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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 631 records · Page 35
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Measurements of the UV and VUV transmission of optical materials during high energy electron irradiation

An experimental program was conducted in which the optical transmission of several transparent materials was measured during high energy electron irradiation. These experiments were conducted using the Dynamitron electron accelerator as a continuous source of 1.5 MeV electrons and the LINAC electron accelerator as a pulsed source of 5-7 MeV electrons. The experimental program consisted of three major portions. The first portion, the optical transmission of fused silica, BeO, MgF2, and LiF was measured at vacuum ultraviolet wavelengths in the range 1550-2000 A during ambient temperature, 1.5 MeV electron irradiation at ionizing dose rates to 0.5 Mrad/sec. In the second portion of the program, the optical transmission of fused silica and BeO was measured in the range 2000-3000 A during high dose rate, elevated temperature 1.5 MeV electron irradiation. In particular, accurate measurements of the optical transmission were made at ionizing dose rates as high as 10 Mrad/sec. In the final portion of the program, the optical transmission of fused silica and BeO was measured in the wavelength range 2000-3000 A during pulsed 5 and 7 MeV electron irradiation from the LINAC accelerator. The maximum time averaged ionizing dose rate was limited to 0.75 Mrad/sec due to accelerator limitations.

Palma, G. E.↗
DOE OSTI2026

Degenerate coupled-cluster theory

A size-extensive, converging, black-box, ab initio coupled-cluster (ΔCC) ansatz is introduced that computes the energies and wave functions of states from any degenerate or nondegenerate Slater-determinant references with any numbers of α- and β-spin electrons, any patterns of orbital occupancy, any spin multiplicities, and any spatial symmetries. For a nondegenerate reference, it reduces to the single-reference coupled-cluster ansatz. For a degenerate multireference, it is a natural coupled-cluster extension of degenerate Møller–Plesset perturbation (ΔMP) theory. For ionized and electron-attached references, it is a coupled-cluster Green’s function, although the present theory is convergent toward the full-configuration-interaction limits, while the Feynman–Dyson many-body Green’s function (MBGF) theory generally is not. Its single-excitation instance is a projection Hartree–Fock theory as per the Thouless theorem, which may be useful for core ionizations, high-spin states, and possibly electron affinities. Additionally, a new multireference coupled-cluster theory for a general model space is developed. This quasidegenerate coupled-cluster (QCC) theory is exactly converging, but not black-box, and intended for strong correlation. Determinant-based, general-order algorithms of ΔCC and QCC theories are implemented and compared with configuration-interaction (CI) and equation-of-motion coupled-cluster (EOM-CC) theories through octuple excitations and with ΔMP and MBGF theories up to the nineteenth order. An algebraic, optimal-scaling algorithm of the ΔCC theory is computer-synthesized at the levels of single excitations (ΔCCS) and of single and double excitations (ΔCCSD). As a result, the order of performance is QCC ≈ ΔCC > EOM-CC > CI at the same order or QCC ≈ ΔCC > ΔMP > MBGF at the same cost scaling.

Hirata, So [University of Illinois at Urbana-Champ↗
DOE OSTI2021

Ultra-short pulse generation from mid-IR to THz range using plasma wakes and relativistic ionization fronts

In this work, we discuss numerical and experimental results on frequency downshifting and upshifting of a 10 μ m infrared (IR) laser to cover the entire wavelength (frequency) range from λ = 1 to 150 μ m ( ν = 300–2 THz) using two different plasma techniques. The first plasma technique utilizes frequency downshifting of the drive laser pulse in a nonlinear plasma wake. Based on this technique, we have proposed and demonstrated that in a tailored plasma structure, multi-millijoule energy, single-cycle, long-wavelength IR (3–20 μ m) pulses can be generated by using an 810 nm Ti:sapphire drive laser. Here, we extend this idea to the THz frequency regime. We show that sub-joule, terawatts, single-cycle terahertz (2–12 THz or 150–25 μ m) pulses can be generated by replacing the drive laser with a picosecond 10 μ m CO 2 laser and a different shaped plasma structure. The second plasma technique employs frequency upshifting by colliding a CO 2 laser with a rather sharp relativistic ionization front created by ionization of a gas in less than half cycle (17 fs) of the CO 2 laser. Even though the electrons in the ionization front carry no energy, the frequency of the CO 2 laser can be upshifted due to the relativistic Doppler effect as the CO 2 laser pulse enters the front. The wavelength can be tuned from 1 to 10 μ m by simply changing the electron density of the front. While the upshifted light with 5 < λ ( μ m ) < 10 propagates in the forward direction, that with 1 < λ ( μ m ) < 5 is back-reflected. These two plasma techniques seem extremely promising for covering the entire molecular fingerprint region.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

The role of charge in microdroplet redox chemistry

In charged water microdroplets, which occur in nature or in the lab upon ultrasonication or in electrospray processes, the thermodynamics for reactive chemistry can be dramatically altered relative to the bulk phase. Here, we provide a theoretical basis for the observation of accelerated chemistry by simulating water droplets of increasing charge imbalance to create redox agents such as hydroxyl and hydrogen radicals and solvated electrons. We compute the hydration enthalpy of OH - and H + that controls the electron transfer process, and the corresponding changes in vertical ionization energy and vertical electron affinity of the ions, to create OH • and H • reactive species. We find that at ~ 20 - 50% of the Rayleigh limit of droplet charge the hydration enthalpy of both OH - and H + have decreased by >50 kcal/mol such that electron transfer becomes thermodynamically favorable, in correspondence with the more favorable vertical electron affinity of H + and the lowered vertical ionization energy of OH - . We provide scaling arguments that show that the nanoscale calculations and conclusions extend to the experimental microdroplet length scale. The relevance of the droplet charge for chemical reactivity is illustrated for the formation of H 2 O 2 , and has clear implications for other redox reactions observed to occur with enhanced rates in microdroplets.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1976

Statistical equilibrium calculations for silicon in early-type model stellar atmospheres

Line profiles of 36 multiplets of silicon (Si) II, III, and IV were computed for a grid of model atmospheres covering the range from 15,000 to 35,000 K in effective temperature and 2.5 to 4.5 in log (gravity). The computations involved simultaneous solution of the steady-state statistical equilibrium equations for the populations and of the equation of radiative transfer in the lines. The variables were linearized, and successive corrections were computed until a minimal accuracy of 1/1000 in the line intensities was reached. The common assumption of local thermodynamic equilibrium (LTE) was dropped. The model atmospheres used also were computed by non-LTE methods. Some effects that were incorporated into the calculations were the depression of the continuum by free electrons, hydrogen and ionized helium line blocking, and auto-ionization and dielectronic recombination, which later were found to be insignificant. Use of radiation damping and detailed electron (quadratic Stark) damping constants had small but significant effects on the strong resonance lines of Si III and IV. For weak and intermediate-strength lines, large differences with respect to LTE computations, the results of which are also presented, were found in line shapes and strengths. For the strong lines the differences are generally small, except for the models at the hot, low-gravity extreme of our range. These computations should be useful in the interpretation of the spectra of stars in the spectral range B0-B5, luminosity classes III, IV, and V.

Kamp, L. W.↗
NASA NTRS1991

An experimental investigation of hollow cathode-based plasma contactors

Experimental results are presented which describe operation of the plasma environment associated with a hollow cathod-based plasma contactor collecting electrons from or emitting them to an ambient, low density Maxwellian plasma. A one-dimensional, phenomenological model of the near-field electron collection process, which was formulated from experimental observations, is presented. It considers three regions, namely, a plasma cloud adjacent to the contactor, an ambient plasma from which electrons are collected, and a double layer region that develops between the contactor plasma cloud and the ambient plasma regions. Results of the electron emission experiments are also presented. An important observation is made using a retarding potential analyzer (RPA) which shows that high energy ions generally stream from a contactor along with the electrons being emitted. A mechanism for this phenomenon is presented and it involves a high rate of ionization induced between electrons and atoms flowing together from the hollow cathode orifice. This can result in the development of a region of high positive potential. Langmuir and RPA probe data suggest that both electrons and ions expand spherically from this hill region. In addition to experimental observations, a one-dimensional model which describes the electron emission process and predicts the phenomena just mentioned is presented and shown to agree qualitatively with these observations.

Williams, John D.↗
NASA NTRS1991

Energy degradation of fast electrons in hydrogen gas

An equation is derived for calculating the energy distribution of fast electrons in a partially ionized gas and a method is provided to solve for the electron degradation spectrum and the energy deposition in different forms (ionization, excitation, or heating). As an example, the energy degradation of fast electrons in a gas of pure hydrogen is calculated, considering excitations to the lowest 10 atomic levels. The Bethe approximation and the continuous slowing-down approximation are discussed and it is concluded that these approximations are accurate to the order of 20 percent for electrons with initial energy of greater than about keV. The method and results can be used to determine heating, excitations, and ionizations by high-energy photoelectrons or cosmic-ray particles in various astrophysical circumstances, such as the interstellar medium, supernova envelopes, and QSO emission-line clouds.

Xu, Yueming↗
NASA NTRS1991

Model of electron collecting plasma contactors

In laboratory experiments, plasma contactors are observed to collect ampere-level electron currents with low impedance. In order to extend the laboratory experience to the low-earth-orbit environment, a model of plasma contactors is being developed. Laboratory results are being used to support and validate the model development. The important physical processes observed in the laboratory are that the source plasma is separated from the background plasma by a double layer and that ionization of the expellant gas by the collected electrons creates the bulk of the ions that leave the source plasma. The model, which uses Poisson's equation with a physical charge density that includes the ion and electron components of both the source and the ambient plasmas, reproduces this phenomenon for typical experimental parameters. The calculations, in agreement with the laboratory results, show little convergence of the accelerated electrons. The angular momentum of the incoming electrons dramatically reduces the peak electron density. These electrons ionize enough gas to generate the source plasma. Calculations show that the increase in ionization rate with potential produces a steep rise in collected current with increasing potential as seen in the laboratory.

Davis, V. A.↗
DOE OSTI2021

In Situ Generation of High-Energy Spin-Polarized Electrons in a Beam-Driven Plasma Wakefield Accelerator

We report that in situ generation of a high-energy, high-current, spin-polarized electron beam is an outstanding scientific challenge to the development of plasma-based accelerators for high-energy colliders. In this Letter, we show how such a spin-polarized relativistic beam can be produced by ionization injection of electrons of certain atoms with a circularly polarized laser field into a beam-driven plasma wakefield accelerator, providing a much desired one-step solution to this challenge. Using time-dependent Schrödinger equation (TDSE) simulations, we show the propensity rule of spin-dependent ionization of xenon atoms can be reversed in the strong-field multiphoton regime compared with the non-adiabatic tunneling regime, leading to high total spin polarization. Furthermore, three-dimensional particle-in-cell simulations are incorporated with TDSE simulations, providing start-to-end simulations of spin-dependent strong-field ionization of xenon atoms and subsequent trapping, acceleration, and preservation of electron spin polarization in lithium plasma. We show the generation of a high-current (0.8 kA), ultralow-normalized-emittance (~ 37 nm ), and high-energy (2.7 GeV) electron beam within just 11 cm distance, with up to ~31% net spin polarization. Higher current, energy, and net spin-polarization beams are possible by optimizing this concept, thus solving a long-standing problem facing the development of plasma accelerators.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Improvements in the orbitalwise scaling down of Perdew–Zunger self-interaction correction in many-electron regions

The Perdew-Zunger (PZ) method offers a way to remove the self-interaction (SI) error from density functional approximations on an orbital by orbital basis. The PZ method provides significant improvements for the properties such as barrier heights or dissociation energies but results in over-correcting the properties well described by SI-uncorrected semi-local functional. One cure to rectify the over-correcting tendency is to scale down the magnitude of SI-correction of each orbital in the many electron region. We have implemented the orbitalwise scaled down SI-correction (OSIC) scheme of Vydrov et al. [J. Chem. Phys. 124, 094108 (2006)] using the Fermi-L owdin SI-correction method. After validating the OSIC implementation with previously reported OSICLSDA results, we examine its performance with the most successful non-empirical SCAN meta-GGA functional. Using different forms of scaling factors to identify one-electron regions, we assess the performance of OSIC-SCAN for a wide range of properties: total energies, ionization potentials and electron affinities for atoms, atomization energies, dissociation and reaction energies, and reaction barrier heights of molecules. Our results show that OSIC-SCAN provides superior results than the previously reported OSIC-LSDA, -PBE, and -TPSS results. Furthermore, we propose selective scaling of OSIC (SOSIC) to remove its major shortcoming that destroys the -1/r asymptotic behavior of the potentials. The SOSIC method gives the highest occupied orbital eigenvalues practically identical to those in PZSIC and unlike OSIC provides bound atomic anions even with larger powers of scaling factors. Furthermore, SOSIC compared to PZSIC or OSIC provides more balanced description of total energies and barrier heights.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

The effects of laser pulse length and collisional ionization on the acceleration of titanium ions

Abstract The interaction of a relativistic laser pulse ( > 10 18 W cm −2 µ m 2 ) with foil targets can accelerate ions to energies of tens of MeV u −1 with optimized laser and target parameters. We report the results on simulations of the interaction of a 6.0 × 10 20 W cm −2 laser pulse incident on ultrathin (10–500 nm) titanium foils to investigate the roles of laser pulse duration and ionization mechanisms in the acceleration of titanium ions. While holding peak intensity constant, two laser pulse durations were investigated, 140 and 650 fs. The optimum thickness is dependent on pulse duration, as it requires the concurrence of target transparency with the incidence of the peak laser intensity. The collisional processes do not play a significant role in Ti ion beam generation from the 140 fs laser pulse duration at the optimum thickness (30 nm). However, for the 650 fs laser optimum, collisions improve the conversion efficiency of highly energetic ( > 10 MeV u −1 ), high charge titanium (Ti 21 − 22 + ) by a factor of 20, and the titanium ion cutoff energy by ∼15%. This improvement is due to the fact that collisional ionization increases the electron density of the plasma, which delays the time of relativistic transparency, causing collisions to decrease the optimum foil thickness from 150 to 100 nm. Additionally, collisional ionization increases the charge-to-mass ratio of the titanium, and injects more electrons into the accelerating sheath field. At the optimum thickness, target normal sheath acceleration is the dominant mechanism of acceleration, with additional contributions from radiation pressure and shock wave acceleration.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Spectroscopic diagnostics of high-temperature plasma in stellar coronae using Fe XXIV-XXIV K-shell lines with XRISM

The RS CVn type binary star GT Muscae was observed during its quiescence using the Resolve X-ray microcalorimeter spectrometer onboard XRISM. The main and satellite lines of the Fe XXIV-XXIV K-shell transitions were resolved for the first time from stellar sources. We conducted line ratio analysis to investigate any deviations from collisional ionization equilibrium and Maxwell electron energy distribution with a single temperature. By using five combinations of direct excitation lines and dielectronic recombination satellite lines in three line complexes (Fe He$\alpha$, Ly$\alpha$, and He$\beta$), we found that the plasma is well characterized by two-temperature thermal plasmas with temperatures of 1.7 and 4.3 keV, which is consistent with thermal broadening of Fe xxv, and the broad-band fitting results in the 1.7–10 keV band. Other forms of deviation from a single-temperature plasma, such as different ionization and electron temperatures or the $\kappa$ distribution for the electron energy distributions, are not favored, which is reasonable for stellar coronae at quiescence. This study demonstrates the utility of the Fe K-shell line ratio diagnostics to probe plasma conditions using X-ray microcalorimeters.

X-rays: stars↗
DOE OSTI2026

Resonance Ionization Spectroscopy Experiment at Facility for Rare Isotope Beams

This manuscript reports on the commissioning of the Resonance Ionization Spectroscopy Experiment (RISE) at the BEam COoler and LAser spectroscopy (BECOLA) facility at Facility for Rare Isotope Beams (FRIB). The instrument implements the collinear resonance ionization spectroscopy technique for sensitive measurements of isotope shifts and hyperfine structure of short-lived isotopes produced at FRIB. The existing BECOLA beamline was extended to integrate an electrostatic ion-beam bender and an ion detector at ultrahigh vacuum. An injection-seeded titanium-sapphire laser and a multiharmonic pulsed neodymium-doped yttrium aluminum garnet laser were installed to perform resonant excitation and selective ionization. Commissioning tests were performed to demonstrate the capabilities of the instrument by measuring the hyperfine structure of stable 27 Al produced in an offline ion source. The RISE instrument is ready and operational for future studies of short-lived isotopes at FRIB.

Atomic spectra↗
DOE OSTI2025

Nuclear Recoil Calibration at Sub-keV Energies in LUX and Its Impact on Dark Matter Search Sensitivity

Dual-phase xenon time projection chamber (TPC) detectors offer heightened sensitivities for dark matter detection across a spectrum of particle masses. To broaden their capability to low-mass dark matter interactions, we investigated the light and charge responses of liquid xenon (LXe) to sub-keV nuclear recoils. Using neutron events from a pulsed Adelphi Deuterium-Deuterium neutron generator, an in situ calibration was conducted on the LUX detector. We demonstrate direct measurements of light and charge yields down to 0.45 keV and 0.27 keV, respectively, both approaching single quanta production, the physical limit of LXe detectors. Furthermore, these results hold significant implications for the future of dual-phase xenon TPCs in detecting low-mass dark matter via nuclear recoils.

Dark matter detectors↗