DOE/NA-0030

Office of Research, Development, Test, and Evaluation Quarterly

VOLUME 5 | NUMBER 2 | JUNE 2015

essage from the Assistant Deputy Administrator for Research, M Development, Test, and Evaluation, Dr. Kathleen Alexander This issue of the Stockpile Stewardship Quarterly addresses some of our latest research areas, ranging from computing

describesto manufacturing. why it is The number first articleone in on the world20-petaflop according to the Graph 500 data analytics benchmark. This is a remarkable tool which supports

stewardship. High energy density physicsa required experiments capability arefor stockpilean important element of stockpile stewardship. An example is given in the second article which describes a new class of ablators, diamond and beryllium, which can result

Ignition Facility ignition shots. in more efficient implosions for National This issue also includes yet a different approach to achieving thermonuclear burn in the laboratory. It is a pulsed power approach utilizing magnetically driven cylindrical implosions. The approach, called magnetized liner inertial fusion (MagLIF) is being studied on the Z machine. Burn conditions are achieved through insulating magnetic

certain Laboratory Directed Research andfields. Development The last article projects presents have how paid Theapproximately University 70of Rochesterposters, ranging Laboratory from forlaboratory Laser Energetics astrophysics hosted to high-end the Seventh simulations OMEGA Laserand to dividends for additive manufacturing Users Group (OLUG) Workshop on April 22-24, 2015. Students and postdoctoral scholars presented (AM). Examples of AM projects are given and the staff who enabled this progress diagnostic development. Attendees received tours of the world-class OMEGA Laser Facility. Read more about the OLUG Workshop on page 12. are highlighted. Inside With the arrival of the warmer season, 2 Sequoia’s Graph 500 Performance Paves the Way for Future Stockpile Stewardship Work I wish everyone a safe (and relaxing) 5 The Advantages of Beryllium and Diamond Capsules for the National Ignition Facility summer with family and friends. 7 Recent Progress and Future Potential of Magnetized Liner Inertial Fusion (MagLIF) 9 Lawrence Livermore Additive Manufacturing LDRD Investments Pay Strong Dividends to the Nuclear Security Enterprise 11 Highlights

Comments The Stockpile Stewardship Quarterly is produced by the 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

Sequoia’s Graph 500 Performance Paves the Way for Future Stockpile Stewardship Work by Don Johnston (Lawrence Livermore National Laboratory)

In a feat of computational derring-do, scientists from IBM and Lawrence

Livermore National Laboratory (LLNL) Graphpushed 500 the data Sequoia analytics supercomputer benchmark (see Figure 1) to the top performance on the from the graph processing algorithms atin the2014. core The of Graph many analytics500 gets itsworkloads name in application domains such as cyber security, bioinformatics, and social network analysis.

Sequoia, a 20-petaflop IBM Blue Gene/Q completingsystem housed the atlargest LLNL, problem retained scale the No. 1 ranking in the world by trillionever attempted—‘41 traversed edges scale’ per orsecond 2.2 trillion vertices—with a performance of 23.751 between two vertices in a graph and the metric(teraTEPS). consists An edgeof measuring is a connection the number of edges processed per second when Figure 1. Sequoia, an IBM Blue Gene Q system, consists of 12 rows with 8 racks each for a total of following connected vertices. 1.6 million cores. Peak power draw is 9.6 megawatts. The machine is 90 percent water cooled, which is significantly more efficient than air cooling and saves millions in energy costs. computational capabilities of advanced and Graph 500 is about memory and to new limits, achieving this record architectures has always been a part of communication interconnect. GraphNot unlike 500 pushingperformance a supersonic was a technical jet A graph is made up of interconnected the Advanced Simulation and Computing sets of data with edges and vertices, network performance capability and the computational backbone of stockpile stewardship.(ASC) Program’s charter; the Program is which in a social media analogy might balancing act that stressed the machine’s resemble a graphic image on Facebook, algorithms. The end result was improved The latest Graph 500 ranking with each vertex representing a user and required the development of innovative edges the connection between users. The Graph 500 ranking is compiled using system efficiency and reliability, not International Conference for High was announced at the SC14: The a massive dataset test. The speed with stewardshipjust for a ‘data applications. analytics’ graph problem, which a supercomputer, starting at one but for Sequoia’s day-to-day stockpile vertex, can discover all other vertices The result also underscored the Blue Performance Computing, Networking, Storage and Analysis supercomputing determines its ranking. data analytics performance has been Figureconference 2). The in New growing Orleans importance last of November with some fanfare (see Gene/Q system’s versatility. “Sequoia’s the Graph 500 over the last three Blue Gene/Q systems have dominated surprising,” said Scott Futral of Livermore securitydata analytics, programs, or ‘big has data,’ put theto scientific Graph 500research, ranking including in the high the NNSA’s performance national thisComputing. way. But “We we seedid thisnot necessarilydata analytics supercomputeryears. What this for means processing is that Sequoia computing (HPC) community spotlight expect Sequoia to be performant in gargantuanis the world’s datasets highest of performance petabyte size core workload capability of the machine.” as a critical measure of performance capability as an additional benefit to the along with the better-known Top500 (quadrillionsLeading the algorithm of ). development machine, was deployed as an advanced standard for measuring computer power. technologySequoia, a third-generation system to take on Blue the Gene LINPACK benchmark—the industry the Graph 500 performance possible is most challenging nuclear weapons and optimization techniques that made modeling and simulation calculations Sequoia held the No. 1 ranking on the theTop500 Graph in 500June and 2012 the soon Green after 500 coming list WatsonFabrizio Research Petrini of Center. IBM’s HPC The Analyticsexplosion online as well as the No. 1 ranking on ofDepartment big data has at madethe company’s data analytics Thomas and J. stockpileat the heart stewardship of the National mission. Nuclear While related applications of great interest to dataSecurity analytics Administration’s was not intended (NNSA’s) to be a focusesof the world’s on CPU most performance energy efficient or speed HPC systems. The LINPACK benchmark and national security communities. industry as well as the scientific research focus area for Sequoia, exploring the full in floating operations per second () Volume 5 | Number 2 | June 2015 Stockpile Stewardship Quarterly 3

engineering simulation codes critical to understanding and predicting nuclear weapons performance. HPC modeling and simulation are a cornerstone of the effort to ensure the safety, reliability, and security of the remaining nuclear weapons stockpile since nuclear testing ended 23 years ago. The integrated simulation codes are critical to all elements of stockpile stewardship, including stockpile maintenance, the Life Extension Programs, addressing the discovery of any issues in weapons systems, and supporting dismantlement.

Program.Sequoia represented The computational a giant leap power from of previous systems employed by the ASC

the Blue Gene/Q systems ushered in understandingthe use of uncertainty weapons quantification performance. Traditionally,(UQ) as a standard advanced method technology for better Figure 2. From left to right: Robin Goldstone of LLNL’s HPC Advanced Technologies Office, Dona Crawford, LLNL Associate Director for Computation, and Maya Gokhale, LLNL Distinguished the domain of large, single physics Staff Scientist and IEEE Fellow, display the No. 1 Graph 500 certificate at SC14 (Supercomputing simulationsystems such codes as Sequoia that could were be primarily ported conference) in New Orleans, LA last November (2014). They are standing in the DOE booth (which represented 17 national labs). to those machines relatively easily. Preparatory machines, such as the In the introduction to a paper produced example, computer scientists develop named Dawn, the initial delivery nonproliferation analysts to pinpoint 500-teraflop Blue Gene/P machine for the 2014 IEEE International Parallel techniques for organizing data that allow code developers working on the large, & Distributed Computing Symposium, of data. multiphysicsmachine associated weapons with simulation Sequoia, codesgave bytesIBM’s ofFabio data—so Checconi much and that Petrini 90 percent noted anomalous behavior in a huge quantity an opportunity to begin the long, slow ofthat: the “Every data in day, the we world create today 2.5 has quintillion been The stockpile stewardship science to process of modifying those codes to created in the last two years alone. This be able to run on these new machines. used to gather climate information, posts performancewhich Sequoia represents is dedicated as scientistsalso will weapons simulation codes could begin data comes from everywhere: sensors preparebenefit from to work the advanceson next-generation the Graph 500 to social media sites, digital pictures and Several years after the arrival of Dawn, videos, purchase transaction records, and , such as Trinity, a to take advantage of Sequoia, with its 98,304 nodes containing 1.5 million cellChecconi phone and GPS Petrini signals, also to namenote the a few.” system40-petaflop that isCray scheduled XC30 system, for deployment and challenge of sifting through massive , a more than 100-petaflop IBM uncertaintiescores (16 cores in pernumerical node), forsimulations running of has not traditionally been a big driver weaponslarge ensembles performance. of small jobs to quantify opportunities” that same data represents. forat LLNL stockpile in 2018. stewardship While data work, analytics datasets as well as the “nearly limitless computational scientists believe it will play an important role as weapons two-dimensional simulations have To date, UQ ensembles of up to 70,000 specimen,“Decoding makingdata can new help discoveries scientists share more codes are adapted to next-generation been performed. Each run differs from information from a single, hard-to-find supercomputing systems. previous runs with slight variations data can yield advances in the study of in input parameters that measure thepossible human and brain, frequent. offering Understanding the prospect, big the sensitivity of simulations to input perhaps someday soon, to be able to help are limited by both memory bandwidth variability. In this way, scientists can and“Increasingly latency and multiphysics network latency,” simulations said better understand the likelihood of critical diseases.” certain outcomes when some inputs are doctors and scientists find a cure for not known with precision. From a national security perspective, Dr. Maya Gokhale, LLNL computer extracting essential nuggets of HPCscientist is to and focus IEEE on thoseFellow. aspects “The true of the Future systems, such as Los Alamos information, sometimes called data supercomputerbenefit of the Graph that 500have to become traditional critical to scaling performance.” in large datasets, is important to such National Laboratory’s (LANL’s) Trinity mining and/or recognizing patterns Trinitysystem isand scheduled LLNL’s Sierra, for deployment will permit in atmospheric monitoring, intelligence, UQ runs in three dimensions (3D). bioinformatics,NNSA missions andas nonproliferation, energy. For integratedAs a workhorse nuclear for weapons NNSA’s tri-lab physics and more reliant on weapons performance ASC Program, Sequoia runs the 2016. “As the stockpile ages, we become

Office of Research, Development, Test, and Evaluation Volume 5 | Number 2 | June 2015 4 simulations to certify the stockpile,” distinctly different from the modeling said Chris Clouse, Deputy Associate The stockpile stewardship and simulation used for stockpile Program Leader for Computational science to which Sequoia is stewardship and climate research. Integration Principal Directorate. dedicated also will benefit Physics in LLNL’s Weapons and Complex from the advances the Graph traditional HPC communities seemed 500 performance represents headed“A few years in opposite ago the directions,” data analytics said and Rob “Sequoia is a bridge to future as scientists prepare to architectures,” Clouse said. “Sequoia gets work on next-generation changing.”Neely of LLNL’s Center for Advanced us to the edge of 3D UQ with an entry- supercomputers, such as Scientific Computing (CASC). “But that’s thelevel issues capability. associated 3D UQ with is critical aging becometo the Trinity, a 40-petaflop Cray In a commentary published in morelong-term 3D in certification nature.” of the stockpile as XC30 system, and Sierra, a more than 100-petaflop IBM Innovation: America’s Journal of weapons codes that have been developed system that is scheduled for andTechnology Jim Brase, Commercialization Deputy Associate in 2014, over“Adapting many and years optimizing to new HPC nuclear architectures deployment at LLNL in 2018. Dimitri Kusnezov, NNSA Chief Scientist, that the difference between the big to 3 years to get to a point where we could dataDirector and fortraditional Computation HPC communities at LLNL, said is no trivial matter,” he said. “It took us 2 are far from optimized for that machine, development and investment. andmake we good expect use the of Sequoia, challenges but of our future codes simulation science. For example, pattern was reflected both in technology architectures to be even greater.” Dawn big data techniques to weapons that would differentiate simulations andrecognition—finding debugging—would unique have featuresuseful “Looking ahead, this separation will provided the transition to Sequoia just as applicability. He also said that these complexchange,” Kusnezovphenomena and and Brase the toolswrote. of Sequoia is serving as a bridge to Trinity data“Particular analytics aspects will need of simulation to converge, of and Sierra. back to the original perturbations that as societal issues demand more simple—and slow—processors by disrupttechniques or even could kill be code applied runs. to tracking understanding coupled to the existing providing“Sequoia made huge upnumbers for its relativelyof them, but data analysis and reduction.” our challenge was improving the codes Looking to the more distant future, to be able to out scale across the nearly Clouse says data analytics as it applies

to improve code performance on large, Kusnezov and Brase point out that codes100,000 to runnodes at ofscale.” the machine,” said complexto ‘machine HPC learning’ systems. has Machine the potential learning arenational driven priorities both by todaydata analytics require and Clouse. “Today, Sequoia allows weapons consists of using data analytics to teach a simulation.”“computing in parts of the spectrum that leap in computing power with the to prevent problems by adjusting inputs Business and research communities commensurateSierra will be an technical even greater challenges for tomachine the simulation.” “what to look for and what to do are looking for the faster network communications and interconnects associated with traditional HPC ofASC issues scientists we need that to come address with for adapting adapting iterative and time-consuming process,” and the greater memory bandwidth codesto a new to futurearchitecture. architectures,” “There’s continued a long list he“Currently, said, adding identifying that preventing problems problems is an characteristic of big data. has allowed us to work on a subset of the throughput for users.” As a bridge to future HPC systems, theClouse. things “As we a transition need to tackle machine, for future Sequoia before they occur would “greatly boost balanced HPC system can do in both the exploring machine learning and looking dataSequoia analytics offers anda glimpse modeling of what domains, a well- systems. We’re still reaching the peak Computer scientists at LLNL are out-scalingof what we can[achieving do on Sequoia. parallelism With across applied to optimize code performance at other ways ‘data analytics’ may be hundredsSequoia, we’ve of thousands gotten a ofgood nodes],” jump Clouseon on future systems. With each generation traditionalconsequently HPC helping and big to data.” set the stage of supercomputer generating ever for what Neely calls “a marriage of [achieving parallelism within each research in machine learning, deep node].”said. “Now we need to focus on in-scaling spectrum of applications, data analytics willgreater inevitably quantities play of a databigger across role inthe the computingNeely underscores and neural the networksimportance to of management of applications, including running applications on future systems. These have the potential to be powerful TrinityASC scientists supercomputer will have comesthe opportunity online at to take the next step in 2016 when the theTraditionally, codes used modeling by ASC scientists. and simulation themselves to be more robust” as have been regarded as being at the welltools as that allowing would forallow improved “codes tomesh teach LANL.While data analytics have not opposite end of the supercomputing management for complex simulations. traditionally been a big driver for applications spectrum from data the stockpile stewardship mission, analytics. Technologies, tools, and Clouse sees opportunities for applying ● “This may sound futuristic,” he said. “But requirements for analytics were seen as that’s what we do at the labs.” Volume 5 | Number 2 | June 2015 Stockpile Stewardship Quarterly 5

The Advantages of Beryllium and Diamond Capsules for the National Ignition Facility by Douglas . Wilson (Los Alamos National Laboratory [LANL]), and Darwin Ho (Lawrence Livermore National Laboratory [LLNL]), and the Inertial Confinement Fusion Teams at LANL and LLNL

As part of stockpile stewardship, the Pure CH, Be, or HDC Doped the fuel outside the hot spot must be low. program has focused on exploring fusion Pure Torequired achieve to that, compress a relatively it, the low entropy pressure of Inertial Confinement Fusion (ICF) DT ice the DT fuel, which is then compressed burn at the National Ignition Facility nearlyfirst shock adiabatically. (about 0.5 -1 Mbar) transits (NIF). The process attempts to use lasers, x-rays, implode, and fuse deuterium (D) DT gas andrather tritium than nuclear(T) in a smallfission, capsule. to generate Laser Higher Density – Higher Picket light is directed into a gold or uranium Temperature and Shorter Laser Pulses x-rays that penetrate, heat, and explode The high initial densities of HDC thecylinder exterior (a “hohlraum”) of a spherical producing capsule. The (3.5 resulting inward pressure compresses the them several advantages over plastic g/cc) and Be (1.8) ablators give central temperatures and densities that pressure can be used in these denser theinterior fuel fuses, DT fuel, releasing creating energy sufficiently in the formhigh ablators(1.06). One to createis that thea higher same initialpressure shock in of helium nuclei and neutrons. If these DT as with CH. Because a shock crossing alpha particles and neutrons can deposit enough of their energy in the surrounding DT fuel before it can expand, the capsule isthe greater), ablator/DT a higher ice interface pressure is shock partially can capsules. bereflected initiated (more in a ifBe the ablator, density and difference a yet energy. To date, this DT ignition has been Figure 1. Schematic of CH, Be, and HDC NIF higher pressure in HDC. This higher successfullywill “ignite” releasingcreated in much boosting more the yield pressure shock is driven by a higher of nuclear explosives. Achieving this in the The HDC capsule uses only one dopant radiation temperature in the hohlraum, laboratory has been a major goal for the which for Be and CH leads to more national ICF program since its conception All ablators have a pure inner ~ 5-mm- radiative stabilization of the Rayleigh- thicklayer; layer, the CH followed and Be bydivide doped it into layer(s) three. Taylor instability at the capsule surface. and an outer thick layer of pure ablator. This greater stabilization is one of the 4 understandingin the late 1960s. of Overcomingthe detailed physicsthe of fusionremaining burn challenges in conditions will similar require to a betterthose uses copper, HDC uses tungsten, and CH foot” plastic capsule implosions that occurring in a nuclear device. usesEach silicon.ablator Theuses dopant a different purpose dopant: is the Be havereasons demonstrated for the recent fuel success temperature in “high- same, to minimize instability growth increase from alpha-particle heating5 The vast majority of DT-containing and is probably also an advantage for capsule compresses. HDC. These targets are mounted by a from glow discharge polymer with a at the ablator/DT ice interface as the thin membrane called a tent. A weaker compositioncapsules tested of ~at CNIF haveH ,been i.e., plastic.made tent perturbation could be a welcome If we think of the laser and hohlraum laser (~2 MJ) cannot provide nearly advantage for higher density ablators. as providing a bath0.56 of x-rays,0.44 then the And compress it must. Because the NIF capsule material that most effectively device, the x-rays in an ICF hohraum signature of the tent supporting the as much energy as a fissioning nuclear absorbs x-rays would be the best. Ease of can only compress a small fuel mass, HDCExperiments capsule. show a less significant approximately 0.2 mg. The small initial areal density of the fuel 3 An additional advantage of higher berylliumfabrication (Be) made and plastic diamond-like the first choicehigh 2) is not density is shorter laser pulses. Figure 2 densityfor NIF capsules.carbon (HDC) Only begunrecently to behave tested enough, once it is heated(~ to 0.25 several g/cm keV temperatures,* 70e-4 cm = 1.75e-3 to force g/cm alpha particles to HDC, Be, and CH capsules. The shortest more effectively uses x-rays than either deposit their energy, raise the burn rate pulsecompares is for NIF HDC, laser then pulse CH, lengthsand slightly for HDCat NIF. or Be, plastic. because The ofhigher its lower density opacity, of HDC yet higher, and ignite a run-away burn. longer for Be. The shorter HDC pulse Be offer other A total fuel areal density of 2 arises because a higher power laser advantages compared to CH . is needed to ignite. Fortunately, areal In(3.5 this g/cc) article, and we (1.8will elaborateg/cc) on these density increases with spherical~1.5 g/cm shock through a thinner ablator. When advantages and how they will(1.06 be usedg/cc) in compression by ~(Rinitial )2. A twopicket ablators (at 1 to have 2 ns) similar drives mass, a faster then first the the coming years to further the pursuit of radial compression of ~25 isfinal needed. But higher density one will be thinner. The higher neutron yields and fusion burn. there is not enough energy/R to compress all of the fuel to high temperature. A the ablator. If two designs use the same 2 shockfirst shock pressure will takeand velocityless time in to the transit fuel capsules with CH , HDC2, and Be3 shells a central hot spot with the surrounding (giving it the same entropy), the time to Figuredesigned 1 and with the similar table1 DTcompare fuel masses. NIF minimumfuel kept cold. of ~0.3 To minimize g/cm is requiredthe energy in transit the fuel is the same. The Be pulse

Office of Research, Development, Test, and Evaluation Volume 5 | Number 2 | June 2015 6 is slightly longer because it uses the higher densities of same picket power as CH but gives the HDC and Be also fuel less entropy. The pulse shown here allow higher radiation temperatures in the will be shortened. beginning of the laser is being tuned for the first DT shot and pulse, leading to yet A shorter laser pulse interacts more more stabilization. favorably with the hohlraum. A shorter laser pulse allows less expansion of The Future for the hohlraum wall. There is less laser Beryllium and HDC backscatter out of the hohlraum and in ICF greater x-ray production. In all three Experiments are just hohlraums, the wall is held back by beginning on the

use of both Be and (TW) Laser Power gas apparently also reduces the x-ray HDC as ablators, and a 1.6 mg/cc, helium gas fill. But this production, and increases laser shorter pulses with 6 There have been only backscatter out of the hohlraum. Shorter hohlraums appear to be one path to threelower DT-layereddensity gas HDC fills. increasinglaser pulses x-ray in lower production density-filled and reducing laser backscatter. Be one is scheduled Time (ns) capsules, and the first Lower Opacity – More Efficient Absorption plasticfor June capsules 2015. While have The lower atomic number of beryllium the “high-foot” potential in terms Figure 2. HDC, CH, and Be ablator pulses used at NIF. of different laser pulse shapes and 7 fundamental advantage. It produces rugby shaped hohlraums, Be and HDC (Z=4) compared to carbon (Z=6) is a capsules share those possibilities and R.E. Olson et al., “Shock Propagation, capsule to absorb x-rays deeper and also offer the advantages of higher FusionPreheat, Ablator and X-ray Materials,” Burn Through Phys. Plasmas in morea lower effectively, x-ray opacity producing (κ) allowing a higher the density and improved implosion Indirect-Drive Inertial Confinement mass ablation rate, M, and ablation behaviors. The next few years will be pressure, P, when driven at the same exciting as we continue the challenging 11, 2778, 2004, and “X-ray Ablation radiation temperature. The M, P, and the Rates in Inertial● Confinement Fusion speed, V, of a thermal wave driven by Capsule Materials,” Phys. Plasmas 18, questReferences for alpha heating and ignition. 032706, 2011. x-ray penetration are given by: 1 O.A. Hurricane et al., “The High-Foot Implosion Campaign on the National Contact Us 2Ignition Facility,” Phys. Plasmas, 21, 3) its density, 056314, 2014. What do you where Z is the ablator’s atomic number, T (keV) the radiation temperature, and J.S. Ross et al., “High-Density Carbon think about A its atomic2 weight, ρ (g/cm Capsule Experiments on the National 3 this issue of dependent opacity. 3Ignition Facility,” Phys. Rev. E 91, κ (cm /g) its temperature and density 021101, 2015. the Stockpile Fitting κ to power Beryllium Target Design for Indirectly Stewardship A.N. Simakov et al., “Optimized laws in ρ and T between 150 and 400 eV Quarterly ? yields the following: MBe HDC Be CH Driven Inertial Confinement Fusion We want to 0.2 Be0.08 Experiments on the National Ignition know. Please send (T ) and P CH Be /M ≈3.3/T ; M /M ≈4.6/ Facility,” Phys. Plasmas 21, 022701, 2014. your comments and P 0.8 0.4 4Instabilities in Beryllium Targets for the HDCρ /P ≈ 1.34/T ; P / S.A. Yi et al., “Hydrodynamic suggestions for future 0.08 Measurements ≈ 3.5/T of the mass ablation rate7 issues to Terri Stone at 5National Ignition Facility,” Phys. Plasmas [email protected]. consistent with these conclusions, 21, 092701, 2014. gov. Requests to be are within a factor of 2 quantitatively O.A. Hurricane et al., “Fuel Gain Exceed- added to our mailing list ing Unity in an Inertially Confined Fusion Lower opacity at the same radiation should include your full confirming the advantages of low opacity. Implosion,” Nature 506, 343, 2014. temperature also results in a higher 6 name, email address, and ablation velocity, V, and better IgnitionO.S. Jones Campaign et al., “A Cryogenic High-Resolution Layered affiliation/organization. stabilization of the Rayleigh-Taylor Integrated Model of the National instability at the ablation front. The 4 Experiments,” Phys. Plasmas 19, 056315, 2012. Volume 5 | Number 2 | June 2015 Stockpile Stewardship Quarterly 7

Recent Progress and Future Potential of Magnetized Liner Inertial Fusion (MagLIF) by S.A. Slutz et al.* (Sandia National Laboratories)

Introduction The standard approaches to inertial implosion velocities greater than 300confinement and fusion spherical (ICF) convergence rely on to achieve the high fuel temperatures (T > km/s keV) 2 high 4velocities and are areal achieved densities by heating(ρr1 > 0.3the g/cmoutside) requiredsurface of for a sphericalignition. Such capsule either directly with a large number of laser beams (Direct Drive) Figure 2. The left image shows the target geometry used in these experiments with parts color coded; or with x-rays generated within a anodeLiner radius (blue), (red), cathode current (red), (blue), AR=6 and Be linerlaser (orange),power (black) laser are (green), plotted 0.7 on mg/cc the right. pressurized deuterium hohlraum (Indirect Drive). A much more gas fill (yellow), and polyimide foil (brown) to contain the deuterium and allow the laser to penetrate. the magnetic pressure generated by a end of the tube to heat the fuel to an been performed on the Z Machine. pulsedenergetically power efficient machine approach to directly is driveto use The geometry is shown in Figure 2.12-13 Finally, an axially directed current from the stored energy can be converted to aaverage pulsed-power temperature machine of 100-200 generates eV. a above thean implosion. implosion Inof thisa metal approach tube generally 5-10% of andAn initial below axial the liner.magnetic Z-Beamlet, field14 of 10 a T outside of the liner creating pressure to was generated by field coils 15 implosion velocity is not very high large azimuthal magnetic field on the laser, provided ~ 2 kJ to heat the referred to as a “liner.” However, the deuterium.frequency-doubled The Z Machine neodymium produced YAG is cylindrical (rather than spherical) isdrive nearly the frozen implosion. into bothOn the the time fuel scale and of 70-100 km/s and the convergence the implosion,liner due to the high axial conductivity magnetic andfield high temperatures and areal densities Anpeak experimental currents of 18drive and current, 17 MA for 7.5- neededmaking forit more ignition. difficult to achieve the Tesla) as the liner is experimentaland 10-mm long laser liners, power, respectively. and simulated thus, the magnetic4 field rises to very liner trajectory are plotted in Figure 2 Magneto-inertial fusion (MIF) concepts highinhibits values radial (~ heat10 loss throughout 16 thecompressed. implosion, The but axial particularly magnetic near field stagnation when the losses would be the Fusion(taken fromneutron Reference yields 11).and spectra were highcan significantly temperatures relax through implosion the use velocity of greatest due to the high temperatures. determined by activation and neutron requirements while still achieving Heat loss and alpha particle transport in The the axial direction are unaffected by the shorter 7.5-mm liners produced the insulating magnetic fields to decrease2-3 17-18 time of flight techniques. , theMagLIF heat losses normal to the field and ) as compared to 11 thatincrease is being4-5 fusion studied product on theconfinement. Z facility at magnetic field, but acceptable because best 12 deuterium neutron12 yields (5x10for is a specific MIF concept the liner is adequately long. Thus, closed ICF, the Rayleigh Taylor instability limits 1x10 , and 2x10 11 thefield convergence lines are not of required. MagLIF implosions.As with all bean due average to the yield larger of ~ drive 2.5x10 current SandiaThe three National important Laboratories. stages of this deliveredthe longer to 10-mm the shorter liners. liners This couldor other volume compression and thus, the changes such as the foil thickness. concept are shown in Figure 1. The convergenceThe fuel preheating needed reduces to achieve the fusion required In the best performing experiment, coils.first step A laser is to beam apply then an axial enters magnetic at one the ion and electron temperatures at field of 10-30 Tesla with external field and experiments indicate thick- walledtemperatures. liners with Numerical6-10 an aspect simulations ratio (AR Router wall ~ should maintain deuterium-tritiumstagnation were 2.5 (DT) ± 0.8 neutrons, keV and a 3.1 result+0.7/-0.5 of the keV, tritons respectively. produced Secondary in the = /∆R 6) aneutronic branch of the DD reaction, sufficient areal density to indicate compress that and both were measured with yields up to confine fusion fuel despite4 instabilities. , which indicates a high degree Numerical simulations are necessary to obtain fusion conditions of magnetization10 , since the areal the insulating magnetic field and preheat with these slow implosion velocities. 5x10 19 self-emission image produced from Integrated Experiments on the Z adensity time-integrated is low. An spherical x-ray (6 andcrystal 9 keV) Machine diagnostic is shown in Figure 3 (taken Experiments integrating all three from Reference concept. tall column has a full width at half Figure 1. The three stages of the MagLIF phases of the11 MagLIF concept have 11). The 6-mm-

Office of Research, Development, Test, and Evaluation Volume 5 | Number 2 | June 2015 8

9etR.D. al., McBride,Phys. Rev. M.R. Lett. Martin, 109, R.W.135004, Lemke 2012. et al., Phys.

T.J. Awe, C.A. Jennings, R.D. Plasmas 20, 056309, 2013. McBride10 et al., Phys. Plasmas

21, 056303. 2014. 11 M.R. Gomez, S.A. Slutz, A.B. Sefkow et al, Phys. Rev. Lett. yields as a function of drive current. The smallest current 113, 155003. 2014. Figurecorresponds 4. Optimized to the Z300 MagLIF design simulated and the (dashed=1D vertical dotted solid=2D) line 12 theM.E. Z Pulsed Savage, Power K.R. LeChien, Driver” M.R. Lopez et al., “Status of corresponds to the Z800 design. International Pulsed Power addition of a layer of DT ice on the inside in Proceedings of the 18th image lineouts (center), and axial lineouts Figure(right). 3. Self-emission image (left), horizontal D.V. Rose, D.R. Welch, E.A. Madrid et al., Conference, pp. 983-990, 2011. beof thedelivered liner. However, by the present significantly Z machine. higher 13 mm and exhibits a Twodrive high currents performance are required pulsed-power than can Phys.D.C. Rev. Rovang, ST Accel. D.C. Lamppa, Beams 13, M.E. 010402, Cuneo et small helical perturbation. 2010. maximum of 60-120 designed22 using the Liner Transformer 14 The results from these experiments Drivermachines technology. (Z300 and The Z800) Z300 have design been validate key features of the MagLIF al., Rev. Sci. Instrum. 85, 124701.2014. 15 concept, demonstrating thermonuclear P.K. Rambo, I.C. Smith, J.L. Porter et al., yields, fusion-relevant stagnation Journal of Applied Optics 44, 12, 2005. provides approximately 48 MA to a 16 MagLIF load, while Z800 would provide A.B. Sefkow, S.A. Slutz, J.M. Koning et al. compression. However pre-shot seriesabout 61of LasnexMA. A 23parameterized simulations. TheveninAt each Phys. Plasmas 21, 072711,2014. simulationstemperatures, predictedand magnetic DD yields flux in 17 valueequivalent of the circuit current, was the used MagLIF to drive target a C.L. Ruiz, G.W. Cooper, S.A. Slutz et al., 16 was optimized by varying the length, experiments are obtained if one assumes Phys. Rev. Lett. 93, 015001, 2004. 13 the radius, the fuel density, the initial 18 excess of 10 . Yields comparable to the K.D. Hahn, G.W. Cooper, C.L. Ruiz et al., in the fuel. The leading hypothesis for Rev. Sci. Instrum. 85, 043507, 2014. These optimized results are plotted in 19 only 10% of the laser energy is deposited this discrepancy is poor laser coupling magnetic field and the preheat energy. 20P.F. Schmit, P.F. Knapp, S.B. Hansen et mm-thick polyimide al., Phys. Rev. Lett. 113, 155004, 2014. foil. Indeed recent laser only experiments aFigure layer 4.of AsDT can ice be(Ice seen, Burner), very highwhich yields M. Geissel, L.E. Ruggles, A.B. Sefkow through the 1.5-3.5-20 using Z Beamlet indicate that only (> 1 GJ) are predicted for liners with et al., 41st EPS Conference on Plasma for laboratory fusion and very valuable Physics, 26 June 2014, Berlin, Germany. a 2.0-mm foil. This is probably due to 21 forwould stockpile be a very stewardship. significant achievement 22S.A. Slutz and R.A. Vesey, Phys. Rev. Lett. ~10% of the laser energy penetrates the large variations in laser intensity of 108, 025003, 2012. the unsmoothed Z Beamlet beam near Accel. Beams. focus, which could drive laser plasma References 23Stygar et al., submitted to Phys. Rev. ST instabilities. Beam smoothing is not Comments Plasma Phys. Controlled 12 G.B. Zimmerman and W.B. Kruer, the primary application of Z Beamlet. J. Lindl, Phys. Plasmas 2, 3933, 1995. Fusion*Contributing 2, 51, 1975. Authors required for backlighting, which has been 3I.R. Lindemuth and M.M.R.C. Kirkpatrick, Widner, Phys. University of Rochestester Laboratory Nucl. Fusion 23, 263, 1983. M.R. Gomez, A.B. Sefkow, D.B. Sinars, forExperiments Laser Energetics using Omega are underway lasers at to the test K.D. Hahn, S.B. Hansen, E.C. Harding, laser transmission with smoothed beams. Fluids 24, 746, 1981. P.F. Knapp, P.F. Schmit, C.A. Jennings, T. The preliminary results are encouraging 4 J. Awe, M. Geissel, D.C. Rovang, G.A. S.A. Slutz, M.C. Herrmann, R.A. Vesey, and plans have been made to obtain Chandler, G.W. Cooper, M.E. Cuneo, A. A.B. Sefkow, D.B. Sinars, D.C. Rovang, K.J. phase plates to smooth the spatial beam J. Harvey-Thompson, M.C. Herrmann, 5Peterson, M.E. Cuneo, Phys. Plasmas 17, M.H. Hess, O. Johns, D.C. Lamppa, M.R. 056303, 2010. more effective laser heating of the fuel Martin, R.D. McBride, K. J. Peterson, J. forprofile future of ZMagLIF Beamlet. experiments. This should allow M.E. Cuneo, M.C. Herrmann, D.B. Sinars, L. Porter, G.K. Robertson, G.A. Rochau, S.A. Slutz et al., IEEE Trans. Plasma Sci. C.L. Ruiz, M.E. Savage, I.C. Smith, W.A. 40, 3222, 2012. MagLIF on Future Accelerators 6 Stygar, and R.A. Vesey (Sandia National 7D.B. Sinars, S.A. Slutz, M.C. Herrmann et Laboratories) ● It has been shown numerically that al., Phys. Rev. Lett. 105, 185001, 2010. both high thermonuclear yield 21and gain could be obtained using MagLIF with the D.B. Sinars, S.A. Slutz, M.C. Herrmann et al., Phys. Plasmas 18, 056301, 2011. 8 R.D. McBride, S.A. Slutz, C.A. Jennings Volume 5 | Number 2 | June 2015 Stockpile Stewardship Quarterly 9

Lawrence Livermore Additive Manufacturing LDRD Investments Pay Strong Dividends to the Nuclear Security Enterprise by Rokaya Al-Ayat and Jason Carpenter (Lawrence Livermore National Laboratory)

stewardship component production, but Landmark LDRD Project Pays AM the Laboratory Directed Research also the way in which those components Dividends andSince Development its creation by (LDRD) Congress Program in 1991, When the Transformational Materials risk, potentially high-payoff research are qualified and certified. LLNL’s AM inhas support enabled of DOE their labs current to explore and future high- work focuses on this qualification and was the largest LDRD project in Initiative (TMI) began in 2006, it itcertification promises to effort bring because to the stockpile of the speed, stewardshipflexibility, and arena. cost improvements developed advanced research options LLNL history. TMI investigated and LDRDmissions. resources Lawrence in projects Livermore that National advance fundamentalLaboratory (LLNL) science has and been technology investing In addition to addressing its stockpile Program could use to transform the that the Stockpile Stewardship with an eye to anticipating and portfolio has achieved many successes stockpile maintenance and production, stewardship mission, LLNL’s LDRD AM NSE by reducing the cost and time of well as helping develop the staff critical in science, technology, collaboration, improving weapon safety, ensuring the addressing DOE and NNSA challenges, as and the recruitment and retention of talent. Projects contributing to its performance. TMI spawned several stockpile’s longevity, and optimizing manufacturingto execute them. (AM) LLNL’s exemplify investments how in these successes range from those that follow-on investigations, many of which the diverse, dynamic field of additive stockpile mission. as the Transformational Materials LDRD has been supporting the NNSA Initiative,predate AM to activitiescurrent projects at LLNL, addressing such investigationshave led to LLNL’s into rapidlynovel sensors developing for The manufacturing needs of the deterministic multifunctional materials embeddedexciting work evaluation, in the field for of example, AM. TMI led and manufacturing and the accelerated directly to current work on cushion

Nuclear Security Enterprise (NSE)—a metals. materials—arecombination of nothigh common quality and drivers for certification of additively manufactured manufacturing (see Figure 1). industrycomplexity, (see low Additive volume, Manufacturing and unique (AM) advance its own AM capability base. sidebar). As such, NNSA must capacityLLNL LDRD-funded to transform AM not projects only stockpile- explore needed solutions to the NSE. AM has the

Additive Manufacturing (AM) AM processes create layers (a) (b) of a polymer- or metal-based material from a 3D model or other electronic data. AM methods can Figureprinters 1. can(a) LLNL’sinclude direct- other components, writing capability such as leda stress to this sensor advanced (the material, metallic whoseribbon), properties during printing can be carefullyso that weapons controlled experts and digitally understand modified. aging (b)issues Because in the direct-ink foam and writingthe objects prints it cushions. the material in layers, complex objects. Commercial AM toolsquickly, cannot easily, make and manyprecisely mixed- create material components desired Staff Highlight: Yong Han platforms have the resolution toby designthe NSE, and nor create do commercial features at the micro- and nano- scales. Chemist Yong Han (PhD, University of California- When combined with the high- high-explosiveSanta Barbara) molecule was recruited that is to critical help recrystallize to the stockpile. performance computing (HPC) and triaminotrinitrobenzene (TATB), a notoriously difficult deep materials expertise available the greater implications of fundamental science on “My involvement in the TMI LDRD introduced me to dramatically expands the design spacewithin to the produce NNSA, better,however, cheaper AM toprogrammatic develop and work,”mature says our Han. initial “Our investment success transitionedin TATB stockpile components and offers to Science Campaign funding from NNSA to continue Campaign, working on other crystals in the stockpile. He is now the Detonator these components and related recrystallization.” Han went on to new roles in the Enhanced Surveillance the potential to certify and qualify support other LDRD projects, using them to attract new talent. Surveillance Program Chemistry Subject Matter Expert, and he continues to systems more efficiently.

Office of Research, Development, Test, and Evaluation Volume 5 | Number 2 | June 2015 10

Multifunctional Materials to Transform NSE Manufacturing “I thought all the warheads complete requalification. To realize The Deterministic Multifunctional AM’s full potential for speed, flexibility, Materials and Manufacturing Initiative the U.S. had just sat on a shelf somewhere. Little did componentsand cost savings, and certifyNNSA must systems. also Livermoreaccelerate thescientists processes and toengineers qualify will materials that support stockpile I know how much science be helping to drive this effort, drawing stewardship,aims to produce nuclear-fusion unique multifunctional ignition, and on foundational capabilities in materials global security missions. According to and engineering go into maintaining the stockpile, synthesis, predictive simulation, advanced manufacturing, and materials or the breadth of knowledge characterization. Chris Spadaccini, who leads this LDRD initiative, LLNL is well poised to address necessary for stockpile NNSA’s needs. stewardship.” steel AM has used a combination of simulations,An LLNL team experiments, working on andstainless- data- “Thanks in large part to our LDRD work,” — Andrew Pascall, LLNL chemists,Spadaccini physicists, explains, “weengineers, have grown and uncover patterns in the simulation computationalto more than 80 scientists material developing scientists, results,mining techniques,identify variables for example, that affect to advanced materials and manufacturing results, and streamline the optimization The work begun in this and other process. The team expects that a similar state-of-the-art AM labs.” This initiative AM-related LDRD projects has the approach could be used to optimize hasprocesses, advanced and AM we in have a multitude created five of other properties of a manufactured part ways, involving collaborations across manufacturing processes. Cushions or other materials. andpotential pads tomanufactured transform a tonumber protect of and NSE position components within a nuclear the NNSA, including the Y-12 National Security Complex, the Kansas City onSince developing the cessation predictive of nuclear models testing, for National Security Campus, the Pantex produceweapon, usingfor example, AM methods. could require regimesLLNL has where focused experimental particular attention data are collaborationsPlant, and the Loshave Alamos been established and Sandia significantly less time and cost to not always available. Researchers have withNational the Laboratories.University of IllinoisKey university at Urbana- used information provided by these Champaign, Harvard University, MIT, ([email protected])For more information on or LLNL’s read this work and UCLA. to improve AM processes, obtain Sciencein this area, and Technologycontact Chris Review Spadaccini article desiredmodels runningmicrostructures, on LLNL andHPC reduce resources manufacturing errors. Two models, Staff Highlight: Andrew Pascall (https://str.llnl.Accelerating Stockpile Certification Before he and Qualification came to based on LLNL-developed codes, have Manufacturing methods and materials smalleralready shownpowder significant scale (see promiseFigure 2). at for Chris both the component/part scale and the LLNL to work used to produce critical NSE components material must be formally qualified to ensure llnl.gov)For more or information read this Science on LLNL’s and work in scientistSpadaccini, tests,they perform costs millions to specification. of dollars, Thisand Technologythis area, contact Review Wayne King (king17@ Andrew process often requires thousands of Pascall (PhD, article (https://str. University takes 5 to 15 years. Later on, even a llnl.gov/january-2015/king). minor process change could require thought that research on nuclear weaponsof California-Santa had ended Barbara) with the Comprehensive Test Ban Treaty in

1992. “I thought all the warheads didthe U.S.I know had how just muchsat on science a shelf and engineeringsomewhere,” go he into admits. maintaining “Little the stockpile, or the breadth of knowledge necessary for stockpile stewardship.” Currently, Pascall is

high-puritydeveloping twometal new components AM techniques to enable printing of high-quality, Figurepower and2. Powder-scale scan speed are modeling high, producing using the an massively undesirable parallel balling multiphysics effect (shown code by ALE3D the red clarifies, and yellow for example,features). howPowder-scale to set process modeling parameters shows that to build lowering a part scan with speed an overhangand power geometry. (bottom scenario)Top: both yields laser materials. a better build. focusing on NNSA-relevant

Volume 5 | Number 2 | June 2015 Stockpile Stewardship Quarterly 11

Staff Highlight: James Lewicki Highlights

addressingJames Lewicki the (PhD,rational University design and of Strathclyde, optimization Scotland) of AM is the principal investigator for an FY 2015 LDRD project 2015 Stewardship Science Graduate compete internally for funding to do innovative R&D was Fellowship (SSGF) Program Review carbon fiber/polymer composites. “The opportunity to from a background in academia and industry and had little ideaand stillof just is a how big drivermuch fundamentalfor me at LLNL,” and Lewicki applied says.research “I came DCThe at 2015 the GrandSSGF Program Hyatt Washington. Review will be held June 29-July 2, 2015 in Washington, include presentations by each of the goes on within the NSE. It’s both a great opportunity and studentsHighlights completing of this year’s their review fellowship will highly scientifically rewarding to be part of it.”

LDRD AM Projects Attract and conversion rate from postdoc to staff Retain Top Talent for Programmatic in 2015, insight from alumni now Missions featuringworking in the Department research supported of Energy by (DOE) Given the current workforce turnover manyincreased of these in FY individuals 2015 from would ~50% likely to laboratories, and Fellows’ Poster Session choose~75%. Withoutacademic such or industrial opportunities, careers. anticipated turnover in the next decade, the DOE NNSA SSGF program. For more across the NSE and especially the earned national recognition through information, visit www.krellinst.org/ train, and retain talent is critical. LDRD awards,LDRD-funded presentations projects athave international frequently ssgf/conf/2015.2015 Computational Science effortsthe LDRD attract Program’s top-tier ability postdoctoral to draw, conferences, papers published in peer- Graduate Fellowship (CSGF) researchers and early-career staff to the reviewed journals, and patents. About Program Review

be held at the Crystal Gateway Marriott NNSA laboratories. Most of these convert projects.one-half of ● patents and one-half of LLNL’s inThe Arlington, 2015 CSGF Virginia Program on JulyReview 27-30, will to full-time staff after engaging firsthand R&D 100 awards have come from LDRD in the national security mission; LLNL’s innovative group learning to use high Staff Highlight: Julie Jackson 2015. DOE CSGF scholars are part of an

performance computing to solve scientific forand these engineering fellows—as problems. well as The program DOE Mehanical engineer Julie Jackson (BS, University of graduate summer intern and has worked on several LDRD CSGF Program Review makes it possible California-Davis) started at LLNL in 2012 as an under- members of the fellowship community— toalumni, share DOE ideas, staff, support faculty one and another other onprojects. disruptive “I was fabrication interested technologies. in being an experimentalist,” I was lucky enough she and discover research opportunities toexplains, transition “so fromin 2013 a student I started intern work to on a anpost-bachelor AM LDRD project appointment, and then to a staff employee. LDRD projects funded by the Department of Energy and at the DOE/NNSA laboratories. Jointly still spend a large percentage of my time on LDRD-related projects,acted as aconstructing stepping stone various for my components career here that at LLNL. are additively I manufactured with National Nuclear Security Administration, projection micro-stereolithography.” technologythe CSGF Program professionals was developed with advanced to meet computerthe Nation’s skills. growing For more need information, for science and ●

Staff Highlight: Eric Duoss visit www.krellinst.org/csgf. Material engineer Eric Duoss (PhD, University of Illinois at Urbana-Champagne) is currently working to advance some of the technologies developed during his LDRD projects

go into upcoming hydrodynamics tests—components that to create unique and cutting-edge components that will

could provide tremendous value to the NSE. Says Duoss, helped“We started write throwing parts of thearound LDRD LDRD proposal, research and ideasafter startingduring my interview. After accepting but before arriving at LLNL, I

here, I supported the proposal presentation. It was certainly a unique opportunity Happy July 4th! for a postdoc to get that level of insight. Before coming to LLNL, I did not know much about the NSE. Because of my LDRD work early in my career, I have gained exposure to the NSE that really would have been otherwise impossible.”

Office of Research, Development, Test, and Evaluation Volume 5 | Number 2 | June 2015 University Partnerships

The Seventh OMEGA Laser Users Group (OLUG) Workshop

and postdoctoral researchers More than 63 graduate students

attended the National Nuclear Security Administration (NNSA)- ofsupported Rochester OLUG Laboratory Workshop for heldLaser on EnergeticsApril 22-24, (LLE). 2015 Forty-sixat the University of those attendees received travel assistance

by the Massachusetts Institute of Technology.from an NNSA Welcoming grant administered remarks were presented by LLE Director Robert McCrory and Attendees of this year’s successful Seventh OMEGA Laser Users Group Workshop held in April. 7 posters by undergraduates Dean Robert Clark. Dr. Keith LeChien, Director of the NNSA Office of Inertial • postdocs scientists—students,OLUG, the Users Group academics, for the and Confinement Fusion, presented the researchersOmega Laser from Facility, 55 universities, comprises 428 Among the workshop highlights were • Invited44 posters science by graduate talks by studentsworld-class and NNSA perspective to attendees. more than 35 centers and national experts • the following:70 contributed posters countries and four continents. The 2 outstanding posters by LLE A young researcher forum on way to laboratories, and 21 different • summer high school students • 14 Findings and Recommendations • • Eighth OLUG Workshop is scheduled improve the Omega Facility. for April 27-29, 2016 at LLE.

Massachusetts Institute of Technology Deputy Administrator for Defense Programs Don Cook recently visited

Plasma Accelerator Facility for Diagnostic and Platform Development the Massachusetts Institute of Technology’s High Energy Density

forRinderknecht, NIF, Omega, Don and Cook, Z. From Alex left Zylstra, to right: Maria Fredrick Gatu Séguin,Johnson, Chikang Brandon Li, David Orozco, Johan Frenje, Emily Armstrong, Richard Petrasso, Hans decided to accept the Lawrence and Reines Postdoctoral Fellowships Lahmann, and Hong Sio. (Rindernnkectht and Zylstra ultimately Labotatory, respectively.) at Lawrence Livermore National Laboratory and Los Alamos National

University of Nevada, Reno The Third International Workshop on Radiation from High Energy Density Plasmas (RHEDP

2015) was held on June 9-12, 2015 in Stateline, Nevada. There were 68 researchers in attendance, 29 of which were students and 6 postdocs.Inertial Fusion, There Theoretical were a total Modeling of 58 presentations and withDiagnostics, 33 invited Pulsed oral Powertalks in Driven six subtopic Plasma, areas: Gas-puff Z-pinches, Laser Produced Plasmas, and Astrophysics and a poster session with 25 presentations. The presentations highlighted

issues and exciting future directions. progress in the field, while identifying current

Volume 5 | Number 2 | June 2015 Stockpile Stewardship Quarterly