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The Fall 2020 edition of Physics Flash includes article briefs on: Patrick Younk, Fusing concepts, technology to past performance of nuclear explosives; LANL inertial confinement fusion programs aims to develop burning plasma for weapons science; Lab's high energy nuclear physics explored at international conference; and, Novel study reveals new details on the impact of thermal interfaces in dynamic compression experiments.
Multiphase reacting flow approach has been adopted for modeling of hotspot formation and growth on sub-zonal scale. Mechanical response of the high explosive (HE) is modeled by the Visco-Plastic SCRAM model which includes plastic work, crack growth, and frictional heating along the cracks. In this work a sub-zonal regions with high temperature, hotspots, are modeled as a new phase. Formation and growth of the hotspot phase from the cold phase is modeled as a phase change. Each phase has its own temperature and pressure. Chemical reactions also progress in both phases. The growth of hotspots are determined by the solution of the heat conduction equation with appropriate heat sources due to friction and plastic heating. Sample calculations using the BABBO code show successful detonation calculations with hotspot formation and growth.
In February 2020, experiments were conducted at Los Alamos National Laboratory measuring the propagation of a sweeping wave through a plate of boron carbide which was induced by detonating an adjacent charge of high explosive. Six such shots were red and in each case progress of the wave along the exposed surface of the plate was tracked using photon doppler velocimetry (PDV). In this report we discuss calculations performed using the Lagrangian hydrocode FLAG to model data taken from these experiments. We discuss the models chosen for the different experimental components, the choice of mesh (focusing on, both, two- and three-dimensional geometries), and compare the results from these calculations to experimentally-extracted PDV traces. Notably, we find that the PDV traces for this experiment are most faithfully reproduced using the full three-dimensional geometry, even when the mesh resolution for the three-dimensional calculations was significantly lower than the resolution for the corresponding two-dimensional calculations. We attribute this to the geometry of the experimental setup. Moreover, we find only negligible differences for the PDV traces obtained using the sesame table equation of state for boron carbide and the Gruneisen equation of state.
New methods for predicting the amplitude and variability of ground shaking from earthquakes (and explosions) are needed for seismic hazard analysis for buildings, nuclear power plants, and critical infrastructure at the NNSS. We are comparing existing 1-D and new 3-D geophysical methods for estimating the shear-wave velocity structure in the upper 30 meters of the ground surface (Vs30), which plays a major role in ground motion amplification and seismic response of buildings. We evaluate the performance of these methodologies at the U1a Complex at the NNSS and develop simple 1-D and high-resolution 3-D Vs30 models. We then emplace these high-resolution models into a background seismic velocity model. We will collaborate with Lawrence Livermore National Laboratory (LLNL) to conduct numerical modeling of the ground shaking at the NNSS using their high-performance computing technology and state-of-the-art ground motion simulation methodology. The primary work that was completed in FY 2019 was to acquire the seismic systems and familiarize staff at the NNSS with their use. We also worked on developing a collection plan with the Device Assembly Facility (DAF) at the NNSS, but due to time constraints and other ongoing projects at the DAF, we had to use U1a as a backup. We were able to coordinate the seismic survey, and we will complete the collection of seismic data in FY 2020. Additionally, during FY 2019, we completed the geologic framework model (GFM) for the U1a Complex and modeled the Yucca fault. LLNL worked with us through FY 2019 to prepare the data files for their modeling software and tested the software for reliability. In FY 2020 we will develop the end-to-end capability so that any facility could easily be modeled and the expected shaking from a local earthquake understood. The work in FY 2020 will include building fault models from the GFM and finalizing the velocity model analysis. The final simulations will be run for multiple rupture models, and final assessments will demonstrate the seismic hazard at the U1a Complex.
Nuclear power plants must be, by design and construction, robust structures and difficult to penetrate. Ideally, for security, the reactors would be sited underground, beneath a massive solid block, too thick to be penetrated by tools or explosives with all communications and power transfer lines also underground and fortified. Limiting access with difficult-to-penetrate physical barriers is going to be key for determining response and staffing requirements.
In 2015, the Lawrence Livermore National Laboratory started development of next-generation multiphysics simulation capabilities for the National Nuclear Security Administration under the Advanced Technologies Development and Mitigation (ATDM) element of the Advanced Simulation and Computing program in collaboration with the Exascale Computing Project (ECP). A key driver for this effort across the NNSA tri-lab was the emergence of advanced high performance computing (HPC) architectures based on heterogeneous compute capabilities, including GPU based systems, as part of the national drive toward exascale computing platforms at multiple Department of Energy (DOE) facilities. Developing a multiphysics code capable of meeting the various simulation needs of the NNSA as defined by the current generation of integrated codes (or ICs), initially developed as part of the Accelerated Strategic Computing Initiative (ASCI) program beginning in 1996, and able to scale to the current 100 petaflop class pre-exascale systems, as well the forthcoming exaflop class computers, is a daunting challenge. To accomplish this ambitious goal, LLNL has embraced two key themes: use of high-order numerical methods and a modular approach to code development. The LLNL next generation effort is organized under the Multi-Physics on Advanced Platforms Project (MAPP). A foundational component of MAPP is the Axom computer science (CS) toolkit which provides infrastructure for the development of modular, performance portable, multi-physics application codes. MARBL is a next-generation application code built on the Axom base to address the modeling needs of the high energy density physics (HEDP) community for simulating high-explosive, magnetic or laser driven experiments such as inertial confinement fusion (ICF), pulsed-power magneto-hydrodynamics (MHD), equation of state (EOS) and material strength studies as part of the NNSA’s stockpile stewardship program (SSP).
The MLLW Flanged Tritium Waste Container (FTWC) Project has been operational since 2007 when, during an audit of the FTWC waste stream, it was determined that four FTWC containers contained lead in amounts greater than LDR treatment standards. From June to August of 2007, four FTWC containers were shipped to TA-54 for disposal as LLW from WETF. The contents of the FTWCs were characterized as high activity LLW and were thought to be in compliance with LANL's Waste Acceptance Criteria (WAC). During the packaging of these FTWC's, 36 intact squib valves (aka actuators), containing detonated squibs were included with the waste stream After being transported to TA-54 Area G, it was determined that the explosive used in some of the squibs was Normal Lead Styphnate (NLS). A recharacterization of the entire contents in the FTWC's was performed with the conclusion that the squib valves exhibited the RCRA toxic characteristic for Lead (D008), thus resulting in the contents of the FTWCs being reclassified as a Mixed LLW.
After decades of R&D, quantum computers comprising more than 2 qubits are appearing. If this progress is to continue, the research community requires a capability for precise characterization (“tomography”) of these enlarged devices, which will enable benchmarking, improvement, and finally certification as mission-ready. As world leaders in characterization -- our gate set tomography (GST) method is the current state of the art – the project team is keenly aware that every existing protocol is either (1) catastrophically inefficient for more than 2 qubits, or (2) not rich enough to predict device behavior. GST scales poorly, while the popular randomized benchmarking technique only measures a single aggregated error probability. This project explored a new insight: that the combinatorial explosion plaguing standard GST could be avoided by using an ansatz of few-qubit interactions to build a complete, efficient model for multi-qubit errors. We developed this approach, prototyped it, and tested it on a cutting-edge quantum processor developed by Rigetti Quantum Computing (RQC), a US-based startup. We implemented our new models within Sandia’s PyGSTi open-source code, and tested them experimentally on the RQC device by probing crosstalk. We found two major results: first, our schema worked and is viable for further development; second, while the Rigetti device is indeed a “real” 8-qubit quantum processor, its behavior fluctuated significantly over time while we were experimenting with it and this drift made it difficult to fit our models of crosstalk to the data.
PAGOSA is a computational fluid dynamics program developed at LANL for the study of high-speed compressible flow and high-rate material deformation. PAGOSA is a three-dimensional Eulerian finite-difference code, solving problems with a wide variety of EOS, material strength, and explosive modeling options. This document presents the finite difference equations that are used in the PAGOSA continuum mechanics computer code. This program is especially intended to be used for the numerical simulation of the interactions of gases, fluids, and solids.
The design and construction of a nuclear power plant must include robust structures and a security boundary that is difficult to penetrate. For security considerations, the reactors would ideally be sited underground, beneath a massive solid block, which would be too thick to be penetrated by tools or explosives. Additionally, all communications and power transfer lines would also be located underground and would be fortified against any possible design basis threats. Limiting access with difficult-to-penetrate physical barriers is a key aspect for determining response and staffing requirements. Considerations considered in a graded approach to physical protection are described.
The CTH multiphysics hydrocode, which is used for a wide range of important calculations, has undertaken in recent years to overhaul its software quality and testing processes. A key part of this effort entailed building a new, robust V&V test suite made up of traditional hydrocode verification problems, such as those listed in the ASC Tri-Lab Test Suite and the Enhanced Tri-Lab Test Suite, as well as validation problems for some of CTHs most frequently used equations of state, materials models, and other key capabilities. Substantial progress towards this goal was made in FY19. In FY20, this test suite has been expanded to include verification and validation tests of the Sesame and JWL equation of state models as well as the Mader verification problem from the Tri-Lab Test Suite and the Blake verification problem - a linear elastic analog to the Hunter problem from the Enhanced Tri-Lab Test Suite. This report documents CTH performance on the new test suite problems. Verification test results are compared to analytic solutions and, for most tests, convergence results are presented. Validation test results are compared to experimental data and mesh refinement studies are included. CTH performs well overall on the new test problems. Convergence rates for the Blake and Mader problems are comparable to those for similar ASC codes. The JWL and Sesame verification tests show good agreement with analytic solutions. Likewise, CTH simulation results show good agreement with experimental validation data for the Sesame and JWL equations of state for the materials tested. Future V&V work will focus on adding tests for other key capabilities like fracture and high explosive models.
We have performed a computational study of TATB. The study is composed of two parts, one where we perform static T = 0 K calculations with several different DFT functionals, to investigate structural properties and obtain a cold curve. Even though the functionals used in this study give poor results at ambient pressure, they perform much better at compression, when the dominance of the van der Waals’ forces in the binding is replaced by more normal interactions. In particular AM05 gives good results, mainly because it doesn’t include any “faulty” van der Waals’. Indeed the van der Waals’ corrected functional (PBE+D2) results shows the worst performance on structural properties. For the cold curve the PBE+D2 functional gives the best results compared to experiments (room temperature) but since the structural properties were bad with this functional we cannot for sure say that this is in any way a validation. It is shown that scaling the AM05 results with a common factor reproduces the experimental data. We leave the question on why to a follow up study but speculate that maybe the experiment and our calculations do not represent the same system set-up. From the structural properties we identify a site in the TATB lattice that contains a high concentration of oxygen and hydrogen. The consequences of this finding, if any, are left to a future project. In the second part of the study we perform extensive high-quality DFT-MD (molecular dynamics with DFT forces) calculations to obtain points on the Hugoniot. This part of the study did not get finished within this project and a more extensive summary of this part will be given in a follow up report at a future date. However, we show that obtaining calculated data is essential for equations of state development since the existing experimental Hugoniot data barely deviates from room temperature isotherm data and thus give no information of the high temperature dependency of materials properties. Our conclusion so far in the project is that being able to calculate materials properties is essential for high explosives since experiments are unable to give information in the high temperature part of phase space. While blind use of DFT cannot (yet) give unambiguous answers, we can still explore qualitatively and use such information to guide us in EOS development. However, the main conclusion is that we need better functionals in DFT to easily extract needed properties from calculations.
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.
The goal of this project is to quantify the effect of adsorption on noble gas transport though rocks that contain zeolite compared with rocks that don't. Success is defined by developing a coefficient called Retardation that describes the separation effect of zeolites. This coefficient can then be used by gas transport modelers to predict field-scale observations of noble gases released underground in a chemical explosion
Motivated by the need to simulate the effects of underwater explosion on ship structures, we develop a new cavitating acoustics formulation. The proposed approach is consistent with existing methods where the cavitation phenomenon is captured with a bilinear constitutive law. However, the new formulation is in terms of velocity potential, as opposed to the existing displacement-potential and pressure formulations. Also unique to the proposed formulation is a new generalized time-stepping procedure specific to cavitating acoustics, which has the ability to introduce numerical damping to control frothing. Numerical examples of varying complexity are presented to illustrate the effectiveness of the proposed approach and the ability to use velocity potential as a primary field variable for cavitating acoustics simulations.
Two decades after the U.S. Senate declined in 1999 to give its consent to ratification of the Comprehensive Nuclear Test Ban Treaty (CTBT), the treaty remains in legal and political limbo. Legally, the treaty cannot enter into force without U.S. ratification. However, the Senate’s rejection does not strip the treaty of its force as an element of customary international law or alter the will of other signatories to see it enter into force. Politically, the debate over the virtues and flaws of the treaty remains as strong as ever, with some CTBT advocates pushing energetically for U.S. re-review while some opponents seek ways to “un-sign” the treaty. Meanwhile, despite the Senate’s rejection of the treaty, the United States acts in a manner consistent with its main obligations by maintaining a moratorium on explosive nuclear testing and providing financial support (as well as technical expertise) to the CTBT Organization (CTBTO)—in particular the CTBTO’s International Monitoring System (IMS). The CTBT may well remain in such limbo for a long time to come, unless some catalytic event comes along to re-shape national perceptions and priorities, one way or the other. The treaty’s future, whatever it might be, will be determined in part by how much perspectives might have changed in light of interim developments. Our purpose is to shed light on some of those developments and to assess their relevance. The 1999 ratification debate addressed a large number of issues. Rejection was driven by various policy and technical judgments. The purpose of this paper is to re-examine those technical judgments in light of what has been learned over the following two decades. On some technical matters, there was explicit recognition of extant uncertainties, as well as a conviction and hope that time would dispel them. To be doubly clear, our purpose is not to recommend a way forward on CTBT ratification. The policy judgments of 1999 and 2020 are beyond the scope of this paper. This technical re-examination proceeds as follows. It begins with a short background section to introduce the key technical matters in discussion in the U.S. ratification process. Then it moves systematically through each of those topics with a review of relevant background information, a discussion of key points in debate, an analysis of subsequent experience, and a current assessment. The historical analysis draws on many sources including the primary documents of the Congressional debate, the official article-by-article interpretation by the Department of State, and the statements of key players in the process. We also relied on key technical reports and publications by subject matter experts that have addressed in more detail many of the issues in our focus. These sources include the 2002 and 2012 reports of the National Academy of Sciences as well as publications by senior technical staff of Lawrence Livermore National Laboratory (LLNL) who were actively involved in the ratification debate, including then-Laboratory Director Bruce Tarter. We also conducted several interviews with government officials from the 1990s, past laboratory directors, and other members of the scientific community. But, except where individuals are specifically cited by name, the judgments offered here are our own and should not be attributed to any other individual or to LLNL as such.
The new Scorpius linear induction electron accelerator is under development for multi-pulse flash radiography of large, explosively-driven hydrodynamic experiments. Beam physics from the cathode to the target was examined with computer simulations, including envelope, ray-trace, and particle-in cell (PIC) codes. Beam instabilities investigated included beam breakup (BBU), image displacement, diocotron, parametric envelope, ion hose, and the resistive wall instability. Beam corkscrew motion and emittance growth from beam mismatch were also studied. The results of these simulations is documented in a series of reports. In this report the computer codes and physical models used for these simulations are described. The conclusion of this study is that Scorpius will produce and accelerate a beam with radiographic quality equivalent to the present accelerators at Los Alamos National Laboratory if the same engineering standards and construction details are upheld.
This report documents the development, implementation, and parameter estimation procedures for aviscoelastic-viscoplastic-viscodamage model. This model is being developed to improve the predictive accuracy of simulations involving plastic bonded explosives (PBX). A representative PBX is PBX9501, which is 95% by weight HMX, 2.5% estane binder and 2.5% nitroplasticizer. Mechanical deformation of this material is primarily accommodated by straining of the polymer binder and rearranging the relatively rigid HMX crystals.