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At least 37 records · Page 2

Cosmic-ray source and local interstellar spectra deduced from the isotopes of hydrogen and helium.

A self-consistent model for cosmic-ray hydrogen and helium propagation from the sources in the Galaxy to the orbit of earth is obtained, taking into account experimental information now available on the isotopes H-1, H-2, He-3, and He-4. The only adjustable parameters include the shape of the energy spectra of H-1 and He-4 at the time of source injection, the distribution of particle path lengths in interstellar space, and the solar modulation parameters. It is found that the allowed form of the source differential spectra of the H-1 and He-4 nuclei is dominated by a power law in total energy.

Comstock, G. M.↗

Upgrading the LANSCE accelerator with a SNS RF-driven H− ion source

The LANSCE accelerator is currently powered by a filament-driven, biased converter-type H− ion source that operates at 10%, the highest plasma duty factor for this type of source, using only ∼2.2 SCCM of H2. The ion source needs to be replaced every 4 weeks, which takes up to 4 days. The measured negative beam current of 12–16 mA falls below the desired 24 mA acceptance of the LANCSE accelerator. The SNS (Spallation Neutron Source) RF-driven, H− ion source injects ∼50 mA of H− beam into the SNS accelerator at 60 Hz with a 6% duty factor and an availability of >99.5% but requires ∼30 SCCM of H2. Up to 7 A h of H− have been produced during the 14-weeks-long source service cycles, which is unprecedented for small emittance, high-current, pulsed H− ion sources. The emittance of the SNS source is slightly smaller than the emittance of the LANSCE source. The SNS source also features unrivaled low Cs consumption and can be installed and started up in <12 h. LANSCE and SNS are working toward the use of SNS H− ion sources on the LANSCE accelerator because they could (a) fill the LANSCE accelerator to its capacity, (b) decrease the source replacement time by a factor of up to 7, and (c) increase source lifetime by a factor of about 4. This paper discusses some of the challenges that emerge when trying to match a different H− source into an existing injector with significantly different characteristics and operating regimes.

Stockli, Martin P.↗

Dark Energy Survey Year 6 Results: Redshift Calibration of the MagLim++ Lens Sample

In this work, we derive and calibrate the redshift distribution of the MagLim++ lens galaxy sample used in the Dark Energy Survey Year 6 (DES Y6) 3x2pt cosmology analysis. The 3x2pt analysis combines galaxy clustering from the lens galaxy sample and weak gravitational lensing. The redshift distributions are inferred using the SOMPZ method - a Self-Organizing Map framework that combines deep-field multi-band photometry, wide-field data, and a synthetic source injection (Balrog) catalog. Key improvements over the DES Year 3 (Y3) calibration include a noise-weighted SOM metric, an expanded Balrog catalogue, and an improved scheme for propagating systematic uncertainties, which allows us to generate O($10^8$) redshift realizations that collectively span the dominant sources of uncertainty. These realizations are then combined with independent clustering-redshift measurements via importance sampling. The resulting calibration achieves typical uncertainties on the mean redshift of 1-2%, corresponding to a 20-30% average reduction relative to DES Y3. We compress the $n(z)$ uncertainties into a small number of orthogonal modes for use in cosmological inference. Marginalizing over these modes leads to only a minor degradation in cosmological constraints. This analysis establishes the MagLim++ sample as a robust lens sample for precision cosmology with DES Y6 and provides a scalable framework for future surveys.

Giannini, G. [Chicago U., Astron. Astrophys. Ctr.;↗

Dark Energy Survey Year 6 results: Redshift calibration of the MagLim++ lens sample

In this work, we derive and calibrate the redshift distribution of the MagLim++ lens galaxy sample used in the Dark Energy Survey Year 6 (DES Y6) 3 x 2pt cosmology analysis. The 3 x 2pt analysis combines galaxy clustering from the lens galaxy sample and weak gravitational lensing. The redshift distributions are inferred using the SOMPZ method - a Self-Organizing Map framework that combines deep-field multi-band photometry, wide-field data, and a synthetic source injection ( B alrog) catalog. Key improvements over the DES Year 3 (Y3) calibration include a noise-weighted SOM metric, an expanded Balrog catalogue, and an improved scheme for propagating systematic uncertainties, which allows us to generate O(10 8 ) redshift realizations that collectively span the dominant sources of uncertainty. These realizations are then combined with independent clustering-redshift measurements via importance sampling. The resulting calibration achieves typical uncertainties on the mean redshift of 1-2%, corresponding to a 20-30% average reduction relative to DES Y3. We compress the n(z) uncertainties into a small number of orthogonal modes for use in cosmological inference. Marginalizing over these modes leads to only a minor degradation in cosmological constraints. Here, this analysis establishes the MagLim++ sample as a robust lens sample for precision cosmology with DES Y6 and provides a scalable framework for future surveys.

dark energy↗

The Dark Energy Camera Plane Survey 2 (DECaPS2): More Sky, Less Bias, and Better Uncertainties

Abstract Deep optical and near-infrared imaging of the entire Galactic plane is essential for understanding our Galaxy’s stars, gas, and dust. The second data release of the Dark Energy Camera (DECam) Plane Survey extends the five-band optical and near-infrared survey of the southern Galactic plane to cover 6.5% of the sky, ∣ b ∣ ≤ 10°, and 6° > ℓ > −124°, complementary to coverage by Pan-STARRS1. Typical single-exposure effective depths, including crowding effects and other complications, are 23.5, 22.6, 22.1, 21.6, and 20.8 mag in g , r , i , z , and Y bands, respectively, with around 1″ seeing. The survey comprises 3.32 billion objects built from 34 billion detections in 21,400 exposures, totaling 260 hr open shutter time on the DECam at Cerro Tololo. The data reduction pipeline features several improvements, including the addition of synthetic source injection tests to validate photometric solutions across the entire survey footprint. A convenient functional form for the detection bias in the faint limit was derived and leveraged to characterize the photometric pipeline performance. A new postprocessing technique was applied to every detection to debias and improve uncertainty estimates of the flux in the presence of structured backgrounds, specifically targeting nebulosity. The images and source catalogs are publicly available at http://decaps.skymaps.info/ .

79 ASTRONOMY AND ASTROPHYSICS↗

SCIDAC Center for simulation of wave particle interactions CompX participation

Harnessing the energy that is released in fusion reactions would provide a safe and abundant source of power to meet the growing energy needs of the world population. The next step toward the development of fusion as a practical energy source is the construction of ITER, a device capable of producing and controlling the high performance plasma required for self-sustaining fusion reactions, or “burning” plasma. The input power required to drive the ITER plasma into the burning regime will be supplied primarily with a combination of external power from radio frequency waves in the ion cyclotron range of frequencies and energetic ions from neutral beam injection sources, in addition to internally generated Ohmic heating from the induced plasma current that also serves to create the magnetic equilibrium for the discharge. The ITER project is a large multi-billion dollar international project in which the US participates. The success of the ITER project depends critically on the ability to create and maintain burning plasma conditions, it is absolutely necessary to have physics-based models that can accurately simulate the RF processes that affect the dynamical evolution of the ITER discharge. The Center for Simulation of WavePlasma Interactions (CSWPI), also known as RF-SciDAC, is a multi-institutional collaboration that has conducted ongoing research aimed at developing: (1) Coupled core-to-edge simulations that will lead to an increased understanding of parasitic losses of the applied RF power in the boundary plasma between the RF antenna and the core plasma; (2) Development of models for core interactions of RF waves with energetic electrons and ions (including fusion alpha particles and fast neutral beam ions) that include a more accurate representation of the particle dynamics in the combined equilibrium and wave fields; and (3) Development of improved algorithms that will take advantage of massively parallel computing platforms at the petascale level and beyond to achieve the needed physics, resolution, and/or statistics to address these issues. CompX provides computer codes and analysis for the calculation of the electron and ion distributions in velocity-space and plasma radius which are necessary for reliable calculations of power deposition and toroidal current drive due to combined radiofrequency and neutral beam at high injected powers. It has also contributed to ray tracing modeling of injected radiofrequency powers, and to coupling between full-wave radiofrequency wave models and the distribution function calculations. In the course of this research, the Fokker-Planck distribution function calculation was made substantially more realistic by inclusion of finite-width drift-orbit effects (FOW). FOW effects were also implemented in a calculation of the phase-space diffusion resulting from radiofrequency full-wave models. Average level of funding for CompX was approximately three man-months per year.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

Final Technical Report for Grant No. DE-FC02-01ER54648, SciDAC Center for Simulation of Wave-Plasma Interactions

Harnessing the energy that is released in fusion reactions would provide a safe and abundant source of power to meet the growing energy needs of the world population. The next step toward the development of fusion as a practical energy source is the construction of ITER, a device capable of producing and controlling the high performance plasma required for self-sustaining fusion reactions, or “burning” plasma. The input power required to drive the ITER plasma into the burning regime will be supplied primarily with a combination of external power from radio frequency waves in the ion cyclotron range of frequencies and energetic ions from neutral beam injection sources, in addition to internally-generated Ohmic heating from the induced plasma current that also serves to create the magnetic equilibrium for the discharge. Since the success of the ITER project depends critically on the ability to create and maintain burning plasma conditions, it is absolutely necessary to have physics-based models that can accurately simulate the RF processes that affect the dynamical evolution of the ITER discharge. The Center for Simulation of Wave-Plasma Interactions (CSWPI) is a multi-institutional collaboration that has conducted ongoing research aimed at developing: (1) Coupled core-to-edge simulations that will lead to an increased understanding of parasitic losses of the applied RF power in the boundary plasma between the RF antenna and the core plasma; (2) Development of models for core interactions of RF waves with energetic electrons and ions (including fusion alpha particles and fast neutral beam ions) that include a more accurate representation of the particle dynamics in the combined equilibrium and wave fields; and (3) Development of improved algorithms that will take advantage of massively parallel computing platforms at the petascale level and beyond to achieve the needed physics, resolution, and/or statistics to address these issues. This research reported in this final technical report is focused on further verification and validation of simulation models for interactions of RF waves with energetic particles in the core with a long term goal of assessing their readiness for inclusion in integrated modeling frameworks and utilizing the world’s largest supercomputers to quantitatively predict the detailed electric field structure in the vicinity of the launching structures.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

The DECADE cosmic shear project II: photometric redshift calibration of the source galaxy sample

We present the photometric redshift characterization and calibration for the Dark Energy Camera All Data Everywhere (DECADE) weak lensing dataset: a catalog of 107 million galaxies observed by the Dark Energy Camera (DECam) in the northern Galactic cap. The redshifts are estimated from a combination of wide-field photometry, deep-field photometry with associated redshift estimates, and a transfer function between the wide field and deep field that is estimated using a source injection catalog. We construct four tomographic bins for the galaxy catalog, and estimate the redshift distribution, $n(z)$, within each one using the Self-organizing Map Photo-Z (SOMPZ) methodology. Our estimates include the contributions from sample variance, zeropoint calibration uncertainties, and redshift biases, as quantified for the deep-field dataset. The total uncertainties on the mean redshifts are $σ_{\langle}$$_z$$_{\rangle} ≈ 0.01$. The SOMPZ estimates are then compared to those from the clustering redshift method, obtained by cross-correlating our source galaxies with galaxies in spectroscopic surveys, and are shown to be consistent with each other.

Anbajagane, D. [Univ. of Chicago, IL (United State↗

Effects of Ag Doping and Point Defect on the Magnetism of ZnO

The magnetism sources and magnetic mechanism of Ag doping and point defect, which coexist in the presence of ZnO, are frequently controversial. To solve these problems, the effects of Ag doping and Zn or O vacancy on the magnetism of ZnO were investigated using geometry optimization and energy calculation according to the first-principles generalized gradient approximation + U (GGA+U) method of density functional theory. Results revealed that the system which Ag doping and Zn vacancy coexists in ZnO could achieve room-temperature ferromagnetism. This system had an extremely high spin polarization, which was advantageous for the spin electron injection sources applied in dilute magnetic semiconductors. Result also revealed that the magnetism of Zn{sub 14}AgO{sub 16} was caused by the electron hybrid coupling effects among the O-2p, Ag-4d, Ag-5s, and Zn-4s orbits. And these effects were produced by the hole carriers after complexes were formed by the Ag doping and Zn vacancy. With regard to the most stable structure of the ground state, all doping systems which Ag replacing Zn and O vacancy coexisted in ZnO and those which Ag replacing Zn, interstitial Ag, and O vacancy coexisted in ZnO were all non-magnetic. Thus, these doping systems were unsuitable for dilute magnetic semiconductors. By contrast, the doping systems of interstitial Ag and Zn vacancy were magnetic, although the magnetism was relatively weak, thus rendering such systems inapplicable as well.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Simulating image coaddition with the Nancy Grace Roman Space Telescope – I. Simulation methodology and general results

The upcoming Nancy Grace Roman Space Telescope will carry out a wide-area survey in the near-infrared. A key science objective is the measurement of cosmic structure via weak gravitational lensing. Roman data will be undersampled, which introduces new challenges in the measurement of source galaxy shapes; a potential solution is to use linear algebra-based coaddition techniques such as imcom that combine multiple undersampled images to produce a single oversampled output mosaic with a desired ‘target’ point spread function (PSF). We present here an initial application of imcom to 0.64 square degrees of simulated Roman data, based on the Roman branch of the Legacy Survey of Space and Time (LSST) Dark Energy Science Collaboration (DESC) Data Challenge 2 (DC2) simulation. We show that imcom runs successfully on simulated data that includes features such as plate scale distortions, chip gaps, detector defects, and cosmic ray masks. We simultaneously propagate grids of injected sources and simulated noise fields as well as the full simulation. We quantify the residual deviations of the PSF from the target (the ‘leakage’), as well as noise properties of the output images; we discuss how the overall tiling pattern as well as Moiré patterns appear in the final leakage and noise maps. We include appendices on interpolation algorithms and the interaction of undersampling with image processing operations that may be of broader applicability. The companion paper (‘Paper II’) explores the implications for weak lensing analyses.

79 ASTRONOMY AND ASTROPHYSICS↗

Assembly of Fissionable Material in the Presence of a Weak Neutron Source

Here, the probability distribution in time at which the neutron population in a slightly supercritical system attains a prescribed level is considered for the case where a source injects well under one neutron per neutron lifetime. For the case of ramp insertion of reactivity, it is shown that the energy released in the consequent burst of fissions may in some cases (e.g., unmoderated enriched uranium systems) exceed by over a factor of 100 the energy release predicted by the reactor kinetics equations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

Transport of an intense proton beam from a cone-structured target through plastic foam with unique proton source modeling

Laser-accelerated proton beams are applicable to several research areas within high-energy density science, including warm dense matter generation, proton radiography, and inertial confinement fusion, which all involve transport of the beam through matter. Here, we report on experimental measurements of intense proton beam transport through plastic foam blocks. The intense proton beam was accelerated by the 10 ps, 700 $\textit{J}$ OMEGA EP laser irradiating a curved foil target, and focused by an attached hollow cone. The protons then entered the foam block of density 0.38 g/cm 3 and thickness 0.55 or 1.00 mm. At the rear of the foam block, a Cu layer revealed the cross section of the intense beam via proton- and hot electron-induced Cu-K α emission. Images of x-ray emission show a bright spot on the rear Cu film indicative of a forward-directed beam without major breakup. 2D fluid-PIC simulations of the transport were conducted using a unique multi-injection source model incorporating energy-dependent beam divergence. Along with postprocessed calculations of the Cu – $K_α$ emission profile, simulations showed that protons retain their ballistic transport through the foam and are able to heat the foam up to several keV in temperature. The total experimental emission profile for the 1.0 mm foam agrees qualitatively with the simulated profile, suggesting that the protons indeed retain their beamlike qualities.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

Effects of Co Doping and Point Defect on the Ferromagnetism of ZnO

The effects of different doping proportions of Co doping and oxygen vacancies (V{sub O}) on the ferromagnetism of zinc oxide (ZnO) are controversial. To solve this problem, we investigated the effects of Co doping and point defects (V{sub O}, V{sub Zn}, H{sub i}, and Zn{sub i}) on the ferromagnetism of ZnO through first-principle calculations by using generalized gradient approximation + U (GGA + U) under density functional theory. Results show that the closer the distance between Co and vacancies (V{sub O} or V{sub Zn}), the lower the formation energy and the more stable the system will be. Co-doped ZnO with V{sub O} or V{sub Zn} exhibits long-range ordered ferromagnetism and Curie temperature above the room temperature. Especially, Co-doped ZnO with V{sub Zn} shows a half-metallic behavior, resulting in 100% conduction hole polarizability, which is highly beneficial for dilute magnetic semiconductors (DMSs) as a hole injection source. The ferromagnetism of Zn{sub 14}CoO{sub 16} is caused by the double exchange effects among the electrons of the O–2p, Co–3d, and Zn–3d orbits mediated by the hole carriers after complexes were formed by the Co doping and Zn vacancy. Similarly, the origin of ferromagnetism in Zn{sub 15}CoO{sub 15} is derived from the double exchange effects among the electrons of O–2p, Co–3d, and Zn–4s states mediated by the electron carriers after complexes were formed by the Co doping and O vacancy. In addition, the result shows that Co-doped ZnO with interstitial H (H{sub i}) or Zn (Zn{sub i}) is unfavorable for ferromagnetism and should be avoided experimentally.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Effect of Fe Doping and O Vacancies on the Magnetic Properties of Rutile TiO{sub 2}

Magnetism sources of Fe doping and O vacancies, which coexist in the presence of rutile TiO{sub 2}, are controversial and require a resolution. The effects of Fe doping and point defect on the magnetism of rutile TiO{sub 2} were studied using geometry optimization and energy calculation based on the first principle generalized gradient approximation + U method (GGA+U) of density functional theory. Fe/Vo ratio is 1:1 in rutile TiO{sub 2}. The next closest distance between Fe and Vo is 0.04082 nm. The formation energy of the doping system is the smallest. This doping system has the highest stability. The coexistence of Fe doping and O vacancy achieved ferromagnetic long-range order. The different ratios of Fe/Vo are 1:1, 1:2, 2:1, and 2:2. The magnetic properties of the doping system are significantly different. At a ratio of 2:1, the magnetic moment is the largest among all doping systems. Moreover, the Curie temperature of the doping system can be higher than room temperature. These findings can obtain dilute magnetic semiconductors with potential application value. At a Fe/V{sub O} ratio of 2:2, the Ti{sub 14}Fe{sub 2}O{sub 30} system produces a half-metallic property of 100% electron spin polarizability. This is the most valuable application for designing and preparing novel spintronic injection source dilute magnetic semiconductors. The magnetic source is mainly mediated by the holes generated by Fe doping and O vacancy complexes, thereby causing the spin polarization double exchange effect on the electron of Ti–3d orbital atoms near the O vacancy, O–2p electron orbital, and Fe–3d electron orbital. This feature is consistent with the following theories: the mean field approximation and the double exchange mechanism theories.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Theoretical analysis of a refrigerant injection-enhanced air source heat pump with thermal energy storage for extended cold-climate and defrosting operations

This study investigates a conceptual refrigerant injection-enhanced air source heat pump with integrated thermal energy storage (ITES-ASHP) that combines two-phase flash tank injection with phase change material (PCM) thermal energy storage (TES) to extend cold-climate operation and maintain indoor heating during defrost. A steady-state, mode-based thermodynamic cycle model is developed to evaluate heating and defrosting modes with and without refrigerant injection and TES integration over an outdoor temperature range of 8 to −25 °C. The framework is applied to refrigerants R-290, R-454B, R-410 A, and R-32. A parametric study is conducted for an 18-kW system rated for an outdoor temperature of 8 °C, with the compressor frequency scheduled to 150 Hz. The optimal PCM phase-change temperature is identified as 20 °C for R-290, R-454B, and R-410 A, and 15 °C for R-32. At the design condition of −25 °C outdoor temperature, the proposed concept achieves a combined COP of 2.22 for R-290, corresponding to a 60% increase relative to the theoretical single-stage baseline for combined heating and defrosting operation. Safety screening based on compressor discharge temperature (≤ 120 °C) and injection quality (≥ 0.65), together with performance evaluation, indicates that R-290 is the most suitable candidate, followed by R-410 A and R-454B. Under the assumptions and constraints used here, R-32 is found to be less suitable due to excessive discharge temperatures and a higher risk of wet compression.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗

Effect of Fe Doping and Point Defects (V{sub O} and V{sub Sn}) on the Magnetic Properties of SnO{sub 2}

We investigated the effects of Fe doping and point defects (oxygen and tin vacancies, V{sub O} and V{sub Sn}, respectively) on the ferromagnetism of SnO{sub 2} through first-principles calculations by using generalized gradient approximation + U under density functional theory. Calculation results show that Fe-doped SnO{sub 2} with V{sub O} or V{sub Sn} exhibit long-range ordered ferromagnetism and Curie temperature above room temperature. The system has different magnetic properties with different doping modes, which are beneficial to the magnetic adjustment of dilute magnetic semiconductor (DMS). The double-exchange effects among the electrons of O–2p and Fe–3d states are the origin of ferromagnetism in Sn{sub 15}FeO{sub 31}. Similarly, ferromagnetism in Sn{sub 14}FeO{sub 32} is derived from the double-exchange effects among the electrons of O–2p and Fe–3d states. These effects are produced by hole carriers after complexes form by Fe doping and V{sub O} or V{sub Sn}. Simultaneously, Sn{sub 14}FeO{sub 32} shows a half-metallic behavior, thus resulting in 100% conduction hole polarizability, which is highly beneficial to DMSs as a hole-injection source. Moreover, results also show that the decreased distance between Fe and vacancies (V{sub O} or V{sub Sn}) lowers formation energy and thus increases the system stability.

36 MATERIALS SCIENCE↗

Introduction of performance boosters like Ge as channel material for the future of CMOS

High mobility materials are being considered to replace Si in the channel to achieve higher drive currents and switching speeds. Ge is one of new attractive channel materials that require CMOS scaling For future technology nodes and future high performance P-MOSFETS, we have studied a nanoscale SOI DG MOSFETs using quantum simulation approach on DG MOSFETs within the variation of Ge channel concentration and in the presence of source and drain doping by replacing Silicon in the channel by Ge using various dielectric constant. The use of high mobility channel (like Ge) to maximize the MOSFET IDsat and simultaneously circumvent the poor electrostatic control to suppress short-channel effects and enhance source injection velocity. The leakage current (I{sub off}) can be controlled by different gates oxide thickness more ever the required threshold voltage (V{sub TH}) can be achieved by keeping gate work function and altering the doping channel.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

A new cryogenic apparatus to search for the neutron electric dipole moment

A cryogenic apparatus is described that enables a new experiment, nEDM@SNS, with a major improvement in sensitivity compared to the existing limit in the search for a neutron Electric Dipole Moment (EDM). This apparatus uses superfluid 4 He to produce a high density of Ultra-Cold Neutrons (UCN) which are contained in a suitably coated pair of measurement cells. The experiment, to be operated at the Spallation Neutron Source at Oak Ridge National Laboratory, uses polarized 3 He from an Atomic Beam Source injected into the superfluid 4 He and transported to the measurement cells where it serves as a co-magnetometer. The superfluid 4 He is also used as an insulating medium allowing significantly higher electric fields, compared to previous experiments, to be maintained across the measurement cells. Finally, these features provide an ultimate statistical uncertainty for the EDM of 2-3× 10 -28 e-cm, with anticipated systematic uncertainties below this level.

47 OTHER INSTRUMENTATION↗