DOE/NA-0070

Office of Research, Development, Test, and Evaluation Stockpile Stewardship Quarterly

VOLUME 8 | NUMBER 1 | MARCH 2018

essage from the Assistant Deputy Administrator for Research, M Development, Test, and Evaluation, Dr. Kathleen Alexander This issue of the Stockpile Stewardship explosives in weapon geometries and Quarterly focuses on the intersection data on the performance differences between computer modeling and between surrogate metals and plutonium in experiments. experiments that provide the phenomenologicalthe design and conduct basis of for scientific computer Another article discusses a complementary models. We kick off this issue with an approach that uses laser or pulsed-power article that discusses the relationship facilities to achieve a high energy density between verifying and validating the (HED) state of matter. The majority of modern nuclear weapons codes and weapon processes occur in the HED the hierarchy of experiments that must state, and so understanding the physics be performed to provide the necessary that occurs in this state is essential to data. With the cessation of nuclear modeling weapon systems. These HED testing, computer modeling has become The research on display during the Poster experiments are sized in the centimeter- key to assessing the safety, security, Session of this year’s Stewardship Science to-micrometer range yet still are able to and performance of weapon systems Academic Programs Annual Review examine integrated weapons phenomena. whose designs have evolved from tested Symposium, held in Bethesda, Maryland on February 21-22, 2018, generated much We close this issue with a nod to the next- excitement. Above right and inset, Sarah generation scientists and engineers. We Hickam, University of Notre Dame, discusses interactingconfigurations. physics This phenomena. requires higher The level her research with Dr. Alexander. Read about the share a review of and honor the awardees fidelity codes that incorporate multiple, symposium and winning posters on page 10. from the 2018 Stewardship Science data to verify these codes ranges from Academic Programs Annual Review Symposium that drew a record number of small-scaleof experimentation experiments required designed to provide to for upcoming life extension programs, attendees, and we highlight an academic assess a single physics problem to fully as well as future assessments and integrated experiments that evaluate the opportunity at the University of Michigan interaction of the physics involved in a full weapon system. certifications.This issue also features an article on the Incredible work is happening in the latest subcritical experimental series, in the HED field. nuclear security enterprise, and this work Subcritical experiments are performed Gemini, Leda, and Lyra. These series is vital to the security of our Nation. to gather data of complex, interacting were designed to provide data on the weapons physics. The Enhanced physics response of using insensitive Capabilities for Subcritical Experiments high explosives versus conventional project portfolio is working to achieve the design and creation of a next- Inside generation suite of diagnostics that will allow for data to be gathered on 2 Integrated High Energy Density Experiments Yield Critical Data for the ASC Program the relevant physics involved in the 4 Continuous Evolution of the Stockpile Stewardship Program: Enhanced Capabilities for late-stage implosion of plutonium in Subcritical Experiments weapons-relevant geometries. This 6 Vega & the Lyra Series data will feed the complex computer 8 Integrated Experiments in the Stockpile Stewardship Program simulations to inform design options 9 Highlight: 2018 High Energy Density Summer School 10 2018 SSAP Annual Review Symposium and Poster Winners Comments The Stockpile Stewardship Quarterly is produced by the National Nuclear Security Administration (NNSA) Office of Research, Development, Test, and Evaluation. Questions and comments regarding this publication should be directed to Terri Stone at [email protected]. Technical Editor: Dr. Joseph Kindel | Publication Editor: Millicent Mischo 2 Integrated High Energy Density Experiments Yield Critical Data for the Advanced Simulation and Computing Program by Bradley Beck (Los Alamos National Laboratory), David Etim (National Nuclear Security Administration), Curt Nilsen (Sandia National Laboratories), Joe Sefcik (Lawrence LIvermore National Laboratory), and Arthur Brown (Sandia National Laboratories)

During the era of nuclear testing, At the most complete and complex legacy computational codes were used end of the hierarchical approach is the to design the United States nuclear integrated system tests. Examples include weapons stockpile. Throughout experiments conducted at the following development of each and every weapon, nuclear weapon tests played the Nevada National Security Site (NNSS); a critical role in calibrating the models thelocations Dual-Axis (see RadiographicFigure 2): U1a Hydrodynamic Complex at and in assessing actual performance. Test Facility (DARHT) at Los Alamos Since the cessation of nuclear testing National Laboratory; the Contained Firing in 1992, improved codes with higher Facility (CFF) at Lawrence Livermore National Laboratory; and the Thunder Range Facility at Sandia National assessfidelity safety, physics security, models and were performance required Laboratories. Experiments conducted ofto theprovide current confidence and future in the stockpile. ability to at these facilities enable an integrated system assessment and more completely To accomplish the science-based test the multi-physics computational Stockpile Stewardship Program (SSP) the full problem physics. codes in these challenging environments. Figure 1. Hierarchical approach to V&V spans As the NNSA weapons laboratories Simulation and Computing (ASC) program continue to work towards delivering mission requires that the Advanced develop simulation codes that accurately In the development of the ASC nuclear fully validated codes, the historical predict and assess the full physics weapon simulation codes, the appropriate nuclear testing archive and historical and engineering environments these physics must be assessed through integrated experiments are assessed and weapons encounter or may encounter. incorporated into the analysis; these tests These modern computational codes must are critical to validation efforts as they are simulate the complexities of nuclear numericaldetermination models of the and proper then incorporated equations. the experimental means that explore the physics, weapons component responses, intoThese the equations codes. After are implementation,approximated into the full nuclear weapon detonation physics. the weapons systems as a whole, and laboratories verify that the numerical determine the impact of design changes models are accurately reproducing the Integrated Hydrotest Experiments and aging on the nuclear weapons stockpile. Additionally, these modern Integrated hydrotests experiments codes serve as a means to evaluate intended equations (Code Verification)1 provide critical data for the SSP. These the full range of a nuclear weapon’s and confirm that the codes are solving the experiments enable scientists to detonate operation. For these purposes, the correct equations (Code Validation). modern nuclear weapon computational program employs a hierarchical approach nuclear weapon, but with surrogate codes must couple numerous physics (seeThe ASCFigure Verification 1) in order & toValidation span the (V&V) materials.a “mock-up” Instead of the ofprimary using plutonium, stage of a models together accurately. Integration of numerous physics models makes these physics experiments (e.g., modeling of material to simulate the desired tools fundamentally different from other Highentire Explosive required detonation)physics regimes. provide Single- the characteristics.scientists use a non-fissile surrogate focus only on single physics models or on to validate individual physics models. integrationscientific computation of a few physics codes models. that normally Dueprogram to the with numerous required individual information physics used record arrival time of an explosively drivenBoth the surface CFF and through DARHT use field of pin diagnostics domes Development of these codes and numerous experimental campaigns. Multi- determining the accuracy of their physicsmodels required,tests (e.g., this radiation necessitates hydrodynamic probes (see Figure 3). The pin dome capabilities is further complicated due experiments) enable a small number recordsand photon when Doppler a surface velocimetry interacts with(PDV) the to the realization that the full physics of physics models be combined for an encountered by a nuclear weapon assessment. Subcomponent physics velocity record of the surface using laser are unlike normal operating physics tests increase the number of interacting velocimetry.pin while the High-energy PDV probe records radiographs a time regimes on Earth. Critically important physics models assessed, and increase the of the experiment are also captured is an examination that these codes are with high-speed cameras to allow for accurately representing the necessary and (e.g., pRad experiments, inertial increased exploration of the implosion correct physical models. complexity of the required experiments dynamics. This combination of diagnostics

confinement fusion experiments). 1

Code verification is “the process of determining that the numerical algorithms are correctly implemented in the computer code and or identifying errors in the software.” Code validation is “the process of determining the degree to which a model is an accurate representation of the real world from the perspective of the intended uses of the model.” ASME 2006, “Performance Test Code Committee 60: Verification and Validation in Computational Solid Mechanics,” Guide for Verification and Validation in Computational Solid Mechanics, American Society for Mechanical Engineers, New York, Standard No. ASME V&V 10-2006. Volume 8 | Number 1 | March 2018 Stockpile Stewardship Quarterly 3

Plutonium and in a situation where the experimentexperiments, is but prevented in a configuration from going with critical. These experiments provide critical data that is then used by the ASC codes to determine an accurate assessment of their capabilities. Whereas critical data is provided by the current subcritical experiments, the Enhanced Capabilities for Subcritical Experiments project (ECSE) is planning for improved capabilities and diagnostics that will increase the experimental data available for the SSP and for future assessments.

Engineering Challenges Due to the diversity of engineering challenges that a nuclear weapon may encounter, a variety of types of integrated

Examples of these tests at Sandia National Laboratoriesengineering system include tests nuclear are required.safety tests 2 Figure 2. Key integrated experimental facilities, such at the Burn Facility, centrifuge/vibrafuge as DARHT (top left), U1a (top right), CFF (bottom left), experiments at the Large Centrifuge and Thunder Range (bottom right) enable integrated Facility, and explosive testing at the experiments that provide the SSP with critical data used Thunder Range to study the effects of to validate the multi-physics computational codes. hostile atmospheric blast. Thunderpipe tests were performed recently at Thunder Range to support the Navy and Air Force programs (see Figure 2). The data generated are used to validate modeling predictions from ASC tools for the shock loading and weapon response. Together, experimental data and simulation predictions support current and future

weaponConclusion qualification efforts. To accomplish the mission of sustaining a safe, secure and effective nuclear

Figure 3. Methods for measuring implosion dynamics; left image is a pin dome where each individual

that measures the velocimetry of a surface by measuring the Doppler shift of optical illumination. anddeterrent validated requires models that of the an SSPincreased has pin records a time of impact; right image is a multiplexed photon Doppler velocimetry (MPDV) probe modern computational tools with verified deliver these capabilities are integrated provides a critical capability to obtain assessment of how well these materials experimentsphysics fidelity. that Critical explore to thebeing full able physics to comprehensive data on the implosion represent the actual materials. Critically phases of integrated weapon experiments. important is understanding the material These integrated experiments provide Critical to the assessment of these dynamics similarities and differences. criticalrequired data as completelyto the NNSA as programs possible. and experiments, the laboratories perform a Subcritical experiments conducted in the enable critical assessments of the nuclear pre-shot prediction of the experimental U1a Complex of the NNSS provide critical weapon computational simulation codes. results and a post-shot analysis. data by studying plutonium in relevant Facilities such as DARHT, CFF, U1a, and Thunder Range enable these experiments Integrated Subcritical Experiments Whereas hydrotest experiments provide configurations. future assessments. ● critical data for the ASC program and SSP, recently conducted provide similar and increase confidence for current and diagnosticsExperiments to like the the current Vega hydrotestexperiment the use of surrogate materials requires an 2

Vibrafuge is a combined examination of vibration testing on a centrifuge. Office of Research, Development, Test, and Evaluation Volume 8 | Number 1 | March 2018 4

Continuous Evolution of the Stockpile Stewardship Program: Enhanced Capabilities for Subcritical Experiments by Kirk Keilholtz (National Nuclear Security Administration)

The United States conducted 1,054 In addition to the aging of critical nuclear tests before entering the current components, NNSA must regularly (a) moratorium in 1992. The archived data replace or refurbish many other weapon from these tests is the backbone of our components. Many of the materials and Stockpile Stewardship Program (SSP) processes that were used in the original to continue the annual assessment and production are no longer available. Changes to our original designs, materials, of our nuclear stockpile without full- scalecertification nuclear of testing. the safety The andSSP reliabilityrelies on an extensive program of surveillance, small-scaleand processes and require large-scale qualification integrated and examining the current and aging stockpile, experiments.certification that, Necessarily, in turn, requireeach change new coupled with advanced computational that we make moves us incrementally models which are, in turn, validated away from the designs and processes that against both new and archived small- were successfully tested and archived and large-scale integrated experimental in our nuclear testing database. Barring data. As computing power, and the a return to nuclear testing, the SSP is sophistication of the physics-based responsible for ensuring our nuclear (b) simulation models, has increased over the weapons continue to work as designed. years, our understanding of fundamental Every year, the three directors at the operations of weapon systems and NNSA national laboratories—Los Alamos especially the behavior of weapon National Laboratory (LANL), Lawrence materials has also evolved, leading to Livermore National Laboratory (LLNL), and Sandia National Laboratories NNSA addresses these gaps through the (Sandia)—assess for the President developmentthe identification of new of knowledge theoretical gaps. and whether the stockpile is safe, secure, analytic models, implemented in advanced reliable, and effective. Each year, this has been the case. diagnostics and drivers needed to produce thesimulation experimental techniques, data to and validate through the the We have developed important (c) simulations. This methodology, applied experimental platforms such as the for over 25 years of stockpile stewardship, National Ignition Facility (see Figure 1a), has allowed NNSA to develop a deep Z Pulsed Power Facility (see Figure 1b), understanding of nuclear weapon science Omega Laser Facility, Joint Actinide and engineering—both reinforcing our Shock Physics Experimental Research existing hypotheses and allowing us to (JASPER) facility, Advanced Photon form new ones. Source, THOR, Los Alamos Neutron Science Center, Cygnus, and others that One area that NNSA is currently exploring in detail is the aging of our nuclear the extreme conditions encountered in theprobe operation specific ofmaterial a nuclear properties weapon under(see in the special nuclear materials. Our Stockpile Stewardship Quarterly Figure 1. Some of NNSA's experimental weaponsweapon systems are composed and, specifically, of a variety changes December Other facilities explore of materials and understanding their the interaction of materials in nuclear V7 N4, optics, (b) Z Pulsed Power Facility, and (c) interaction during weapon operation is weapon geometries2017). such as the Dual Axis DARHT.platforms: (a) the National Ignition Facility extremely important to assess the safety Hydrodynamic Test Facility (DARHT) (see and reliability of the stockpile. Through Figure 1c) at LANL and the Flash X-Ray- Contained Firing Facility (FXR-CFF) at Experiments (SCE) at the Nevada Nuclear weapons program, that understanding LLNL. However, these facilities do not Security Site (NNSS). SCE provide wasmost developed, of the first and 50 years then demonstrated,of the nuclear have the capability to perform dynamic essential information for stockpile through nuclear testing. Throughout the implosion experiments with plutonium, life of the program, our scientists and the special nuclear material at the heart of many weapons. understandinglife extension programs, of how the significant stockpile weapon system will behave with the same evolves.finding investigations, SCE address one and of advance the critical the characteristicsengineers have afteralways 30 questioned years, and withoutif a To explore the dynamic behavior of high- knowledge gaps in the properties of underground tests, those scientists and explosively-driven plutonium in weapon- plutonium by measuring its behavior engineers have had to look elsewhere to like geometries and near weapon-like conditions, the NNSA conducts Subcritical implosion. To make those measurements, during the final stages of a primary answer this critical question. Volume 8 | Number 1 | March 2018 Stockpile Stewardship Quarterly 5

Figure 3. Daisy Acosta-Lech performing design

pulser. verification testing on the five stage solid state

Figure 2. Shown is an illustration of the Scorpius Infrastructure at the NNSS. The main accelerator hall

(“drift”) will be just over 400 feet long. high precision penetrating radiography beam into, and through, the accelerator. (such as that used with surrogate The accelerator subsystem consists of a materials at DARHT and FXR-CFF) and series of many 10s of similar accelerator a diagnostic under development known cells each of which applies a pulsed as the Neutron Diagnosed Subcritical Experiments (NDSE) are the essential beam. The energy added at each cell is tools. aelectric small fractionfield adding of the energy total energyto the electron and Figure 4. Two-Pulse Test Cell from LANL is typically limited by the engineering NNSA’s activities in support of these undergoing multi-pulse testing on Centipede at Sandia. essential tools is called the Enhanced and pulsed power system powering Capabilities for Subcritical Experiments requirements of the accelerator cell (ECSE) portfolio, which includes the to in a Memorandum of Agreement project to deploy a new radiographic throughthe cell. Afterthe accelerator the beam hascells, acquired it enters signed by the three laboratory directors system (Scorpius) under the Advanced the downstreamrequired energy transport while transiting subsystem of their respective LLCs and supported Sources and Detectors (ASD) component that transports and focuses the beam by industrial partners such as L-3 of the portfolio; the U1a Complex onto a Bremsstrahlung x-ray converter Technologies and several component and Enhancements Project Line Item that will where the x-rays that will penetrate the subsystem development contractors, and construct the underground laboratory; experimental test object are created. the Naval Research Laboratory. With this and, the NDSE diagnostic currently under Beyond the experimental test object, many organizations involved, the project development. the detector subsystem uses advanced team must continuously emphasize Scorpius is a DARHT-class, multi-pulse, scintillators to convert the x-rays to visible single axis, linear induction accelerator light, captures and stores the images on communication. a very high-speed digital camera, and the need for frequent and engaging (LIA)-based radiographic system. With ECSE coming online in the mid In addition to the four components of 2020s, our weapon scientists and Project is responsible for the technology engineers will have diagnostic tools The ECSE Radiography & Integration therecords radiographic the data forsystem, subsequent operation analysis. of maturation, design, fabrication, at their disposal to answer important installation, and commissioning of Scorpius at the NNSS. Scorpius requires detailed attention to nuclear weapons stockpile as well as to The Scorpius LIA-based radiographic tooling,the “Global” and safetyengineering systems) support common systems questions about the Nation’s current to(control, all parts power, of the fluid accelerator and gas, and mechanical, the injector, accelerator, downstream interface with the U1a Complex to support thatprovide are flexibilitynecessary in for the our form life ofextension materials transport,system consists and detector of four major(see Figure subsystems: installation, commissioning, accelerator programs.and advanced ● manufacturing techniques 2). The injector subsystem generates a high current electron beam using a pulsed, high-voltage vacuum diode. The readiness certification, and the transition high current of the beam means that toThe operations project, led for by the LANL, final isScorpius composed system. space charge effects dominate the beam of partners at LLNL, Sandia, and NNSS transport so that externally applied (see Figures 3 and 4). The team works under a governance structure agreed magnetic fields are used to guide the Office of Research, Development, Test, and Evaluation Volume 8 | Number 1 | March 2018 6

Vega & the Lyra Series by Garry R. Maskaly (Los Alamos National Laboratory)

The Vega Experiment Leda (8/14) 3667 (7/15) CHE IHE served as the capstone to the Lyra series, Surrogate A Surrogate A wasVega, executed the plutonium in the U1aexperiment Complex that at the Nevada Nuclear Security Site (NNSS) on H4080 (12/11) Castor (8/12) Orpheus (9/16) Eurydice (3/17) challenges, including the need for an CHE CHE IHE IHE enhancedDecember authorization 13, 2017. After basis facing and many to Surrogate B Surrogate B Surrogate B Surrogate C

Pollux (12/12) Vega (12/17) sincereauthorize Pollux workwas executed at TA-55, in Vega December became CHE IHE 2012.the first subcritical experiment (SCE) fired SNM SNM In Gemini, a conventional high explosive (CHE)-driven primary implosion was DARHT - LANL U1a - NNSS SNM - U1a - NNSS HE change Metal change studied in both a surrogate (Castor) Figure 1. The Gemini/Leda/Lyra series differential experiment framework. H4080 was a and in plutonium (Pollux). The Lyra developmental experiment with limited velocimetry coverage.. series provided data comparing that performance to experiments using the same pit driven with insensitive high on any one surrogate, which might than trying to understand deviations that explosives (IHE). In both series, scaling is be computationally represented with might be caused by part variations. used to reduce the reactivity of the device imperfect models and could then lead to and to keep it subcritical. erroneous model calibration. In addition The Need for Advanced Diagnostics for Lyra, the design team focused on Learning from the Gemini series, the IHE is being strongly considered for creating a device that used various design potential future designs and also for reuse features to minimize the experiment’s of a CHE pit in an IHE implosion system. sensitivity to other potential areas of design team has identified what types physics uncertainty. This approach particular,of questions velocimetry can be asked enables with thea whole performed any experiments for which allowed for a more direct focus on new diagnostics now being fielded. In thereHowever, was beforea direct Vega, measurement the Nation of had the not plutonium dynamic behavior driven by experiment. new series of questions to be asked of the an IHE charge. As part of a plan to certify the plutonium dynamics in the final advancesdata. In addition, in diagnostics. other questions were a new design without nuclear testing, By building off of the Gemini series and raised that would benefit from continued the models being used to underwrite Lyra series allowed for a very direct physics hypotheses that would be plutonium data are required to validate comparisonusing the same of the pit dynamicsconfiguration, between the directlyIn Vega, testedwe started in the with series. 11 primaryThat list has important step in that process. a CHE- and an IHE-driven implosion. grown as new data were taken and now that design. The Vega experiment is an This approach provided a useful means stands at around 15 hypotheses, some As shown in Figure 1, the experiments to understand the impacts the drive of which have already been addressed. difference had without a large need to together with those from the Gemini and focus on understanding the impacts of could perhaps be better answered with Ledaconducted series under in a differential the Lyra series experiment fit the design changes as well. This approach newerIn that diagnosticslist, there were in conjunction questions that with framework with only one change between also more directly tied to several pit reuse the original multiplexed velocimetry. In each experiment. Two experiments were particular, there were times when more conducted at the Dual-Axis Radiographic be asked of a weapons system. dynamic range would have aided the Hydrotest (DARHT) facility, and six were concepts for which similar questions will analysis. In Lyra, Generation 3 Multiplexed conducted at the U1a Complex. In the In order to execute this series, a large framework, there were six surrogate experiments that provided a means to Scope included such activities as Photon Doppler Velocimetry (MPDV) better understand the high explosive partsteam acrossmanufacturing, the complex vessel was systems, required. largewas fielded increase on ina dynamicsignal-to-noise experiment over the drive which then, ultimately, allowed for diagnostics development, materials for the first time; as expected, it gave a a better understanding of the plutonium science, design physics, assembly, and new to Lyra were 8 channels of Broadband dynamics in the SCE. Multiple surrogate original systems fielded on Pollux. Also experiments provide a means to reduce extensive team to produce high-precision any compensating errors that might transportation. Each assembly required an Laser Ranging (BLR) fielded to address be introduced by relying too heavily allow for a focus on the physics rather teamspecific pushed areas for of physics.the incorporation Building off of parts. This precision was required to some questions on Pollux, the design

Volume 8 | Number 1 | March 2018 Stockpile Stewardship Quarterly 7

Figure 2. Many of the Lyra team members at U1a.

complexity of plutonium dynamic released in 2018. After this, the design behavior, surrogates simply do not combinationof stereoscopic of visualthese diagnosticsimaging (first and provide all of the properties needed to post-shot report, which is expected to be Cygnusfielded onradiography Leda with allowsmonovision). for cross- The understand the details of a plutonium completedteam will begin approximately preparing onethe finalyear after correlation between each diagnostic to implosion. The data obtained in these experiments enable model validation and appear in the data. model development that will be used in Acknowledgementthe release of the final data package. better understand questions that might the current assessment process but that While many people contributed to the also will become even more important as success of these experimental series, David we become further removed from direct As the final experiment in the series, the Holtkamp was instrumental in having a calibration to the nuclear test history. vision for all-optical hydrodynamic and plutonium.Vega experiment The diagnostic did not disappoint. suite It subcritical experiments. He also was performedprovided exquisite as hoped, detail providing of the aimploding means The Next Steps in the Lyra Series instrumental in developing the diagnostics to better understand what is happening Analysis within the device. Even though the data Shortly after the Eurydice experiment, analysis is in its early phases, several being analyzed, and a preliminary data Davidneeded passed to ask away these suddenly. important He questions. is deeply hypotheses have already been addressed, packageThe data was acquired delivered in December in February. are Thisnow missed by those with whom he interacted, data package will give the primary physics and his large contributions of these raised. Even within an experiment and several new questions have been teams involved a chance to examine the experiments, to the SCE program, and to data and see if there are any regions the Nation will be felt for many years. start, there is still room for exploratory ● that need further examination before observationsthat has defined that hypotheses are not related from to the those preliminary data package will be released their own. the final data package is released. The hypotheses, but that raise questions of simultaneously to the three laboratories This series again points to the need that provided a preshot prediction. The for a strong SCE program. Due to the

final data package is expected to be

Office of Research, Development, Test, and Evaluation Volume 8 | Number 1 | March 2018 8

Integrated Experiments in the Stockpile Stewardship Program by Njema Frazier and Sean Finnegan (National Nuclear Security Administration)

Predicting the performance of an three such efforts that typify how these current focus of research. Similar efforts experiments are used in today’s SSP. are underway exploring the physics of understanding both how matter behaves These examples are drawn from the alternate compression schemes at the Z inoperating the high nuclear energy weapondensity (HED)requires regime NIF, but comparable experiments are and Omega facilities. and also the nature of key physical performed on the Z and Omega facilities. phenomena such as radiation transport, An exciting emerging application of radiation driven hydrodynamics, and Ignition and Uncertainty these ignition experiments is to test and thermonuclear burn. The Inertial Quantification Ignition research and development (UQ) methodology. A multi-disciplinary advance our uncertainty quantification within the National Nuclear Security involves some of the most complex team of weapons scientists, ICF scientists, Confinement Fusion (ICF) Program integrated experiments performed at engineers, and computational scientists provides experimental access to extreme the HED facilities. In these experiments, is developing new tools for application HEDAdministration environments (NNSA) through uniquely a set of solid cryogenic layers of deuterium- across the stockpile stewardship complementary, specialized facilities. tritium (DT) fuel are imploded nearly enterprise, using deep learning methods The National Ignition Facility (NIF) symmetrically inside millimeter radius to combine simulation results and at the Lawrence Livermore National experimental observation. Ignition Laboratory, the Z Pulse Power Facility attempt to ignite DT fuel (see Figure 1). experiments at NIF are providing a at Sandia National Laboratories, and the Thesecapsules experiments to pressures are required heavily diagnosedin an stressing test of these new methods, Omega Laser Facility at the University of with x-ray and nuclear instruments and particularly where little to no data yet Rochester provide data that are informing are designed to test hypotheses aimed exist. design options for Life Extension at understanding and improving target Programs, validating models important performance. At present, implosions on Material Strength of Solids at High for weapon design codes, and providing the NIF are approaching the burning Pressure hostile environments for vulnerability plasma regime in which the alpha particle Understanding the strength of materials and hardness testing. However, there energy deposited in the fuel is almost at high pressure is important to the SSP. are limits to our current capabilities. To more completely access HED regimes by the imploding capsule. This extra material’s resistance to deformation and in the laboratory, HED facilities capable heatingequal to from the mechanical the fusion alphaenergy particles provided affectsStrength compressibility is a quantitative and measure the material’s of a of driving experiments with hundreds evolution under deformation. It is a for the experiment. Analysis suggests function of temperature, pressure and The demonstration of ignition is the thatresults shell in distortionsa yield amplification resulting fromrequired strain rate. Microscopically, strength is of megajoules of energy are required. drive asymmetries and hydrodynamic the resistance to dislocation generation future multi-megajoule capability, and it instability cause the assembled fuel and transport. Direct observation of isrequired for this technological reason, as well threshold as nearer-term to that to disassemble before the fusion self heating from alpha particles has time to electron microscopy (TEM)-level spatial a major Stockpile Stewardship Program run away. Resolving these issues is the resolutiondislocations and requires is not availabletransmission in current (SSP)benefits, goal that of thedemonstrating ICF Program. ignition Each of is developing the underpinning science and the HED facilities plays a unique role in to an igniting plasma. technology towards enabling the first step The experiments conducted in support of the ICF mission fall into two broad that attempt to isolate and test our categories: (1) focused experiments algorithm or material property such as radiativeunderstanding opacity; of aand specific (2) integrated code experiments of varying complexity that serve several distinct functions. While Figure 1. Schematic of a NIF hohlraum surrounding a capsule containing a cryogenic solid layer of together they enable the study of physical phenomenaeach facility usingprovides different unique drivers capabilities, in conesDT fuel. of Thebeams fuel positioned is injected so through that the a x-raysultra-fine generated fill tube inside less than the hohlraum5 µm in diameter symmetrically (a human illuminate hair regimes of overlap that is essential for theis 100 capsule µm in and diameter). implode NIF’s it symmetrically. 192 laser beams Actual enter NIF thehohlraum hohlraum (right) from is thea highly top and complex bottom multi- in 4 the cryogenic environment. in new HED regimes. Below we describe component assembly that must be assembled to tolerances of a few 10s of µm and that must survive building confidence in results obtained

Volume 8 | Number 1 | March 2018 Stockpile Stewardship Quarterly 9

(a) (b)

Initial undriven target

Material After implosion (right), the D and T reactants have mixed producing DT neutrons. The signal increases with asFigure the mixing 3. (a) Schematic increases. of(b) the Three-dimensional capsule used in the direct two-shock numerical experiment. simulation Initial of interface configuration mixing (left).during strength deceleration stage using the high-order code Miranda, showing diffusive mixing in the interior of the capsule near the hot-spot, and turbulent mixing further out in the cooler regions of the shell.

(RT) instability (see Figure 2). Detailed time, RT instability causes the deuterated measurements of the seeded instability Material growth are compared with hydrodynamic layers of the T gas, cooling the mixed without simulations to assess the veracity of layercapsule of gasmaterial and reducing to “mix” theinto TT the neutron outer strength various strength models. yield. The further the capsule material penetrates, the lower the TT yield. Some Two-Shock Campaign of the capsule material that penetrates the Figure 2. Simulations of material samples (red) The recent NIF two-shock campaign [S.F. gas mixes with the tritium at an atomic accelerated to the right viewed in a frame level. If this material contains deuterium moving with the sample. The degree to which (2016)], so called because it uses a two- from the tracer layer, the magnitude of Khan et al., Phys. Plasmas 23, 042708 the resulting DT neutron signal diagnoses depends on the strength of the material. shock x-ray pulse to implode a capsule, pre-imposed perturbations become amplified was designed to test the effectiveness of how much of the tracer material has strength models under conditions relevant for various implosion phase mix modeling penetrated the gas and mixed atomically. theMeasuring SSP. this amplification allows us to test The DD neutron signal over and above that consistent with the DT signal is a separate tritiumtechniques gas whileimportant a deuterated for the SSP. plastic In this measure how much tracer material dynamic experiments. Instead, integrated tracerplatform, layer a plastic is situated capsule at the is filledinner with surface penetrated the tritium hot spot but did experiments on the NIF assess material of the capsule (see Figure 3). As the not mix atomically. Together, these signals strength by measuring its effect in capsule decelerates during stagnation, the provide a tight constraint on models. ● suppressing the growth of hydrodynamic instabilities such as the Rayleigh-Taylor TT neutrons are produced. At the same tritium makes a “hot spot” and copious

Highlight

2018 High Energy Density Summer of state, (2) shocks, rarefactions, and School their interacations, (3) hydrodynamic Suggestions To promote the spread of broad, instabilities, (4) radiative transfer, (5) fundamental knowledge and to train radiation hydrodynamics, (6) creating or high energy density conditions, Comments? energy density physics, the University fusion, (8) experimental astrophysics, (9) relativistic systems, and ofnew Michigan, entrants Ann into Arbor the field is offering of high a Do you have a great idea for High Energy Density Summer School (10)(7) inertial magnetohydrodynamic. an article or comments about from June 11-22, 2018. The in-depth For more information, you may contact this issue of the Stockpile approximately 40 hours of lectures Stewardship Quarterly? If so, overintroduction 11 days. to The the lectures field will will include be based engin.umich.edu/workshops/hedss/Jan Beltran at (734) 936-0494 (jbeltran@ please email Terri Stone at primarily on the book High-Energy- index.html.umich.edu) ●visit http://clasp-research. Density Physics, 2nd ed., by Prof. R. Paul [email protected]. Drake. Topics to be covered include (1) fundamental equations and equations Office of Research, Development, Test, and Evaluation Volume 8 | Number 1 | March 2018 10

2018 Stewardship Science Academic Programs Annual Review Symposium

This year's Stewardship Science Academic review symposium held in Bethesda, Yuankan Fang Programs Annual Review Symposium Maryland on February 21-22, 2018. The University of California, San drew a record number of attendees. symposium featured overviews of work to Diego Approximately 350 individuals from the date from ongoing grants and cooperative High Pressure Effects on BiS2- National Nuclear Security Administration agreements from the Stewardship Science Based Compounds (NNSA) and other government agencies, Academic Alliances Program; the NNSA- DOE/NNSA national laboratories, and supported grants from the Joint Program Dan Hoff academia attended this year’s annual for High Energy Density Laboratory Washington State University in Plasmas; and grants awarded under the St. Louis National Laser Users’ Facility Program. Producing Huge Spin Alignment in Inelastic The of Research, Development, Excitations of Clustered Nuclei Test, and Evaluation's Dr. KathleenOffice B. Alexander gave the keynote Rebecca Lewis address this year. She shared(RDT&E's) with the Michigan State University attendees the experiences that led to Experimentally Constrained her current role as the Assistant Deputy 73Zn(n,g)74Zn Cross Section Administrator for She highlighted her work at the national labs, and the Marc-Andre Schaeuble value of those experiencesRDT&E. in her work at University of Texas, Austin NNSA. She also spoke to how she came Helium at White Dwarf to the decision to enter management Photosphere Conditions: at the Federal level, and the personal Experimental Line Shifts and commitment that that decision Widths When asked what she plans to do next, Dr. Alexander replied, "I have therequired. best job Hannah Shelton in the Federal Government. Why would I University of Hawaii, Manoa want to do anything else?" Cristobalite X-I: A Bridge Between Low and High Density The Poster Session and reception followed. Silica Polymorphs There were approximately 135 posters, of which were student posters, on Hong Sio, Massachusetts view during this year’s session on topics Institute of Technology including107 low energy nuclear science, Implications of Differences radiochemistry, properties of materials Between Measured and under extreme conditions and/or hydro- Rad-Hydo-Simulated Reaction (ND), presented her poster, Transformation ofTop: Uranyl Haylie Phosphate Lobeck, University and Arsenate of Notre Minerals Dame to dynamics, and high energy density physics. Histories in Hydro-like Implosions Soluble Nanoscale Cage Clusters, during the The winners of the Poster Session follow. on OMEGA

inset from the cover featuring Sarah Hickam. Kristyn Holley Brandenburg Jeff Woolstrum Theposter title session. of her posterBottom: is Full-sizeDissolution photo of Uraniumof the Ohio University University of Michigan Dioxide in Uranyl Peroxide Cluster-Forming Developing a Long Counter New Computational and for (alpha,n) Measurements Radiographic Capabilities at Conditions: Influence of Alkali Metals. Relevant to the Alpha-Process the University of Michigan and Nuclear Reactor Diagnostics at Ohio University Liangyu Yao Oregon State University Samantha Couper Target Making for Nuclear University of Utah Reaction Studies Deformation of a Lower Mantle Assemblage at High Temperature To copies of the 2018 SSAP Annual, contact Terri Stone at terri. Sakun Duwal request Washington State University ● Transformation of [email protected]. 2018 Stewardship Science Academic Programs Hydrazinium Azide (N5H5) to Annual N8 at 40 GPa

Volume 8 | Number 1 | March 2018 Stockpile Stewardship Quarterly