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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

The effects of kinetic instabilities on the electron cyclotron emission from runaway electrons

In this paper we show that the kinetic instabilities associated with runaway electron beams play an essential role for the production of high-level non-thermal electron–cyclotron-emission (ECE) radiation. Most of the non-thermal ECE comes from runaway electrons in the low-energy regime with large pitch angle, which are strongly scattered by the excited whistler waves. The power of ECE from runaway electrons is obtained using a synthetic diagnostic model based on the reciprocity method. The electron distribution function is calculated using a kinetic simulation model including the whistler wave instabilities and the quasilinear diffusion effects. Simulations based on DIII-D low-density discharge reproduces the rapid growth of the ECE signals observed in DIII-D experiments. Unlike the thermal ECE where radiation for a certain frequency is strongly localized inside the resonance region, the non-thermal ECE radiation from runaway electrons is nonlocal, and the emission-absorption ratio is higher than that of thermal electrons. The runaway electron tail is more significant for ECE with higher frequencies, and the ECE spectrum becomes flatter as RE population grows. The nonlinear behavior of the kinetic instabilities is illustrated in the oscillations of the ECE waves. In conclusion, the good agreement with the DIII-D experimental observations after including the kinetic instabilities clearly illustrate the significance of the scattering effects from wave-particle interactions, which can also be important for runaway electrons produced in disruptions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Understanding Formation of Irradiation-Induced Defects through 4D-STEM, Electron Tomography, and WBDF-STEM

A major challenge in advancing nuclear materials for next-generation fission and proposed fusion reactors is to comprehensively understand the formation of irradiation-induced defects. Here it is essential to correlate the evolution of irradiation-induced defects and the degradation of mechanical properties, as they collectively dictate the material's lifespan and ensure nuclear safety. Scanning transmission electron microscopy (STEM) based techniques have emerged as indispensable tools for irradiation-induced defect characterization, offering high spatial resolution imaging and chemical analysis, such as electron energy loss spectroscopy (EELS) and energy dispersive X-ray spectroscopy (EDXS). These techniques have been effectively used to obtain an atomic-scale view of the defect structure. Recent advances in electron microscopy, particularly in 4D-STEM, offer detailed insight into microstructural evolution by capturing full 2D diffraction patterns at every pixel position. Using high-speed direct electron detectors, this technology generates a four-dimensional dataset, overcoming the limitations of traditional STEM imaging.

36 MATERIALS SCIENCE↗
DOE OSTI2017

First observation of low energy electron neutrinos in a liquid argon time projection chamber

Liquid argon time projection chambers (LArTPCs) produce remarkable fidelity in the observation of neutrino interactions. Here, the superior capabilities of such detectors to reconstruct the spatial and calorimetric information of neutrino events have made them the detectors of choice in a number of experiments, specifically those looking to observe electron neutrino ($\nu_e$) appearance. The LArTPC promises excellent background rejection capabilities, especially in this "golden" channel for both short and long baseline neutrino oscillation experiments. We present the first experimental observation of electron neutrinos and anti-neutrinos in the ArgoNeut LArTPC, in the energy range relevant to DUNE and the Fermilab Short Baseline Neutrino Program. Additionally, we present a demonstration of separation of electrons from gammas using neutrino data.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2018

Electron Bulk Acceleration and Thermalization at Earth’s Quasiperpendicular Bow Shock [Electron Acceleration and Thermalization at Earth's Quasi-Perpendicular Bow Shock]

Electron heating at Earth’s quasiperpendicular bow shock has been surmised to be due to the combined effects of a quasistatic electric potential and scattering through wave-particle interaction. Here we report the observation of electron distribution functions indicating a new electron heating process occurring at the leading edge of the shock front. Incident solar wind electrons are accelerated parallel to the magnetic field toward downstream, reaching an electron-ion relative drift speed exceeding the electron thermal speed. The bulk acceleration is associated with an electric field pulse embedded in a whistler-mode wave. The high electron-ion relative drift is relaxed primarily through a nonlinear current-driven instability. Here, the relaxed distributions contain a beam traveling toward the shock as a remnant of the accelerated electrons. Similar distribution functions prevail throughout the shock transition layer, suggesting that the observed acceleration and thermalization is essential to the cross-shock electron heating.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Femtosecond electron-phonon lock-in by photoemission and x-ray free-electron laser

The interactions that lead to the emergence of superconductivity in iron-based materials remain a subject of debate. It has been suggested that electron-electron correlations enhance electron-phonon coupling in iron selenide (FeSe) and related pnictides, but direct experimental verification has been lacking. Here we show that the electron-phonon coupling strength in FeSe can be quantified by combining two time-domain experiments into a “coherent lock-in” measurement in the terahertz regime. X-ray diffraction tracks the light-induced femtosecond coherent lattice motion at a single phonon frequency, and photoemission monitors the subsequent coherent changes in the electronic band structure. Comparison with theory reveals a strong enhancement of the coupling strength in FeSe owing to correlation effects. Given that the electron-phonon coupling affects superconductivity exponentially, this enhancement highlights the importance of the cooperative interplay between electron-electron and electron-phonon interactions.

Gerber, S. (ORCID:0000000257172626)↗
DOE OSTI2019

Electron Beam Dynamics Simulation for Electron Lenses

A test stand is under construction at CERN to study high perveance electron guns, electron beam dynamics, and electron beam diagnostics for electron lenses. It will be used to test electron guns for the Hollow Electron Lenses under consideration for beam halo control for High Luminosity LHC (CERN), and for the Space Charge Compensation at SIS18 (GSI) in the frame of the EU funded ARIES project. In order to prepare for this test stand, simulations will be presented and compared with experiments undertaken at the Fermilab (FNAL) electron lens test stand. These were conducted using a hollow electron gun, with the magnetic field configuration and beam current varied to study their effect. The impact of imperfections on the beam dynamics and overall quality of the electron beam will be discussed. A method for comparing experimental data with simulation is also presented to allow bench-marking of the computer models and simulation tools that will later be applied to the analysis of measurements performed at CERN.

43 PARTICLE ACCELERATORS↗
DOE OSTI2019

Laser and Electron Beam Technology for Parity Violating Electron Scattering Measurements

Parity violating electron scattering (PVES) is a precision tool used in a broad program of experiments which include studying the structure of protons and nuclei and searching for new Beyond the Standard Model (BSM) physics. In parity violation electron scattering experiments, a longitudinally polarized electron beam is incident on an unpolarized target. The sign of the longitudinal polarization is changed (making a parity transformation), and the fractional rate difference between right and left helicity states, dσ R and dσ L , is measured. An interference between the electromagnetic and weak amplitudes, M γ and M Z respectively, gives rise to a parity violating asymmetry A PV = $\frac{σ_{R}-σ_{L}}{σ_{R}-σ_{L}}$, defined by the fractional rate difference between right and left helicity states. A PV can be measured to extraordinarily high precision and is proportional to the ratio of the weak and electromagnetic amplitudes. This thesis highlights three such PVES experiments as well as a new polarized beam source which will improve their precision. The PVES experiments are PREX-II, MOLLER, and a 12 C transverse asymmetry measurement at Mainz. Chapters 1-3 of this thesis cover introductions to MOLLER and PREX-II, Chapter 4 contains the results of the 12 C transverse asymmetry measurement at Mainz, and Chapters 5-6 contain the original work performed by this author. PREX-II, the Lead Radius Experiment, measures the weak skin of the 208 Pb nucleus, provides a clean measurement of R N , the RMS radius of neutrons in a heavy nucleus, and constrains the equation of state (EOS) of highly dense matter which is important for describing neutron star structure, heavy ion collisions, and atomic parity violation experiments. The 12 C transverse asymmetry measurement at Mainz, and the future Mainz program of measuring the 208 Pb transverse asymmetry as well, addresses an important systematic correction for PREX and other PVES experiments preformed with heavy-nuclei. MOLLER (Measurement Of Lepton Lepton Electroweak Reaction) is an extremely precise PVES experiment searching for new neutral currents in electron-electron scattering. It’s called MOLLER because it will measure A PV in the Moller ee scattering process, and will infer the weak charge of the electron $Q^e_W$ to extremely high precision. MOLLER is sensitive to new Beyond the Standard Model physics at MeV and multi-TeV scales and will serve as an indirect complementary measurement to direct searches at high energy colliders. To achieve high precision measurements on A PV for MOLLER, we have developed an innovative Rubidium Titanyl Phosphate (RTP) Pockels cell in the polarized source to satisfy both statistical and systematic requirements as regards the electron beam produced. This new ultra-fast RTP cell design uses electric field gradients to provide unprecedented control over helicity correlated beam asymmetries and has been demonstrated to be capable of producing precisely controlled polarized electron beam at Jefferson Laboratory, controlling beam steering down to the nm-level. The precision reached with the RTP cell offers sufficient control over and minimization of helicity correlated beam asymmetries to perform PREX II. The RTP Pockels cell system will provide fast flipping and suitable control helicity correlated beam asymmetries and parity quality beam for the future MOLLER experiment, providing an unprecedented precision on the electron weak charge and electroweak mixing angle.

Palatchi, Caryn↗
DOE OSTI2020

Probing Electron Correlations in 1D Electronic Materials Using Single Quantum Channels (Final Technical Report)

This research focuses on the investigation of strong electron correlations in quasi-one-dimensional oxide nanostructures. The archetypical system consisting of heterostructures formed from an ultrathin layer of LaAlO 3 and TiO 2 -terminated SrTiO 3 offers a unique laboratory for probing strong correlations due to intrinsic richness of the physical system and its ability to be modulated at extreme nanoscale dimensions. Under suitable conditions, SrTiO 3 is known to exhibit a variety of important properties associated with strong electronic correlations, especially superconductivity, magnetism. Understanding the nature of these electronic correlations at fundamental scales, and in reduced spatial dimensions, will provide the scientific basis for new energy technologies, information technologies, and materials. The research program is motivated by recent discoveries and technical advances in the PIs' lab, specifically, (1) pioneering work to create conductive nanostructures to be created in LaAlO 3 /SrTiO 3 heterointerfaces with 2 nm spatial resolution, (2) the discovery of a novel correlated electronic phases in which electrons pair without forming a superconductor, and (3) the demonstrated ability to form high-quality quantum point contacts (QPCs) and achieve ballistic electron transport over micrometer-scales in LaAlO 3 /SrTiO 3 nanowires. The program has three major components. First, we have press forward to develop a full microscopic understanding of the mechanism for electron pairing in LaAlO 3 /SrTiO 3 nanostructures. Understanding the “glue” that leads to pairing and superconductivity in a doped semiconductor will help to form a scientific basis for the correlated oxide nanoelectronics platform being developed. Second, we have used their ability to create well-defined quantum channels in nanowires allows to allow novel “scattering” experiments to be performed that probe fundamentally new quasiparticle excitations using an unprecedented combination of experimental methodologies. Experiments already underway with artificially defined superlattices (5 nm period) demonstrate the feasibility of this approach. Third, we have investigated 1D correlations in proximally coupled nanowires, which are predicted exhibit Majorana-like zero modes in the absence of superconductivity or spin-orbit coupling. These studies provide insight not only into new and emergent phenomena in the rich class of complex oxides, but also fundamental mechanisms of superconductivity and magnetism. Thematically, the research aims to combine some of the most important and interesting challenges in the physics of semiconductor nanostructures and correlated electronic materials. The increased understanding of electron correlations can pave the way to the development of new materials with outstanding or novel properties, which could be relevant for energy-related technologies such as low-power high performance computing, quantum computation, or the development of novel materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

A high-current electron gun for the electron beam ion trap at the National Superconducting Cyclotron Laboratory

The Electron Beam Ion Trap (EBIT) in NSCL’s reaccelerator ReA uses continuous ion injection and accumulation. In order to maximize capture efficiency and minimize breeding time into high charge states, the EBIT requires a high-current/high current-density electron beam. A new electron gun insert based on a concave Ba-dispenser cathode has been designed and built to increase the current transmitted through the EBIT’s superconducting magnet. With the new insert, stable EBIT operating conditions with 0.8 A of electron beam have been established. The design of the electron gun is presented together with calculated and measured perveance data. In order to assess the experimental compression of the electron beam, a pinhole CCD camera has been set up to measure the electron beam radius. The camera observes X-rays emitted from highly charged ions, excited by the electron beam. Initial tests with this camera setup will be presented. They indicate that a current density of 640 A/cm{sup 2} has been reached when the EBIT magnet was operated at 4 T.

43 PARTICLE ACCELERATORS↗
DOE OSTI2013

Electron polarimetry at low energies in Hall C at JLab

Although the majority of Jefferson Lab experiments require multi-GeV electron beams, there have been a few opportunities to make electron beam polarization measurements at rather low energies. This proceedings will discuss some of the practical difficulties encountered in performing electron polarimetry via Mo/ller scattering at energies on the order of a few hundred MeV. Prospects for Compton polarimetry at very low energies will also be discussed. While Mo/ller scattering is likely the preferred method for electron polarimetry at energies below 500 MeV, there are certain aspects of the polarimeter and experiment design that must be carefully considered.

43 PARTICLE ACCELERATORS↗
DOE OSTI2013

Observation of strongly forbidden solid effect dynamic nuclear polarization transitions via electron-electron double resonance detected NMR

We present electron paramagnetic resonance experiments for which solid effect dynamic nuclear polarization transitions were observed indirectly via polarization loss on the electron. This use of indirect observation allows characterization of the dynamic nuclear polarization (DNP) process close to the electron. Frequency profiles of the electron-detected solid effect obtained using trityl radical showed intense saturation of the electron at the usual solid effect condition, which involves a single electron and nucleus. However, higher order solid effect transitions involving two, three, or four nuclei were also observed with surprising intensity, although these transitions did not lead to bulk nuclear polarization—suggesting that higher order transitions are important primarily in the transfer of polarization to nuclei nearby the electron. Similar results were obtained for the SA-BDPA radical where strong electron-nuclear couplings produced splittings in the spectrum of the indirectly observed solid effect conditions. Observation of high order solid effect transitions supports recent studies of the solid effect, and suggests that a multi-spin solid effect mechanism may play a major role in polarization transfer via DNP.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Excitation energies with linear response density matrix functional theory along the dissociation coordinate of an electron-pair bond in N-electron systems

Time dependent density matrix functional theory in its adiabatic linear response formulation delivers exact excitation energies ω{sub α} and oscillator strengths f{sub α} for two-electron systems if extended to the so-called phase including natural orbital (PINO) theory. The Löwdin-Shull expression for the energy of two-electron systems in terms of the natural orbitals and their phases affords in this case an exact phase-including natural orbital functional (PILS), which is non-primitive (contains other than just J and K integrals). In this paper, the extension of the PILS functional to N-electron systems is investigated. With the example of an elementary primitive NO functional (BBC1) it is shown that current density matrix functional theory ground state functionals, which were designed to produce decent approximations to the total energy, fail to deliver a qualitatively correct structure of the (inverse) response function, due to essential deficiencies in the reconstruction of the two-body reduced density matrix (2RDM). We now deduce essential features of an N-electron functional from a wavefunction Ansatz: The extension of the two-electron Löwdin-Shull wavefunction to the N-electron case informs about the phase information. In this paper, applications of this extended Löwdin-Shull (ELS) functional are considered for the simplest case, ELS(1): one (dissociating) two-electron bond in the field of occupied (including core) orbitals. ELS(1) produces high quality ω{sub α}(R) curves along the bond dissociation coordinate R for the molecules LiH, Li{sub 2}, and BH with the two outer valence electrons correlated. All of these results indicate that response properties are much more sensitive to deficiencies in the reconstruction of the 2RDM than the ground state energy, since derivatives of the functional with respect to both the NOs and the occupation numbers need to be accurate.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2014

Reduced model prediction of electron temperature profiles in microtearing-dominated National Spherical Torus eXperiment plasmas

A representative H-mode discharge from the National Spherical Torus eXperiment is studied in detail to utilize it as a basis for a time-evolving prediction of the electron temperature profile using an appropriate reduced transport model. The time evolution of characteristic plasma variables such as β{sub e}, ν{sub e}{sup ∗}, the MHD α parameter, and the gradient scale lengths of T{sub e}, T{sub i}, and n{sub e} were examined as a prelude to performing linear gyrokinetic calculations to determine the fastest growing micro instability at various times and locations throughout the discharge. The inferences from the parameter evolutions and the linear stability calculations were consistent. Early in the discharge, when β{sub e} and ν{sub e}{sup ∗} were relatively low, ballooning parity modes were dominant. As time progressed and both β{sub e} and ν{sub e}{sup ∗} increased, microtearing became the dominant low-k{sub θ} mode, especially in the outer half of the plasma. There are instances in time and radius, however, where other modes, at higher-k{sub θ}, may, in addition to microtearing, be important for driving electron transport. Given these results, the Rebut-Lallia-Watkins (RLW) electron thermal diffusivity model, which is based on microtearing-induced transport, was used to predict the time-evolving electron temperature across most of the profile. The results indicate that RLW does a good job of predicting T{sub e} for times and locations where microtearing was determined to be important, but not as well when microtearing was predicted to be stable or subdominant.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Observation of an electron band above the Fermi level in FeTe{sub 0.55}Se{sub 0.45} from in-situ surface doping

We used in-situ potassium (K) evaporation to dope the surface of the iron-based superconductor FeTe{sub 0.55}Se{sub 0.45}. The systematic study of the bands near the Fermi level confirms that electrons are doped into the system, allowing us to tune the Fermi level of this material and to access otherwise unoccupied electronic states. In particular, we observe an electron band located above the Fermi level before doping that shares similarities with a small three-dimensional pocket observed in the cousin, heavily electron-doped KFe{sub 2−x}Se{sub 2} compound.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

The scaling of electron and positron generation in intense laser-solid interactions

This study presents experimental scalings of the electrons and positrons produced by intense laser-target interactions at relativistic laser intensities (10 18 –10 20 W cm -2 ). The data were acquired from three short-pulse laser facilities with laser energies ranging from 80 to 1500 J. We found a non-linear (≈E L 2 ) scaling of positron yield [Chen et al., Phys. Rev. Lett. 114, 215001 (2015)] and a linear scaling of electron yield with the laser energy. These scalings are explained by theoretical and numerical analyses. Positron acceleration by the target sheath field is confirmed by the positron energy spectrum, which has a pronounced peak at energies near the sheath potential, as determined by the observed maximum energies of accelerated protons. The parameters of laser-produced electron-positron jets are summarized together with the theoretical energy scaling. Finally, the measured energy-squared scaling of relativistic electron-positron jets indicates the possibility to create an astrophysically relevant experimental platform with such jets using multi-kilojoule high intensity lasers currently under construction.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

On the elimination of the electronic structure bottleneck in on the fly nonadiabatic dynamics for small to moderate sized (10-15 atom) molecules using fit diabatic representations based solely on ab initio electronic structure data: The photodissociation of phenol

In this work, we demonstrate that for moderate sized systems, here a system with 13 atoms, global coupled potential energy surfaces defined for several electronic states over a wide energy range and for distinct regions of nuclear coordinate space characterized by distinct electron configurations, can be constructed with precise energetics and an excellent description of non-adiabatic interactions in all regions. This is accomplished using a recently reported algorithm for constructing quasi-diabatic representations, H{sup d}, of adiabatic electronic states coupled by conical intersections. In this work, the algorithm is used to construct an H{sup d} to describe the photodissociation of phenol from its first and second excited electronic states. The representation treats all 33 internal degrees of freedom in an even handed manner. The ab initio adiabatic electronic structure data used to construct the fit are obtained exclusively from multireference configuration interaction with single and double excitation wave functions comprised of 88 × 10{sup 6} configuration state functions, at geometries determined by quasi-classical trajectories. Since the algorithm uses energy gradients and derivative couplings in addition to electronic energies to construct H{sup d}, data at only 7379 nuclear configurations are required to construct a representation, which describes all nuclear configurations involved in H atom photodissociation to produce the phenoxyl radical in its ground or first excited electronic state, with a mean unsigned energy error of 202.9 cm{sup −1} for electronic energies <60 000 cm{sup −1}.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Beyond the ponderomotive limit: Direct laser acceleration of relativistic electrons in sub-critical plasmas

We examine a regime in which a linearly polarized laser pulse with relativistic intensity irradiates a sub-critical plasma for much longer than the characteristic electron response time. A steady-state channel is formed in the plasma in this case with quasi-static transverse and longitudinal electric fields. These relatively weak fields significantly alter the electron dynamics. The longitudinal electric field reduces the longitudinal dephasing between the electron and the wave, leading to an enhancement of the electron energy gain from the pulse. The energy gain in this regime is ultimately limited by the superluminosity of the wave fronts induced by the plasma in the channel. The transverse electric field alters the oscillations of the transverse electron velocity, allowing it to remain anti-parallel to laser electric field and leading to a significant energy gain. The energy enhancement is accompanied by the development of significant oscillations perpendicular to the plane of the driven motion, making trajectories of energetic electrons three-dimensional. Proper electron injection into the laser beam can further boost the electron energy gain.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Physics design of the in-vessel collection optics for the ITER electron cyclotron emission diagnostic

Measurement of the electron cyclotron emission (ECE) is one of the primary diagnostics for electron temperature in ITER. In-vessel, in-vacuum, and quasi-optical antennas capture sufficient ECE to achieve large signal to noise with microsecond temporal resolution and high spatial resolution while maintaining polarization fidelity. Two similar systems are required. One views the plasma radially. The other is an oblique view. Both views can be used to measure the electron temperature, while the oblique is also sensitive to non-thermal distortion in the bulk electron distribution. The in-vacuum optics for both systems are subject to degradation as they have a direct view of the ITER plasma and will not be accessible for cleaning or replacement for extended periods. Blackbody radiation sources are provided for in situ calibration.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗