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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Beam physics research with the IOTA electron lens

The electron lens in the Fermilab Integrable Optics Test Accelerator (IOTA) will enable new research in nonlinear integrable optics, space-charge compensation, electron cooling, and the stability of intense beams. This research addresses scientific questions on high-brightness beams and operational challenges of high-power accelerators for nuclear and particle physics. We review the roles that electron lenses play in this field and the physical principles behind their applications. The design criteria and specifications for the IOTA storage ring and electron lens are then discussed. We conclude with a description of the components of the apparatus.

43 PARTICLE ACCELERATORS↗
DOE OSTI2025

Improved laser-plasma accelerator stability via high-bandwidth longitudinal focal position stabilization of a 100 TW-class laser system

Laser-plasma accelerators (LPAs) offer an attractive alternative to conventional accelerators for the development of compact electron sources and next-generation light sources. Due to orders-of-magnitude larger accelerating gradients, LPAs enable the acceleration of high-brightness electron beams to ultrarelativistic energies in millimeter- to centimeter-scale distances. However, LPA stability is limited by shot-to-shot fluctuations of the driving laser system. Specifically, fluctuations in the final-focus longitudinal position result in correlated instability in LPA electron beam qualities, including total beam charge, average beam energy, and energy spread. We demonstrate active stabilization of the longitudinal focal position for a 100 TW-class laser system. This repetition-rate scalable stabilization system leverages noninvasive wave front monitoring of a copropagating, unamplified kHz pulse train to guide corrective adjustments to the focal position of a 1 Hz amplified drive laser via an upstream telescope on millisecond timescales. In this demonstration, the approach limits standard deviation fluctuations of the amplified drive beam’s longitudinal focal position to ±0.22⁢ mm (representing at least a 53% reduction), achieved with a correction bandwidth that reaches the Nyquist frequency limit. Consequently, we observe marked improvements in both long-term and shot-to-shot LPA stability in terms of charge and spectrum.

Beam control↗
DOE OSTI2026

Over 8 hours of continuous operation of a free-electron laser driven by a laser-plasma accelerator

Since the emergence of laser-plasma accelerators (LPAs), substantial work has been dedicated to using LPAs to drive free-electron lasers (FELs) for a broad range of applications. Despite recent breakthroughs, which have proven the fundamental feasibility of operating FELs with an LPA source, stable FEL operation over multiple hours without operator input had yet to be achieved. In this work, we report significant improvements to the stability of a hundred terawatt laser system, resulting in successful demonstration of reliable, long-term operation of an LPA-driven FEL in the self-amplified spontaneous emission (SASE) regime at 420 nm. The LPA source delivered 100 MeV electron beams at 1 Hz with high stability over more than 10 h, enabling over 8 h of continuous FEL operation without operator input. The acquired data were subsequently used to investigate correlations between the measured undulator radiation and parameters of the drive laser, plasma source, and electron beam. The revealed connections between LPA and FEL performance gave important additional insights into ways to further improve and stabilize the system, thus demonstrating the capability of our setup to serve as a powerful platform for future studies of LPA-driven FEL operation. The one-of-a-kind integration of multiple stabilization concepts onto the LPA facility discussed in this manuscript yielded significant accelerator and light source improvements (with residual correlations suggesting even more is possible), which will positively impact LPA applications at large.

Kohrell, Finn [Lawrence Berkeley National Laborato↗
NASA NTRS2011

The Impact of Return-Current Losses on the Observed Emissions from Solar Flares

Electrons accelerated in solar flares are expected to drive a co-spatial return current in the ambient plasma when they escape the acceleration region. This return current maintains plasma neutrality and the stability of the beam of streaming electrons. The electric field that drives this return current also decelerates the energetic electrons in the beam. The corresponding energy loss experienced by the accelerated electrons can affect the observed properties of the X-ray and radio emissions from flares and the evolution of the thermal flare plasma. I will discuss the properties of the flare emissions expected in a classical, steady-state model. As part of this discussion, I will examine Gordon Emslie's 1980 conjecture that return-current losses result in a maximum brightness for the hard X-ray emission from flares.

Holman, Gordon D.↗
NASA NTRS1984

Electron precipitation in solar flares - Collisionless effects

A large fraction of the electrons which are accelerated during the impulsive phase of solar flares stream towards the chromosphere and are unstable to the growth of plasma waves. The linear and nonlinear evolution of plasma waves as a function of time is analyzed with a set of rate equations that follows, in time, the nonlinearly coupled system of plasma waves-ion fluctuations. As an outcome of the fast transfer of wave energy from the beam to the ambient plasma, nonthermal electron tails are formed which can stabilize the anomalous Doppler resonance instability responsible for the pitch angle scattering of the beam electrons. The non-collisional losses of the precipitating electrons are estimated, and the observational implication of these results are discussed.

Vlahos, L.↗
NASA NTRS1986

The effect of beam-driven return current instability on solar hard X-ray bursts

The problem of electrostatic wave generation by a return current driven by a small area electron beam during solar hard X-ray bursts is discussed. The marginal stability method is used to solve numerically the electron and ion heating equations for a prescribed beam current evolution. When ion-acoustic waves are considered, the method appears satisfactory and, following an initial phase of Coulomb resistivity in which T sub e/T sub i rise, predicts a rapid heating of substantial plasma volumes by anomalous ohmic dissipation. This hot plasma emits so much thermal bremsstrahlung that, contrary to previous expectations, the unstable beam-plasma system actually emits more hard X-rays than does the beam in the purely collisional thick target regime relevant to larger injection areas. Inclusion of ion-cyclotron waves results in ion-acoustic wave onset at lower T sub e/T sub i and a marginal stability treatment yields unphysical results.

Cromwell, D.↗
NASA NTRS2019

Evidence for Oscillating Two-Stream Instability and Spatial Collapse of Langmuir Waves in a Solar Type II Radio Burst

We present the high time resolution in situ observations of Langmuir waves, likely excited by an electron beam accelerated by a coronal-mass ejection-driven super-critical quasi-perpendicular interplanetary shock into its upstream solar wind, which happens to be the source region of a solar type II radio burst. We show that (1) these waves occur as coherent localized magnetic-field-aligned, one-dimensional wave packets with durations of a few milliseconds and with peak intensities well in excess of the threshold for strong turbulence processes, (2) they provide what is believed to be the first evidence for: (a) the oscillating two-stream instability (OTSI) L(sub 1) + L(sub 2) S/⟶ U + D, where L(sub 1) and L(sub 2), U and D, and S are the pump Langmuir waves, up- and down-shifted side bands, and ion sound waves, respectively, (b) a three-wave interaction U + D ⟶ T(sub 2f(sub pe)), where T(sub 2f(sub pe)) is the second harmonic electromagnetic wave, (3) they satisfy the threshold condition for formation of collapsing solitons, and (4) they are accompanied by their ponderomotive force induced density cavities with δn(sub p)/n(sub e) > δn(sub b)/n(sub e), where δn(sub p)/n(sub e) is the level of ponderomotive force induced density fluctuations and δn(sub b)/n(sub e) is that of the ambient fluctuations. These findings strongly suggest that the observed wave packets provide evidence for the collapsing solitons formed as a result of OTSI. The implication is that the strong turbulence processes probably play very important roles in excitation of type II radio emissions as well as in stabilization of shock-accelerated electron beams.

Sun radio radiation↗
DOE OSTI2025

Broadband coherent XUV light from e − / e + microbunching in an intense laser pulse

Attosecond pulses of coherent extreme ultraviolet (XUV) light are instrumental for investigating subatomic dynamics and can be produced using a free-electron laser (FEL). It has been suggested that an optical FEL, which employs a laser pulse in place of a conventional undulator, could enable a dramatically more compact implementation of such a light source. Yet, the high electron density and subsequent high emittance implied by an optical FEL makes this concept challenging to realize with an electron beam. There has been impressive progress in recent years producing collimated dense and relativistic beams of electrons and positrons in the laboratory. As we demonstrate here, the inherent stability of a quasi-neutral electron-positron beam mitigates Coulomb expansion, and renders it a promising alternative source of coherent light. Specifically, we show via computer simulations that broadband coherent light in the XUV domain, which takes the form of 8-as pulses at 92-as intervals, can be generated by microbunching of relativistic electrons and positrons in a laser pulse. This process occurs over a sub-millimeter length scale, enabling the development of light sources which are orders-of-magnitude more compact than existing sources, with potential applications in physics, chemistry, biology, and industry.

47 OTHER INSTRUMENTATION↗
DOE OSTI2023

Dephasingless laser wakefield acceleration in the bubble regime

Abstract Laser wakefield accelerators (LWFAs) have electric fields that are orders of magnitude larger than those of conventional accelerators, promising an attractive, small-scale alternative for next-generation light sources and lepton colliders. The maximum energy gain in a single-stage LWFA is limited by dephasing, which occurs when the trapped particles outrun the accelerating phase of the wakefield. Here, we demonstrate that a single space–time structured laser pulse can be used for ionization injection and electron acceleration over many dephasing lengths in the bubble regime. Simulations of a dephasingless laser wakefield accelerator driven by a 6.2-J laser pulse show 25 pC of injected charge accelerated over 20 dephasing lengths (1.3 cm) to a maximum energy of 2.1 GeV. The space–time structured laser pulse features an ultrashort, programmable-trajectory focus. Accelerating the focus, reducing the focused spot-size variation, and mitigating unwanted self-focusing stabilize the electron acceleration, which improves beam quality and leads to projected energy gains of 125 GeV in a single, sub-meter stage driven by a 500-J pulse.

43 PARTICLE ACCELERATORS↗
DOE OSTI2024

Operando Freezing Cryogenic Electron Microscopy of Active Battery Materials

Abstract Understanding structural and chemical evolution of battery materials during operation is critical to achieving safe, efficient, and long-lasting energy storage. Cryogenic electron microscopy (cryo-EM) has become a valuable tool in battery characterization, leveraging low temperatures to improve stability of sensitive materials under electron beam irradiation. However, typical cryo-EM sample preparations leave extended time between the electrochemical point of interest and ex situ freezing of samples, during which active structures may relax, degrade, or otherwise evolve. Here, we detail a method for operando freezing cryo-EM to preserve and characterize native electrode and interfacial structures that arise during battery cycling, based on an operando plunge freezer and cold sample removal process. We validate the method on multiple electrode materials and quantify and discuss the freezing rate achieved. Operando freezing cryo-EM can be used to directly visualize transient features that arise at active electrochemical interfaces, to enable deeper understanding of structural evolution and interfacial chemistry in batteries and other electrochemical systems.

25 ENERGY STORAGE↗
NASA NTRS1977

Effects of high temperature and e-beam irradiation on the stability of refractory thin films

Refractory thin films of Al2O3, ZrO2, MgO, ThO2, and BN have been investigated in situ in an UHV transmission electron microscope. The electron transparent refractory films were prepared by electron-beam evaporation, anodization, RF sputtering, and thinning of bulk crystal materials. The study concentrates on monitoring the thermal and mechanical stability of the films, phase and structural changes, and electron irradiation effects as a function of film-preparation conditions. With increasing temperatures, five different crystallographic phases were observed for both anodized and electron-beam-evaporated alumina films. Zirconia films exhibited two phase transitions upon heating to 1200 C and electron-irradiation-induced crystallization of ZrO2 even at room temperature. MgO, ThO2, and BN films did not undergo any noticeable phase transformation but ruptured due to sintering below 1200 C.

Lee, E. H.↗
NASA NTRS2018

Temperature Mapping Above and Below Air Film-Cooled Thermal Barrier Coatings Using Phosphor Thermometry

Thermal barrier coatings (TBCs) are typically used in conjunction with air film cooling to maximize overall cooling effectiveness and reliability while minimizing sacrifices in engine performance. The effects of thermal barrier coating (TBC) thermal protection and air film cooling effectiveness have usually been studied separately; however, their contributions to combined cooling effectiveness are interdependent and are not simply additive. The combined cooling effectiveness is always less than the sum of the cooling effectiveness of stand-alone TBC protection and stand-alone air film cooling. These diminishing returns arise because adding the thermally insulating TBC between the cooling air and the surface to be cooled reduces the air film cooling effectiveness and because the air film cooling reduces the heat flux through the TBC and therefore reduces the temperature difference sustained across the TBC thickness. Due to these considerations, combined cooling effectiveness must be measured to achieve an optimum balance between TBC thermal protection and air film cooling. In this investigation, temperature mapping above and below air film-cooled TBCs was performed using luminescence lifetime imaging-based phosphor thermometry. Measurements were performed in the NASA GRC Mach 0.3 burner rig on a TBC-coated plate using a scaled-up cooling hole geometry where both the hot mainstream gas temperature and the blowing ratio were varied. Surface temperature maps were obtained from a Cr-doped GdAlO3 thermographic phosphor deposited on the surface of the electron-beam vapor-deposited yttria-stabilized zirconia (YSZ) TBC. From separate plates, temperature maps from the bottom of the TBC were obtained from a thin Er-doped YSZ layer integrated into the TBC below the overlying undoped YSZ. Procedures for temperature and cooling effectiveness mapping above and below the air film-cooled TBC surface are described. Most importantly, these measurements enable mapping the combined cooling effectiveness below the TBC, which is more important than surface cooling effectiveness when there is a barrier coating between the hot mainstream gas and the surface that needs thermal protection. Advantages of the luminescence lifetime imaging method over infrared thermography, as well as its limitations to steady-state conditions are discussed.

cooling effectiveness.↗
NASA NTRS2016

Electron Jet of Asymmetric Reconnection

We present Magnetospheric Multiscale observations of an electron-scale current sheet and electron outflow jet for asymmetric reconnection with guide field at the subsolar magnetopause. The electron jet observed within the reconnection region has an electron Mach number of 0.35 and is associated with electron agyrotropy. The jet is unstable to an electrostatic instability which generates intense waves with E(sub parallel lines) amplitudes reaching up to 300 mV/m and potentials up to 20% of the electron thermal energy. We see evidence of interaction between the waves and the electron beam, leading to quick thermalization of the beam and stabilization of the instability. The wave phase speed is comparable to the ion thermal speed, suggesting that the instability is of Buneman type, and therefore introduces electron-ion drag and leads to braking of the electron flow. Our observations demonstrate that electrostatic turbulence plays an important role in the electron-scale physics of asymmetric reconnection.

Khotyaintsev, Yu. V.↗
NASA NTRS1990

Simulation studies of plasma waves in the electron foreshock - The generation of downshifted oscillations

The generation of waves with frequencies downshifted from the plasma frequency, as observed in the electron foreshock, is analyzed by particle simulation. Wave excitation differs fundamentally from the familiar excitation of the plasma eigenmodes by a gentle bump-on-tail electron distribution. Beam modes are destabilized by resonant interaction with bulk electrons, provided the beam velocity spread is very small. These modes are stabilized, starting with the higher frequencies, as the beam is broadened and slowed down by the interaction with the wave spectrum. Initially a very cold beam is also capable of exciting frequencies considerably above the plasma frequency, but such oscillations are quickly stabilized. Low-frequency modes persist for a long time, until the bump in the electron distribution is completely 'ironed' out. This diffusion process also is quite different from the familiar case of well-separated beam and bulk electrons. A quantitative analysis of these processes is carried out.

Dum, C. T.↗
DOE OSTI2021

Accurate prediction of mega-electron-volt electron beam properties from UED using machine learning

To harness the full potential of the ultrafast electron diffraction (UED) and microscopy (UEM), we must know accurately the electron beam properties, such as emittance, energy spread, spatial-pointing jitter, and shot-to-shot energy fluctuation. Owing to the inherent fluctuations in UED/UEM instruments, obtaining such detailed knowledge requires real-time characterization of the beam properties for each electron bunch. While diagnostics of these properties exist, they are often invasive, and many of them cannot operate at a high repetition rate. Here, we present a technique to overcome such limitations. Employing a machine learning (ML) strategy, we can accurately predict electron beam properties for every shot using only parameters that are easily recorded at high repetition rate by the detector while the experiments are ongoing, by training a model on a small set of fully diagnosed bunches. Applying ML as real-time noninvasive diagnostics could enable some new capabilities, e.g., online optimization of the long-term stability and fine single-shot quality of the electron beam, filtering the events and making online corrections of the data for time-resolved UED, otherwise impossible. This opens the possibility of fully realizing the potential of high repetition rate UED and UEM for life science and condensed matter physics applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Analysis of neoclassical tearing mode stabilization experiment by electron cyclotron injection in KSTAR

We report the neoclassical tearing mode (NTM) stabilization experimental results by injection of the electron cyclotron (EC) beam in KSTAR, and its analysis with integrated modelling. In the KSTAR experiment, NTM was intentionally induced and the EC beam was injected by the plasma control system (PCS) to stabilize it. Here, the EC angle was controlled based on the minimum seeking algorithm for the island growth rate. Although the EC angle was not changed significantly, the island width significantly decreased towards the end of the experiment followed by the recovery of plasma performance. To assess the NTM stabilization experiment from a stability perspective, we performed integrated modelling with TRIASSIC utilizing the reconstructed equilibrium with magnetic diagnostics and motional stark effect diagnostics. As a result, we observed that the NTM is stabilized by EC.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗