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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,↗
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↗
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↗
DOE OSTI2021

Beam Envelope Stability in an Advanced Linear Induction Accelerator

A new linear induction accelerator (LIA) is under development for multipulse flash radiography. Because it has substantially more cells than present LIAs, higher magnetic focusing fields are needed to suppress beam breakup (BBU). It is, therefore, more susceptible to the parametric beam envelope instability (PEI), which has an instability threshold that has usually been typified by the vacuum phase advance per cell exceeding some large fraction of π . Here we derive a threshold criterion for PEI that depends not only on the magnetic field, but also on the beam space charge and emittance. A tune designed to suppress BBU in Scorpius is shown to be stable to the PEI according to this criterion, and also by the lack of emittance growth in particle-in-cell (PIC) code simulations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

DARHT Axis 1 Time-Resolved Injector Energy Measurement

The Dual-Axis Radiographic Hydrodynamic Test (DARHT) facility provides flash radiography capabilities using electron Linear Induction Accelerators (LIA’s). The strict requirements for flash radiography require a detailed understanding of the LIA’s performance, including precision measurements of the injected electron beam energy. The DARHT Axis 1 injector of produces a 3-4 MeV, 1-2 kA, 80-ns-FWHM electron beam. Injector capacitive monitors (EVACSUM) are summed to give the injector beam energy. Calibration of EVACSUM was last done in 1999 and is needed. In addition, the flatness of the injector drive voltage is controlled by a peaking capacitor in a Blumlien that is charged by the prime power tank. Time resolved measurements are used to optimize the value of this capacitor.

47 OTHER INSTRUMENTATION↗
DOE OSTI2020

Scorpius injector emittance measurements with solenoid scans

A classic scan solenoid can establish that the injector meets emittance requirements. Incorporating an aperture plate can validate predictions of much lower emittance. Measurements of beam parameters on the injector and ITS can inform predictions for the full LIA. Injector beam data is needed to tune the full LIA for initial turn-on and operation. Emittance measurements on the Scorpius injector are difficult because the beam is space-charge dominated. Emittance measurements on Scorpius injector and ITS will need large beam size to prevent overheating.

43 PARTICLE ACCELERATORS↗
DOE OSTI2020

Optimization of DARHT Axis 1 Injector Voltage

The Dual-Axis Radiographic Hydrodynamic Test (DARHT) facility provides flash radiography capabilities using two electron Linear Induction Accelerators (LIA’s). Axis-1 of DARHT produces a 20- MeV, 2-kA, 80-ns-FWHM electron beam. The strict requirements for flash radiography require a detailed understanding of the LIA’s performance, including precision measurements of the injector electron beam energy. The technique for time resolved measurement of the electron beam energy using electron Permanent Magnet Spectrometer (ePMSpec) has been developed. The electron energy then is used to infer the voltage produced by the injector pulsed power. The injector pulsed power of DARHT I consists of a 1.5-MV, glycol-insulated Blumlein that is pulsecharged by a step-up transformer and switched by four, laser-triggered spark gaps. A series of increasing impedance transmission lines are used to transform the output voltage of the Blumlein to a maximum of 3.8MV at the diode. Figure 1a shows a graphic of the Axis-1 prime power tank, Blumlein and downstream transmission lines. The injector pulse power is designed to produce voltage on a velvet cathode located in the vacuum vessel. The specifications of the voltage-pulse flat-top over 60ns is +/-1%. A key element in the high-voltage circuit is the ethylene glycol Blumlein. The outer volume, adjacent to the laser triggered switches of the Blumlein, is a peaking capacitor. This is an independent volume that contains a mixture of ethylene glycol and water to make it an adjustable capacitor of 380 to 750 pF.

43 PARTICLE ACCELERATORS↗