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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Above-threshold ionization at laser intensity greater than 10 20 W / cm 2

Here we present experimental observation of above-threshold ionization (ATI) electrons produced by ionization of the neon K shell in a laser field where intensity exceeds 10 20 W/cm 2 . An array of plastic scintillating calorimeter detectors was used to measure the high-energy electrons at four angles in the laser forward direction. Coarse energy resolution was obtained using aluminum filters of several thicknesses to block lower-energy electrons. A threshold intensity around 2×10 20 W/cm 2 is observed for production of energetic ATI electrons in the laser forward direction, with maximum electron energy exceeding 10 MeV. L-shell electrons with energies <1.4 MeV are scattered farther forward along the laser direction than expected. We present comparisons of the measured total electron energies to the predictions of Monte Carlo models employing the ADK-PPT ionization model and the Augst barrier suppression ionization model.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2024

Estimation of mean electron energy in helium surface ionization waves on dielectric substrates

Abstract The determination of basic plasma parameters in atmospheric pressure discharges is critical to advancing their use in applications. Atmospheric pressure plasma jets have found use in the fields of medicine, agriculture, material modification and others. Atmospheric pressure plasma jets often generate plasma surface ionization waves (SIW) which interact with and propagate over surfaces. Electrical diagnostics are challenging in SIW due to high collision frequencies and small scale of the plasma discharge. This work employs a passive optical emission line ratio technique to estimate the mean electron energy in SIW over planar dielectric substrates. The method uses an intensity ratio of two helium triplet lines: He( 3 3 S ) at 706.5 nm and He( 3 3 D ) at 587.56 nm. A collisional-radiative model is used to correlate line ratio to mean electron energy and determine dependencies on electron density and He/air gas mixture. Mean electron energies ranging from 3–8 eV are determined in He/air mixtures and are found to remain constant as the surface wave propagates radially. This work provides a 2D, time-resolved, mean electron energy diagnostic for surface ionization wave propagation and validation of numerical modeling in atmospheric pressure systems with spatially varying He/air gas mixtures. The model in question is designed for use with any He line ratio in the n = 3 excitation level.

Morsell, Joshua (ORCID:0000000331073002)↗
DOE OSTI2023

Facility-Level Industry Representation for Decarbonization Modeling [Slides]

The largest facilities of energy-intensive materials processing industries are disproportionate contributors to U.S. greenhouse gas (GHG) emissions. In general, industrial energy system modeling for the United States currently represents industrial demands at a much lower resolution than other end-use sector modeling. Therefore, characterizing even a subset of energy-intensive materials processing facilities will capture a significant portion of industrial GHG emissions. In order to further the development of publicly-available data to support modeling of industrial decarbonization, we summarize a set of approaches and results for characterizing the location, energy intensity and mix, process emissions intensity, and general production technology of existing clinker, ammonia, and iron and steel facilities in the United States. We also characterize facilities that represent options for reducing GHG emissions from each industry.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗
DOE OSTI2022

Vacuum laser acceleration of super-ponderomotive electrons using relativistic transparency injection

Abstract Intense lasers can accelerate electrons to very high energy over a short distance. Such compact accelerators have several potential applications including fast ignition, high energy physics, and radiography. Among the various schemes of laser-based electron acceleration, vacuum laser acceleration has the merits of super-high acceleration gradient and great simplicity. Yet its realization has been difficult because injecting free electrons into the fast-oscillating laser field is not trivial. Here we demonstrate free-electron injection and subsequent vacuum laser acceleration of electrons up to 20 MeV using the relativistic transparency effect. When a high-contrast intense laser drives a thin solid foil, electrons from the dense opaque plasma are first accelerated to near-light speed by the standing laser wave in front of the solid foil and subsequently injected into the transmitted laser field as the opaque plasma becomes relativistically transparent. It is possible to further optimize the electron injection/acceleration by manipulating the laser polarization, incident angle, and temporal pulse shaping. Our result also sheds light on the fundamental relativistic transparency process, crucial for producing secondary particle and light sources.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Dense Pair and Gamma-Ray Creation Using Ultra-Intense Lasers (Final Technical Report)

Lasers with intensity >1.4x10 18 W.cm -2 irradiating solid targets couple 10-50% of its energy to “hot electrons” near the critical surface, with temperature kT > mc 2 . When these hot electrons impact high-Z target ions (e.g. Au, Pt), they emit copious bremsstrahlung gamma-rays and create e + e - pairs via the Trident process. For targets thicker than ~0.1mm, the gamma-rays create secondary pairs via the Bethe-Heitler processes. The concept of using lasers to create pairs was first studied by Shearer et al (1973). Motivated by the rapid advance of short-pulse ultra-intense lasers based on chirped-pulse amplification, Liang (1994) first proposed irradiating solid Au targets with laser intensity ≥10 20 W.cm -2 to create dense e + e - pairs. Using particle-in-cell (PIC, Birdsall and Langdon, 1991) simulations, Liang et al (1998, 2002) estimated that high-energy PW lasers can in principle achieve ultra-high in-situ pair densities. Subsequent studies supported this idea and found that for gold foils thicker than ~50 μm, the pair yield is dominated by the Bethe-Heitler (BH, Heitler 1954) process. Cowan et al (1999, 2000) using the LLNL Nova PW-laser to irradiate 125μm gold foils first observed pair creation, followed by Chen et al (2009) who demonstrated copious BH pair creation using the Titan, Omega-EP and Orion lasers. However, the emerging e + /e - ratio of these experiments was ≤ few %, and the pair density was only 10 13 /cc so that the pair jet transverse size R(~mm) was < pair skin depth c/ω + (=8πn+e 2 /m) 1/2 ). This was insufficient to qualify as a bona fide ”pair plasma”.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Experimental determination of electron attenuation lengths in complex materials by means of epitaxial film growth: advantages and challenges

Accurate electron attenuation lengths are of critical importance in using electron spectroscopic methods to quantitatively characterize complex materials. Here we show that analysis of core-level and valence-band x-ray photoelectron spectra excited with monochromatic AlK? x-rays from the substrate and measured as a function of film thickness can be used to determine electron attenuation lengths in epitaxial SrTiO3 films on Ge(001). Closely lattice-matched epitaxial heterojunctions are ideal systems for determining attenuation lengths provided the films grow in a layer-by-layer fashion, leading to atomically flat surfaces, and the buried interfaces are atomically abrupt. In principle, either the rate of attenuation of substrate peak intensities or the rate of increase of film peak intensities can be used for this purpose. However, we find that structural nonuniformities in the films reduce the accuracy of electron attenuation lengths determined from photoelectrons that originate within the films. A more reliable source of information is found in photoelectrons from the substrate which traverse the film. By using the energy dependence of calculated electron attenuation lengths from the NIST database in combination with Ge 3d core and Ge-derived valence band intensities, we determine electron attenuation length as a function of kinetic energy for SrTiO3.

Chambers, Scott A.↗
DOE OSTI2023

Demand-side solutions in the US building sector could achieve deep emissions reductions and avoid over $100 billion in power sector costs

Buildings are energy-intensive and a primary source of US end-use sector carbon emissions. Although building emissions today are 25% below their 2005 peak, far deeper reductions are needed to reach the US 2050 net-zero emissions goal. However, plausible decarbonization pathways that consider both buildings and their interactions with the power grid remain poorly understood. Here, we couple detailed modeling of building energy use and the grid to quantify building decarbonization potential and associated grid impacts. We find up to a 91% reduction in building CO 2 emissions from 2005 levels by 2050 using a portfolio of building efficiency, demand flexibility, and electrification measures alongside rapid grid decarbonization. Building efficiency and flexibility could generate up to $107 billion in annual power system cost savings by 2050, offsetting over a third of the incremental cost of full grid decarbonization. Our results underscore multiple benefits of demand-side solutions for deep decarbonization of US buildings.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗
NASA NTRS2014

Implementing Badhwar-O'Neill Galactic Cosmic Ray Model for the Analysis of Space Radiation Exposure

For the analysis of radiation risks to astronauts and planning exploratory space missions, accurate energy spectrum of galactic cosmic radiation (GCR) is necessary. Characterization of the ionizing radiation environment is challenging because the interplanetary plasma and radiation fields are modulated by solar disturbances and the radiation doses received by astronauts in interplanetary space are likewise influenced. A model of the Badhwar‐O'Neill 2011 (BO11) GCR environment, which is represented by GCR deceleration potential theta, has been derived by utilizing all of the GCR measurements from balloons, satellites, and the newer NASA Advanced Composition Explorer (ACE). In the BO11 model, the solar modulation level is derived from the mean international sunspot numbers with time‐delay, which has been calibrated with actual flight instrument measurements to produce better GCR flux data fit during solar minima. GCR fluxes provided by the BO11 model were compared with various spacecraft measurements at 1 AU, and further comparisons were made for the tissue equivalent proportional counters measurements at low Earth orbits using the high‐charge and energy transport (HZETRN) code and various GCR models. For the comparison of the absorbed dose and dose equivalent calculations with the measurements by Radiation Assessment Detector (RAD) at Gale crater on Mars, the intensities and energies of GCR entering the heliosphere were calculated by using the BO11 model, which accounts for time‐dependent attenuation of the local interstellar spectrum of each element. The BO11 model, which has emphasized for the last 24 solar minima, showed in relatively good agreement with the RAD data for the first 200 sols, but it was resulted in to be less well during near the solar maximum of solar cycle 24 due to subtleties in the changing heliospheric conditions. By performing the error analysis of the BO11 model and the optimization in reducing overall uncertainty, the resultant BO13 model corrects the fit at solar maxima as well as being accurate at solar minima. The BO13 model is implemented to the NASA Space Cancer Risk model for the assessment of radiation risks. Overall cumulative probability distribution of solar modulation parameters represents the percentile rank of the average interplanetary GCR environment, and the probabilistic radiation risks can be assessed for various levels of GCR environment to support mission design and operational planning for future manned space exploration missions.

Kim, Myung-Hee Y.↗
NASA NTRS2022

Ames-2021 CO 2 Dipole Moment Surface and IR Line Lists: Toward 0.1% Uncertainty for CO 2 IR Intensities

A highly accurate CO 2 ab initio dipole moment surface (DMS), Ames-2021, is reported along with 12 C 16 O 2 infrared (IR) intensity comparisons approaching a 1–4‰ level of agreement and uncertainty. The Ames-2021 DMS was accurately fitted from CCSD(T) finite-field dipoles computed with the aug-cc-pVXZ (X = T, Q, 5) basis for C atom and the d-aug-cc-pVXZ (X = T, Q, 5) basis for O atoms, and extrapolated to the one particle basis set limit. Fitting σ(rms) is 3.8 × 10^(–7) au for 4443 geometries below 15 000 per cm . The corresponding IR intensity, S Ames-2021 , are computed using the Ames-2 potential energy surface (PES), which is the best PES available for CO 2 . Compared to high accuracy IR studies for 2001i–00001 and 3001i–00001 bands, S Ames-2021 matches NIST experiment-based intensities [S NIST-HIT16 or S HIT20 ] to −1.0 ± 1.3‰, or matches DLR experiment-based intensities [S DLR-HIT16/UCL/Ames ] to 1.9 ± 3.7‰. This indicates the systematic deviations and uncertainties have been significantly reduced in S Ames-2021 . The S UCL2015 (or S HITRAN2016 ) have larger deviations (vs S DLR ) and uncertainties (vs S DLR , S NIST ) which are attributed to the less accurate Ames-1 PES adopted in UCL-296 line list calculation. The S Ames-2021 intensity of 12 C 16 O 2 and 13 C 16 O 2 is utilized to derive new absolute 13 C/ 12 C ratios for Vienna PeeDee Belemnite (VPDB) with uncertainty reduced by 1/3 or 2/3. Further evaluation of S Ames-2021 are carried out on those CO 2 bands discussed in the HITRAN2020 update paper. Consistent improvements and better accuracies are found in band-by-band analysis, except for those bands strongly affected by Coriolis couplings, or very weak bands measured with relatively larger experimental uncertainties. The Ames-2021 296 K IR line lists are generated for 13 CO 2 isotopologues, with 18,000 per and S 296K > 1E–31) cm/molecule cutoff and then combined with CDSD line positions (except 14 C 16 O 2 ). The Ames-2021 DMS and 296 K IR line lists represent a major improvement over previous CO 2 theoretical IR intensity studies, including Ames-2016, UCL-296, and recent UCL DMS 2021 update. A real 1 permille level of agreement and uncertainty will definitely require both more accurate PES and more accurate DMS.

Chemical calculations↗
DOE OSTI2023

A buffer-gas trap for the NEPOMUC positron beam: optimization studies with electrons

Buffer-gas traps (BGTs) use inelastic interactions with nitrogen molecules to capture positrons from a continuous beam. These devices are invaluable for high-resolution studies of matter–antimatter interactions, antihydrogen research and positronium laser spectroscopy. We present a new project with the goal of producing a non-neutral plasma containing ${\sim }10^8$ low-energy positrons by installing a BGT on the NEPOMUC (NEutron induced POsitron source MUniCh) high-intensity positron beam. Details of the BGT are outlined and results are presented from experiments in which an electron beam, with a similar intensity and energy spread to the remoderated NEPOMUC beam, was used to create pulses of non-neutral electron plasma. The device is a vital component of the APEX (A Positron Electron eXperiment) project, which aims to create a low-temperature electron–positron pair plasma.

Physics↗
DOE OSTI2022

Electron Ion Collider Strong Hadron Cooling Injector and ERL

Intra-beam Scattering (IBS) and other diffusion mechanisms in the EIC Hadron Storage Ring (HSR) degrade the beam emittances during a store, with growth times of about 2 hours at the nominal proton energies of 275GeV, 100 GeV, and 41 GeV. Strong Hadron Cooling (SHC) can maintain good hadron beam quality and high luminosity during long collision stores. A novel cooling method ’ Coherent electron Cooling (CeC) ’ is chosen as the baseline SHC method, due to its high cooling rates. An Energy Recovery Linac (ERL) is used to deliver an intense high-quality electron beam for cooling. In this paper, we discuss the beam requirements for SHC-CeC and describe the current status of the injector and ERL designs. Two designs of injector and ERL will be presented: one for dedicated SHC and another one for SHC with precooler.

Wang, E.↗
NASA NTRS2007

The Roles of Flares and Shocks in determining SEP Abundances

We examine solar energetic particle (SEP) event-averaged abundances of Fe relative to O and intensity versus time profiles at energies above 25 MeV/nucleon using the SIS instrument on ACE. These data are compared with solar wind conditions during each event and with estimates of the strength of the associated shock based on average travel times to 1 AU. We find that the majority of events with an Fe to 0 abundance ratio greater than two times the average 5-12 MeV/nuc value for large SEP events (0.134) occur in the western hemisphere. Furthermore, in most of these Fe-rich events the profiles peak within 12 hours of the associated flare, suggesting that some of the observed interplanetary particles are accelerated in these flares. The vast majority of events with Fe/O below 0.134 are influenced by interplanetary shock acceleration. We suggest that variations in elemental composition in SEP events mainly arise from the combination of flare particles and shock acceleration of these particles and/or the ambient medium.

Cane, H. V.↗
DOE OSTI2020

Initial Assessment of Availability and Reliability for the PIP-II Superconducting Radio Frequency Linear Accelerator Facility

The Proton Improvement Plan -II (PIP-II) is a high intensity and high energy proton accelerator which will be used to support the neutrino program at Fermilab. The accelerator will deliver a 2 mA average beam current at a kinetic energy of 800 MeV. Due to the requirements from experiments, this accelerator is designed to be a highly reliable and available system. A target availability of the complete accelerator facility was prescribed to be 90%. An availability and reliability assessment of the accelerator was carried out to ascertain that the design can meet the target availability specification. The results were estimated for the nominal operational mode, when an 800 MeV beam is delivered on the target and for the critical operational mode, when a 600 MeV output beam was incident on the target. The design of a complete accel-erator system is a complex arrangement of a large number of components. To simplify the analysis, a few components were shortlisted and based on their functions, an accelerator model was created. The model is represented in the form of reliability block diagrams. Availability and reliability were estimated for each operational mode. To increase the availa-bility and reliability of the overall accelerator, redundancy of one cavity per section in the superconducting portion of the Linac was introduced.

43 PARTICLE ACCELERATORS↗
NASA NTRS1991

Analytic gradients for coupled-cluster energies that include noniterative connected triple excitations - Application to cis- and trans-HONO

An efficient formulation of the analytic energy gradient for the single and double excitation coupled-cluster method that includes a perturbational estimate of the effects of connected triple excitations is presented. The formulation has a small computational cost, and the algebraic manipulations may be applied generally to the analytic gradient of Moller-Plesset perturbation theory energies. The new formulation has been implemented in an efficient set of programs that utilize highly vectorized algorithms and has been used to investigate the equilibrium structures, harmonic vibrational frequencies, IR intensities, and energy separation of cis- and trans-HONO.

Lee, Timothy J.↗
NASA NTRS2002

Magnetized Target Fusion Driven by Plasma Liners

Magnetized target fusion is an emerging, relatively unexplored approach to fusion for electrical power and propulsion application. The physical principles of the concept are founded upon both inertial confinement fusion (ICF) and magnetic confinement fusion (MCF). It attempts to combine the favorable attributes of both these orthogonal approaches to fusion, but at the same time, avoiding the extreme technical challenges of both by exploiting a fusion regime intermediate between them. It uses a material liner to compress, heat and contain the fusion reacting plasma (the target plasma) mentally. By doing so, the fusion burn could be made to occur at plasma densities as high as six orders of magnitude higher than conventional MCF such as tokamak, thus leading to an approximately three orders of magnitude reduction in the plasma energy required for ignition. It also uses a transient magnetic field, compressed to extremely high intensity (100's T to 1000T) in the target plasma, to slow down the heat transport to the liner and to increase the energy deposition of charged-particle fusion products. This has several compounding beneficial effects. It leads to longer energy confinement time compared with conventional ICF without magnetized target, and thus permits the use of much lower plasma density to produce reasonable burn-up fraction. The compounding effects of lower plasma density and the magneto-insulation of the target lead to greatly reduced compressional heating power on the target. The increased energy deposition rate of charged-particle fusion products also helps to lower the energy threshold required for ignition and increasing the burn-up fraction. The reduction in ignition energy and the compressional power compound to lead to reduced system size, mass and R&D cost. It is a fusion approach that has an affordable R&D pathway, and appears attractive for propulsion application in the nearer term.

Thio, Y. C. Francis↗
NASA NTRS1988

Determination of electron density and temperature in non-LTE plasmas from spectral lines of impurity ions

A novel approach for calculating the populations of the excited Li-like ions C IV, N V, O VI, and Ne VIII is presented. The populations of the 2(2P), 3(2S), 3(2P), and 3(2D) electronic levels in these ions in optically thin plasmas with a broad range of electron density, N(e), and temperature, T(e), are determined from the collisional-radiative model by solving the system of rate equations for the production of excited ions; the equations are linear with respect to the excited ion populations, and the N(e) and T(e) are taken as independent variables. These populations are used to determine the ratios of line intensities for dipole allowed transitions between various energy levels. This approach can be applied to impurities other than the lithiumlike ions and is especially useful for diagnostics of systems where nonintrusive spectroscopic techniques must be used.

Kunc, Joseph A.↗
NASA NTRS1990

Laboratory studies of photodissociation processes relevant to the formation of cometary radicals

The strength of the C2(d 3 Pi g yields a 3 Pi u) Swan band emission in the spectra of cometary comae identifies this species as a prominent constituent of the coma gas. It was previously suggested that the formation of cometary C2 proceeds via the secondary photolysis of the C2H radical. The detection of C2H in the interstellar medium and the recent analysis of the radial variation in C2(delta V=O) surface brightness of Comet Halley support the postulate that C2 is a third-generation molecule. Measurement of the C2 and C2H translational energy distributions produced from the multiphoton dissociation (MPD) of acetylene at 193 nm are identified . Time-resolved FTIR emission studies of the nascent C2H radical formed in the C2H2 yields C2H + H reaction verify that this species is produced both vibrationally and electronically excited. A survey of the internal energy distributions of the C2 fragments produced from the MPD of acetylene using a high intensity ArF laser is currently in progress in the laboratory. Recent experiments have focused on the measurement of rotational energy distribution for the C2(A 1 Pi u, a 3 Pi u) fragments. The C2(a 3 Pi u) detection capability is currently being improved by performing this experiment in a molecular beam, thus allowing for discrimination between initial emission and laser-induced fluorescence (LIF). Although the experiments performed to date provide considerable evidence in support of C2H yields C2 + H reaction, there is an important distinction to be made when comparing the laboratory conditions to those typically found in comets. The C2H radicals generated in the laboratory experiments are formed vibrationally and/or electronically excited. Any rotationally/vibrationally excited C2H present in cometary comae will quickly undergo radiative relaxation in the infrared to their lowest rotational and vibrational state. Experiments are currently under way to confirm the cometary formation of C2 via the VUV dissociation of cold C2H.

Urdahl, R. S.↗
NASA NTRS1988

Phase Length Optical Phase-Locked-Loop Sensor

The invention is a device that provides a high resolution measurement of the change in optical phase length from the device optical system source to an optical reflector. The invention consists of a optical phase locked loop that uses a laser beam as a carrier of an intensity modulated energy source. The novelty of the invention appears to lie in the overall combination of elements which provide high resolution without loss of wide dynamic range. The invention does not depend on coherent reflection from a target, and thus can measure targets that do not have special preparation or corner reflectors. The use of carrier modulation achieves high resolution without the problems of high speed pulse duration systems. Thus the invention has the advantages of simplicity, low cost, and small size without sacrificing resolution.

Heyman, Joseph S.↗