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December 1996

Lawrence

Livermore

National

Laboratory

Science &

Technology Review

Lawrence Liverm

ore National Laboratory

P.O.B

ox 808, L-664Liverm

ore, California 94551

Printed on recycled paper.

Nonprofit O

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PAID

Livermore, C

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it No.154

Crossing thePetawatt ThresholdCrossing thePetawatt Threshold

Also in this issue: • Stockpile Surveillance• Earth Core Studies• 3-D Computer Motion

Modeling

About the Review

Adjusting a diagnostic lens in LawrenceLivermore’s new ultrashort-pulse laser, calledthe Petawatt, is laser physicist DeannaPennington. World-record peak power of 1.25petawatts (1.25 quadrillion watts) was reachedMay 23, 1996. In this issue beginning on p. 4,we discuss the challenges and development ofthis extraordinary laser.

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About the Cover December 1996

Lawrence

Livermore

National

Laboratory

Crossing thePetawatt ThresholdCrossing thePetawatt Threshold

Also in this issue: • Stockpile Surveillance• Earth Core Studies• 3-D Computer Motion

Modeling

Lawrence Livermore National Laboratory is operated by the University of California for theDepartment of Energy. At Livermore, we focus science and technology on assuring our nation’s security.We also apply that expertise to solve other important national problems in energy, bioscience, and theenvironment. Science & Technology Review is published ten times a year to communicate, to a broadaudience, the Laboratory’s scientific and technological accomplishments in fulfilling its primary missions.The publication’s goal is to help readers understand these accomplishments and appreciate their value tothe individual citizen, the nation, and the world.

Please address any correspondence (including name and address changes) to S&TR, Mail Stop L-664,Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94551, or telephone(510) 422-8961. Our electronic mail address is [email protected].

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SCIENTIFIC EDITOR

Ravi Upadhye

PUBLICATION EDITOR

Sue Stull

WRITERS

Bart Hacker, Arnie Heller, Dale Sprouse,Katie Walter, and Gloria Wilt

ART DIRECTOR

George Kitrinos

DESIGNERS

Paul Harding, George Kitrinos, and Ray Marazzi

GRAPHIC ARTIST

Treva Carey

INTERNET DESIGNER

Kathryn Tinsley

COMPOSITOR

Louisa Cardoza

PROOFREADERS

Al Miguel and Jill Sprinkle

S&TR is a Director’s Office publication,produced by the Technical InformationDepartment, under the direction of the Officeof Policy, Planning, and Special Studies.

2 The Laboratory in the News

3 Commentary by E. Michael CampbellOpportunities for Science from the Petawatt Laser

Features4 Crossing the Petawatt Threshold

The new Petawatt laser may make it possible to achieve fusion using much less energy than currently envisioned.

12 High Explosives in Stockpile Surveillance Indicate ConstancyA well-established portion of the Stockpile Evaluation Program performs extensive tests on the high-explosive components and materials in Livermore-designed nuclear weapons.

Research Highlights18 Visualizing Body Motion21 Studying the Earth’s Formation: The Multi-Anvil Press at Work

24 Patents and Awards

26 Abstracts

27 1996 Index

S&TR Staff December 1996

LawrenceLivermoreNationalLaboratory

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Available fromNational Technical Information ServiceU.S. Department of Commerce5285 Port Royal RoadSpringfield, Virginia 22161

UCRL-52000-96-12Distribution Category UC-700December 1996

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3

Science & Technology Review December 1996

Commentary by E. Michael Campbell2 The Laboratory in the News


Director looks at Lab’s technical challengesDescribing himself as very optimistic about Lawrence

Livermore’s progress and future, Director Bruce Tarter saysthat in the coming year, the Laboratory will “have to deliveron major products” in addition to “first rate R&D” in the areasof national security, energy, and biotechnology.

With the country committed to no nuclear testing under theComprehensive Test Ban Treaty, Lawrence Livermore must“focus on providing Congress and the President with highconfidence in the stockpile,” the Director said. “This means anenhanced effort on surveillance and life extension of thecurrent stockpile and rapid progress on major initiatives.” Hestressed that the National Ignition Facility (NIF) must remainon schedule and within costs and that the AcceleratedStrategic Computing Initiative (ASCI) must be a “fast-trackprogram.” NIF and ASCI are two key components of the effortto ensure the integrity of the nation’s nuclear weaponsstockpile without nuclear testing.

Tarter said the Laboratory’s challenge in energy is proving,with the U.S. Enrichment Corp. (USEC), that “laser isotopeseparation can work in the commercial environment.” USEChas designated the Lab’s isotope separation technology as theway to make reactor fuel in the 21st century (see AVLIS newsitem next column).

In biotechnology, Tarter said, stronger productioncapability will be needed to sequence the human genome.Explained the Director: “For the last half dozen years, we havebeen mapping with markers to lay out the structure of thegenome; now we have to sequence it, that is, fill in all thedetails—a much more production-oriented activity that isdriven by national and international competition.”

Tarter outlined the challenges facing the Laboratory in thecoming year in an address to employees in early October.Discussing the budget for FY 1997, Tarter said the Lab’s totalcosts will be $1,057 million, with $929 million going tooperating costs and the remainder to construction and majorcapital procurements.Contact: Jeff Garberson, LLNL Media Relations, (510) 422-4599([email protected]).

Reis dedicates ASCI–Blue PacificMission, partnership, and technology were the themes as

Vic Reis, the DOE’s assistant secretary for Defense Programs,visited the Laboratory in late October. At Livermore, hededicated ACSI–Blue Pacific, the 3-trillion-calculations-per-second supercomputer being built as part of the DOE’sAccelerated Strategic Computing Initiative (ASCI).

Targeted for demonstration in December 1998, thesupercomputer is a collaboration between Livermore and IBMin which, said Reis, “both partners bring unusual talent.”

“The deterrence mission remains the underpinning of ournational security,” Reis noted, and the ASCI supercomputerwill be a “central tool” in efforts to keep the nation’sstockpiled nuclear weapons safe and reliable.Contact: Jeff Garberson, LLNL Media Relations, (510) 422-4599([email protected]).

AVLIS team puts enrichment technology through its paces

The Laboratory’s Atomic Vapor Laser Isotope Separation(AVLIS) team has a new goal: extend operating hours forthe Livermore-developed uranium enrichment technology,demonstrating the reliability required of a fully functioningenrichment plant by the end of the calendar year. Achievingthat goal means around-the-clock, seven-day-a-weekoperation of the key AVLIS Demonstration Facility areas:lasers, separators, and control devices.

AVLIS personnel have been running ever-lengtheningendurance tests at Livermore for the U.S. Enrichment Corp.(USEC). These design verification runs are aimed atbringing the technology to the point where USEC can use itfor commercial production of enriched uranium.

USEC, a U.S. government corporation in the process ofprivatizing, produces and markets uranium enrichmentservices worldwide. It selected Lawrence Livermore-developed AVLIS enrichment technology as the“technology of choice” to ensure that the U.S. maintains itslead in the world uranium enrichment market.

In a 200-hour test in September, the AVLIS separatoroperated around the clock for 6 days, processing 3 metrictons of uranium.Contact: Bruce Warner, Lawrence Livermore AVLIS ProgramManager, (510) 422-9237 ([email protected]) or Victor Lopiano,USEC Director of AVLIS Enrichment and Livermore Operations,(510) 424-2851 ([email protected]).

Nonproliferation, arms control focus of Labworkshop

As a followup to a 1995 workshop in Snezhinsk, Russia,Russian and American scientists met at Livermore inSeptember to explore the possibility of joint projects in armscontrol and nonproliferation technologies. Discussed at theworkshop were possible collaborations on technicalapproaches to a wide range of international problems.

Principal attendees were from the Russian Ministry ofAtomic Energy, the All Russian Institute of ExperimentalPhysics, the All Russian Institute of Technical Physics, andLos Alamos, Sandia, and Lawrence Livermore NationalLaboratories. Also represented were the U.S. Departmentsof Energy, Defense, and State and the Russian Ministry ofForeign Affairs.Contact: Paul Herman (510) 423-0945 ([email protected]).

URING the past 25 years, Lawrence Livermore hasbecome a world-renowned research center for designing,

building, and utilizing high-peak-power and high-energylasers. Starting with the 100-million-watt, two-beam Januslaser in 1974, we designed and built a series of laser systems,each providing five to ten times more irradiance (power perunit area) than its predecessor.

Our series of increasingly more capable facilities nowculminates in a revolutionary one-aperture laser, the Petawatt,with output power exceeding a quadrillion watts. Using thetechnique of chirped-pulse amplification, which enables us toproduce very short (less than a trillionth of a second) energeticpulses on one arm of the ten-arm Nova laser, the Petawatt isable to exceed the total power of Nova by a factor of 10.

Even more impressive than its output power is thePetawatt’s extraordinary brightness. Coupled with innovativefocusing schemes, this brightness will enable the Petawatt tobe focused to irradiances that produce an electric fieldexceeding by a factor of 100 the force that binds an electronto a proton in the hydrogen atom.

“Crossing the Petawatt Threshold,” beginning on p. 4,describes the major technical and scientific advances thatwere required to make a petawatt laser a reality at Livermore.

D These advances in laser science and optical componentfabrication have enabled revolutionary new concepts in laserscience and machining as well as information displayproduction technologies.

What’s more, the enormous energy density of thePetawatt will push back the frontiers of knowledge aboutlaser–matter interaction and expand our knowledge of matterunder extreme conditions. For the first time in a laboratorysetting, we will be exploring relativistic plasma physics andnew sources of coherent and incoherent radiation at highphoton energy.

Finally, the Petawatt will allow us to test a new pathway tolaser fusion, called “fast ignition,” that was developed atLawrence Livermore early in this decade. As described in thearticle, the fast-ignition concept cleverly sidesteps the mostdifficult aspects of achieving fusion ignition withconventional inertial confinement fusion design.

The enormous opportunities created by the Petawatt willkeep Lawrence Livermore in the forefront of high-powerlaser physics and high-energy-density physics for theforeseeable future.

■ E. Michael Campbell is Associate Director, Laser Programs.

Opportunities for Sciencefrom the Petawatt Laser

to keep a 100-watt light bulb burningfor about 6 seconds.

By crossing the petawatt threshold,the laser heralds a new age in laserresearch. Lasers that provide a petawattof power or more in a picosecond maymake it possible to achieve fusion usingsignificantly less energy than presentlyenvisioned, through a novel Livermoreconcept called fast ignition. (SeeScience & Technology Review,September 1995, for more information.)The Petawatt laser will also enableresearchers to study the fundamentalproperties of matter, thereby aiding theDepartment of Energy’s stockpilestewardship efforts and opening entirelynew physical regimes to study.

Coincidentally, University ofCalifornia at Berkeley professor Charles

Townes was visiting the Laboratory onthe same day, May 23, as a member of apanel reviewing the Laser Programs(see Figure 1). Townes was awarded theNobel Prize in 1964 for co-inventingthe first laser, which generated only afew thousandths of a watt.

“When the laser first came along, I never imagined it getting up thathigh,” Townes told reporters. “Whenwe first invented them, I was thinkingabout very modest powers. It neveroccurred to me it would be in this kindof ballpark.”

Indeed, the Petawatt is only the latestof a family of lasers with increasingirradiance (power per unit area) thatbegan in the 1970s with LLNL’s Argus,Shiva, and then Nova laser systems (seeFigure 2). The introduction in the

mid-1980s of a unique new lasermaterial—titanium-doped sapphire(Ti:sapphire)—offered high gain over abroad range of wavelengths. Togetherwith a new technology—chirped-pulseamplification (CPA) to minimize lasermaterials damage—they offered thepossibility of creating high-powersubpicosecond pulses directly from asolid-state laser. Lawrence Livermoreresearchers began work on short-pulselasers in the mid-1980s and completed a10-terawatt (TW) laser in 1989. Theembodiment of most of the advancessince that time resides in the Petawatt.

With its full-aperture beam of 58 centimeters in diameter (to beinstalled in early 1997 to replace a 46-cm beam), the Petawatt will produceabout 1 kilojoule of energy in less than

5


Petawatt

OR more than three decades,Lawrence Livermore’s Laser

Programs have earned a worldwidereputation for pushing the limits of lasertechnology. But few accomplishmentshave rivaled the one celebrated in theearly morning hours of May 23, 1996,by an exhausted but exuberant crew thatjust used a revolutionary laser thatproduced more than a quadrillion wattsof energy, a world record.

The extraordinarily powerful laser iscalled the Petawatt because the prefix“peta” refers to a quadrillion, or 1015.The laser reached a peak of 1.25petawatts of peak power, about 25%more powerful than expected and morethan ten times the peak power ofLawrence Livermore’s Nova laser, theworld’s largest. The historic shotsshattered the existing record for laserpower (125 trillion watts) by more thana factor of 10, set by Livermoreresearchers using a Petawatt prototypeduring the summer of 1995.

Although the shots exceeded by morethan 1,200 times the entire electricalgenerating capacity of the U.S., theylasted less than half a picosecond (a trillionth, or 10–12, of a second). Inthat exceedingly fleeting moment,nearly 10,000 times shorter than thetypical Nova laser shot, only enoughenergy (about 600 joules) was generated

4


Petawatt Crossing thePetawatt Threshold

An extraordinarily powerful new

laser promises to help make fusion

power more easily attainable with

“fast ignition.” The laser beam’s

ultrashort pulses and extremely

high intensities will also enable

researchers to advance their

understanding of the fundamental

nature of energy and matter.

F

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Year8674 94 98 02

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LLNL 10-TW Nd:glass laser

Rutherford Vulcan CPACEA-Limeil P102

LLNL 100-TW Nd:glass laser

LLNL 1,250-TW (petawatt) Nd:glass laser (May 1996)

T3 University of Rochester

NIF (single beam)

Nova (single beam)

Shiva (single beam)

Argus

Figure 1. With the Petawatt is laser inthe background, Livermore’s MichaelPerry (left) shows how far thetechnology has come to UC BerkeleyProfessor Charles Townes, who co-invented the laser.

Figure 2. Milestones in laser development: early lasers (yellow), long-pulse technology (green),and chirped-pulse amplification technology (blue).

Laser physicist Deanna Penningtonadjusts a diagnostic lens within thePetawatt’s compressor chamber. At rightis one of the diffraction gratings, whilebehind her are a turning mirror and thesecond compressor grating.

compressed using a pair of diffractiongratings each 74 centimeters indiameter. By reversing the process ofthe stretcher (now the red componentstravel a longer length than the blue),the pulse is compressed down to lessthan half a picosecond (nearly itsoriginal duration), thereby increasingits peak power nearly 10,000 times tomore than a petawatt. Such pulses mustbe compressed in a vacuum becausethe irradiance of the beam leaving thesecond grating is over 700 GW/cm2,far too great to pass through anymaterial (including air) withoutresulting in damage.

The Grating ChallengeOne of the most challenging

tasks was the fabrication of pulsecompression gratings of sufficient size,optical quality, and ability to withstandthe enormous power of the Petawattlaser pulse. Said Perry, “When theproject began, there wasn’t a facility inthe world capable of making therequired gratings, so we created one.”

The diffraction gratings that areused in the Petawatt laser are nearly 1 meter in diameter, some eight timeslarger and twice as resistant to damageas the previous state of the art.Livermore’s successful development ofdiffraction grating technology for thePetawatt led to the selection of gratingsfor many uses on the National IgnitionFacility (NIF), a 192-beam laserfacility planned for Livermore.

Initially, achieving a petawatt ofpeak power was expected to require anentirely new optical component—ahigh-efficiency, multilayer dielectricgrating. That advanced technology wasdeveloped by the Petawatt team in1993 and 1994, an achievementrecognized in 1994 with an R&D 100Award. However, the dielectricgratings were not used in the currentexperiments because new metallicgratings developed by the team haveproven satisfactory for petawatt pulsesat 0.5-picosecond durations. These

metallic gratings are simpler tomanufacture than the multilayergratings. Multilayer gratings would berequired to achieve the multikilojoulepulses necessary to achieve ignition iffast-ignitor capability is added to theNIF. Interestingly, the multilayerdielectric grating technology hasalready produced its own spinoff. (See

this and other spinoff technologiesdiscussed in the box below.)

With the grating technology in hand,the focus of the Petawatt team moved toinstallation of the petawatt system onthe Nova laser. Numerous large-scaleoptical and mechanical componentscapable of working at extreme precisionunder vacuum had to be designed,

7


Petawatt

0.5 picosecond. In contrast, onebeamline of Nova typically produces 10 kilojoules of energy in 1 nanosecond(billionth of a second), some 1,000 timesslower. Nova and the National IgnitionFacility (NIF) planned for Livermoreare long-pulse lasers (nanoseconds andlonger), specifically designed toproduce high-pulse energy.

Petawatt DevelopmentThe Petawatt Advanced Fusion

Project was proposed in 1992 as a high-risk, potentially high-payoff project todevelop the capability to test the fast-ignitor concept for inertial confinementfusion (ICF) and to provideLivermore—and the world—with aunique capability in high-energy-density physics. Michael Perry, leaderof Lawrence Livermore’s Short-PulseLasers, Applications, and TechnologyProgram, won a competitive grant in1993 from LLNL’s in-house LaboratoryDirected Research and Developmentprogram to begin building the laser.

Perry formed a core team ofphysicists, engineers, and technicianswith backgrounds in laser physics,optics, engineering, materials science,and atomic physics. Team membersknew that success required advances inknowledge of the basic behavior ofoptical materials, development of newdiffraction grating technology,substantial improvements in short-pulselaser technology, and advancement of asound theoretical basis for the fast-ignitor concept. Finally, they recognizedthat although an all-Ti:sapphire lasercould not provide sufficient power, ahybrid system starting with a Ti:sapphirelaser and using new, smaller, and moreefficient neodymium glass amplifierscould provide the necessary pulse energyand bandwidth to achieve a petawatt.

Much of the Petawatt’s early effortwas devoted to further developing CPAtechnology. CPA was first developed toincrease the power of radar systems andwas discussed for use in lasers in themiddle 1970s. The first successful

demonstration occurred for solid-statelasers in the late 1980s at the Universityof Rochester. Further developments atRochester, Lawrence Livermore, andelsewhere along with the introduction ofnew laser materials (e.g., Ti:sapphire)have revolutionized high-power laserresearch. (See Figure 3.)

CPA is critical because laser pulses ofextremely high power density(gigawatts/centimeter2, or GW/cm2) canseverely damage optical componentssuch as amplifiers, lenses, and mirrors.With CPA technology, it became possibleto generate very short laser pulses withextremely high peak powers by stretchinga low-energy laser pulse more than10,000 times its duration prior toamplification and then recompressing thepulse back to near the original durationafter amplification. Because passagethrough the laser optics occurs when thepulse is long, there is no damage.

Using this technology, the Petawattlaser begins with a broad-bandwidth,low-power pulse lasting less than 0.1 picosecond in a temperature-controlled clean room in the basement ofthe Nova building. Instead of consistingof a single, very specific wavelength(color) produced in conventional lasers,these ultrashort pulses contain a broadspectrum. Before amplification, the short-pulse beam is sent to the pulse stretcher.Here, the pulse is stretched by using adiffraction grating to spread out thedifferent wavelengths (colors), separatingeach frequency component. By passingeach color through a different opticalpath length (the red components travel ashorter length than the blue), the pulse isstretched in time by a factor of 30,000 to3 nanoseconds. The pulse is thenamplified more than a trillion timeswithout damaging the laser glass as thepulse travels through a series of amplifiermodules, including a portion of one armof the Nova laser for the final amplifierstage.

After amplification, the beam is then sent to the vacuum chamber 3 ¥ 11meters long, where the pulse is

6


Petawatt

Initial short pulse

Short-pulse oscillator

Long, low pulse

High-energy pulse

High-energy ultrashort pulse

Metallic gratings

Second pair of metallic gratings

Power amplifiers

Petawatt Spinoffs

The technology developed for the Petawatt has provided many unexpectedspinoffs. In particular, Lawrence Livermore’s experimental and theoretical studies oflaser-induced damage, carried out in support of the Petawatt laser’s development, havecreated valuable new technologies. Researchers, led by Brent Stuart, using the petawattfront end made pioneering measurements of the laser damage threshold for a multitudeof optical materials (crystal and glass) lasting from 0.1 picosecond to 1 nanosecond. Afundamental change in the damage mechanism is observed when the pulse length isless than approximately 20 picoseconds. This change in mechanism is accompanied bya dramatic change in the morphology of the damage site.

The discovery and explanation of this difference formed the basis of acollaborative program with medical researchers on the interaction of short laser pulseswith human tissue. Laser ablation of tissue (removal of tissue by its being “blown off”)has great promise in a number of therapeutic situations requiring precise materialremoval with minimal disturbance of the surrounding tissue. Potential applicationsinclude precision cutting (as in keratonomy), perforation (applicable to middle earsurgery), pressure release for hydroencephaly, and dental drilling. The advantage forsurgery with lasers whose pulses last less than a picosecond is that the duration is fartoo short to transfer heat to surrounding tissue. (See the October 1995 S&TR for moreon LLNL efforts to develop short-pulse lasers as safe and painless surgical tools.) Theability to cut and drill material with no heat or shock has also found importantapplication in LLNL’s role in nuclear weapon stockpile management.

Two R&D 100 Awards were earned as a result of the need to manufacturediffraction gratings to a size, precision, and resistance to optical damage never beforeattained. The first, earned in 1994, was the development of multilayer dielectricgratings for use in dispersing light into constituent colors, or wavelengths, for manydifferent applications. These gratings, made of multiple layers of thin dielectric film,have much higher damage thresholds than metallic gratings and can be customdesigned for narrow- or broad-bandwidth use. Besides their use in new generations ofextremely high-powered lasers, they may be used in entirely new products in suchareas as remote sensing and biomedical diagnostic systems. (See the September 1994E&TR for more information.) Furthermore, the grating development laboratory andtechnology will be used for developing the extensive diffractive optics used throughoutthe final focus assembly of the planned National Ignition Facility.

The technology developed to produce the multilayer and metallic gratings withextremely small features (down to 0.1 micrometer) may also give a dramatic boost toAmerican producers of flat-panel displays. The LLNL process to laser interferencelithography enables the production of large-area field-emission displays (FEDs). Thisdisplay can be thinner, brighter, larger, and lighter and can consume less power thantraditional active matrix liquid crystal displays. The new technology earned itsinventors an R&D 100 Award in 1996 (see the October 1996 S&TR).

Figure 3. The concept of how chirped-pulse amplification and other new technologiesenable the production of the petawatt (quadrillion-watt) pulses.

installed between the Petawatt’scompression chamber and Nova’s ten-beam chamber. It will permit thePetawatt laser to be used independentlyof Nova.

The decision to develop a targetchamber exclusively devoted to petawattlaser use, while retaining the ability toperform experiments in Nova’s ten-beamtarget chamber, was prompted by thehigh level of interest expressed byresearchers at LLNL and other centers.

Building a petawatt target chambermakes good sense, says Perry, “becauseit will allow us to work the bugs out ofthe Petawatt’s focusing system andenable simple, single-beam experimentswithout impacting operation of the Novachamber.”

The 100-TW laser was constructed inearly 1995 as a crucial stepping stone tothe Petawatt. Using most of thePetawatt’s components, but not takingadvantage of the full complement ofNova’s amplifiers, the 100-TW isconnected to Nova’s two-beam targetarea. It was successfully test fired for thefirst time on July 31, 1995, surpassingthe 120 trillion watts produced by Novaand making it the most powerful laserever tested at the time.

“The 100-TW was only a warm-upfor the Petawatt,” says project engineerGreg Tietbohl, noting that the laser hasbeen used to test some of the basicconcepts and advanced componentsunderlying the Petawatt. Laser–plasmaexperiments being performed on the 100-TW laser are producing data that enablethe design of a more comprehensiveseries of experiments to test the fast-ignitor concept on the Petawatt. The 100-TW laser continues to operate as theworld’s second most powerful laser, andit is now used extensively by researchersfrom LLNL and the internationaluniversity community. The 100-TWoperations will end in July 1997 becauseNova’s two-beam target bay will bedisassembled in order to build an opticsassembly area for NIF.

Focusing Petawatt PulsesA significant problem with petawatt

pulses is how to focus them.Conventional approaches such as lenses or mirrors with debris shieldscannot be used because these bothinvolve transmissive optics that wouldbe damaged by the extreme powerdensity of the petawatt pulse (over 700 GW/cm2).

A radical concept proposed by Perryand Associate-Director-at-Large JohnNuckolls was the use of a so-called“plasma mirror.” The intense petawattbeam strikes the front surface of a pieceof polished glass, creating a very-short-lived critical-density plasma in the earlypart of the pulse. Because the petawattpulse is so short, the plasma does nothave time to expand during the pulse.The remainder of the pulse then reflectsoff the critical-density plasma andstrikes the target of interest.

The resulting detonation of the targetcreates a large amount of debris (typicalof all target experiments) that hits theplasma mirror substrate instead ofsensitive and expensive diagnosticequipment and optics. (See Figure 5 forthe difference in optical- and plasma-mirror irradiances.) The curvature of themirror can be easily changed to

accommodate a wide variety ofexperimental conditions and targets. Todate, over 90% reflectivity has beendemonstrated in small-scaleexperiments conducted with thePetawatt’s front end.

Possible Key to FastIgnition

The Petawatt provides researcherswith their first tools to explore the fast-ignitor fusion concept, conceived byLivermore’s Max Tabak and others in1992. Focusing a high-power laserpulse gives rise to an extremely highdensity of energy, or light pressure.This light pressure can enable the laserpulse to interact with very-high-densitymaterial at the core of an implodedfusion pellet instead of being stoppedby lower-density plasma in the corona.These intense pulses also generate largeamounts of energetic electrons. Thesehigh-intensity phenomena form thebasis of the patented fast-ignitor fusionconcept. (See Figure 6.)

In this scheme, laser energycompresses a spherical volume offusion fuel to high density—exactly asin the conventional approach to ICF.However, conventional ICF relies onthe formation of a hot central core

9


Petawatt

fabricated, and installed. Significantmodifications to the ten-beam target baywere performed over many weekends,when the Nova laser is usually not usedfor target experiments. A new beamlinewas installed to route the beam from thePetawatt’s master oscillator room to the disk amplifier section of Nova’sbeamline number 6 for finalamplification. A particularly challengingtask was installation of the enormouscompression chamber in the target baywithout disrupting the normal operationof the Nova system.

With everything in place, three seriesof experimental shots were performed. Inthe first series, performed in December1994, the Petawatt’s beam waspropagated to Nova’s two-beam targetbay to study CPA effects. For the secondshot series, performed in March 1995, thebeam was propagated into the newlyconstructed compression chamber to

produce a short pulse length. Followingthe March 1995 shot series, the newinjection beamline between the Petawatt’smaster oscillator room and the Novapreamplifier was activated, along with thecompression chamber vacuum system anda full suite of optical diagnostics. Thefinal test series performed in May 1996produced the record-shattering result, butnot without exceptionally hard work. “Wehad to work 16-hour days, 7 days a weekfor more than a month to make sureeverything was ready for thedemonstration shots. It was a true teameffort between the Nova engineers,operations crew, and the Petawatt projectteam,” recalls Perry, who furnished non-alcoholic champagne for the historicnight. (See Figure 4.)

Four OptionsAs the Petawatt laser is now

configured, the beamline from the

underground master oscillator room cantake one of four courses. First, it can beinjected into the Nova chain to thePetawatt’s compressor chamber andused along with nine of Nova’s tenbeams as a large-scale hybrid system totest the fast-ignitor concept andinvestigate new concepts in laser–matterinteractions and plasma physics. Second,the beam can be shunted to a small roomnext door to the master oscillator room,where it is used for researching issuesrelated to the use of lasers in medicineand material processing, development ofplasma mirrors, and harmonicconversion to a shorter wavelength forNova x-ray diagnostics development.

Third, through early next summer,the laser can be used as the core of a100-trillion-watt laser to study plasmaphysics and begin research on fast-ignitor physics. Finally, early thiswinter, a target chamber will be

8


Petawatt

Figure 4. The Livermorecrew after the firstsuccessfulaccomplishment ofpetawatt peak power(1,250 trillion watts) onMay 23, 1996. 125

Mic

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150 162 175 188 200Micrometers Micrometers

140 160 180 200

Figure 5. False-color contour plot of far-field irradiance distributions from (a) a precision optical mirror (diffraction-limited spot) and (b) a plasma mirror.

the core to over 100 million degreesCelsius. The fusion burn propagatesfrom this small volume on the edgethroughout the remaining fuel beforehydrodynamic disassembly of the core.

The fast-ignitor technique offers, inprinciple, a method of reducing theenergy and precision required toachieve ignition compared withconventional ICF. Perry cautions that,compared with the firm scientificfoundation of conventional ICF, thefast-ignitor concept is still in its infancybecause it resides in a region of untestedphysics. If, however, upcoming fast-ignition tests prove successful, apetawatt laser could be added to the NIFfor fast-ignitor capability at a moderateadditional cost.

The Petawatt’s beam would be firedto inject energy into a small region ofthe deuterium–tritium target capsule toinitiate ignition a few billionths of asecond after NIF’s beams are fired. APetawatt–NIF combination mightenable the achievement of a higherfusion energy gain than currentlyenvisioned.

A New Chapter in PhysicsThe ultrashort pulses and extremely

high irradiance of the Petawatt laserwill also enable researchers to advancetheir understanding of laser–matterinteractions and, indeed, advanceunderstanding of the fundamentalnature of energy and matter. Theenormous irradiance that will begenerated by the Petawatt, some 1021

W/cm2, will make possible anirradiance unlike any produced in thelaboratory to date. These unprecedentedlaboratory conditions will becharacterized by electric fields about100 times stronger than the field thatbinds electrons to atomic nuclei. Suchfields have the potential to trapelectrons and accelerate them to highenergies within just a few centimeters,

instead of many kilometers as inconventional particle accelerators.

The enormous electric fields createdby the Petawatt will impart enormousoscillatory (“quiver”) energy to the freeelectrons in the plasma. At 1021 W/cm2,the quiver energy of a free electronwould be more than 10 million electronvolts. The electrons would be moving atspeeds approaching the speed of lightand at densities never before seen in thelaboratory.

These plasmas will be similar to thosebelieved to exist in many astrophysicalobjects. Scientists could then studyconditions predicted to exist in the centerof stars and surrounding celestial bodiessuch as black holes and brown dwarves.

Additionally, high-energy photons(0.1 to 10 megaelectron volts) producedfrom the interaction of the petawatt pulsewith high-atomic-number targets offerthe potential for time-resolvedradiography of dense objects. The short-pulse duration, potentially small sourcesize, and simple production of multiplepulses separated in time make this anattractive source for multiple-exposureflash x-ray radiography. The plasmasthemselves can provide important

information to Lawrence Livermorescientists supporting DOE’s StockpileStewardship and Management Program.

The Petawatt laser is currentlyundergoing a long series of tests as it istransformed into an operational facilityfor target experiments. Its development isexpected to continue into the next decadeas LLNL scientists continue to advancethe state of the art in optics and thetechnology of short-pulse lasers. Perrynotes that several years of hard work lieahead in exploring the fast-ignitorconcept with the Petawatt. The overallgoal, as it was with the development ofLivermore’s first generation of lasers, isto speed the arrival of laser fusion as asource of virtually inexhaustible energyfor society. Another goal, admittedlycloser at hand, is to aid the nation’sStockpile Stewardship Program.

Key Words: chirped-pulse amplification, fastignition, laser interference lithography,multilayer dielectric gratings, NationalIgnition Facility, Nova, Petawatt laser, plasmamirror, Ti:sapphire laser, 100-TW laser.

For further information contact Michael Perry (510) 423-4915([email protected]).

11


Petawatt

within the dense deuterium–tritium fuelto spark ignition. This condition isachieved by the rapid, highlysymmetrical and spherical implosion ofthe capsule driven by pulses deliveredeither directly by many laser beams orindirectly by x rays. Because of theextreme requirements on symmetry andthe necessity to achieve both hightemperature and density in theimplosion, conventional ICF requires

substantial energy and precision fromthe laser.

By contrast, the fast-ignitor conceptadds two laser beams that are timed tostrike the target at the moment ofmaximum compression. Because thePetawatt was conceived to use Nova,eight of Nova’s ten beamlines wouldstrike the target and form a plasma.Then a 1-TW, 100-picosecondchanneling beam supplied by the

Petawatt laser bores through the plasmaand pushes the deuterium–tritium fuel inits path toward a higher density near thecore of the target. At the optimummoment, a petawatt ignitor beampropagates through the channel formedby the channeling beam, striking thehigh-density, preimploded core. Thepetawatt pulse generates hot, high-energy electrons, which instantaneouslyraise a small region on the periphery of

10


Petawatt

Conventional ICF

Fast-Ignitor ICF

Laser energy

Inward transported thermal energy

Thermonuclear burn

Blowoff

Atmosphere formation Laser or particle beams rapidly heat the surface of the fusion target, forming a surrounding plasma envelope.

Compression Fuel is compressed by rocket-like blowoff of the surface material.

Ignition During the final part of the implosion, the fuel core reaches 20 times the density of lead and ignites at 100,000,000°C.

Burn Thermonuclear burn spreads rapidly through the compressed fuel, yielding many times the driver input energy.

Ignition At the moment of maximum compression a short (1 to 10 picoseconds), high-intensity (1020 watt/centimeter2) pulse ignites the capsule.

Burn Thermonuclear burn spreads rapidly through the compressed fuel, yielding many times the driver input energy.

Figure 6. Contrast of conventionalinertial confinement fusion (ICF) and thefast-ignitor ICF, which is used on thePetawatt laser. MICHAEL PERRY joined Lawrence Livermore National

Laboratory as a physicist in October 1987. He is a graduate ofthe University of California at Berkeley with a B.S. in bothnuclear engineering and chemical engineering (Summa CumLaude, 1983), an M.S. in nuclear engineering (1984), and aPh.D. in nuclear engineering/physics (1987). He is currentlythe leader of the Petawatt Laser Project and Associate ProgramLeader for Short-Pulse Lasers, Applications, and Technology.He has authored more than 70 professional publications.

About the Scientist


NY weapon in the U.S. nucleararsenal, if ever deployed, must

work exactly as intended. Americansexpect that assurance even thoughinternational relations since 1989 havebrought dramatic and fundamentalchanges to the U.S. nuclear weaponsprogram. Responsibility for assuringreliability, performance, and safety ofthe nuclear weapons stockpile belongsto the nuclear design and productioncommunity, which conducts the widerange of activities in the Department ofEnergy’s New Material and StockpileEvaluation Program.

Although stockpile evaluation is notnew, methods and tests have undergonemarked changes since the program’sinception almost four decades ago.Today, each of the participatingnational laboratories—LawrenceLivermore, Los Alamos, and Sandia—isresponsible for the extensive andrigorous tests to evaluate the portionsand components of the stockpileweapons that each has designed. Thisoverview of Livermore high-explosives(HE) tests of nuclear stockpile weaponsillustrates the degree of assurancetoward which the laboratories work.

Stockpile Evaluation “Stockpile surveillance” is the third,

or maintenance, phase of a spectrum ofspecial tests that begins during aweapon’s design and ends only with itsretirement from the stockpile (see boxon p. 13 and Figure 1). Such tests noware the principal means of evaluatingthe condition of U.S. nuclear weapons.For this phase, stockpile laboratory testsprovide “indicators of constancy”through comparison with baseline datagathered during weapon developmentand production.

Stockpile laboratory tests usuallybegin during the third or fourth yearafter the weapon’s production begins.Sample weapons removed from thestockpile are dismantled, componentsare inspected and tested, and then theweapons are reassembled and restoredin the stockpile. Increasingly,surveillance activities have focused onone central question: How can aweapon’s useful service life bepredicted?

In addition to checking for materialsand production defects, stockpilesurveillance involves monitoringpotentially damaging changes to a

weapon’s components caused by agingor environmental factors. Simplybecause nothing is wrong, the inferencecannot be made that the weapon willlast indefinitely. Livermore’s EnhancedSurveillance Program is currentlyexamining concepts that improvepredictive capabilities.

Should problems appear, theincreasing body of data will guide theprogram to accommodate or eliminateadverse effects. Old or damaged partsare replaced or upgraded before aweapon is reassembled for thestockpile. This aspect of surveillanceresembles keeping a stored car indriving condition. Regular inspectionscan spot signs of damage ordeterioration before they become toocostly to repair. The vehicle can also beupgraded by installing improvedreplacement parts.

High ExplosivesThe ideal high-energy explosive

must balance different requirements.HE should be easy to form into partsbut resistant to subsequent deformationthrough temperature, pressure, ormechanical stress. It should be easy to

detonate on demand but difficult toexplode accidentally. The explosiveshould also be compatible with allthe materials it contacts, and itshould retain all its desirablequalities indefinitely.

No such explosive existed in 1944.While using what was available tomeet wartime demands, scientists atLos Alamos began to develop a high-energy, relatively safe, dimensionallystable, and compositionally uniformexplosive. By 1947, scientists at LosAlamos had created the first plastic-bonded explosive (PBX), an RDX*-polystyrene formulation laterdesignated PBX 9205. Althoughother PBXs have since beensuccessfully formulated for a widerange of applications, only a handfulhave displayed the combination ofadequate energy content, mechanicalproperties, sensitivity, and chemicalstability required for stockpilenuclear weapons. Since the 1960s,Livermore has been researching anddeveloping safer HE for Livermore-designed weapons.

The plastic coating that binds theexplosive granules, typically 5 to20% of each formulation by weight,is what gives each PBX its distinctivecharacteristics. Pressing a PBXmolding powder converts it into asolid mass, with the polymer binderproviding both mechanical rigidityand reduced sensitivity to accidental

detonation. The choice of binder affectshardness, safety, and stability.

Too brittle a PBX can sustaindamage in normal handling andsuccumb to extreme temperature swingsor thermal shocks, while too soft a PBXmay be susceptible to creep and maylack dimensional stability or strength.To achieve safe and stable PBXs, theLaboratory uses two main chargeexplosives based on HMX and TATB.†

12

A

HMX is more energetic than RDX butretains good chemical and thermalstability, important for long-termstorage and survival in extremeenvironments. Sensitivity of any PBXis a complex characteristic stronglyaffected by HE particle sizedistribution, viscoelastic properties,binder-to-HE wetting, and storageenvironment. Only the TATB-basedformulations (Figure 2) of Livermore’s


High Explosives in StockpileSurveillance Indicate ConstancyLivermore actively seeks to improve the analysis of high explosives in stockpiled nuclearweapons, keeping in mind the purposes of traditional surveillance: to look for defects inmaterials and processes, to monitor indicators of both constancy and change, and toconfirm that design choices did not cause problems.

Development

Screening tests • Chemical reactivity tests • Weight loss • Coupon testsAccelerated coresample tests

(Early in production)Accelerated aging testsNew materials laboratory testsCore test unitShelf storage unitsLong-term storage units

Production Stockpile maintenance Retirement

Dismantlement

Stockpile laboratory tests

Figure 1. Phases of evaluation in stockpile surveillance.

* RDX is 1,3,5-trinitro-1,3,5-triazacyclohexane.† HMX is 1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane; TATB is 1,3,5-triamino-2,4,6-trinitrobenzene. See S&TR, November1996, for more information on TATB.

HE’s Role in a Nuclear Weapon

The nuclear explosive package includes nuclear and non-nuclear components thatcomprise a primary explosive device and a secondary, both enclosed within aradiation-proof case. A key component of a primary is typically a shell of fissilematerial—the pit—to be imploded by a surrounding layer of chemical high explosive(HE) termed the main charge.

Stockpile evaluation requires a comprehensive battery of tests that addresses allfunctional aspects of a weapon throughout its so-called stockpile-to-target sequence,stopping short of actual detonation with nuclear yield. Although the moratorium onunderground nuclear testing has precluded detonating a stockpile weapon to assess itsreliability, performance, and safety, stockpile evaluation is working to provide anadequate alternative route to the same goal of reliability assessment.

The HE clearly plays a role vital to proper weapon function, but many questionssurround the long-term stability of the complex organic molecules of which the HE iscomposed. To provide assurance that stockpile quality is maintained, Livermore’sStockpile Evaluation team develops diagnostic tests that are performed on the HE inthe main charges of stockpile weapons.

13

In both stockpile laboratory tests and accelerated aging tests, densitydistribution is measured using coredsamples. These measurements are thencompared with recorded densities fromeach material lot. Laboratory test resultsshow that accelerated aging conditionsdo not significantly alter the uniformityof HE density; density actuallybecomes more uniform throughout themain charge.

Tests of Mechanical PropertiesAs an integral part of the explosive

package’s structure, HE must retain itsown structural integrity. Therefore,tensile and compressive mechanicalproperties of HE are monitored (seeFigure 3). These mechanical propertieswere found to be correlated with HEcomposition and density, as well as thecrystallinity and nature of the polymericbinder. Mechanical properties may alsobe affected by changes in the propertiesof the explosive–binder interface, butthese can only be addressed indirectly.

Tensile strength testing. Tensiletests are performed on LX-17, forexample, at a low temperature (–20°C)and a slow rate because theseconditions simulate the expected worstcase (due to thermal expansionmismatches of the materials). This testbest shows differences in materialquality. Test data for three Livermoreweapon systems show no apparentaging trends in LX-17 tensile stress andstrain at failure.

Compression testing. Forsimulating the worst-case conditions forcreep (displacement under fixed load)in the warhead, compression tests areperformed on LX-17 at an elevatedtemperature (50°C) and a slow rate (1,440 microstrain per hour).

In surveillance testing, compressionvalues for LX-17 have not failed orfallen outside of material qualificationlimits. Data on stockpile-aged materialfrom the W87 warhead, however, do

show an apparent stiffening of the LX-17 with age (see Figure 4).Although this phenomenon may actuallyreflect an increase in the crystallinity ofthe binder, the LX-17 continues to bemonitored and will be compared withthe behavior in other systems.

15


Stockpile Surveillance

LX-17 and Los Alamos’s PBX 9502 areconsidered “insensitive” high explosives(IHE); others are termed “conventional.”

Evaluating the PackageLivermore is responsible for

surveillance of the stockpile weaponsthat are based on its own designs. TheEngineering Directorate and the Defenseand Nuclear Technologies Directoratecollaborate on Livermore’s StockpileSurveillance Program. Generalprocedures for the annual evaluationbegin with a predetermined number ofsamples of each weapon type chosen atrandom from the stockpile. All aredisassembled to varying degrees forevaluation, but typically only oneweapon has its explosive packagereduced to its component parts: pit,explosive, detonators, and secondary.

Livermore mechanical engineers andmaterials scientists develop prototypetests, and then Pantex workers performthe tests on actual stockpile weaponscomponents and materials. The testsfocus on what would alter the estimatedminimum warhead life or requireretrofitting.

The complete evaluation entails four major investigations, each withrigorous safety and technical protocols:(1) examining the HE for changes inappearance and texture, includingsurface discoloration, cracks (using dyepenetrant), or tackiness of any materials;(2) measuring physical and mechanical(tensile, compressive) properties,including density and contour; (3) measuring chemical properties,including HE and binder composition,binder molecular weight, and warhead atmosphere analysis; and (4) conducting performance tests,including pin hydrodynamic tests,“snowball” tests, and detonator testfiring or disassembly.

In characterizing materials,Livermore surveillance addressesinterrelationships among components.Environmental factors such asradiation, heat, and chemicalincompatibility can affect the behaviorof components and their interfacesthroughout the initiation chain: thedetonator, booster, and main charge.Explosives could also suffer agingeffects in such properties as creep,

growth and density gradients,thermomechanical integrity, initiationcapability, detonation performance,sensitivity, and safety.

These concerns are addressed duringthe warhead’s development and earlyproduction phases, largely through testsusing accelerated aging techniques(primarily elevated temperature) tosimulate the long-term effects of internaland external environment. The main goalof accelerated aging tests is determiningwhether materials, parts, and assembliesare compatible with each other and retaintheir essential properties.

During surveillance, actual aging andenvironmental effects are evaluated,using new materials laboratory tests andmaterial qualification test results asbaseline data.

Tests of Physical PropertiesDensity and density uniformity are

parameters easily measured with highprecision. If HE chemical and densitydistributions remain substantiallyconstant during storage, no significantchange is expected in specific energy ordetonation velocity.

14



Tests of ChemicalCharacteristics

As HE ages or degrades, itscompatibility with other materials in theprimary may suffer. Thus, several typesof analysis are employed to evaluate theHE’s chemical composition.

Figure 2. TATB material is being preparedfor an aging test.

Figure 3. High-explosiveschemist Mark Hoffman setsup HE for mechanical tests.

Com

pres

sive

str

ess,

MP

a

10

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6

4

2

0

Com

pres

sive

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ess,

MP

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Stockpile age, years

10

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5,0004,000 3,000 2,000 1,000

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(a)

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Microstrain

Figure 4. (a) The compressive stress tests for the LX-17 high explosive recovered from the W87new materials laboratory test (NMLT) units and stockpile laboratory test (SLT) units. The datashow a stiffening of the LX-17 at all strain levels, which may be consistent with a gradualincrease in the crystallinity of the Kel-F-800 binder. For reasons not clear at this time, this trendis not supported by the observations from the B83 (b) NMLT units and (c) SLT units.

HE. A machined shell of LX-17 isassembled with a booster and detonator toform a “snowball.” When this assemblyis fired, a streak camera captures spatialand temporal information of the initial, or“breakout,” detonation wave on the outersurface of the LX-17 snowball (seeFigure 5). The relatively flat curves at thebottom of the image data indicate a good,uniform explosion. Changes in thebreakout profile would be used to trackthe performance of the booster and thecondition of the interface with the HE.

Aging tests. So far, surveillance dataon HE from the B83, W84, and W87programs show no evidence of agingeffects. Because the W87 system must be requalified for an additional 25 to 30 years, additional data are beinggathered and analyzed to improveLivermore’s long-term predictivecapability. Aged LX-17 is being subjectedto far more comprehensive testing thanusual for stockpile laboratory test units. Inessence, properties of control materialfrom various sources are compared to thechemical, physical, mechanical, andperformance properties of aged LX-17 forsigns of age-induced changes.

Changes, if any, will be studiedfurther in the Enhanced SurveillanceProgram. Should no changes bediscovered, confidence in the projectedlongevity of the W87’s HE materialswill be scientifically supported.

A compatibility program initiatedduring W84 warhead production ispaying dividends by serving as a sourceof aged materials for advanced study.Some specimens of LX-17, UF-TATB(ultrafine TATB) boosters, and LX-16pellets from W84 production are alreadybeing subjected to accelerated aging in aweapon-like atmosphere for ten years.

The Next Step inSurveillance

Continually sought to improve theanalysis of HE in weapons in thestockpile, technologies must still fulfillthe purposes of traditional surveillance.

First, early in a weapon’s stockpile life,materials and processes are scrutinizedfor defects, and then they are monitoredto confirm that design choices do notcause problems.

Other improvements are beingevaluated for inclusion in the program:(1) fundamental understanding of agingmechanisms in stockpile materials, (2) better selection of stockpile samplesfor testing and evaluation, (3) betteruses of available materials (stockpile-aged materials, such as those fromretired and dismantled weapons), and(4) peer review of surveillance data.

Accordingly, the LivermoreStockpile Surveillance Program hasproposed revisions in the surveillancemission to achieve the followingcapabilities:• Detecting and identifying changes instockpile-aged materials that previoussurveillance methods may not havediscovered.• Predicting—not simply monitoring—any identified age-induced changes inmaterials through the use of models.• Providing information on agedmaterials to weapons designers, who

can assess effects on weaponsperformance.• Verifying the safety of aged materialsvia testing and modeling.

These changes will help improve analready successful Livermore stockpileevaluation program. They will enhancesurveillance techniques to assure thenation and its armed forces thatLivermore-designed weapons can besafely stored and transported and thatthey can work exactly as intendedthroughout their stockpile life.

Key Words: accelerated aging, highexplosive (HE), LX-17, nuclear weapon,PBX, pin-dome test, predictive capability,snowball tests, stockpile evaluation, stockpilesurveillance, TATB.

For further information about stockpilesurveillance contact Anders W. Lundberg(510) 422-4263 ([email protected]).For information about chemical andmaterials science in stockpile surveillancecontact Fran Foltz (510) 422-7829([email protected]) or James LeMay (510)423-3599 ([email protected]).

17



Chemical composition analysis.Relative percentages of binder and HEare compared with values obtainedfrom qualification tests of newlyproduced HE. Percentages of HEdifferent from nominal values couldsignal significant chemicaldegradation, which would mean lowerenergy density for LX-17. To date,however, aging has not affectedchemical composition. Changes, if

any, remain too subtle for currentanalytic techniques.

Molecular weight analysis. For thisanalysis, the polymer binder is extractedfrom the HE and subjected to gelpermeation chromatography (also calledsize exclusion chromatography).Current techniques have yet to revealsignificant aging effects on themolecular weight or molecular weightdistribution of LX-17 binder. Small

changes in molecular weight that mightindicate the onset of degradation,however, are very difficult to detect andcharacterize. In Livermore’s EnhancedSurveillance Program, methods arebeing developed to improve the abilityto detect aging effects.

Warhead atmosphere gassampling. Mass spectroscopy and gaschromatography of warhead gas samplescan identify material outgassing andongoing chemical reactions, both ofwhich may indicate degradation ordecomposition of the organiccompounds in the HE. They also help toverify whether warhead environmentalseals have leaked.

Performance TestsPerformance tests tell about the

detonation response of the material. Pinhydrodynamic tests check the implosionreliability and performance of the maincharge; “snowball” tests help determinethe initiation reliability of the booster.Detonators also are test-fired, andcertain ones are disassembled forinspection and analysis.

Pin hydrodynamic test. This testmonitors changes in the implosionbehavior of HE. The test assemblycomprises three main subassemblies: apin-dome assembly, a mock pit, and theHE. The test measures elapsed timefrom initiation until the explosive drivesthe mock pit into an array of timingpins, a “pin dome,” of known length andlocation. The HE implodes the mock pitonto the timing pins, which provide dataabout the temporal and spatialuniformity of implosion. A nonuniformimplosion could indicate an HEproblem. Excessive density variations,voids, or cracks in the HE, for example,can disrupt the shock-wave propagationfrom the detonation. To date,surveillance testing has observed noneof these problems in stockpile samples.

Snowball test. This test checksreliability of the initiation chain byconfirming that the booster initiates the

16



View Camera

Booster pellet

LX-17

Mirror Mirror

View

Figure 5. (a) A “snowball” testassembly (bottom) is aligned withsamples of snowball test data (top)as recorded by the streak camera.(b) The schematic shows the mirrorsthat reflect the left and right sets ofsnowball data.

For illustration, vertical lines aredrawn between the photographicbreakout record and the markers onthe snowball surface. The relativelyflat curves at the bottoms of theimage data indicate a good, uniformexplosion.

ANDERS W. LUNDBERG has supported nuclear weaponsengineering and testing at Lawrence Livermore since 1961. Hereceived both his B.S. and M.E. in mechanical engineering fromthe University of California at Berkeley in 1959 and 1961,respectively. At Livermore, he has been a project engineer andgroup leader in the Weapons Program and the Nuclear TestProgram; currently, he is group leader for Stockpile Surveillancein the Mechanical Engineering Department.

About the Engineer

(a)

(b)

collected, the data are oftwo-dimensional imageplanes that must still betransformed into 3-Dmoving images. This ishardly a simple task,given that each imageframe from each cameramay contain as many as250,000 data points.Thus, it is no surprisethat the key componentof CyberSight is itscomplex image-processing code.

The code transforms2-D objects into 3-Dobjects by mimickinghuman stereo vision.When we look at anobject, each eye receivesa slightly different imagebecause it sees from aslightly different angle.This angular differenceprovides us with depthperception. Thegeometric expression of depth perception has been adapted bythe computer code to calculate depth, using the two views ofeach data point sensed by the stereo cameras. The computercalculation is based on the principle of triangulation, ameasurement technique that uses two known points to derive athird value. The triangulation uses the known, left–right viewsof an image point, the geometry of the camera arrangement,baseline distance, and converging optical angles to establishthe position of that image point in space. The figure on thenext page simplifies the basis of triangulation.

Camera geometry is determined by means of a calibrationprocess. During calibration, images are taken of referencetarget points with known spatial positions, and these are usedto back-calculate the camera geometry and lens parameters tobe used for actual videotaping.

Matching the Left and Right “Eyes”Before the calculations for depth can be made, the left and

right views of the data points must be accurately matched.This difficult, time-consuming task requires a very highdegree of computational complexity. The matching involvesassociating the correct left and right views of the same data

point, associating them fromthe same image frame, andthen tracking them fromframe to frame so thatmovement reconstruction islogical. Additionalcomplications come fromchanges in perspective, suchas curvatures and orientation,caused by the moving object.Yet another type of problemintrudes when, on occasion,one view of a data point iseclipsed from the commonview of both cameras, so notevery data view has a stereocounterpart.

The computationaltechniques for left–rightmatching, like the 3-Dtransformation techniquethat imitates stereo vision,use principles based on therelationship betweenphysical and mentalprocesses, i.e., how stimulilead to sensation. The

computations imitate the human eye’s ability to pick upintensity changes, make use of high-contrast features in animage (such as edges and intersections), and filter or“smooth” received data. They also use dynamicprogramming, in which small subproblems are solved. Thosesolutions are used to solve larger and larger subproblemsuntil eventually the problem itself is solved. The techniquesresult in a code with some ability to interpret “context” inperforming the left–right matches and to fill in some missingdetails, such as the eclipsed data views.

Building on Past WorkThe work on CyberSight follows earlier robotic motion

studies that Lu and Johnson performed for LLNL’s in-houseLaboratory Directed Research and Development project. Thepurpose of that work was to program robotic “hands” tohandle hazardous waste. The work captured the interest ofpediatric hospitals that are seeking better ways to designtreatment for cerebral palsy. Their need gave Lu and Johnson

The reconstruction of a facial sequence displayed as (a) a normal surfacedisplay at one-thirtieth of a second and (b) a rendered image fromdifferent perspectives

19Body Motion


18Research Highlights


Research Highlights

How to Get CyberSightThe line grid projected onto a moving subject comes from a

glass slide precisely etched with parallel black lines; such slidesare commonly used for calibrating instrumentation optics. Otherthan this slide and the projector, the CyberSight systemcomponents are similar to those of other motion imagingsystems. Two charge-coupled device (CCD) cameras, which aresemiconductor image sensors, produce the video signals. Tosense the data points, the cameras are firmly positioned a smalldistance apart from each other to take “snapshots” from twoperspectives. Operated from 1 to 10 feet away, the cameras takethe snapshots at the standard video rate of 30 frames persecond. The CCD images are digitized by an image framegrabber and stored in memory boards. From there, they aretransferred to a host computer for calculation andreconstruction into 3-D computer representations that can bepresented as rendered images.

The sample images of a facial expression sequence in thefigure on the next page are taken from CyberSight data thatwere reconstructed into several perspectives. Unlike aconventional photograph, the images are generated from acomputer model of true dimensionality that can bemanipulated, analyzed, and visualized. This feature makesCyberSight useful for biomechanical analyses. The complexinformation will allow computer models to calculate bodysurfaces and volumes, determine relationships between bonesand muscles, and estimate velocity and force of movements.

Calculating Three-Dimensional SpaceBy solving the problem of collecting complete, voluminous

motion data, CyberSight has uncovered another problem. As

Visualizing BodyMotion

HEN you think about it, lots of people could use theknowledge obtained from capturing, re-creating, and

analyzing body motion in 3-D (three-dimensional) form. Onegroup might be specialists: orthopedic surgeons, to plansurgery or physical therapy; athletes, to maximize theirtraining and performance; robotic engineers, to “teach” robotshow to interpret motion; and animators and video gamedesigners, to make their animations more realistic. Anothergroup might be the folks who want to understand their owncommon ailments, such as repetitive motion problems ortendonitis.

Studying body motion is not a new activity, but the data-gathering techniques for these studies have changed over theyears. Currently, one common way of collecting motion datais by attaching reflective markers on a human actor at strategicpoints—on shoulders, elbows, hips, knees, ankles—and thenvideotaping the actor in motion. The video images aredigitized for computer extraction and calculation of the 3-Dlocations of the markers. The calculated results are presentedin graphical form, which may be plots or stick figures. Whileuseful, these graphics are only coarse approximations of actualhuman movement. If used for animation purposes, forexample, they would require a great deal of rendering beforethey could be considered finished. For studying biomechanics,their accuracy and level of detail are limited by the relativelysmall number of data points from which their information hasbeen extrapolated.

Recently, Lawrence Livermore engineers Shin-Yee Lu andRobert K. Johnson demonstrated the next step in motionimaging systems. Dispensing with reflective markers, Lu andJohnson devised a system that detects data points on a grid ofparallel, closely spaced vertical lines that have been projectedonto a moving object (see figure above), which is thencaptured at video speed. Motion information collected in thisway is dense, continuous, and uniform. It can be used toproduce a real-time, complex visualization of movement thatis realistic enough to be pasted directly into an animation. Luand Johnson call this system CyberSight.

W(a) A vertical line grid projected onto the face of Livermore engineerRobert Johnson to capture information from closely spaced pointsalong the lines results in (b) this CyberSight visualization.

(a) (b) (a)

(b)

20


the impetus to develop a more advanced motion imagingtechnique, and CyberSight was the result.

The most immediate applications for CyberSight areexpected to be animation and virtual reality projects. Withsubsequent development, the CyberSight code will be apowerful tool with far-ranging applications from orthopedicsurgical planning, speech therapy, and physical therapy tosecurity applications such as facial recognition systems. This image-processing technology could also be used inmanufacturing to provide rapid prototyping of new productsand to personalize products such as prostheses, gas masks,clothes, and shoes. It has potential nonhuman-relatedapplications as well. Surface deformations of materials couldbe monitored during the manufacturing process, or stress andstrain analyses could be performed on materials and structures(such as vehicle air bags or the vehicle itself) to determinesafety and functionality. The ingenuity of the CyberSight datacollection technique, supported by its complex computercode, portends numerous and exciting future applications.

Key Words: 3-D visualization, biomechanics, image processing,motion study, movement reconstruction.

For further information contact Shin-Yee Lu (510) 424-3796 ([email protected]) or Robert K. Johnson(510) 422-8375 ([email protected]).

Body Motion

Figure 3. Triangulation is used inthe CyberSight computer code tolocate the data points in space.

Optical axis

A point in the object

Optical lineMatching left–right data points

Left view

Right view

BaselineCommon focal point

21Research Highlights

Studying the Earth’sFormation: The Multi-AnvilPress at Work

(a) The ceramicoctahedron with thesample material inside itfits inside eight tungstencarbide cubes that inturn sit inside (b) the splitcones of the multi-anvilpress. (c) The closedpress is also shown.

(b)

(c)

(a)


ANY things that scientists study are invisible to them.Announcements about the discovery of planets around

other stars do not come because astronomers have seen theplanets, although they would certainly love to. The discoveryis more likely based on observations of the star’s motion thatindicate strong nearby gravitational forces. So it is withdiscoveries about the Earth’s core and mantle. Because thedeepest well ever drilled extends down just 12 kilometers, noteven pricking the mantle, researchers have to employ indirectmethods to study the Earth.

Using meteorites and seismological evidence as clues,scientists have known almost since the beginning of thecentury that the Earth has a solid, mostly iron, inner core anda molten outer core with a mantle and crust of rocky, silicatematerial. But for just as long they have been puzzled abouthow the core and mantle separated. The primordial planetEarth grew out of bits of gas and dust, aggregating over timeinto a larger, more solid body. Was there then somecataclysmic event billions of years ago that melted much ofthe planet, prompting the metals and silicates to separate asoil and water do? Or was the separation the result of a moregradual process, a trickling down of the denser molten metalsbetween solid silicate mineral grains to the center of theEarth?

Recent research at Lawrence Livermore NationalLaboratory by geochemist William Minarik has helped todispel the second, “trickle down,” theory. Using the larger ofLivermore’s two multi-anvil presses to mimic the pressuresand temperatures that exist deep in the Earth, he has shownthat metals like those in the Earth’s core could not havetrickled down (see figure at right).

The materials used in the experiments were olivine, asilicate mineral that makes up much of the Earth’s uppermantle, and an iron–nickel–sulfur–oxygen combination torepresent the core.

The multi-anvil press is a relatively rare research tool.Livermore’s two presses have been used for a variety ofmaterial property studies, including diffusion and deformationof ceramics and metals, deep-focus earthquakes, and the high-pressure stability of mineral phases. The larger, 1,200-tonhydraulic press can produce pressures of

M

steel buckets as shown in the figure on p. 21. In several stages,the steel buckets pushed on the carbide cubic anvils, whichpushed on the octahedral volume inside.

The multi-anvil press is not Livermore’s only device forstudying the behavior of the Earth’s innards, but in many waysit is the best for this type of study. The diamond-anvil cell canproduce 100-GPa pressures, comparable to the pressures at thecenter of the Earth (see Science & Technology Review, March1996). But it can accommodate only a 20-micrometer sample,too small for much post-experiment evaluation. With thepiston-cylinder press, the sample volume is about 500 millimeters3, but it has only a 4-GPa pressure capability,which is comparable to a depth of just 120 kilometers. Themulti-anvil press is in the middle, providing pressures usefulfor studies of this type and accommodating a sample largeenough for evaluation after the experiment.

In Minarik’s experiments, the press took about 4 hours tobring the samples to full pressure, after which the sampleswere heated for periods ranging from 4 to 24 hours. Duringthis time, the porosity of the sample collapsed, and the stablemicrostructure developed. Then the unit was cooled down and allowed to decompress for about 12 hours. During thisprocess, the graphite capsule turned to diamond, which mustbe ground off before the sample could be sliced and polishedfor evaluation.

Despite being molten and much denser than the olivine, themetallic melt showed no signs of separating and draining tothe bottom of the capsule. For the molten metal to drip downalong the silicate grain edges, it has to be able to wet theedges. But in none of the experiments did wetting occur.1Rather, the iron–nickel mixture beaded up at the corners of thesilicate grains like water does on a waxed car, as shown in thefigure on p. 22.

Livermore’s findings agree with similar, lower-pressurestudies that have melted meteorites and iron–nickel–sulfur–oxygen mixtures and failed to wet the silicate minerals.Together, these experiments indicate that much highertemperatures were required to separate the Earth’s core andmantle—temperatures high enough to melt most of the Earth.

All of these data lend credence to the theory that the young,growing Earth was repeatedly bombarded by large planetoids,with some of these collisions generating temperatures highenough to form a magma ocean from which drops of densemolten metal separated. The largest collision may have beenwhen a large celestial body, about the size of Mars, collidedwith Earth nearly 4.5 billion years ago, melting most of it andcausing the core and mantle to separate. The leading theorytoday for the Moon’s formation postulates that some materialfrom that collision was ejected into orbit and condensed intothe Earth’s Moon.

2322


Livermore scientists have long studied material propertiesand the effects of high temperatures and pressures. Their workhas resulted in some mighty big bangs but none as large as theones Minarik has postulated.

“We plan to look next at the geochemical aspects of thisproject, the partitioning of trace elements between moltenmetal and silicates at the same high temperatures andpressures,” says Minarik. “There are many scientists in thiscountry and elsewhere studying the formation of the Earth,and all of us are in the same boat. With all of the directevidence of the Earth’s formation buried far beneath our feet,these laboratory experiments are our only way to recreatewhat might have happened.”

Key Words: Earth core formation, multi-anvil press.

References1. W. G. Minarik, et al., “Textural Entrapment of Core-Forming

Melts,” Science 272, 530–533 (April 26, 1996).

For further information contact William Minarik (510) 423-4130([email protected]) or Frederick Ryerson (510) 422-6170([email protected]).

Earth Core StudiesEarth Core Studies


25 gigapascals (GPa), which is equivalent to 250,000 times theatmospheric pressure at sea level, or the pressure that occurs700 kilometers deep in the Earth. In addition to pressing on thesample, the experiment passes an electric current through afurnace within the assembly to generate temperatures up to 2,200°C.

These experiments using the multi-anvil press generated ahigh pressure of 11 GPa, or 110,000 times the atmosphericpressure at sea level. This corresponds to 380 kilometers deepinto the Earth, or pressures at the center of moons or asteroids2,500 kilometers in radius (about the size of Mercury). Thesample was also heated to a temperature of 1,500°C. Underthose conditions, the metal melts and the olivine remains solid.

The geometry of the press is key to creating these enormouspressures. For the 11-GPa experiment, a ceramic octahedronhad a 10.3-millimeter-long hole with a tiny rhenium furnace, athermocouple to measure temperatures, and a graphite capsulecontaining the olivine and iron–nickel–sulfur–oxygen sampleinserted in it. The octahedron rested in the center of eight 32-millimeter tungsten carbide cubes whose inside cornerswere truncated to accommodate the sample. (Tungsten carbideis used for the cubes, or anvils, because of its hardness, whichis close to that of diamonds but at a much lower cost.) Tinyceramic gaskets were placed at the edges of the carbide cubesto contain the pressure. This assembly of an inner octahedronand eight carbide anvil cubes was put in the press’s split-cone,

A 30-micrometer-thick slice ofan experiment sample indouble exposure. The field ofview is about 500 micrometers.Transmitted light reveals thecolorful olivine grains, whilelight reflected from the topshows the brown sulfides at thecorners of the olivine grains.The sulfides have not wettedthe edges of the olivine grains.Oxides appear black.

25


Summary of disclosure

An interferometer having the capability of measuring opticalelements and systems with an accuracy of ¬/1,000, where ¬ is thewavelength of visible light. This interferometer uses an essentiallyperfect spherical reference wavefront generated by the fundamentalprocess of diffraction. The interferometer is adjustable to give unityfringe visibility, which maximizes the signal to noise and has themeans to introduce a controlled, prescribed relative phase shiftbetween the reference wavefront and the wavefront from the opticsunder test.

A silicon wafer that has slots sawed in it that allow diode laser barsto be mounted (soldered) in contact with the silicon. Microchannelsare etched into the back of the wafer to provide cooling of the diodebars. The channels are rotated from an angle perpendicular to thediode bars, allowing increased penetration between the mounteddiode bars. Low thermal resistance of heatsinks allow high averagepower operation of two-dimensional laser diode arrays.

Method for fabricating a multilayer structure with selectablefeatures: propagating reaction front velocity V, reaction initiationtemperature attained by application of external energy, and amountof energy delivered by a reaction of alternating unreacted layers ofthe multilayer structure. Because V is selectable and controllable, avariety of different applications for the multilayer structures arepossible, including use as ignitors, in joining applications, infabrication of new materials such as smart materials, and in medicalapplications and devices.

A method using a tunable laser for determining the density of a gasvapor component that absorbs light at an expected maximumfrequency. A laser is tuned to transmit a laser source beam at alocal maximum absorptance frequency of the component bytransmitting at last one laser source beam through at predeterminedpath of gas vapor. The frequency of the laser source beam is sweptthrough a frequency range, including the expected maximumabsorptance frequency.

AwardsLaboratory scientists Bruce Hammel and Laurance Suter have

been elected fellows by the American Physical Society. Theirelection brings to 30 the number of APS fellowships earned by theLaboratory’s Inertial Confinement Fusion Program in the last 20 years.

The citation on Hammel’s certificate reads “for measurementsand understanding of x-ray-driven hydrodynamic instabilities and x-ray drive asymmetry.” Hammel is currently head of experimentalresearch within the ICF Program and is responsible for experimentson the Nova laser.

Suter was cited for “pioneering work and leadership in thedesign, modeling, and analysis of experiments using laser-heatedhohlraums that quantify and control x-ray drive, symmetry, andpulse-shaped implosions.” He is currently the leader of the Hohlraum

Group in the Theory and Target Design (X) Division of the LaserPrograms Directorate and is working on a new type of source forproducing x rays with high-powered lasers for the future NationalIgnition Facility.

Sixteen organizations were awarded the 1996 DOE EnergyQuality Awards in October, including Livermore’s Business ServicesDepartment, in recognition of substantial achievement in qualitymanagement.

“These award winners have demonstrated excellence in‘reinventing government’ in support of the President’s NationalPerformance Review principles: putting customers first, cutting redtape, empowering employees, and getting back to basics,” said DOESecretary Hazel O’Leary.

Patent issued to

Gary E. Sommargren

William J. BenettRaymond J. BeachDino R. Ciarlo

Troy W. Barbee, Jr.Timothy Weihs

Karla HagansLeon BerzinsJoseph GalkowskiRita Seng

Patent title, number, and date of issue

Phase Shifting DiffractionInterferometer

U.S. Patent 5,548,403August 20, 1996

Monolithic Microchannel Heatsink

U.S. Patent 5,548,605August 20, 1996

Method for Fabricating an IgnitableHeterogeneous Stratified MetalStructure

U.S. Patent 5,547,715August 20, 1996

Self-Tuning Method for Monitoringthe Density of a Gas VaporComponent Using a Tunable Laser

U.S. Patent 5,550,636August 27, 1996

Patents and Awards24


Each month in this space we report on the patents issued to and/orthe awards received by Laboratory employees. Our goal is toshowcase the distinguished scientific and technical achievements ofour employees as well as to indicate the scale and scope of thework done at the Laboratory.

Patents and Awards

Patent issued to

James L. Kaschmitter

Gerald W. CouttsJohn F. BushmanTerry W. Alger

Charles L. Bennett

William F. KrupkeRalph H. PageLaura D. DeLoachStephen A. Payne

Ravindra S. UpadhyeFrancis T. Wang

Don E. FischerDon WalmsleyP. Derek Wapman

Malcolm CaplanClifford C. Shang

Patent title, number, and date of issue

Three-Dimensional AmorphousSilicon/Microcrystalline Silicon Solar Cells

U.S. Patent 5,538,564July 23, 1996

Mass Spectrometer Vacuum Housing andPumping System

U.S. Patent 5,539,204July 23, 1996

Method for Determining and Displayingthe Spatial Distribution of a SpectralPattern of Received Light

U.S. Patent 5,539,518July 23, 1996

Transition-Metal-Doped Sulfide, Selenide,and Telluride Laser Crystal and Lasers

U.S. Patent 5,541,948July 30, 1996

Clean Process to Destroy Arsenic-Containing Organic Compounds withRecovery of Arsenic

U.S. Patent 5,545,800August 13, 1996

Crimp Sealing of Tubes Flush With orBelow a Fixed Surface

U.S. Patent 5,546,783August 20, 1996

Vacuum-Barrier Window for Wide-Bandwidth High-Power MicrowaveTransmission

U.S. Patent 5,548,257August 20, 1996

Summary of disclosure

Solar cells that use deep (high-aspect-ratio) p and n contacts to createhigh electric fields within the carrier collection volume material of the cell.The deep contacts are fabricated using repetitive pulsed laser doping soas to create the high-aspect p and n contacts. The provision of the deepcontacts that penetrate the electric field deep into the material where thehigh strength of the field can collect many of the carriers results in a high-efficiency solar cell.

A vacuum housing that is composed of cleaned and welded stainless-steel tube components and includes flanges sealed with metal gaskets.The housing is broadly composed of two interconnected tubularsections (each section having a flange at the outer end and at the mainbody section). The vacuum pumps require simple and minimal electricalcontrols and use minimal electrical power. These attributes allowpackaging into a small, lightweight volume that will operate with minimalpower.

An imaging Fourier transform spectrometer employing an interferometercoupled to a digital framing camera. Output from the digital framingcamera is provided to a computer that, by manipulation of that data, candisplay a two-dimensional representation of measured spectra and/ornumerical data pertaining to those spectra. The digital framing camera isoptically and electrically coupled to the output of the interferometer suchthat an interferogram is recorded at precise intervals in synchrony withthe movement of the moving mirror of the interferometer.

A new class of solid-state laser crystals and lasers that are formed ofmaterials that have fourfold coordinated substitutional sites. The hostcrystals include II-VI compounds that are doped with a transition metallaser ion (e.g., chromium, cobalt, or iron). Important aspects of theselaser materials are the tetrahedral site symmetry of the host crystal, lowexcited-state absorption losses, high luminescence efficiency, and thed4 and d6 electronic configurations of the transition metal ions.

A process using a reducing agent to decompose an organic compoundcontaining arsenic. The reducing agents may include alkali metals,alkaline earth metals, hydrides, and hydrogen gas. In the case of a puremetal reducing agent, an intermediate metal arsenide is formed that maybe acidified to form an arsenic-containing gas, such as arsine. Thearsine gas is then reduced to pure arsenic by a thermal or chemicalprocess. This reduction process avoids the costly separation or disposalof arsenic oxide.

An apparatus used when a ductile metal tube and valve assembly areattached to a pressure vessel that has a fixed surface around the base ofthe tube at the pressure vessel. A flat anvil is placed against the tube, dieguides are placed against the tube on a side opposite the anvil, and apinch-off die is inserted into the die guides against the tube. Adequateclearance for inserting the die and anvil around the tube is needed belowthe fixed surface. The anvil must be flat, so that, after crimping, it may beremoved without deforming the crimped tubes.

A vacuum output window that comprises a planar dielectric material withidentical systems of parallel ridges and valleys formed in oppositesurfaces. The valleys in each surface neck together along parallel linesin the bulk of the dielectric. Liquid-coolant conduits are disposed linearlyalong such lines of necking and have water or liquid nitrogen pumped toremove heat. The ridges focus the incident energy in ribbons thatsqueeze between the liquid-coolant conduits without significant lossesover very broad bands of the radio spectrum.

Patents

27


1996 Index

Science and Technology Review Page

January/February 1996The Laboratory in the News 2Patents and Awards 4Commentary on Environmental Restoration 5Features

Groundwater Cleanup Using Hydrostratigraphic Analysis 6Micropower Impulse Radar 16

Research HighlightsProbing with Synchrotron-Radiation-Based Spectroscopies 30Operating a Tokamak from across the Country 32

March 1996The Laboratory in the News 2Commentary on Industrial Ecology 4Features

The Safe Disposal of Nuclear Waste 6The Diamond Anvil Cell: Probing the Behavior of Metals under Ultrahigh Pressures 17

Research HighlightsGetting along without Gasoline—The Move to Hydrogen Fuel 28

Patents 32

April 1996The Laboratory in the News 2Patents 3Commentary on Laboratory Directed Research and Development 5Features

MACHO: Collaboration Is Key to Success 6A New Look at an Old Idea—The Electromechanical Battery 12

Research HighlightsGraffiti-Removal by Laser 20Adding Agility to Manufacturing 22

May 1996The Laboratory in the News 2Commentary on ES&H Technology 3Features

Mitigating Lightning Hazards 4Groundwater Modeling: More Cost-Effective Cleanup by Design 13Dual-Band Infrared Computed Tomography: Searching for Hidden Defects 23

Research HighlightsPlating Shop Moves to Finish Off Waste 28

Patents 31

June 1996The Laboratory in the News 2Patents and Awards 4Commentary on Materials Modeling and Stockpile Stewardship 5Features

Theory and Modeling in Materials Science 6LLNL and DOE Collaborate on Successful Fusion Facility Cleanup 14

Research HighlightsSolving the Mammoth Mountain CO2 Mystery 20A Closer Look at Osteoporosis 22

26


Crossing the Petawatt Threshold

A revolutionary new laser called the Petawatt, developedby Lawrence Livermore researchers after an intensive three-year development effort, has produced more than 1,000 trillion (“peta”) watts of power, a world record. Bycrossing the petawatt threshold, the extraordinarily powerfullaser heralds a new age in laser research. Lasers that providea petawatt of power or more in a picosecond may make itpossible to achieve fusion using significantly less energythan currently envisioned, through a novel Livermoreconcept called “fast ignition.” The petawatt laser will alsoenable researchers to study the fundamental properties ofmatter, thereby aiding the Department of Energy’s StockpileStewardship efforts and opening entirely new physicalregimes to study. The technology developed for the Petawatthas also provided several spinoff technologies, including anew approach to laser material processing.■ Contact: Michael Perry (510) 423-4915 ([email protected]).

High Explosives in Stockpile SurveillanceIndicate Constancy

Although stockpile evaluation is not new, methods andtests have undergone marked changes since the program’sinception almost four decades ago. Today LawrenceLivermore, Los Alamos, and Sandia National Laboratories areresponsible for the extensive and rigorous tests to evaluate theportions and components of the stockpile weapons that eachhas designed. An overview of Livermore high-explosives testsof components in nuclear stockpile weapons illustrates thedegree of assurance that the laboratories work toward.Evaluation includes tests for changes in physical properties,mechanical properties with tensile and compression tests, andperformance with pin-dome, “snowball”, and aging tests.Looking toward the future, the program is working to improvepredictive capabilities so that weapons designed at Livermorecan safely be stored and work exactly as intended throughouttheir stockpile life.■ Contact: Anders W. Lundberg (510) 422-4263 ([email protected]).

Abstracts

29


© 1996. The Regents of the University of California. All rights reserved. This document has been authored by the The Regents of the University of California under Contract No. W-7405-ENG-48 with the U.S. Government. To request permission to use any material contained in this document, please submit your request in writing to the Technical Information Department,Publication Services Group, Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94551, or to our electronic mail address [email protected].

This document was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor the University of Californianor any of their employees makes any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information,apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service bytrade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or theUniversity of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or the University of California andshall not be used for advertising or product endorsement purposes.

U.S. Government Printing Office: 1996/583-059-60006

November 1996The Laboratory in the News 2Commentary on Countering Terrorism with Computers 3Features

Simulations to Save Time, Money, and Lives 4The Secrets of Crystal Growth 12

Research HighlightsAddressing a Cold War Legacy with a New Way to Produce TATB 21DNA Sequencing: The Next Step in the Search for Genes 24

Patents and Awards 27

December 1996The Laboratory in the News 2Commentary on Opportunities for Science from the Petawatt Laser 5Features

Crossing the Petawatt Threshold 4High Explosives in Stockpile Surveillance Indicate Constancy 12

Research HighlightsVisualizing Body Motion 20Studying the Earth’s Formation: The Multi-Anvil Press at Work 23Patents and Awards 26

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July 1996The Laboratory in the News 2Commentary on the University Relations Program 3Features

Frontiers of Research in Advanced Computations 4The Multibeam Fabry–Perot Velocimeter: Efficient Measurement of High Velocities 12

Research HighlightsHigh-Tech Tools for the American Textile Industry 20Rock Mechanics: Can the Tuff Take the Stress? 24

Patents 27

August 1996The Laboratory in the News 2Commentary on Stockpile Stewardship 4Features

Keeping the Nuclear Stockpile Safe, Secure, and Reliable 6Research Highlights

Molten Salt Takes the Bang out of High Explosives 16Security Clearances Meet the Electronic Age 18Exploring Oil Fields with Crosshole Electromagnetic Induction 24


September 1996The Laboratory in the News 2Commentary on the Next Frontiers of Advanced Lasers Research 3Features

Taking Lasers beyond the National Ignition Facility 4Jumpin’ Jupiter! Metallic Hydrogen 12

Research HighlightsModeling Human Joints and Prosthetic Implants 19


October 1996The Laboratory in the News 2Patents 4Commentary on the Importance of Climate Change 5Features

Assessing Humanity’s Impact on Global Climate 6Research Highlights

Livermore Wins Six R&D 100 “Oscars” 14Electronic Dipstick Signals New Measuring Era 16Signal Speed Gets Boost from Tiny Optical Amplifier 18SixDOF Sensor Improves Manufacturing Flexibility 20A Simple, Reliable, Ultraviolet Laser: the Ce:LiSAF 22Giant Results from Smaller, Ultrahigh-Density Sensor 24Thinner Is Better with Laser Interference Lithography 26

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