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At least 253 records · Page 14

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DOE OSTI2013

Model-independent particle accelerator tuning

We present a new model-independent dynamic feedback technique, rotation rate tuning, for automatically and simultaneously tuning coupled components of uncertain, complex systems. The main advantages of the method are: 1) It has the ability to handle unknown, time-varying systems, 2) It gives known bounds on parameter update rates, 3) We give an analytic proof of its convergence and its stability, and 4) It has a simple digital implementation through a control system such as the Experimental Physics and Industrial Control System (EPICS). Because this technique is model independent it may be useful as a real-time, in-hardware, feedback-based optimization scheme for uncertain and time-varying systems. In particular, it is robust enough to handle uncertainty due to coupling, thermal cycling, misalignments, and manufacturing imperfections. As a result, it may be used as a fine-tuning supplement for existing accelerator tuning/control schemes. We present multi-particle simulation results demonstrating the scheme’s ability to simultaneously adaptively adjust the set points of twenty two quadrupole magnets and two RF buncher cavities in the Los Alamos Neutron Science Center Linear Accelerator’s transport region, while the beam properties and RF phase shift are continuously varying. The tuning is based only on beam current readings, without knowledge of particle dynamics. We also present an outline of how to implement this general scheme in software for optimization, and in hardware for feedback-based control/tuning, for a wide range of systems.

42 ENGINEERING↗

DOE OSTI2025

Latent diffusion can map beam loss to two-dimensional phase-space projections

Beam loss monitors (BLMs) and beam current monitors (BCMs) are ubiquitous at particle accelerators around the world. These simple devices provide noninvasive high-level beam measurements but give no insight into the detailed 6D (𝑥,𝑦,𝑧,𝑝 𝑥 ,𝑝 𝑦 ,𝑝 𝑧 ) beam phase-space distributions or dynamics. We show that generative conditional latent diffusion models can learn intricate patterns to solve the extreme inverse problem of mapping waveforms of tens of BLMs or BCMs along an accelerator to detailed 2D projections of a charged particle beam’s 6D phase-space density. This transformational method can be used at any particle accelerator to transform simple noninvasive devices into detailed beam phase-space diagnostics. We demonstrate this concept via multiparticle simulations of the high-intensity beam in the kilometer-long Los Alamos Neutron Science Center linear proton accelerator.

43 PARTICLE ACCELERATORS↗

DOE OSTI2024

Experimental Safe Extremum Seeking for Accelerators

Here, we demonstrate the recent designs of safe extremum seeking (Safe ES) on the 1-km-long charged particle accelerator at the Los Alamos Neutron Science Center (LANSCE). Safe ES is a modification of extremum seeking (ES) which, in addition to minimizing an analytically unknown cost, also employs a safety filter based on an analytically unknown control barrier function (CBF) safety metric. Tuning is necessitated by accelerators being large complex systems, with many drifting parameters due to thermal effects and degradation. At the same time, safe operation (the maintenance of state constraints) is crucial, as damage brings astronomical costs, both financially and in operation downtime. Our measured (but analytically unknown) safety metric is the beam current. We perform multivariable Safe ES on three accelerator applications, in which we adapt 4, 6, and 3 magnet strength parameters, respectively. Two of the three applications are for validated simulation models of beamlines at LANSCE: the first for the proton radiography (pRad) beamline of 800-MeV protons for spot size tuning; the second on a high-performance code, HPSim, for tuning the low-energy beam transport (LEBT) region that contains a beam of 750-keV protons. The third is an experimental tuning of the steering magnets in the LEBT at LANSCE.

43 PARTICLE ACCELERATORS↗

DOE OSTI2014

Analysis of Radiation Effects in Silicon using Kinetic Monte Carlo Methods

The transient degradation of semiconductor device performance under irradiation has long been an issue of concern. Neutron irradiation can instigate the formation of quasi-stable defect structures, thereby introducing new energy levels into the bandgap that alter carrier lifetimes and give rise to such phenomena as gain degradation in bipolar junction transistors. Normally, the initial defect formation phase is followed by a recovery phase in which defect-defect or defect-dopant interactions modify the characteristics of the damaged structure. A kinetic Monte Carlo (KMC) code has been developed to model both thermal and carrier injection annealing of initial defect structures in semiconductor materials. The code is employed to investigate annealing in electron-irradiated, p-type silicon as well as the recovery of base current in silicon transistors bombarded with neutrons at the Los Alamos Neutron Science Center (LANSCE) “Blue Room” facility. Our results reveal that KMC calculations agree well with these experiments once adjustments are made, within the appropriate uncertainty bounds, to some of the sensitive defect parameters.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗

DOE OSTI2024

A compact furnace to support in situ neutron imaging of hydrogen dynamics in yttrium hydride moderators

A compact, nuclear microreactor that utilizes low-enriched uranium fuel is a promising solution to meet U.S. energy demands in nonconventional nuclear markets such as remote and decentralized energy grids. Yttrium hydride (YHx) is a potential moderator material for a microreactor design that reduces the amount of required fuel and provides superior retention of hydrogen at high reactor operating temperatures. Hydrogen diffusion properties in YHx are highly sought after for computer model validation and reactor prototyping. To characterize hydrogen diffusion, a compact dual-zone furnace was developed at Los Alamos National Laboratory and analyzed via neutron imaging at the Los Alamos Neutron Science Center (LANSCE). The goal of these measurements is to assess hydrogen diffusion in YHx samples as a function of applied temperature gradients. Included herein is recent progress in technique and furnace developments as well as initial results from concentration- and temperature-gradient measurements at LANSCE.

Torres, James↗

DOE OSTI2013

AOT & LANSCE Focus: Proton Radiography Facility

Invented at Los Alamos National Laboratory, proton radiography (pRad) at the Los Alamos Neutron Science Center (LANSCE) employs a high-energy proton beam to image the properties and behavior of materials under a variety of conditions. The penetrating power of high-energy protons, like that of x-rays, makes them an excellent probe of a wide range of materials under extreme pressures, strains, and strain rates. The invention of proton radiography is the direct result of the synergy between the Laboratory’s defense mission and basic science research scientists and supports the Laboratory’s national security science mission as well as provides for fundamental science discoveries. This new capability has revolutionized dynamic materials science at Los Alamos, providing a new window for the study of shock physics, materials damage, and high explosives science. The Proton Radiograpy Facility, a national user facility, has performed more than 500 dynamic experiments in support of the Weapons program, Global Security, and other customers since it was commissioned more than a decade ago. This information helps Los Alamos maintain the reliability of the U.S. nuclear stockpile. The pRad capability is primarily supported by the NNSA Science Campaigns.

36 MATERIALS SCIENCE↗

DOE OSTI2014

Total Cross Sections as a Surrogate for Neutron Capture: An Opportunity to Accurately Constrain (n,γ) Cross Sections for Nuclides Beyond the Reach of Direct Measurements

There are many (n,γ) cross sections of great interest to radiochemical diagnostics and to nuclear astrophysics which are beyond the reach of current measurement techniques, and likely to remain so for the foreseeable future. In contrast, total neutron cross sections currently are feasible for many of these nuclides and provide almost all the information needed to accurately calculate the (n,γ) cross sections via the nuclear statistical model (NSM). I demonstrate this for the case of 151 Sm; NSM calculations constrained using average resonance parameters obtained from total cross section measurements made in 1975, are in excellent agreement with recent 151 Sm (n,γ) measurements across a wide range of energy. Furthermore, I demonstrate through simulations that total cross section measurements can be made at the Manuel Lujan Jr. Neutron Scattering Center at the Los Alamos Neutron Science Center for samples as small as 10μg. Samples of this size should be attainable for many nuclides of interest. Finally, I estimate that over half of the radionuclides identified ~20 years ago as having (n,γ) cross sections of importance to s-process nucleosynthesis studies (24/43) and radiochemical diagnostics (11/19), almost none of which have been measured, can be constrained using this technique.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2014

New Opportunity for Improved Nuclear Forensics, Radiochemical Diagnostics, and Nuclear Astrophysics: Need for a Total-Cross-Section Apparatus at the LANSCE

Total-cross-section measurements are feasible on a much wider range of radioactive samples than (n,γ) cross-section measurements, and information extracted from the former can be used to set tight constraints on the latter. There are many (n,γ) cross sections of great interest to radiochemical diagnostics, nuclear forensics, and nuclear astrophysics which are beyond the reach of current direct measurement, that could be obtained in this way. Our simulations indicate that measurements can be made at the Manuel Lujan Jr. Neutron Scattering Center at the Los Alamos Neutron Science Center for samples as small as 10μg. There are at least 40 high-interest nuclides which should be measurable, including 88 Y, 167,168,170,171 Tm, 173,174 Lu, and 189,190,192 Ir.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2016

Comparison of CAP88 and MCNP for Overhead Gamma-emitting Plumes

The purpose of this paper is to use the Monte Carlo N-Particle Code (MCNP) to investigate the dose from gamma-emitting radionuclides such as Carbon-11 when a plume passes overhead. MCNP results are compared with results from the EPA program, CAP88. In some cases, typically near the source during stable conditions, the CAP88 results are less than the MCNP results. However, in the case of a receptor 800 m from a source at the Los Alamos Neutron Science Center (LANSCE), the CAP88 result is greater than the MCNP result.

61 RADIATION PROTECTION AND DOSIMETRY↗

DOE OSTI2016

Needs and Requirements for Future Research Reactors (ORNL Perspectives)

The High Flux Isotope Reactor (HFIR) is a vital national and international resource for neutron science research, production of radioisotopes, and materials irradiation. While HFIR is expected to continue operation for the foreseeable future, interest is growing in understanding future research reactors features, needs, and requirements. To clarify, discuss, and compile these needs from the perspective of Oak Ridge National Laboratory (ORNL) research and development (R&D) missions, a workshop, titled “Needs and Requirements for Future Research Reactors”, was held at ORNL on May 12, 2015. The workshop engaged ORNL staff that is directly involved in research using HFIR to collect valuable input on the reactor’s current and future missions. The workshop provided an interactive forum for a fruitful exchange of opinions, and included a mix of short presentations and open discussions. ORNL staff members made 15 technical presentations based on their experience and areas of expertise, and discussed those capabilities of the HFIR and future research reactors that are essential for their current and future R&D needs. The workshop was attended by approximately 60 participants from three ORNL directorates. The agenda is included in Appendix A. This document summarizes the feedback provided by workshop contributors and participants. It also includes information and insights addressing key points that originated from the dialogue started at the workshop. A general overview is provided on the design features and capabilities of high performance research reactors currently in use or under construction worldwide. Recent and ongoing design efforts in the US and internationally are briefly summarized, followed by conclusions and recommendations.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗

DOE OSTI2017

Future Muon Source Possibilities at the SNS

The workshop “Future Muon Source Possibilities at the SNS” was held September 1-2, 2016 at Oak Ridge National Laboratory. The workshop aimed to examine the technical feasibility and scientific need to construct a μSR and/or β-NMR facility at the SNS. During the course of the workshop it became evident that recently developed technology could enable the development of a world leading pulsed muon source at SNS, without impacting the neutron science missions of the SNS. The details are discussed below.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

In memoriam: David Holtkamp

David Holtkamp passed away June 16 after retiring from Neutron Science and Technology (P-23) earlier in the month. He was interviewed just prior to his retirement.

99 GENERAL AND MISCELLANEOUS↗

DOE OSTI2018

Physics Flash April 2018

Meet Physics Division's newest converted staff researchers: Young Jin Kim (Applied Modern Physics, P-21), Matt Freeman and Ralph Massarczyk (Neutron Science and Technology, P-23), and Xuan Li, Kun Liu, Levi Neukirch, and Zhaowen Tang (Subatomic Physics, P-25). These staff members conduct a range of applied and fundamental research—from making precision magnetic measurements to constructing sensitive detectors that may show how matter evolved and to exploring physics beyond the Standard Model.

99 GENERAL AND MISCELLANEOUS↗

DOE OSTI2019

Numerical investigation of the drag on a shock accelerated particle

In this report, we summarize the work that was done in collaboration with the Extreme Fluids (EF) team from the Neutron Science and Technology group (P-23). The EF team, led by Dr. Katherine Prestridge, have performed a series of experiments of dilute microparticles being accelerated by an incoming shock. Their measurements of the location of the particles after being hit by the shock suggest that the particles experience a much higher drag than predicted by classical drag models. We performed fully-resolved numerical simulations using an immersed boundary technique to replicate the post-shock conditions around the sphere. Our results were more compatible with the classical drag model than the experimental measurements. The source of this apparent drag increase is still unknown.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2019

LANSCE Pulse

For more than four decades, the United States has relied on the Los Alamos Neutron Science Center (LANSCE) accelerator to deliver high-energy, high-power proton beams in support of national security science. Today the LANSCE facility is a center for materials and nuclear research supporting National Nuclear Security Administration (NNSA) and Department of Energy (DOE) missions.

43 PARTICLE ACCELERATORS↗

DOE OSTI2019

LANSCE Diagnostic Robot Localization

Los Alamos Neutron Science Center (LANSCE) operates a linear particle accelerator (LINAC) that is used for a number of scientific research projects. Due to the presence of harmful radiation, researchers are not allowed in the beam tunnel during operation. Since the beam tunnel is inaccessible, an autonomous mobile robot is to be developed and deployed in the tunnel, monitoring the accelerator during operation. The robot will present real time data for operators and scientists from sensors such as a video camera, thermal camera, microphones, and muon detectors; allowing for beam diagnostics previously unavailable. Localization is a fundamental step in autonomous navigation of mobile robots, answering the “where am I” question. For this project, an Extended Kalman Filter (EKF) algorithm is implemented as a positional estimator. The EKF relies on an odometric motion model to predict the robot’s position and LIDAR measurement data to update the robot’s position. The measurement model is based on v features extracted from the LIDAR point cluster using the Split-and-Merge algorithm, and the nearest neighbor algorithm associates the features to an a priori feature map of the beam tunnel. The predicted and measured positions are then joined using a weighted value by means of the Kalman gain. The effectiveness of this localization technique is demonstrated using the LabVIEW robotics simulator.

42 ENGINEERING↗

DOE OSTI2019

MARSAME Radiological Release Report for Metal Items from TA 53- Set 15

EPC-ES has evaluated the survey results for metal items from the Los Alamos Neutron Science Center (LANSCE) and found that the metal items described in Table 1 of this report (identified by RP Tracking Numbers) meet the criteria for unrestricted release under DOE Order 458.1 Radiation Protection of the Public and the Environment and can be recycled. This conclusion is based on the known history of the metal items and on radiation survey data (see the completed RP-Form-031 LANSCE Metals Clearance Log for each item). None of the items in this report are located within radiological areas. Therefore, the items are considered unencumbered and are not subject to the moratorium suspension on metal recycling from Department of Energy facilities. Additionally, LANL has determined that there is no practical opportunity for internal DOE reuse or recycling of this metal.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2019

Understanding the U 3 Si 2 crystal structure evolution as a function of temperature by neutron diffraction and simulation

U 3 Si 2 is actively researched as an accident tolerant fuel. Detailed knowledge of the crystal structure evolution, including knowledge of the anisotropic tetragonal lattice parameters, as a function of temperature and chemical composition is of paramount importance for predictions ranging from thermo-mechanical stresses to phase transformations to crystal lattice sites of fission products. Knowledge of the stability range of U 3 Si 2 is of great importance to understand whether changes of the stoichiometry, either from burn-up or due to synthesis variations, will lead to undesirable phase decomposition. To investigate these topics, stoichiometric U3Si2.00 and hyper-stoichiometric U 3 Si 2.01 were synthesized and characterized at ambient conditions and up to 1150°C using time-of-flight neutron diffraction on the HIPPO instrument at the Los Alamos Neutron Science Center (LANSCE) at LANL.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗