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DOE OSTI2020

DARHT Axis 1 Performance Results with and without a Blumlein Charge Unit

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. As DARHT Axis 1 enters its twentieth year of operation, the probability of Blumlein Charge Unit (BCU) failure has increased and the risk of a failure on the day of an explosive experiment has become more likely. Replacement time for a BCU is four to six hours. This report examines the radiographic and beam transport effect of operating the accelerator with a missing or reduced charge voltage BCU. The results are compared with normal, full machine operation. A prescription for alternate operation with missing or reduced charge voltage on BCU22 is given.

47 OTHER INSTRUMENTATION↗

DOE OSTI2021

Expanded Capabilities and Opportunities for Virtual Beamline Code

In the 25 years since LLNL broke ground on the National Ignition Facility (NIF) - a cornerstone of the National Nuclear Security Administration’s Stockpile Stewardship Program - the NIF and Photon Science (NIF&PS) Directorate has steadily pushed the boundaries of laser physics, nonlinear optics, and photonics in service of inertial confinement fusion experiments, and advanced photon sources development. Beyond the 192 beamlines of the primary laser facility with its world-record energy and fusion yields, NIF&PS capabilities have expanded to include chirped-pulse amplification, kilojoule petawatt-class short-pulse systems to generate hard x-ray radiographic probes, high-average power lasers as secondary sources for generation or wake field particle acceleration along directed energy applications, and other scientific pursuits. The Computing Directorate partners with NIF&PS on numerous projects and technologies from diagnostic measurements and high performance control systems to data analysis, information technology infrastructure, and scientific simulation code development. “This strong collaboration enables cutting-edge science, particularly with regard to physics-based modeling and simulation,” says physicist Jean-Michel Di Nicola. One crucial capability for NIF&PS is the Virtual Beamline (VBL) laser simulation code. It can model all the major laser physics and technology involved in the design optimization, commissioning, and operations of advanced laser architectures from tabletop to NIF-scale. VBL provides researchers with high-fidelity models and high-resolution calculations of laser performance predictions—including for the entire NIF laser system, the Advanced Radiographic Capability, parts of the High Repetition-Rate Advanced Petawatt Laser System laser delivered to the Czech Republic, and the Optical Science Laser. After more than two decades of experimentally verified physics and computing enhancements, this unique workhorse code is wrapping up another major milestone: migration from Java to C++ with a flurry of user interface and optimization features, as well as laser physics and high-resolution enhancements thanks to parallel execution on Livermore Computing platforms.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2022

DARHT : Enduring Lessons from a Technical Project in a National Laboratory Context [Slides]

The Dual-Axis Radiographic Hydrodynamic Test (DARHT) facility at Los Alamos National Laboratory (LANL) is the world’s first flash x-ray facility able to take multiple high-resolution radiographs of the interior features of fast-moving dense objects during a single experiment. DARHT’s radiography and complimentary diagnostics makes it an important diagnostic tool in support of the US Department of Energy’s (DOE)/National Nuclear Security Administration (NNSA)’s stewardship of the US nuclear deterrent. The project to construct DARHT ran from 1988 through 2003. Initial Operating Capability along a single axis began in 1999. A technical issue delayed Critical Decision 4 for the full dual-axis capability until 2008. DARHT was characterized by several directed changes resulting from an environmental impact study, changes to the global security context resulting from the end of underground nuclear testing, and rapid evolution of applicable technology. Conventional building and lab-space construction were part of the project, but the project was dominated by Special Facility Equipment that, together with the mission to support the nuclear weapons program, required the project to be completed by national laboratories. Although the project pre-dated implementation of DOE Order 413.3, several important lessons for national laboratory projects remain applicable today and will be discussed here, including projects appropriate for the national laboratory environment, scope stability, risk acceptance and mitigation, communication, and collaboration. Finally, considerations for DOE contractor project managers are offered based upon the DARHT experience.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2022

Inferring Heat Flow in Laser Absorption Regions using Diagnostic Magnetic Fields

This research was motivated by the desire to obtain a measurement of heat-flow in overdense regions of a laser ablated plasma for the first time using a high energy proton beam. For sufficiently high energies, the proton beam can pass through overdense regions and only be deflected by electric and magnetic fields. As the transport of magnetic fields in a plasma are intrinsically linked to the transport of thermal energy, it was posited that such a measurement could be used to infer a heat-flow. While the project did not prove the method to be infeasible, difficulties with understanding the proton radiographs without an imposed magnetic field made the final aim of this project unreached. Instead, however, a closer understanding of proton radiographs of laser-solid interactions without an imposed field has been obtained. 5 shot days on The OMEGA Laser Facility have been awarded (3 through ICF and 2 as ride-along) to further investigate some of these features. Extrapolating current results to hohlraum conditions has the magnetic energy being a significant (10%) fraction of the laser drive energy, which has the potential to explain the NIF hohlraum drive deficit.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2023

Inferring Heat Flow in Laser Absorption Regions using Diagnostic Magnetic Fields: Abstract

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2022

Multi-Probe 22A: Post shot Data and Analysis

The Multi-Probe 22A experiments took place on the Omega EP laser in March 2022. The goal was to discover issues with simultaneous x-ray and proton radiography of static and dynamic test objects. The x-ray and proton probes were generated by short-pulse laser-matter interactions. Significant crosstalk between the proton beam and x-ray detector was observed. Several static radiographs were made, including a set of proton images made with different laser energies. No dynamic objects were radiographed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2023

Dark Field Proton Radiography (Los Alamos LDRD Report)

Proton radiography at LANL (pRad) takes advantage of the high flux, high proton energy, and flexible timing structure of LANSCE's 800-MeV proton beam to visualize dense, dynamic systems under extreme strain. With recent needs identified for the development of the W93, the pRad team has been actively searching for ways to increase the facility's radiographic capabilities. Recently, we discovered that utilizing two magnetic lenses (one upstream and one downstream of the object), and specific combinations of collimator choices within the two lenses, that the signal-to-noise ratio was improved by more than a factor of two. However, we did not fully understand the mechanism, and found that results did not match forward modeling predictions. This work specifically sought to implement an engineering solution to solve this problem, through the development of an actuated collimator that reduced the time required to swap collimator settings from a typical 4-8 hours, to less than 30 seconds. This allowed, in combination with a unique multi-material, multi-resolution stepwedge, to acquire an unprecedently enormous dataset, with in total 24 collimation combinations, and multiple diffuser settings and pulse patterns, equivalent to almost a full run cycle's worth of data in a few days. This massive dataset is currently being harnessed to make a fully-predictive, ultra-fast Python-based model of the system, to dial in specific settings for any future experiments that fully optimize that radiographic sensitivity to the material of interest.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2023

Multi-Probe Campaign FY24 Omega EP Shot Request [Slides]

The ultimate goal of the Multi-Probe experimental campaign is to assess the feasibility of using multiple probe species (x-ray, proton, neutron, and electron) in future LANL radiographic facilities. To use Omega EP most efficiently, two different experiments are proposed for each of the two requested days in FY24. In this way, shots may be interleaved on the two short pulse beams and the shot rate doubled. In FY24, we propose to continue to develop the neutron source by first optimizing the “pitcher” source of deuterons/protons and then adding the “catcher” neutron converter on day 2. The second series of experiments continues examining the origin and nature of the x-ray background found in our last two experiments. This background is not well understood or characterized by the community. The first day will measure the electrons emanating from the proton and x-ray targets while also optimizing the background shielding first used in FY23. The second day will test a geometry that enables simultaneous radiographs using both short-pulse beams.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2023

N230227-001 2DConA Postshot report [Slides]

Backlit radiographs of 2DConA N220926 showed prolate symmetry (P2 > 0) at late time. A constant-in-time cone-fraction multiplier of 0.8 was used in shot N230227 to correct the P2. N230227 radiographs show a rounder implosion than N220926. A post-shot HYDRA simulation was done with standard (unchanged) settings to quantify shape vs time. Simulation of N230227 shows remarkable symmetry for all time and at all interfaces. Outer shell P2 changes by ~ 20 µm and inner shell by ~ 5 µm, both toward a rounder implosion. This implosion is an excellent starting point for any future modifications.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2023

High Intensity Gamma Ray Source Scintillation Attenuation Spectrometer and Filter Stack Monoenergetic Calibration

The Laser-Based X-ray Radiographic Imaging team at Los Alamos National Lab is looking for a monoenergetic MeV X-ray source to both verify our Monte Carlo N-particle simulations of detector performance and calibrate the instruments for future measurements. Funded by the Laboratory Directed Research and Development (LDRD) program, our overall goal is to improve the radiographic quality and reliability of laser-based X-ray sources for deployment at both dynamic and static radiography facilities. Laser-based X-ray sources have demonstrated smaller spot sizes to current electron accelerator based sources. The smaller laser spot size leads to significantly improved resolution.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2024

Multi-Probe 24A: Post shot Data and Analysis

The Multi-Probe 24A experiments took place on the Omega EP laser in November 2023. The experiments consisted of shots alternating between Omega EP’s two short-pulse laser beams to generate proton and deuteron ion beams from a range of film thicknesses, and x-ray sources from the established CPC+Ta wire targets. The backlighter was used for ion acceleration in the pitcher series, in which deuteron and proton beams characterized as a function of CD film thickness to develop a pitcher for a pitcher-catcher neutron radiographic source, while also characterizing electrons and x-rays emitted perpendicular to the target (i.e. Crosstalk for sidelighter-driven x-ray beams). The sidelighter was used for electron acceleration in the x-ray series, in which the electron acceleration and subsequent x-rays was characterized from the CPC+Ta wire targets and radiography was conducted with and without electro-magnetic electron defection. For the pitcher series, we found that at 500 J and 0.7 ps the 700-800 nm CD films yielded the greatest number and highest energy for both protons and deuterons. For the x-ray series, results demonstrated: a significant number of <100 keV x-rays are produced within the glue that fills the CPC cone, on-axis electron signal from the x-ray targets produce electrons resolvable up to ~10 MeV, and electron deflection (using MIFEDS) has a notable effect radiograph on noise reduction.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2024

Z-Target Radiography Postprocessing With A Deep Convolution Neural Network

Analyzing X-ray radiographs is crucial for understanding target behavior in Inertial Confinement Fusion (ICF) and High Energy Density (HED) platforms. However, the density of Magneto Raleigh Taylor (MRT) bands and limitations of target materials often obscure relevant spike growth and density information. To address this issue, machine learning postprocessing techniques can be applied to remove darkened regions in radiography images. In this study, a novel method is presented for removing MRT darkened regions from z-target radiographs using a convolutional neural network (CNN). The CNN, consisting of six layers, treats the darkened regions as noise and employs a mixed loss function and end-to-end frameworks to suppress them while preserving sharpness. The six-layer architecture is designed to effectively learn features when provided with a larger volume of learning space. Each layer is optimized using a mixed loss function that combines a standard loss pixel approach with a multi-scaled structural similarity index loss, which considers luminance, contrast, and structure in local neighborhoods. This approach is particularly beneficial for capturing the stochastic structure of MRT limbs. Due to the limited availability of experimental data, training is conducted using synthetic target radiography from 3D Alegra simulations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2024

Development of Short-Pulse Laser-Based Diagnostics for Pulsed Power-Driven Warm Dense Matter

This report summarizes a research project conducted at the Physics Department’s Zebra Pulsed Power Laboratory (ZPPL) at the University of Nevada Reno, aimed at developing short-pulse laser-based diagnostics to probe pulsed-power-driven warm dense matter. ZPPL combines a MegaAmpere (MA) pulsed power generator, Zebra, and a relativistic intensity, short-pulse laser, Leopard, offering a unique university-scale platform for high energy density physics, laboratory astrophysics, and inertial fusion energy research. The project focused on establishing a hard X-ray radiographic capability using high-intensity, short-pulse laser-generated X-rays to probe warm dense matter created by the Zebra current. Initial experiments produced X-ray radiographs of a static (cold) aluminum wire using silver and gold foil and wire targets, but intense background radiation from Zebra shots overwhelmed the laser-produced X-rays. To mitigate this, a radiationhardened detector housing was designed and implemented. Additional diagnostic, including a filter stack bremsstrahlung spectrometer and an X-ray pinhole camera, were developed to characterize laser-produced hard X-ray spectra and locate hard X-ray sources in the vacuum chamber. These revealed that strong hard X-rays (> 20 keV) originated near the anode cap, bombarded by energetic electrons. Due to laser unavailability during some experiments, detector performance was successfully tested using hard X-ray sources from the Zebra current, demonstrating their readiness for coupled experiments. The project supported one Ph.D. student (Dr. Lei Chen), who conducted experimental and numerical research, and provided training opportunities and data for three undergraduate senior theses.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2022

Data Mining – Image Analysis of Radiography for Zr Redistribution

The research effort described in this report represents a first attempt to investigate the radial redistribution of Zr in ternary fuel alloys U-xPu-10Zr (x = 0, 8, 19) irradiated in the in-reactor fuel experiments during the operation of the U.S. Department of Energy’s (DOE’s) Experimental Breeder Reactor II (EBR-II) at Idaho National Laboratory (INL) using methods of image processing on post-irradiation neutron radiographs. Approximately 130,000 metal fuel pins were irradiated in EBR-II during its 30 years of operation to develop and characterize existing and prospective fuels. For many of the metal fuel irradiation experiments, neutron radiography imaging was performed historically now allowing application of modern image analysis techniques to characterize fuel behavior, such as fuel swelling, fluff formation, and now, fuel alloy constituent redistribution. The redistribution of fuel components depends on the temperature field, radially, within the fuel. Specifically, Zr is expected to redistribute radially towards the center of the pin, as well as towards the outer zones. Currently, direct imaging of a pin cross-section through optical methods or scanning electron microscopy (SEM) is used to study the constituents’ redistribution, which is very time-consuming and can only be applied to a limited number of pins. An automated image processing technique allowing for the investigation of fuel radial redistribution zones would significantly accelerate data analysis. In general, if the fuel temperature is hot enough, three redistribution zones are expected, corresponding to the main fuel components (e.g., U, Pu, Zr). While more assessment will be performed in fiscal year (FY)-2023, it seems possible to differentiate the pins according to their fuel composition using image analysis techniques on neutron radiographs of metallic fuel pins based on the analysis to date.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗

DOE OSTI2025

Image Alignment and Flat-Field Correction of Film and Computed Radiography Images on the LLNL Flash Testbed

Computed radiography (CR) imaging plates and film are used in HEAF firing tanks and in the NDE group. The imaging plates allow for the creation of high-resolution digital images with flash X-ray (FXR). A typical treatment of flash X-ray radiographs is flat-field correction, where the image from an experiment is normalized by a “flat-field” or “bright-field” image. This flat-field image is taken in an identical configuration to the experimental image, but without the object or experiment in the field of view (FOV). This treatment reduces spatial effects from the FXR spot size and detector misalignment, as each pixel value in the corrected image represents a ratio of collected radiation with the object in FOV to the collected radiation without the object in FOV. One challenge in the creation of a corrected image is the misalignment of the CR plate or film pack between capturing the flat-field image and the experimental image. Fiducial structures can remedy this issue. Small (3.18mm) stainless steel ball bearings serve as good fiducial structures due to their small size and high radiographic contrast. Spheres are view-agnostic geometry, always presenting a circular cross section no matter the orientation. This process was developed for images from the flash X-ray testbed. The flash testbed was used to compare the X-ray transmission at different thicknesses of aluminum and copper step wedges. Each step wedge section is a rectangular shape, so evaluation is made much simpler if the rectangles are not rotated with respect to the image. This alignment process aligns the object and flat-field images together and leaves the rectangles of each step aligned with the image.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Monitoring the Structural Health of the Stage-Four Gibbs Resistor In Order to Maintain a Functioning Pulse-Forming Network

The Dual-Axis Radiographic Hydrodynamic Test (DARHT) facility at Los Alamos National Laboratory (LANL) is a critical facility used for nuclear weapons research and development (Los Alamos National Laboratory). Its primary function is to provide high-resolution, real-time images of the behavior of materials under extreme conditions, specifically during the hydrodynamic testing of nuclear weapons surrogates. The facility uses advanced radiographic techniques, such as dual-axis X-ray imaging, to capture detailed snapshots of these materials as they react to high-pressure environments. DARHT plays a key role in maintaining the safety, security, and reliability of the U.S. nuclear arsenal, supporting the Stockpile Stewardship Program. The facility helps ensure that nuclear weapons perform as designed without the need for nuclear tests. Its dual-axis radiography provides more precise data than traditional single-axis imaging, offering a comprehensive view of the internal dynamics of a weapon's primary stage.

42 ENGINEERING↗

DOE OSTI2023

Safety and efficacy of peripheral nerve blocks to treat refractory headaches after aneurysmal subarachnoid hemorrhage – A pilot observational study

Objectives: Headache after aneurysmal subarachnoid hemorrhage (HASH) is common, severe, and often refractory to conventional treatments. Current treatment standards include medications including opioids, until the pain is mitigated. Peripheral nerve blocks (PNBs) may be an effective therapeutic option for HASH. We conducted a small before-and-after study of PNBs to determine safety, feasibility, and efficacy in treatment of HASH. Methods: We conducted a pilot before-and-after observational study and collected data for 5 patients in a retrospective control group and 5 patients in a prospective intervention PNB group over a 12-month period. All patients received a standard treatment of medications including acetaminophen, magnesium, gabapentin, dexamethasone and anti-spasmodics or anti-emetics as needed. Patients in the intervention group received bilateral greater occipital, lesser occipital, and supraorbital PNBs in addition to medications. The primary outcome was pain severity, measured by Numeric pain rating scale (NPRS). All patients were followed for 1 week following enrollment. Results: The mean ages in the PNB group and control group were 58.6 and 57.4, respectively. One patient in the control group developed radiographic vasospasm. Three patients in both groups had radiographic hydrocephalus and IVH, requiring external ventricular drain (EVD) placement. The PNB group had an average reduction in mean raw pain score of 2.76 (4.68, 1.92 p = 0.024), and relative pain score by 0.26 (0.48, 0.22 p = 0.026), compared to the control group. The reduction occurred immediately after PNB administration. Conclusion: PNB can be a safe, feasible and effective treatment modality for HASH. Further investigations with a larger sample size are warranted.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2020

Measuring Thickness-Dependent Relative Light Yield and Detection Efficiency of Scintillator Screens

Digital camera-based neutron imaging systems consisting of a neutron scintillator screen optically coupled to a digital camera are the most common digital neutron imaging system used in the neutron imaging community and are available at any state-of-the-art imaging facility world-wide. Neutron scintillator screens are the integral component of these imaging system that directly interacts with the neutron beam and dictates the neutron capture efficiency and image quality limitations of the imaging system. This work describes a novel approach for testing neutron scintillators that provides a simple and efficient way to measure relative light yield and detection efficiency over a range of scintillator thicknesses using a single scintillator screen and only a few radiographs. Additionally, two methods for correlating the screen thickness to the measured data were implemented and compared. An example 6LiF:ZnS scintillator screen with nominal thicknesses ranging from 0–300 μm was used to demonstrate this approach. The multi-thickness screen and image and data processing methods are not exclusive to neutron scintillator screens but could be applied to X-ray imaging as well. This approach has the potential to benefit the entire radiographic imaging community by offering an efficient path forward for manufacturers to develop higher-performance scintillators and for imaging facilities and service providers to determine the optimal screen parameters for their particular beam and imaging system.

42 ENGINEERING↗