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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on LiAs(XeF4)3 by Materials Project

LiAs(XeF4)3 crystallizes in the monoclinic P2_1 space group. The structure is two-dimensional and consists of two LiAs(XeF4)3 sheets oriented in the (0, 1, 0) direction. there are three inequivalent Xe sites. In the first Xe site, Xe is bonded in a linear geometry to two F atoms. Both Xe–F bond lengths are 2.08 Å. In the second Xe site, Xe is bonded in a linear geometry to two F atoms. Both Xe–F bond lengths are 2.08 Å. In the third Xe site, Xe is bonded in a linear geometry to two F atoms. There are one shorter (2.05 Å) and one longer (2.10 Å) Xe–F bond lengths. Li is bonded to six F atoms to form LiF6 octahedra that share a cornercorner with one AsF6 octahedra. The corner-sharing octahedral tilt angles are 31°. There are a spread of Li–F bond distances ranging from 2.01–2.10 Å. As is bonded to six F atoms to form AsF6 octahedra that share a cornercorner with one LiF6 octahedra. The corner-sharing octahedral tilt angles are 31°. There are a spread of As–F bond distances ranging from 1.77–1.82 Å. There are twelve inequivalent F sites. In the first F site, F is bonded in a single-bond geometry to one As atom. In the second F site, F is bonded in a bent 120 degrees geometry to one Xe and one Li atom. In the third F site, F is bonded in a bent 120 degrees geometry to one Xe and one Li atom. In the fourth F site, F is bonded in a bent 120 degrees geometry to one Xe and one Li atom. In the fifth F site, F is bonded in a bent 120 degrees geometry to one Xe and one Li atom. In the sixth F site, F is bonded in a bent 120 degrees geometry to one Xe and one Li atom. In the seventh F site, F is bonded in a single-bond geometry to one Xe atom. In the eighth F site, F is bonded in a bent 150 degrees geometry to one Li and one As atom. In the ninth F site, F is bonded in a single-bond geometry to one As atom. In the tenth F site, F is bonded in a single-bond geometry to one As atom. In the eleventh F site, F is bonded in a single-bond geometry to one As atom. In the twelfth F site, F is bonded in a single-bond geometry to one As atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ba3(LiAs)4 by Materials Project

Ba3(LiAs)4 crystallizes in the orthorhombic Immm space group. The structure is three-dimensional. Li1+ is bonded to four As+2.50- atoms to form LiAs4 tetrahedra that share a cornercorner with one BaAs6 octahedra, corners with ten equivalent LiAs4 tetrahedra, edges with two equivalent BaAs6 octahedra, and edges with three equivalent LiAs4 tetrahedra. The corner-sharing octahedral tilt angles are 52°. There are three shorter (2.82 Å) and one longer (2.97 Å) Li–As bond lengths. There are two inequivalent Ba2+ sites. In the first Ba2+ site, Ba2+ is bonded in a 6-coordinate geometry to six As+2.50- atoms. There are four shorter (3.40 Å) and two longer (3.42 Å) Ba–As bond lengths. In the second Ba2+ site, Ba2+ is bonded to six As+2.50- atoms to form BaAs6 octahedra that share corners with four equivalent LiAs4 tetrahedra, edges with two equivalent BaAs6 octahedra, and edges with eight equivalent LiAs4 tetrahedra. There are four shorter (3.35 Å) and two longer (3.37 Å) Ba–As bond lengths. There are two inequivalent As+2.50- sites. In the first As+2.50- site, As+2.50- is bonded in a 9-coordinate geometry to two equivalent Li1+, six Ba2+, and one As+2.50- atom. The As–As bond length is 2.52 Å. In the second As+2.50- site, As+2.50- is bonded in a 6-coordinate geometry to six equivalent Li1+ and three Ba2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LiAs(HO2)2 by Materials Project

LiAs(HO2)2 crystallizes in the orthorhombic Pna2_1 space group. The structure is three-dimensional. Li1+ is bonded to four O2- atoms to form LiO4 tetrahedra that share corners with two equivalent LiO4 tetrahedra and corners with four equivalent AsO4 tetrahedra. There are three shorter (1.99 Å) and one longer (2.02 Å) Li–O bond lengths. As5+ is bonded to four O2- atoms to form AsO4 tetrahedra that share corners with four equivalent LiO4 tetrahedra. There are a spread of As–O bond distances ranging from 1.68–1.77 Å. There are two inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a linear geometry to two O2- atoms. There is one shorter (1.04 Å) and one longer (1.52 Å) H–O bond length. In the second H1+ site, H1+ is bonded in a linear geometry to two O2- atoms. There is one shorter (1.04 Å) and one longer (1.52 Å) H–O bond length. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a trigonal planar geometry to two equivalent Li1+ and one As5+ atom. In the second O2- site, O2- is bonded in a trigonal planar geometry to one As5+ and two H1+ atoms. In the third O2- site, O2- is bonded in a distorted trigonal planar geometry to one Li1+, one As5+, and one H1+ atom. In the fourth O2- site, O2- is bonded in a trigonal planar geometry to one Li1+, one As5+, and one H1+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LiAs by Materials Project

LiAs crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. there are two inequivalent Li1+ sites. In the first Li1+ site, Li1+ is bonded to six As1- atoms to form a mixture of distorted edge and corner-sharing LiAs6 octahedra. The corner-sharing octahedra tilt angles range from 20–64°. There are a spread of Li–As bond distances ranging from 2.67–2.96 Å. In the second Li1+ site, Li1+ is bonded in a 6-coordinate geometry to six As1- atoms. There are a spread of Li–As bond distances ranging from 2.67–2.94 Å. There are two inequivalent As1- sites. In the first As1- site, As1- is bonded in a 8-coordinate geometry to six Li1+ and two equivalent As1- atoms. There are one shorter (2.50 Å) and one longer (2.52 Å) As–As bond lengths. In the second As1- site, As1- is bonded in a 8-coordinate geometry to six Li1+ and two equivalent As1- atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2023

LIA Performance Limitations

Location: SLAC National Accelerator Laboratory Presenter: Evan R Scott Date: 29 August 2023 Purpose: Part of SDRD for collaboration with SLAC

SDRD, SLAC, linear induction accelerator, cathode,↗
NASA NTRS2013

Tree Line Structure and Dynamics at the Northern Limit of the Larch Forest: Anabar Plateau, Siberia, Russia

The goal of the study was to provide an analysis of climate impact before, during, and after the Little Ice Age (LIA) on the larch (Larix gmelinii) tree line at the northern extreme of Siberian forests. Recent decadal climate change impacts on the tree line, regeneration abundance, and age structure were analyzed. The location of the study area was within the forest-tundra ecotone (elevation range 170-450 m) in the Anabar Plateau, northern Siberia. Field studies were conducted along elevational transects. Tree natality/mortality and radial increment were determined based on dendrochronology analyses. Tree morphology, number of living and subfossil trees, regeneration abundance, and age structure were studied. Locations of pre-LIA, LIA, and post-LIA tree lines and refugia boundaries were established. Long-term climate variables and drought index were included in the analysis. It was found that tree mortality from the 16th century through the beginning of the 19th century caused a downward tree line recession. Sparse larch stands experienced deforestation, transforming into tundra with isolated relict trees. The maximum tree mortality and radial growth decrease were observed to have occurred at the beginning of 18th century. Now larch, at its northern boundary in Siberia, is migrating into tundra areas. Upward tree migration was induced by warming in the middle of the 19th century. Refugia played an important role in repopulation of the forest-tundra ecotone by providing a seed source and shelter for recruitment of larch regeneration. Currently this ecotone is being repopulated mainly by tree cohorts that were established after the 1930s. The last two decades of warming did not result in an acceleration of regeneration recruitment because of increased drought conditions. The regeneration line reached (but did not exceed) the pre-LIA tree line location, although contemporary tree heights and stand densities are comparatively lower than in the pre-LIA period. The mean rate of tree line upward migration has been about 0.35 m/yr (with a range of 0.21-0.58), which translates to a tree line response to temperature of about 55 m/deg C.

Northern Limit↗
NASA NTRS2016

Exploring the Role of Humans and Climate over the Balkan Landscape: 500 Years of Vegetational History of Serbia

We present the first, well-dated, high-resolution record of vegetation and landscape change from Serbia, which spans the past 500 years. Biological proxies (pollen, spores, and charcoal), geochemical analysis through X-ray Fluorescence (XRF), and a detailed chronology based on AMS C-14 dating from a western Serbian sinkhole core suggest complex woodland-grassland dynamics and strong erosional signals throughout the Little Ice Age (LIA). An open landscape with prominent steppe vegetation (e.g. Poaceae, Chenopodiaceae) and minor woodland exists during 1540-1720 CE (early LIA), while the late LIA (1720-1850 CE) in this record shows higher tree percentages possibly due to increased moisture availability. The post LIA Era (1850-2012 CE) brings a disturbed type of vegetation with the presence of weedy genera and an increase in regional woodland. Anthropogenic indicators for agricultural, pastoral and fire practices in the region together attest to the dominant role of humans in shaping this Balkan landscape throughout the interval. The changing nature of human interference, potentially as a response to underlying climatic transitions, is evident through large-scale soil depletion resulting from grazing and land clearance during the early LIA and stabilization of arable lands during the late and post-LIA eras.

Topography↗
DOE OSTI2021

Initial conditions for simulations of beam physics in linear induction accelerators

Flash radiography of hydrodynamic experiments driven by high explosives is a well-known diagnostic technique in use at many laboratories. At Los Alamos, the DualAxis Radiographic Hydrodynamic Test (DARHT) facility two linear induction electron accelerators (LIAs) make the bremsstrahlung radiographic source spots for point projection radiographs from orthogonal views. A new LIA, called Scorpius, is presently under development to advance this technology. To better understand electron-beam physics in these LIAs, numerical simulations are frequently performed with the objective of improving the radiography. At Los Alamos we frequently use the TRAK ray-trace and LSP particle-in-cell (PIC) codes to simulate the injector, and the XTR and LAMDA envelope/centroid codes along with LSP to simulate transport of the accelerated beam through the LIAs. The LIA simulations need the injected beam parameters as initial conditions for calculating beam transport and stability. The determination of these initial conditions is the topic of this note.

43 PARTICLE ACCELERATORS↗
DOE OSTI2021

Spot Size Optimization of the Scorpius Accelerator

The Scorpius Linear Induction Accelerator (LIA) is being developed by the Advanced Sources and Diagnostics (ASD) Project and will complement other U1a capabilities by providing a multi-pulse, DARHT-class, flash-radiography capability. Commissioning activities are expected to end in Spring of 2026. All of the diagnostics discussed in this chapter are relevant to LIAs that generate high-current relativistic electron beams, and some diagnostics will also be relevant to other accelerators. The Scorpius Accelerator will be the world’s most advance LIA. Although significant technological advancements have been incorporated throughout the machine, many performance aspects of Scorpius will be similar to those of FXR and DARHT Axis-I and -II. These LIAs offer the same challenges, whether it is suppressing beam instabilities, improving diagnostic accuracy, validating computer simulations and beam tunes, or reducing beam-target interaction effects. However, the ultimate figure of merit is consistent between these LIAs, which is spot size and dose.

43 PARTICLE ACCELERATORS↗
DOE OSTI2023

Correct Initial Conditions for Simulations of Beam Physics in Linear Induction Accelerators

Flash radiography of hydrodynamic experiments driven by high explosives is a well-known diagnostic technique in use at many laboratories. At Los Alamos, the Dual Axis Radiographic Hydrodynamic Test (DARHT) facility two linear induction electron accelerators (LIAs) make the bremsstrahlung radiographic source spots for point projection radiographs from orthogonal views. A new LIA, called Scorpius, is presently under development to advance this technology. To better understand electron-beam physics in these LIAs, numerical simulations are frequently performed with the objective of improving the radiography. At Los Alamos we frequently use the TRAK ray-trace and LSP particle-in-cell (PIC) codes to simulate the injector, and the XTR and LAMDA envelope/centroid codes along with LSP to simulate transport of the accelerated beam through the LIAs. The LIA simulations need the injected beam parameters as initial conditions for calculating beam transport and stability. The determination of these initial conditions is the topic of this note.

43 PARTICLE ACCELERATORS↗
NASA NTRS2018

An Analysis of the Lightning Jump Algorithm Using Geostationary Lightning Mapper Flashes

Lightning's relation to severe weather has been studied since the 1980's. The invention of the Lightning Mapping Array allowed for total lightning measurements in a 125 km operational range. This brought forth an automated lightning Jump Algorithm (LIA) that predicted severe weather based on two-sigma increases in total lightning. The LIA's biggest downfall is being restrained to the limited field of view (FOV) of LMA's. The launch of the Geostationary Lightning Mapper (GLM) aboard the GOES-16 satellite now gives us hemispheric total lightning measurements. The wide FOV makes the GLM a good candidate to apply the LIA to. However the GLM and LMA have some differences. One being the coarser spatial resolution of GLM. Another being that LMA measures very high frequency (VHF) electromagnetic radiation while GLM measures optical radiation. These differences suggest an extensive study must be done on using the LIA with GLM to understand potential differences in the LIA and to maximize its operational skill. Four deep dive cases are conducted showcasing the differences between the GLM and LMA and their jumps.

Curtis, Nathan↗
NASA NTRS2018

The Little Ice Age and Human-Environmental Interactions in the Central Balkans: Insights from a New Serbian Paleorecord

This paper presents a 600-year well-dated, high-resolution Central Balkan paleo-record including the Little Ice Age (LIA; 1450-850 CE). Utilizing pollen-based REVEALS modelling estimates, geochemical indicators, rarefaction analyses and the AMS 14C-based Bacon age model, this first-hand record from the Sava Basin reveals the transformation of the Central Balkan landscape involving linkages between changing climatic and socio-political regimes. The pre-LIA interval (1370-1418 CE) in the Sava Region reveals a wooded steppe and increased cultivation under warmer/stable climatic and socio-political conditions. In contrast, the LIA interval in the region is expressed through continuous transitions between forest and grassland, extensive land erosion and stressed agriculture, potentially as a collective artifact of the climatic variability and human impact associated with socio- political stressors of the time. The post-LIA/Industrial Era interval (1850-2012 CE) in the Sava Region shows an overall increase in woodland as well as agriculture following the exit of the Ottomans. However, increased population pressures and the subsequent onset of the Industrial Revolution as well as increased trade led to intense deforestation throughout the 20th Century, which continued during the Socialist period.

Societal impacts of climate change↗
DOE OSTI2021

Megavolt bremsstrahlung measurements from linear induction accelerators demonstrate possible use as a FLASH radiotherapy source to reduce acute toxicity

Abstract Recent studies indicate better efficacy and healthy tissue sparing with high dose-rate FLASH radiotherapy (FLASH-RT) cancer treatment. This technique delivers a prompt high radiation dose rather than fractional doses over time. While some suggest thresholds of > 40 Gy s −1 with a maximal effect at > 100 Gy s −1 , accumulated evidence shows that instantaneous dose-rate and irradiation time are critical. Mechanisms are still debated, but toxicity is minimized while inducing apoptosis in malignant tissue. Delivery technologies to date show that a capability gap exists with clinic scale, broad area, deep penetrating, high dose rate systems. Based on these trends, if FLASH-RT is adopted, it may become a dominant approach except in the least technologically advanced countries. The linear induction accelerator (LIA) developed for high instantaneous and high average dose-rate, species independent charged particle acceleration, has yet to be considered for this application. We review the status of LIA technology, explore the physics of bremsstrahlung-converter-target interactions and our work on stabilizing the electron beam. While the gradient of the LIA is low, we present our preliminary work to improve the gradient by an order of magnitude, presenting a point design for a multibeam FLASH-RT system using a single accelerator for application to conformal FLASH-RT.

42 ENGINEERING↗
DOE OSTI2021

Electron-Beam Corkscrew Motion in an Advanced Linear Induction Accelerator

Scorpius is a multipulse linear induction accelerator (LIA) under development for flash radiography. Because it has substantially more cells than present LIAs, higher magnetic focusing fields are needed to suppress beam breakup (BBU). Therefore, it is more susceptible to corkscrew motion of the beam, which also depends on beam energy spread and focusing magnet misalignments. For energy spread and alignment tolerances expected for Scorpius, a magnetic tune designed to suppress BBU is shown to produce corkscrew motion within the range that can be controlled through the use of steering dipoles on existing LIAs. Finally, a gap-voltage modulation scheme is shown to almost completely eliminate chromatic effects such as corkscrew.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Beam Breakup Simulations for the Scorpius Flash-Radiography Accelerator

Beam breakup (BBU) in linear induction accelerators (LIAs) used for flash radiography is problematic because the high-frequency beam motion can blur the source spot, thereby degrading resolution. Amplification of BBU depends directly on details of cell design and is suppressed in operation by the solenoidal magnetic field focusing on the electron beam. Therefore, much effort has gone into design of the cells and magnetic focusing for the new Scorpius radiography LIA. Here, in this article, we use computer simulations to demonstrate that BBU in Scorpius should be no more than in present radiography LIAs at the Los Alamos National Laboratory.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Beam breakup in a solid state powered linear induction accelerator

It has been proposed to use solid-state pulsed-power modules to power the new Scorpius accelerator. Since this highcurrent accelerator would have 360 gaps (more than five times the number of cells as present radiography LIAs), it is natural to be concerned about the beam-breakup (BBU) instability. Earlier calculations of this effect used a half-scale model of the accelerator to avoid the limitation to 200 gaps in the code. We have now updated the code to accommodate the extraordinary number of gaps in this proposed LIA. The results of these early simulations are presented here. They indicate that BBU can only be suppressed to the same level as in designs powered by conventional pulsed power, if the calculated cell impedance can truly be achieved in practice. The magnetic focusing field required for this is of the same order as the field required for a conventionally powered LIA only if the transverse impedance can indeed be constrained to the values obtained in some simulations of the cell.

42 ENGINEERING↗
DOE OSTI2021

Current-Pulse Excitation of Beam Breakup in Scorpius

Perhaps the most dangerous instability for electron linear induction accelerators (LIA) is the beam breakup (BBU) instability. For flash-radiography LIAs like DARHT or Scorpius it is particularly troublesome, because low-level high-frequency BBU motion can blur the source spot. Theoretically, the number of e-foldings Γ of exponential BBU growth in an LIA is linearly proportional to beam current I, number of accelerating cells N, and transverse coupling impedance Z ⊥ , and inversely proportional to the strength of magnetic focusing B.

43 PARTICLE ACCELERATORS↗