Grad) for fluid dynamics with a set of vector bases (H-Curl and H-Div) for Maxwell's equations. This discretization allows for multi-fluid plasma modeling without violating Gauss' laws for the electric and magnetic fields. This initial study presents a discussion of the major elements of this formulation and focuses on demonstrating accuracy in the linear wave regime and in the MHD limit for both a visco-resistive and a dispersive ideal MHD problem.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Beam-plasma instability in charged plasma in the absence of ions

We report on the possibility of the beam-plasma instability development in the system with electron beam interacting with the single-component hot electron plasma without ions. As considered system, we analyse the interaction of the low-current relativistic electron beam (REB) with squeezed state in the high-current REB formed in the relativistic magnetically insulated two-section vircator drift space. The numerical analysis is provided by means of 3D electromagnetic simulation in CST Particle Studio. We have conducted an extensive study of characteristic regimes of REB dynamics determined by the beam-plasma instability development in the absence of ions. As a result, the dependencies of instability increment and wavelength on the REB current value have been obtained. The considered process brings the new mechanism of controlled microwave amplification and generation to the device with a virtual cathode. This mechanism is similar to the action of the beam-plasma amplifiers and oscillators.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1983

Role of thermal conduction in the acceleration of the solar wind

The thermal and suprathermal processes involving solar wind electrons are discussed from a theoretical point of view. A model for the electron distribution function, f(e), based on the solutions of the Boltzmann equation in Krook's approximation is outlined: the angular and energy dependences of for various distances from the Sun between the coronal base and the Earth are presented with the express purpose of obtaining the radial profile of the heat flux generated by the suprathermals. The basic fluid-dynamical equations for the solar wind plasma as a whole along any given magnetic field line are solved. Results are in good agreement with observations. The predicted density and temperature profiles for positive ions exhibit the characteristics of recent measurements, both in the corona (above the coronal holes) and between 0.3 and 1 A.U. (the Helios region). It is concluded that the suprathermal electrons play an important role in the formation and the dynamics of the solar wind.

Olbert, S.↗
DOE OSTI2024

Operando XPS for Plasma Process Monitoring: A Case Study on the Hydrogenation of Copper Oxide Confined under h-BN

Here, we demonstrate that ambient pressure x-ray photoelectron spectroscopy (APXPS) can be used for in situ studies of dynamic changes in surface chemistry in a plasma environment. This opens a new and vast application space for XPS and greatly complements modern spectroscopy techniques to probe plasma-solid/liquid interactions relevant to process monitoring in the semiconductor industry, bio-medical plasma applications and plasma remediation technologies. Hexagonal boron nitride (h-BN) grown on Cu was used in this study as a well-defined model system for plasma process monitoring and because of its unique chemical, optical and electrical properties that make it a prospective material for advanced electronics. To better understand the stability and surface chemistry of h-BN during plasma assisted processing, we track in real time the plasma-induced chemical state changes of B, N and the underlying Cu substrate using APXPS equipped with an AC discharge plasma source operating at 13 Pa. Residual gas analysis (RGA) mass-spectra were concurrently collected during plasma-XPS to track reaction products formed during plasma exposure. A clear reduction of Cu x O is seen, while an h-BN layer remains intact, suggesting hydrogen radical (H • ) species can attack the exposed and h-BN covered Cu oxide patches and partially reduce the underlying substrate without significantly damaging the overlaying h-BN, which is of practical importance for development of h-BN encapsulated devices and interfaces. In addition to demonstration of plasma-XPS capabilities we discuss the observed challenges (e.g., parasitic plasma-chamber walls reactions and charging effects) and propose potential solutions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Fueling limits in a cylindrical viscosity-limited reactor

Recently, a method to achieve a “natural hot-ion mode” was suggested by utilizing ion viscous heating in a rotating plasma with a fixed boundary. We explore the steady-state solution to the Braginskii equations and find the parameter regime in which a significant temperature difference between ions and electrons can be sustained in a driven steady state. Here, the threshold for this effect occurs at ρ i ≳ 0.1R. An analytic, leading order low flow solution is obtained, and a numerical, moderate Mach number M ≲ 2 is investigated. The limitation is found to be at moderate Mach numbers.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2026

Unitary Qubit Lattice Algorithms for Plasma Physics

This final technical report summarizes research conducted under DOE Award DE-SC0021653 to develop unitary Quantum Lattice Algorithms for modeling electromagnetic wave propagation and scattering in complex media, including plasmas. The project developed and validated quantum-inspired formulations of Maxwell's equations that preserve unitary evolution and can be evaluated on classical high-performance computing systems while providing a foundation for future quantum-computing implementations. Major accomplishments include the development of two- and three-dimensional algorithms for electromagnetic scattering; scalable, distributed-memory implementations demonstrated on the Perlmutter supercomputer; formulations for nonlinear lossless fluid dynamics and cold, lossless, inhomogeneous magnetized plasmas; and an explicit quantum algorithm for a time-discretized Lorenz model. Simulations reproduced a range of characteristic wave phenomena, including transient effects that are not readily apparent in conventional frequency-domain studies, demonstrating the effectiveness of the proposed approach for modeling complex electromagnetic and plasma systems. The work establishes a unified theoretical and computational framework for quantum and quantum-inspired simulation and provides a foundation for future implementation on fault-tolerant quantum systems.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Electron dynamics in radio frequency magnetron sputtering argon discharges with a dielectric target

Abstract We demonstrate a self-consistent and complete description of electron dynamics in a typical electropositive radio frequency magnetron sputtering (RFMS) argon discharge with a dielectric target. The electron dynamics, including the electron power absorption dynamics in one radio frequency (RF) period, is studied via a fully kinetic 2d3v particle-in-cell/Monte Carlo collision (PIC/MCC) electrostatic simulation. The interplay between the fundamental plasma parameters is analyzed through their spatiotemporal dynamics. Due to the influence of magnetic trap on the electron transport, a spatially dependent charging that perturbs the electric potential is observed on the dielectric target surface, resulting in a spatially dependent ion energy distribution along the target surface. The E × B drift-to-discharge current ratio is in approximate agreement with Bohm diffusion. The electron power absorption can be primarily decoupled into the positive Ohmic power absorption in the bulk plasma region and the negative pressure-induced power absorption near the target surface. Ohmic power absorption is the dominant electron power absorption mechanism, mostly contributed by the azimuthal electron current. The power absorption due to electron inertial effects is negligible on time-average. Both the maximum power absorption and dissipation of electrons appear in the bulk plasma region during the second half of the RF period, implying a strong electron trapping in magnetron discharges. The contribution of secondary electrons is negligible under typical RFMS discharge conditions.

Physics↗
DOE OSTI2014

Growth of ring ripple in a collisionless plasma in relativistic-ponderomotive regime and its effect on stimulated Raman backscattering process

A theoretical and numerical study has been made of the propagation of a ring rippled laser beam in collisionless plasma with dominant relativistic ponderomotive nonlinearity and its effect on the excitation of electron plasma wave and stimulated Raman backscattering process. The growth of ring ripple, riding on an intense Gaussian laser beam in plasma has also been studied. A paraxial-ray and WKB approximation has been invoked to understand the nature of propagation of the ring rippled Gaussian laser beam in plasma, electron plasma wave and back reflectivity under the influence of both nonlinearities. The growth rate and focusing of a ring rippled beam is found to be considerably affected by the power of the main beam and the phase angle between the electric vectors of the main beam and the ring ripple. It has also been observed that the focusing is released by the coupling of relativistic and ponderomotive nonlinearities, which significantly affected the dynamics of the excitation of electron plasma wave and back reflectivity of stimulated Raman scattering (SRS). Due to the strong coupling between ring rippled laser beam and the excited electron plasma wave, back reflectivity of SRS is enhanced. It has been observed from the computational results that the effect of the increased intensity leads to suppression of SRS back reflectivity. The results have been presented for established laser and plasma parameters.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1982

Highlights of theoretical progress related to the International Magnetospheric Study

U.S. theoretical research efforts have addressed three areas within the International Magnetospheric Study. The first, solar wind/magnetosphere interaction, is presently concerned with the suggestion that magnetic merging may predominantly occur near the polar cusps rather than near the subsolar point. Mechanisms have been proposed for noncollisional diffusion of solar wind plasma across the closed magnetopause entailed by such a phenomenon. The second area considers the importance to magnetotail dynamics of a continuous source of solar wind plasma, and of sporadic plasma loss associated with an unsteady convection cycle. In the third area, the electrodynamic magnetosphere/ionosphere interaction, an advanced state has been reached in the understanding of the relevant physics, with respect both to coupling in the subauroral region and the large scale structure of auroral zone electric fields parallel, and perpendicular to, the magnetic field.

Hill, T. W.↗
DOE OSTI2019

Understanding the release of helium atoms from nanochannel tungsten: a molecular dynamics simulation

The design of highly radiation-tolerant plasma-facing materials (PFMs) is of great importance for fusion reactors. Our recent experiments have shown that nanochannel tungsten (W) films have clearly superior radiation tolerance properties. In the present work, helium clustering and release from nanochannel tungsten were studied by molecular dynamics simulations. The effects of temperature and vacancy concentration on the helium release from a tungsten cylinder were investigated. Our results show that nanochannel W that consists of thin W cylinders releases He atoms more quickly than bulk W with flat surfaces, thus greatly reducing the He concentration and suppressing the formation and growth of He bubbles, which leads to increased radiation tolerance. Moreover, the micro-structural changes due to increasing He fluence are smaller in nanochannel W than those in bulk W. Although vacancies in nanochannel W will trap He atoms, the nanochannel W also has a stronger tendency to stabilize helium retention than bulk W. The mechanism of helium release from nanochannel W was also examined. The results reported here are beneficial for guiding future work in the design of radiation resistant PFMs.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Interactions of mobile helium clusters with surfaces and grain boundaries of plasma-exposed tungsten

We report results of atomistic computations for the interactions of small mobile helium clusters (He{sub n}) with free surfaces and grain boundaries (GBs) in tungsten toward development of continuum drift-diffusion-reaction models for the dynamics of mobile helium clusters in plasma-exposed tungsten. Molecular-statics (MS) simulations based on reliable many-body interatomic potentials are carried out for He{sub n} (1 ≤ n ≤ 7) clusters near sinks to obtain the potential energy profiles of the He{sub n} clusters as a function of the clusters' center-of-mass distance from a sink. Sinks investigated include surfaces, GBs, and regions in the vicinity of junctions where GBs intersect free surfaces. Elastic interaction potentials based on elastic inclusion theory provide an excellent description of the MS results for the cluster-sink interactions. The key parameter in the elastic models is the sink segregation strength, which is found to increase with increasing cluster size. Such cluster-sink interactions are responsible for the migration of small helium clusters by drift and for helium segregation on surfaces and grain boundaries in tungsten. Such helium segregation on sinks is observed in large-scale molecular-dynamics simulations of helium aggregation in model polycrystalline tungsten at 933 K upon helium implantation.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Electromagnetic analysis of the plasma chamber of an ECR-based charge breeder

The optimization of the efficiency of an ECR-based charge breeder is a twofold task: efforts must be paid to maximize the capture of the injected 1+ ions by the confined plasma and to produce high charge states to allow post-acceleration at high energies. Both tasks must be faced by studying in detail the electrons heating dynamics, influenced by the microwave-to-plasma coupling mechanism. Numerical simulations are a powerful tools for obtaining quantitative information about the wave-to-plasma interaction process: this paper presents a numerical study of the microwaves propagation and absorption inside the plasma chamber of the PHOENIX charge breeder, which the selective production of exotic species project, under construction at Legnaro National Laboratories, will adopt as charge breeder. Calculations were carried out with a commercial 3D FEM solver: first, all the resonant frequencies were determined by considering a simplified plasma chamber; then, the realistic geometry was taken into account, including a cold plasma model of increasing complexity. The results gave important information about the power absorption and losses and will allow the improvement of the plasma model to be used in a refined step of calculation reproducing the breeding process itself.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1972

Quantum statistical mechanics of dense partially ionized hydrogen.

The theory of dense hydrogenic plasmas beginning with the two component quantum grand partition function is reviewed. It is shown that ionization equilibrium and molecular dissociation equilibrium can be treated in the same manner with proper consideration of all two-body states. A quantum perturbation expansion is used to give an accurate calculation of the equation of state of the gas for any degree of dissociation and ionization. In this theory, the effective interaction between any two charges is the dynamic screened potential obtained from the plasma dielectric function. We make the static approximation; and we carry out detailed numerical calculations with the bound and scattering states of the Debye potential, using the Beth-Uhlenbeck form of the quantum second virial coefficient. We compare our results with calculations from the Saha equation.

Dewitt, H. E.↗
DOE OSTI2022

QLBT: a linear Boltzmann transport model for heavy quarks in a quark-gluon plasma of quasi-particles

Abstract We develop a new heavy quark transport model, QLBT, to simulate the dynamical propagation of heavy quarks inside the quark-gluon plasma (QGP) created in relativistic heavy-ion collisions. Our QLBT model is based on the linear Boltzmann transport (LBT) model with the ideal QGP replaced by a collection of quasi-particles to account for the non-perturbative interactions among quarks and gluons of the hot QGP. The thermal masses of quasi-particles are fitted to the equation of state from lattice QCD simulations using the Bayesian statistical analysis method. Combining QLBT with our advanced hybrid fragmentation-coalescence hadronization approach, we calculate the nuclear modification factor $$R_\mathrm {AA}$$ R AA and the elliptic flow $$v_2$$ v 2 of D mesons at the Relativistic Heavy-Ion Collider and the Large Hadron Collider. By comparing our QLBT calculation to the experimental data on the D meson $$R_\mathrm {AA}$$ R AA and $$v_2$$ v 2 , we extract the heavy quark transport parameter $$\hat{q}$$ q ^ and diffusion coefficient $$D_\mathrm {s}$$ D s in the temperature range of $$1-4~T_\mathrm {c}$$ 1 - 4 T c , and compare them with the lattice QCD results and other phenomenological studies.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗