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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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Effect of changing resultant linear acceleration relative to human subject on nystagmus generated by angular acceleration
Langmuir probe velocity and acceleration measurements for coaxial Hall accelerators
Langmuir probe velocity and acceleration measurements for coaxial Hall accelerators
The concerns about greenhouse gas emissions have triggered investigations among the scientific community. The accelerated carbonation curing has been used as a tool to capture CO 2 at early stages of cement-based material fabrication. In a previous study, the authors quantified the amount of CO 2 captured in portland cement pastes by thermal analysis, at high relative humidity precure conditions. In the present work, the authors quantified the amount of CO 2 captured in binary pastes derived from engineered cementitious composites (ECC), a family of composites worldwide used, whose one of their features is the precure at low relative humidity conditions. Two types of ECC pastes (1.2 and 2.2) were submitted to 4 h and 24 h of accelerated carbonation after 24 h of initial hydration. Using thermogravimetry and derivative thermogravimetry, the amounts of captured CO 2 and respective carbonation degrees were quantified. Furthermore, the results showed that ECC paste 1.2 presented the highest values of captured CO 2 and carbonation degree, considering all reactive components. In contrast, ECC paste 2.2 presented the highest values of these two parameters, when considering only portland cement as reactive component. For both pastes, the hydration degrees of the carbonated samples were higher than those of the non-carbonated references, indicating that in the used operating conditions, carbonation enhances ECC paste hydration.
Benzo[a]pyrene (BaP), produces tumors of skin, lung, liver, kidney and stomach in animals, enhances lung cancer in epidemiological studies and is a known human carcinogen. The EPA cancer slope risk factor for oral BaP exposure is 1 per mg/kg-day. The remarkable sensitivity (attomole 14C; precision 0.5-2% in biological samples) of accelerator mass spectrometry (AMS) makes possible [14C]-BaP dosing of humans with de minimus risk. A micro-dose of 46 ng (5 nCi), was given in 3 separate cycles to 5 human volunteers with a minimum 2 weeks between dosing. Blood was collected over 72 hours and BaP and BaP metabolites ([14C]-BaPeq) measured using AMS. [14C]-BaPeq appeared in plasma with an average Tmax of 75 minutes and Cmax 116-326 fM (29-82 fg/mL). Non-compartmental half-lives in plasma ranged from 30.7-114.2 hours and area under the curve values (AUC0-72 hr) 649-2060 fg x hr x mL-1. A two compartmental model yielded first-order rate constants (Ka, K12, K21, Kela and Kelß) of 0.92, 0.49, 0.12, 0.05 and 0.01 fg/hr, respectively. The T1/2a and T1/2ß were 1.14 and 89 hours, respectively. The actual interval between dosing was 20-420 days with no impact on a low intra-individual variation. No covalent [14C]-BaPeq-DNA adducts from peripheral blood mononuclear cells (PBMCs) were detected (LLOD of 10 fg [14C]-BaPeq adducts/mg DNA) 12-72 hours post-dosing negating the use of this cancer biomarker in risk assessment. We assert that the most relevant model for humans is humans. AMS and micro-dosing could be used to enhance the accuracy of pharmacokinetics and potentially risk assessments.
We report on the successful demonstration of selective acceleration of deuterium ions by target-normal sheath acceleration (TNSA) with a high-energy petawatt laser. TNSA typically produces a multi-species ion beam that originates from the intrinsic hydrocarbon and water vapor contaminants on the target surface. Using the method first developed by Morrison et al. [Phys. Plasmas 19, 030707 (2012)], an ion beam with >99% deuterium ions and peak energy 14 MeV/nucleon is produced with a 200 J, 700 fs, >10{sup 20}W/cm{sup 2} laser pulse by cryogenically freezing heavy water (D{sub 2}O) vapor onto the rear surface of the target prior to the shot. Within the range of our detectors (0°–8.5°), we find laser-to-deuterium-ion energy conversion efficiency of 4.3% above 0.7 MeV/nucleon while a conservative estimate of the total beam gives a conversion efficiency of 9.4%.
It is demonstrated that synthesizing an ultrahigh-bandwidth, negatively chirped laser pulse by incoherently stacking pulses of different wavelengths makes it possible to optimize the process of electron self-injection in a dense, highly dispersive plasma (n{sub 0}∼10{sup 19} cm{sup −3}). Avoiding transformation of the driving pulse into a relativistic optical shock maintains a quasi-monoenergetic electron spectrum through electron dephasing and boosts electron energy far beyond the limits suggested by existing scaling laws. In addition, evolution of the accelerating bucket in a plasma channel is shown to produce a background-free, tunable train of femtosecond-duration, 35–100 kA, time-synchronized quasi-monoenergetic electron bunches. The combination of the negative chirp and the channel permits acceleration of electrons beyond 1 GeV in a 3 mm plasma with 1.4 J of laser pulse energy, thus offering the opportunity of high-repetition-rate operation at manageable average laser power.
We report on the successful operation of a newly developed cryogenic jet target at high intensity laser-irradiation. Using the frequency-doubled Titan short pulse laser system at Jupiter Laser Facility, Lawrence Livermore National Laboratory, we demonstrate the generation of a pure proton beam a with maximum energy of 2 MeV. Furthermore, we record a quasi-monoenergetic peak at 1.1 MeV in the proton spectrum emitted in the laser forward direction suggesting an alternative acceleration mechanism. Using a solid-density mixed hydrogen-deuterium target, we are also able to produce pure proton-deuteron ion beams. With its high purity, limited size, near-critical density, and high-repetition rate capability, this target is promising for future applications.
Here, the direct laser acceleration (DLA) of electrons in a laser wakefield accelerator (LWFA) operating in the forced or quasi-blowout regimes has been investigated through experiment and simulation. When there is a significant overlap between the trapped electrons and the drive laser in a LWFA cavity, the resulting electrons can gain energy from both the LWFA and the DLA mechanisms. Experimental work investigates the properties of the electron beams produced in a LWFA with ionization injection by dispersing those beams in the direction perpendicular to the laser polarization. These electron beams show certain spectral features that are characteristic of DLA. These characteristic features are reproduced using particle-in-cell simulations, where particle tracking was used to elucidate the roles of LWFA and DLA to the energy gain of the electrons in this experimental regime and to demonstrate that such spectral features are definitive signatures of the presence of DLA in LWFA.
Experimental studies of the simultaneous acceleration of three-charge-state 129 Xe 49+,50+,51+ beam from 17 to 180 MeV/nucleon in a superconducting linear accelerator are presented. The beam parameters for each individual- and multiple-charge-state beam were measured and compared with the particle tracking simulations. Detailed measurements were performed to characterize the multiple-charge-state beam’s recombination after a second-order achromat and isopath 180° bending system. As a result of the recombination of three charge states in the six-dimensional phase space, the xenon beam intensity was increased by 2.5-fold compared to the single-charge-state beam. Lastly, the results presented in the Letter fully validate the possibility to produce and utilize high-quality multiple-charge-state heavy-ion beams in a large-scale superconducting linac to increase the available beam power on an isotope production target.
A direct current (dc) high voltage photo-emission electron gun operating at 130 kV is utilized at the Jefferson Lab (JLab) Continuous Electron Beam Accelerator Facility to generate spin-polarized electrons for nuclear physics experiments. Over the past decade, JLab has tested and implemented inverted-geometry ceramic insulators in photoguns, connecting the cathode electrode in vacuum to the high voltage power supply using commercial high voltage cables. This contribution reports on tests performed up to 375 kV dc, implementation of inverted insulators in a 300 kV dc photogun generating magnetized electron beams, and describes plans to develop a reliable insulator-cable connector for applying 500 kV dc to a future polarized beam photogun operating reliably and without field emission at 350 kV.
Nb₃Sn is a next-generation superconducting material for the accelerator cavities with higher critical temperature and superheating field, both twice compared to Nb. It promises superior performance and higher operating temperature than Nb, resulting in significant cost reduction. So far, the Sn vapor diffusion method is the most preferred and successful technique to coat niobium cavities with Nb₃Sn. Although several post-coating techniques (chemical, electrochemical, mechanical) have been explored to improve the surface quality of the coated surface, an effective process has yet to be found. Since there are only a few studies on the post-coating heat treatment at lower temperatures, we annealed Nb₃Sn-coated samples at 800 C - 1000 C to study the effect of heat treatments on surface properties, primarily aimed at removing surface Sn residues. This paper discusses the systematic surface analysis of coated samples after annealing at temperatures between 850 C and 950 C.
An Accelerated Life Test (ALT) of the Phytron stepper motor used in the LCLS-II cavity tuner has been conducted at JLab. Since the motor will reside inside the cryomodule, any failure would lead to a very costly and arduous repair. As such, the motor was tested for the equivalent of 30 lifetimes before being approved for use in the production cryomodules. The 9-cell LCLS-II cavity is simulated by disc springs with an equivalent spring constant. Plots of the motor position vs. tuner position ' measured via an installed linear variable differential transformer (LVDT) ' are used to measure motor motion. The titanium spindle was inspected for loss of lubrication. The motor passed the ALT, and is set to be installed in the LCLS-II cryomodules.
Over a two-day period, March 8-9, 2017 the Office of High Energy Physics convened a workshop in Gaithersburg, MD to seek community input on development of a radiofrequency (RF) research ten-year roadmap to guide the General Accelerator Research and Development Program (GARD). As described in the charge, the roadmap should reflect the Particle Physics Project Prioritization Panel strategy and the subsequent HEPAP Accelerator Subpanel recommendations. The charge for the workshop can be found in Appendix A. At the workshop, proponents of superconducting radiofrequency technology (SRF) and normal conducting radiofrequency technology (NCRF), along with invited university and laboratory experts, critically discussed opportunities, gaps, and requirements relevant to the development of a roadmap. The roadmap workshop was preceded by preparatory workshops at SLAC on NCRF and Fermilab on SRF.
Additional effect of centripetal acceleration on nystagmus in humans already exposed to angular acceleration
An experiment was designed and data were taken to demonstrate that a tightly focused laser on vacuum can accelerate an electron beam in free space. The experiment was proof-of-principle and showed a clear effect for the laser beam off and on. The size of the effect was about 20% and was consistent over 30 laser and beam shots.
Thin‐film solid‐state metal dealloying (thin‐film SSMD) is a promising method for fabricating nanostructures with controlled morphology and efficiency, offering advantages over conventional bulk materials processing methods for integration into practical applications. Although machine learning (ML) has facilitated the design of dealloying systems, the selection of key thermal treatment parameters for nanostructure formation remains largely unknown and dependent on experimental trial and error. To overcome this challenge, a workflow enabling high‐throughput characterization of thermal treatment parameters is demonstrated using a laser‐based thermal treatment to create temperature gradients on single thin‐film samples of Nb‐Al/Sc and Nb‐Al/Cu. This continuous thermal space enables observation of dealloying transitions and the resulting nanostructures of interest. Through synchrotron X‐ray multimodal and high‐throughput characterization, critical transitions and nanostructures can be rapidly captured and subsequently verified using electron microscopy. The key temperatures driving chemical reactions and morphological evolutions are clearly identified. While the oxidation may influence nanostructure formation during thin‐film treatment, the dealloying process at the dealloying front involves interactions solely between the dealloying elements, highlighting the availability and viability of the selected systems. Further, this approach enables efficient exploration of the dealloying process and validation of ML predictions, thereby accelerating the discovery of thin‐film SSMD systems with targeted nanostructures.
We describe a number of recently developed techniques for improving the performance of large-scalenuclear configuration interaction calculations on high performance parallel computers. We show thebenefit of using a preconditioned block iterative method to replace the Lanczos algorithm that hastraditionally been used to perform this type of computation. The rapid convergence of the block iterativemethod is achieved by a proper choice of starting guesses of the eigenvectors and the construction of aneffective preconditioner. These acceleration techniques take advantage of special structure of the nuclearconfiguration interaction problem which we discuss in detail. The use of a block method also allows usto improve the concurrency of the computation, and take advantage of the memory hierarchy of modernmicroprocessors to increase the arithmetic intensity of the computation relative to data movement. Wealso discuss the implementation details that are critical to achieving high performance on massivelyparallel multi-core supercomputers, and demonstrate that the new block iterative solver is two to threetimes faster than the Lanczos based algorithm for problems of moderate sizes on a Cray XC30 system.