lawrence livermore national laboratory livermore

September 1996

Lawrence

Livermore

National

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Science &

Technology Review

Lawrence Liverm

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it No.154

Beyond Fusion Ignitionto Inexhaustible Power Using Lasers

Also in this issue: • Metallized Hydrogen• Computer Modeling of Human Joints

About the Review

This month’s feature article on lasers beyondthe National Ignition Facility concentrates on thediode-pumped solid-state laser. Surrounding it onthe cover are some of the primary technologicaldevelopments that make it a candidate for themeans by which inertial confinement fusion willcreate inertial fusion energy as an inexhaustiblesource of electric power. Clockwise from theupper left are: a ytterbium-doped strontium–fluorapatite (Yb:S–FAP) crystal from which thelaser’s gain element is made; a diode array, thesource of laser’s pump light; a single laser diodepackage; a Yb:S–FAP crystal; and a lens duct.For our report on how these components worktogether to take lasers beyond NIF, turn to p. 4.

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About the Cover September 1996

Lawrence

Livermore

National

Laboratory

Beyond Fusion Ignitionto Inexhaustible Power Using Lasers

Also in this issue: • Metallized Hydrogen• Computer Modeling of Human Joints

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 EDITORS

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Sam Hunter, Robert D. Kirvel, and Dale Sprouse

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George Kitrinos

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Treva Carey

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Louisa Cardoza

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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 CampbellThe Next Frontiers of Advanced Lasers Research

Features4 Taking Lasers beyond the National Ignition Facility

One ultimate goal of laser fusion research is to produce electricity by inertial confinement fusion. Advances in our diode-pumped laser technology promise to take us another step closer to that goal.

12 Jumpin’ Jupiter! Metallic HydrogenCapitalizing on its expertise in shock compression, a Laboratory team was the first to provide evidence for the metallization of hydrogen since the theorywas advanced in the 1930s.

Research Highlight19 Modeling Human Joints and Prosthetic Implants

24 Patents and Awards

Abstracts

S&TR Staff September 1996

LawrenceLivermoreNationalLaboratory

Printed in the United States of America

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

UCRL-52000-96-9Distribution Category UC-700September 1996

Page 4

Page 12

Page 19

3

Science & Technology Review September 1996

HEN the National Ignition Facility comes on-line in2003, it will represent the conclusion of one process and

the beginning of others. It will be the culmination of morethan a decade of research and development to achieve laserignition—the implosion in a laboratory environment of asmall, hydrogen-isotope-filled target by laser beams ofsufficient energy and quality to create, for a micro-instant,inertially confined fusion—a process comparable to that at thecenter of the sun. Simultaneously, it will represent thebeginning of other quests, among them to fulfill the ultimatecivilian goal of NIF—taking lasers beyond NIF to enablethem to create inertial fusion energy, a low-cost,inexhaustible supply of electric power through repeated,sustained laser ignition and fusion energy gain.

Lawrence Livermore National Laboratory recognized andembraced the challenge of taking lasers beyond NIF morethan a decade ago, even before NIF was specifically defined.The Laboratory made the early commitment to identify anddevelop the concepts and technologies that would propel laserapplications beyond NIF because we know that the design,development, and construction of each major newexperimental program facility take at least 10 years or more.Therefore, positioning large-scale programs to be able toexplore the frontiers of new knowledge calls for the earliestpossible anticipation of program facility needs and the timelydevelopment of the necessary enabling technologies.

In the case of NIF, these research management principleshave meant that as the Laboratory solved the scientificproblems and developed the technology to make NIF areality, we almost concurrently had to do the science andprovide the technology to take lasers beyond NIF.

Two articles in this issue of Science & Technology Reviewreport on developments that not only will help inertial fusionachieve its immediate goal—ignition—but may provide theenabling technology to make lasers the means of providinginertial fusion energy.

The feature article, “Taking Lasers beyond the NationalIgnition Facility,” beginning on p. 4, makes the compellingpoint that the flashlamp-pumped neodymium-doped glass(Nd:glass) lasers that NIF will use to create fusion ignition

represent several decades of development and scaling.Flashlamp-pumped solid-state lasers have been developedworldwide as the workhorse laser driver of choice for single-shot inertial confinement fusion and high-energy-densityresearch facilities at Livermore and elsewhere. Yet, it wasgenerally believed that solid-state lasers as a class lackedother qualities necessary to effectively drive an inertial fusionenergy reactor—namely, the capability to generate fusion-like, megajoule pulse energies simultaneously with outputbeams characterized by high quality, high pulse-repetitionrate (about 10 hertz), and high efficiency (greater than 10%).The article goes on to discuss the conceptual andtechnological innovations that overcame this long-heldperception. It focuses on the part the Laboratory played indeveloping (concurrently with NIF) the enabling lasertechnology advances that make diode-pumped, gas-cooledsolid-state lasers a candidate for taking lasers beyond NIF tothe production of unlimited electrical power based on inertialfusion energy.

In a similar vein, the article on metallic hydrogen (p. 12)reports on a recent Laboratory achievement with promising,significant implications for improving the laser targets thatwill be used in NIF, broadening their performance range andmaking them capable of higher performance. The revisedinformation about the equation of state of hydrogen revealedby the Laboratory’s hydrogen metallization studies willcontribute to the refinement of the hydrogen-isotope-filledtargets to be used in the lasers that will make inertial fusionenergy a reality.

Different as these two articles are, they have a similarsubtext: The achievements they discuss illustrate theemphasis of Laboratory and the Laser Programs on forward-looking research management that plans well ahead for thefuture implications and applications of the scientific researchand development done at Livermore. This researchmanagement philosophy is also what makes LawrenceLivermore a continuing key contributor to the globaladvancement of science and its most important applications.

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

Commentary by E. Michael Campbell

W

2 The Laboratory in the News


Livermore, IBM to build world’s fastest supercomputerLawrence Livermore has awarded IBM a $93-million

contract to build the world’s fastest supercomputer—a machine designed to deliver 3 trillion calculations per second(3 teraflops). The 3-teraflop IBM RS/6000 SP productionmodel is scheduled for demonstration in December 1998.

Most of today’s supercomputers are capable of performancein the gigaflop or billion-calculations-per-second range, notesDave Cooper, Associate Director for Computations atLivermore, who suggests that “If computing at gigaflops wererepresented by a one-way trip between San Francisco and Los Angeles, then computing at teraflops represents a roundtrip between San Francisco and the moon in the same amountof time.”

The Livermore–IBM collaboration is the latest project in theDepartment of Energy’s 10-year, $1-billion AcceleratedStrategic Computing Initiative program. The program, whichinvolves three major DOE facilities (Livermore, Los Alamos,and Sandia national laboratories), calls for five generations ofhigh-performance computers. Development of the firstgeneration ASCI machine—a 1.8-teraflop computer—is underway, teaming Sandia with Intel Corporation. The three othersupercomputers that ASCI wants developed will delivercalculation capability in the 10-, 30-, and 100-teraflop range.

In discussing the IBM contract in late July, LawrenceLivermore Director Bruce Tarter said that he expects thisproject to provide Livermore and the other nationallaboratories involved in ASCI “with an opportunity to lead thenext revolution in high-performance computing in support ofimportant national security objectives.”

ASCI supercomputers will be used to construct three-dimensional simulations of stockpiled nuclear warheads,allowing DOE scientists to analyze effects of weapons agingand the implications of potential problems. According to DavidNowak, head of the ASCI program at Livermore and a formerweapon designer, “Numerical simulation is the glue that holdsstockpile stewardship together.”

Advanced computations, specifically three-dimensionalmodeling and simulation capability, are central components of“stockpile stewardship”—the safe and reliable maintenance ofthe nation’s nuclear arsenal in the absence of nuclear testing.Tera-scale computing also will provide a commercial platformfor medical simulations, global climate modeling, aerospaceand automotive design, and other applications.

The system will be based on a building block approach tohigh-performance computing in which the system consists ofclusters of shared-memory processors. The new supercomputerwill be designed to accommodate as many as 512 nodes with

eight processors per node to perform numeric- and data-intensive tasks. It will be delivered with 2.5 trillion bytes ofmemory, as compared with existing high-end systems inwhich the memory is measured in billions of bytes or withpersonal computers where the memory is measured in tens ofmillions of bytes. It can be easily switched between a secureenvironment for national security applications and an openenvironment for university collaboration.

According to Nowak, the system naturally scales to the10-teraflop range by increasing both the processor speed andthe number of processors per node.Contact: Dave Nowak (510) 423-6706 ([email protected]).

Lab receives six awards for R&D innovationR&D Magazine will honor Laboratory researchers in

Philadelphia next month at its annual R&D 100 Awardsdinner. Each year, the magazine selects the top 100commercially viable research and development advances toreceive its coveted award, considered by many the R&Dcommunity’s “Oscar.”

This year, the magazine cited six technologies developedat Lawrence Livermore for R&D 100 honors. That broughtto 61 the number of awards the magazine has bestowed onLaboratory R&D teams since 1978, when Livermore beganparticipating in the competition.

Two of our award-winning developments this yearinvolve industrial partnering agreements. Five stem fromresearch pursuits in our Laser Programs.

Alan Bennett, director of our office of IndustrialPartnerships and Commercialization, described this year’sR&D 100 honors to the Laboratory as “a tribute to theongoing excellent scientific and technical work that routinelytakes place here.” Said Bennett: “Once again, Laboratoryscientists have shown that ideas developed in the course ofour mission activities may have tremendous benefits for theU.S. economy.”

Here is a brief look at the Laboratory’s 1996 R&D 100Award winners. Each will be reported on in detail in theOctober issue of S&TR.

Latest MIR use: the electronic dipstickThe Lab’s Micropower Impulse Radar (MIR) technology

has once again been honored by R&D Magazine, this timefor MIR’s latest application: an “electronic dipstick” to sensethe level of fluid or other material stored in tanks, vats, andsilos. The dipstick also can be used in automobiles to readlevels of a variety of fluids: gasoline, oil, transmission fluid,coolant, and windshield cleaner.

(continued on page 22)

The Next Frontiers ofAdvanced Lasers Research

drive targets, create intense soft x-raysthat can compress a deuterium–tritiumpellet to high-density and high-temperature to realize ignition by inertialconfinement fusion (ICF)—a feat weexpect NIF to achieve in about the year 2005.

NIF will fire approximately onceevery 4 to 8 hours, which is appropriatefor the needs of ICF in the research stageand of stockpile stewardship. However,future ICF needs could call for shot ratesof once every few minutes, and theultimate use of ICF—to produce electricpower—will require 5 to 10 shots persecond, an increase of over 100,000 timescompared to the shot rate achievablewith state-of-the-art fusion lasertechnology. Can a fusion laser driveroperate at this much higher repetitionrate? Lawrence Livermore’s advancedlaser design and small-scaleexperimental results indicate yes.

To date, all of the highest energy laserfacilities have been based on flashlamp-pumped neodymium-doped glass(Nd:glass) lasers because they are mostamenable to large-scale deployment andthey provide the flexibility in outputcharacteristics needed for ICF andweapons-related experiments. However,the completion of NIF, followed by theprospect of fusion ignition in thelaboratory within the next decade,prompts the question of what technologywill best meet our nation’s future needs.

Figure 1, which illustrates how theoutput energy of solid-state lasers hasprogressed over the last two decades,shows that we are considering a shift

from flashlamp-pumped to diode-pumped solid-state lasers, with theobjective of developing an advancedtechnology to provide “shots ondemand” for ICF and stockpilestewardship. In fact, the diode-pumpconcept is ready to be developed for abroad array of near-term (kilojoule-level) Department of Energy andDepartment of Defense missions, aswell as for longer-term megajouleapplications.

Advanced Laser Beamline

The next step in developing diode-pumped laser technology is to build aprototype beamline (i.e., a beamlet) of anadvanced laser facility within the nextfive to ten years (Figure 2). The basiccomponents of this laser are the diode-pump arrays, ytterbium-dopedstrontium–fluorapatite (Yb:S–FAP)crystals, and a gas-cooling system forthese crystals to allow an increased

5


Advanced Solid-State Lasers

IKE computers and stereoequipment, state-of-the-art laserscontinuously are improved by new

developments. In fact, the laser’s stateof the art is being enhanced by arelative of one of the components usedin CD players—the laser diode.

The laser diode, which producespurer monochromatic light than aflashlamp’s full-spectrum of white light,is a candidate for taking the technologyof Lawrence Livermore NationalLaboratory’s planned National IgnitionFacility (NIF) one step further. Thistechnology, which can increase shot

rates by up to 100,000 times, mayenable us eventually to produceelectricity by inertial fusion energy(IFE).1

NIF is one of the key components ofstockpile stewardship, our nationalstrategy to maintain nuclear competencewithout underground testing.2 It isbased on a flashlamp-pumped lasercapable of delivering 1.8 megajoules ofenergy directly or indirectly onto atarget within a few billionths of asecond.3 This energy will induceplasma temperatures of millions ofdegrees and, in the case of indirect-

4


TakingLasersbeyond theNat iona lIgn i t ionFac i l i ty

Tak ingLasersbeyond theNat iona lIgn i t ionFac i l i ty

LNova

NovetteShiva

Argus

Cyclops

Janus

Long Path

High gain region

NIF

Future diode-pumped solid-state lasers

Present diode-pumped solid-state lasers

1960

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1970 1980 1990 2000Year

201010–1

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Diode-pumped lasers

Flashlamp-pumped lasers

Figure 1. Maximum output energy of various LLNL laser fusion systems. Neodymium-dopedglass laser technology will culminate with the construction of the National Ignition Facility, andnext-generation diode-pumped laser technology will require development before it becomesrelevant to high-energy/high-density physics experiments.

By the year 2005, the National Ignition Facility is expectedto achieve fusion ignition—a major step on the road toproducing electricity by fusion. Now the Laboratory hasdeveloped and tested new diode-pumped laser technologythat increases both the power of lasers and their ability tofire rapidly. These advanced capabilities promise to help usachieve the ultimate goal of producing electricity by inertialconfinement fusion.

Figure 2. Model of a 1-kilojoule future “beamlet,” based on diode-pumpedsolid-state laser technology, gas cooling of the laser slabs, and ytterbium-doped strontium–fluorapatite gain medium.

Laser diodesLaser diodes

Spatial filters

Gain medium

Output beam

Gain medium

Prototype Applications

The most energetic diode-pumpedsolid-state lasers today generate about 1 joule of output energy in a pulselasting a few nanoseconds. We believe aprototype beamline operating at about1,000 joules (or even 100 joules) wouldhave near-term utility for experimentsand testing relevant to plasma physicsand ICF. This facility could be run up to10 hertz in repetition rate, although formost plasma physics and laser scienceexperiments conducted today, itessentially will be capable of providing“shots on demand.” Examples ofplasma physics experiments we wouldperform at the prototype beamlinefacility include:• Average-power x-ray lasers.• Average-power x-ray sources forimaging.• Laser-induced shock physics and laserplasma interaction studies.

• X-ray diagnostics development.Optical experiments include:• Large-area multishot damage testing ofNIF optics.• Debris shield survivability studies.Other important uses of a kilojoulefacility are:• Calibrating of x-ray cameras and otherdiagnostics.• Prototyping the design of a futuremegajoule facility.• Testing advanced laser concepts forinertial fusion energy.

Small-Scale Demonstrations

One of the recent outcomes of theexperimental program has been the gas-cooled slab testbed, shown in Figure 5.7This device integrates the accomplishmentswe have made over the last ten years:long-storage-time Yb:S–FAP gainmedium, high-power laser diode

7Advanced Solid-State Lasers

repetition rate. The facility would becapable of generating 1 kilojoule ofenergy on-target, at a repetition rate of upto 10 hertz, with a “wall-plug efficiency”of approximately 10%.

Figure 3 is a photograph of an LLNL-developed laser diode packagecontaining a high-power laser diodearray. This technology producesmonochromatic light output (singlewavelength) rather than the white lightcharacteristic of flashlamps (where allcolors are represented in the output),leading to higher efficiency operationand reduced heating of the laser crystals.Among the other crucial advantages thatlaser diodes offer over flashlamps is thatthey will be able to fire ten billion timeswithout being replaced, while largeflashlamps can offer only about100,000 shots. We have alreadydemonstrated one billion shots for diodesproduced in our laboratories.

Laser diodes are revolutionizingtelecommunications, where they aredeployed in optical amplifiers forundersea applications (with anticipated30-year operating lifetimes), CD players,and high-speed computer networks.Using diode-pump sources at the

megajoule-scale of fusion lasers,however, requires high peak power (largearrays of diodes rather than the singlediodes commonly employed in industrytoday). The cost of the diodes musttherefore be reduced to a “dime perwatt,” compared to the “dollars per watt”presently available.

Our analysis of diode production costssuggests that this cost reduction isplausible but will require a large-scaleapplication, such as laser fusion, to drivedown the cost of diodes. Laser diodesalso permit the long-term vision ofelectrical power production with fusionby virtue of their very high electrical-to-optical conversion efficiency (more than50%). Thus, the overall efficiency of thediode-pumped solid-state laser can bemore than 10 to 20%, because of the highefficiency of the diodes and the efficientmanner in which their output can bedelivered to the Yb:S–FAP crystals.4

The Yb:S–FAP crystals serve as the“gain medium,” which amplifies the lightbeam as it propagates through the laserchain. These novel crystals, invented atLLNL in 1991 and recognized with anR&D 100 Award, essentially willsupplant the Nd:glass used in Nova and

NIF. The main advantage of Yb:S–FAPcrystals is that they can store four timesas much energy as Nd:glass for a givenenergy pumping rate.5 They are alsobetter able to conduct away excess heatthan is laser glass.

Another crucial new technology thatenables the high repetition rate neededfor fusion is the gas-cooled slab,6 assketched in Figure 4. Cooling is neededbecause all lasers produce waste heat,which must be removed withoutdisturbing the sensitive optics.Lawrence Livermore has developed thetechnique of flowing helium gas acrossthe laser crystal surface in a turbulentmanner at about one-tenth the speed ofsound to conduct heat away from thecrystals. Helium gas is employedbecause it has high thermal conductivityand causes only insignificant opticaldistortions. The heat and light passthrough the same surface. Mostimportantly, the gas-cooled slab designhas the added advantage of beingreadily scalable by increasing the areaof the slab. This scalability is a criticalissue because fusion lasers will operatein the megajoule range in an electricalpower plant.

6


Figure 3. Laser diode array produced atLLNL, based on high-peak-power laserdiode bars, efficient microchannel coolerpackaging, and high-brightnessmicrolens collimators.

Turbulent flow diffuser

Deceleration sections

Ytterbium-doped strontium–fluorapatite laser gain element

Acceleration nozzle section

Turbulent diffuser

Helium gas

Helium gas flow stack

30-peak-kW laser diode array

Lens duct

Diode relay lens

Ytterbium-doped strontium–fluorapatite slab

Figure 4. Schematic drawing of the gas-cooled slab concept illustrating the high-speed helium gas flow across the opticalaperture that the laser light also traverses.



Figure 5. The first integrated laser module based on the use ofLLNL laser diode arrays, gas cooling, and ytterbium-dopedstrontium–fluorapatite gain medium. This gas-cooled testbed is asubscale demonstration of the technology relevant to futureadvanced lasers for inertial confinement fusion and stockpilestewardship.

artist’s rendition of a laser-driven ICFpower plant, which consists of fourparts: (1) drivers, which provide manyintense laser beams focused ontotargets, which are mass-produced in (2) the target factory and positioned in(3) the fusion chamber. When thebeams hit the targets, bursts of fusionenergy at 5 to 10 pulses per second areproduced to operate (4) conventionalsteam turbine generators.

Success in reaching the goal ofelectric power production using IFE iscomplicated by a great number ofconcerns that reach far beyond the laserdriver. One is the cost of the powerproduced. Using the same kind ofcalculations that are used to model theNIF and Nova lasers, we predicted thatelectricity produced by ICF would costabout 8.6 cents per kilowatt-hour.4While this is higher than the cost ofpower produced today by fossil fuels (5 to 6 cents per kilowatt-hour), futureenergy costs from traditionalnonrenewable sources are uncertain.

The highest risk issues confrontingthe prospect of ICF-based powergeneration are the level of achievabletarget gain and the survivability of thefinal optic. One of the primary missionsof NIF is to attain sufficient target gainto produce ignition. The final opticplays a critical role because thismaterial must efficiently transmitultraviolet light while simultaneouslyincurring the wrath of the high-energyneutrons and gamma rays that emanatefrom the target and the target chamber.

The best prospect for the final opticis heated fused silica. Although the ratesat which the final optic will bebombarded by radiation in NIF aresignificantly less than those for inertialfusion energy (about 50 kilorads peryear versus 50 kilorads per second!), thebasic physical mechanisms may besimilar. Figure 7 shows that differenttypes of fused silica have significantlydifferent levels of radiation-hardness, asindicated by the blackening of the

material. This blackening can beavoided easily, however, by choosingfused silica materials that are free ofaluminum impurities. Our investigationalso revealed that germanium impuritiesalso reduce radiation hardness.

After determining that certain fusedsilicas had neither aluminum norgermanium impurities, we identified theintrinsic defects that were created solelyby the neutrons and gamma rays. Our

light absorption measurementsindicate that, if the appropriate typeof fused silica is used, theabsorption loss at the NIF laserwavelength of 0.35 micrometers willbe 1% after 30 years of operation,which is the life expectancy of NIF.In another series of experiments, wedetermined that defects that areformed by the neutrons and gammarays are annealed, or repaired, if the

9



arrays, and turbulent gas cooling. Thelaser testbed demonstrates solutions tothe technical hurdles that are unique tofuture high-repetition-rate fusionlasers. The laser has produced 50 wattsof power output in a tabletop package,a power regime that is regarded assignificant by the laser community. At50 watts, the thermal load beingtransferred to the helium gas (flowingat about 0.1 Mach) is more than3 watts per square centimeter. Ourestimate of the requirement for amegajoule system running at 10 hertzis about 1 to 2 watts per squarecentimeter. The Yb:S–FAP laser slab

did not fracture until more than 50% ofthe theoretical stress limit of thematerial was reached, which is abouttwo times higher than required forfuture megajoule ICF facilities.

Another crucial issue of diode-pumped technology involves the overallefficiency of the system. Our smallYb:S–FAP diode-pumped laser hasyielded an overall electricity-to-lightconversion efficiency of more than10%.8 We are working to correct someproblems, such as impurity absorptionsin the laser crystals and unoptimizedoptical coatings, and we believe that wecan achieve an efficiency that exceeds

20% in long-pulse operations. Toachieve this objective, the crystals andcoatings need to have optical damagethresholds of greater than 10 joules persquare centimeter for 10-nanosecondpulses. We have found that selectedcrystals that are completely free ofdefects meet this criterion, althoughincreased quality control will be neededto attain this standard routinely.

Energy Production Is Goal

An ultimate goal of all laser fusionefforts is to tap this inexhaustible sourceof producing electricity. Figure 6 is an

8



Generators

Target factory Drivers

Drivers

Output beam

Laser diodes

Fusion chamber

Gain mediumGain medium Switchout

Driver

Spatialfilter

Laser diodes

Figure 6. An artist’s rendition of a laser fusion power plant drivenby diode-pumped solid-state lasers. Experiments at the NationalIgnition Facility will help clarify whether it is economically feasibleto generate electricity by laser fusion.

Figure 7. Picture ofvarious fused silicasamples that receivedradiation dosescomparable to thosepredicted for the finaloptic at the NationalIgnition Facility. On thebasis of our studies,the appropriate“radiation-hard” opticalmaterials wereidentified.

Heated fused silica final optic Reactor

chamber

First wall

Spatial filter

Pulse injectionPolarizer

Diodes

Output pulse

Gas-cooled harmonic

conversion

Gas-cooled gain medium

Gas-cooled Pockels cell

Neutron absorber

Dichroic mirror

Figure 8. Schematic of a beamline designed on the basis of laser physics, achievableperformance specifications, and reasonable cost. The basic architecture involves a multipassamplifier and frequency conversion (as does the National Ignition Facility), as well as thetechnology enhancements discussed in this article.

Illus

trat

ion

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a K

. Lyn

n

Robey, “Heat Removal in a Gas-CooledSolid-State Laser Disk Amplifier,”AIAA Journal 30, 431–435 (1992).

7. C. D. Marshall, et al., “Diode-PumpedGas-Cooled-Slab Laser Performance,”Proceedings of Advanced Solid StateLasers Conference (Optical Society ofAmerica, Washington, D.C., 1996).

8. C. D. Marshall, et al., “Diode-PumpedYtterbium-Doped Sr5(PO4)3F LaserPerformance,” to be published in IEEEJournal of Quantum Electronics 32(1996).

9. W. R. Meier and L. M. Waganer,“Recent Heavy-Ion Fusion Power PlantStudies in the U.S.,” Il Nuovo Cimento106A, 1983–1995 (1993).

STEPHEN PAYNE, one of the primary contributors to thisarticle, joined the Laser Programs when he came to theLaboratory in 1985. Since 1995 he has been the AssociateProgram Leader responsible for the Advanced Lasers andComponents element of the Laser Science and TechnologyProgram. He has co-authored more than 100 scientific papers onspectroscopy and laser physics. Payne received his B.S. inchemistry from the State University of New York at Binghamton

in 1978 and a Ph.D. in chemistry from Princeton University in 1983. From 1983 to1985 he was a post-doctoral fellow at the University of Pennsylvania.

CHRISTOPHER MARSHALL, the other primary contributor,came to the Laboratory in 1992 as a member of the LaserPrograms. He is the Project Leader responsible for developingadvanced diode-pumped lasers for inertial confinement fusionand has co-authored more than 20 scientific papers on laserphysics and materials since coming to the Laboratory. Marshallreceived his B.S. in physical chemistry from RensselaerPolytechnic Institute in Troy, New York, in 1987 and a Ph.D. inchemical physics from Stanford University in 1992.

Other colleagues who contributed to this article include: Bill Krupke, whoproposed the idea of using diode-pumped solid-state lasers for fusion energy;Howard Powell, who provided technical management and guidance; Grant Logan,who gave advice concerning the development pathway; Lloyd Chase and hisassociates, who introduced the heated fused silica concept; Charles Orth, whoexecuted the power plant study; and the many members of the Advanced Lasersand Components Team who developed the diodes, laser crystals, lens ducts, gascooling, and other components used in this work.

options to driving targets will becomeclearer during the next decade. Thepromise of fusion for energy productionand the relative utility of different driveroptions is best left as an open questionuntil after NIF ignites a target. Yet thediode-pumped option is certainly a majorcontender as the vehicle for the ultimateapplication of NIF technology—theproduction of unlimited electrical powerfrom inertial confinement fusion.

In the near-term, uses for advancedhigh-repetition-rate lasers also abound.In addition to offering us a pathway tofuture inertial fusion studies andstockpile stewardship applications, oursmall-scale experiments attest to thescientific viability of diode-pumpedsolid-state lasers for fusion, as do thesynergistic laser development efforts insupport of numerous military and civilianapplications (see the box on p. 10).

Key Words: diode-pumped solid-statelasers, final optic, gas-cooled slab (GCS),gain medium, inertial confinement fusion(ICF), inertial fusion energy (IFE).

References1. “The Role of NIF in Developing Inertial

Fusion Energy,” Energy & TechnologyReview, UCRL-52000-94-12 (December1994), pp. 30–42.

2. “Keeping the Nuclear Stockpile Safe,Secure, and Reliable,” Science &Technology Review, UCRL-52000-96-8(August 1996), pp. 6–15.

3. “The National Ignition Facility: AnOverview,” Energy & TechnologyReview, UCRL-52000-94-12 (December1994), pp. 1–6.

4. C. D. Orth, S. A. Payne, and W. F.Krupke, “A Diode-Pumped Solid-StateLaser Driver for Inertial Fusion Energy,”Nuclear Fusion 36, 75–116 (1996).

5. S. A. Payne, et al., “Gain Medium forLaser-Driven Inertial Fusion Energy,”Inertial Confinement Fusion QuarterlyReport 2, 51–59 (1992), UCRL-LR-105821-92-2.

6. S. B. Sutton, G. F. Albrecht, and H. F.

11



optic is held at an elevated temperature.At 400°C, the defects should not causeundue absorption of the laser light—even at the radiation dose rate predictedfor a power plant.

The beamline for a fusion powerplant, including the heated fused silicafinal optic, is shown schematically inFigure 8. It is similar to the prototypebeamline of NIF in that a pulse (about1.7 joules) is injected and then allowedto traverse the multipass amplifier fourtimes before being ejected at about10 kilojoules. However, the higher gainand energy storage possible with diodepumping and Yb:S–FAP gain crystalseventually will allow for betterreliability, beam quality, compactness,and efficiency, all of which arenecessary in a power plant. Thisbeamline is considered capable of an

efficiency approaching 10% for on-target properly conditioned laser light,a level upon which the feasibility of aworking power plant critically depends.Figure 8 also depicts the gas cooling ofthe laser crystals and the harmonicconversion crystals (which nonlinearlyconvert the 1.047-micrometerfundamental output wavelength of thelaser to the third harmonic at0.35 micrometers). Both technologiestogether with the heated fused silicafinal optic are fundamental toproducing electricity based on laserfusion. When 5,175 beamlets aregrouped in 345 beamlines, the systemcould deliver 3.7 megajoules on-target.An assumed target gain of 76 wouldlead to gross energy production of300 megajoules with 40 megajoules pershot recycled to power the laser and

other systems.3

To and beyond Ignition

While the flashlamp-pumptechnology of NIF will achieve ignitionand be used to explore weapons issuesduring the beginning of the nextcentury, diode-pumped solid-state lasersrepresent a promising laser driverbeyond NIF. Other fusion driver optionsexist with the potential of effectingfusion energy production—the heavy-ion accelerator is one example; light-ionaccelerators and krypton–fluoride lasersare others.1 And each hascomplementary risks and benefits forfusion energy production.9 At thisjuncture, however, many physics andengineering issues need to be resolvedfor any option. The applicability of these

10



For further information contact StephenPayne (510) 423-0570 ([email protected])or Christopher Marshall (510) 422-9781([email protected]).

Diode-pumped solid-state lasers are a rapidly emergingtechnology that is likely to have broad impact in many areasthroughout industry, government, and the military. In addition toinertial confinement fusion, our laser science and technologyteam is currently developing diode-pumped solid-state lasers formaterials processing, x-ray lithography, medical surgery,position calibration, remote sensing, and other purposes. Theseare specialty lasers that have required the deployment ofuncommon laser materials and unique architectures. Forexample, the laser in the picture at the right is a high-power,2.01-micrometer thulium-doped yttrium–aluminum–garnet(Tm:YAG) laser capable of delivering more than 100 watts, apower level nearly ten times greater than that previouslypossible. Its power and compact size are in part based on the useof a lens duct* that collects and funnels the light output of thelaser diode array into the Tm:YAG gain medium. Thephotograph shows the specialized laser diode array packagesused in the laser, including the microchannel cooling techniqueand the microlens conditioned output of the individual packages.

* “A Light Funnel for Diode-Pumped, Solid-State Lasers,” Science &Technology Review, UCRL-52000-95-11/12 (November/December1995), pp. 26-27.

Many Uses for Diode-Pumped Solid-State Lasers

Alternative example of diode-pumped solid-state laserdevelopment pursued by the research team. Developed atLivermore by Eric Honea and his collaborators, this laser, witha 2-micrometer thulium-doped yttrium–aluminum–garnet laserhead, achieved power levels nearly ten times greater thanthose previously possible.

About the Scientists

YDROGEN is the simplest and mostabundant of elements. Composed of

one proton and one electron, it makes up90% of our universe (by number of atoms).On Earth, hydrogen is commonly found asa diatomic molecular gas. But on Jupiter,where interior pressure is millions of timesgreater than that at our planet’s surface, thehydrogen molecule is theorized to exist as asuperhot liquid metal.

The theory that hydrogen turns metallicunder extreme pressure was first advancedin 1935 by Eugene Wigner, who would goon to win a 1963 Nobel Prize in physics forhis work in quantum mechanics. Findingexperimental evidence of Wigner’shydrogen metallization theory, however,has proven to be extremely difficult for thescientific community. While studies of theuniverse’s lightest material led to discoveryof hydrogen’s solid and liquid phases,metallic hydrogen remained out of reach—until recently.1

At Lawrence Livermore NationalLaboratory, in a series of shockcompression experiments funded byLaboratory Directed Research andDevelopment grants, we successfullyended a 60-year search for hard evidence ofmetallic hydrogen and the precise pressureat which metallization occurs at a particulartemperature.

Our success in metallizing hydrogenwould not have been achieved without theshock-wave technology built up over morethan two decades to support LawrenceLivermore’s nuclear weapons program. Itrepresents the integration of theLaboratory’s broad capabilities andexpertise in gas-gun technology, shockphysics, target diagnostics, hydrodynamiccomputational simulations, cryogenics,and hydrogen and condensed-matterphysics.

Knowing what happens when matter,such as hydrogen, encounters enormouslyhigh pressure and temperature is critical forthe success of the Laboratory’s research inareas relevant to our science-basedstockpile stewardship mission, such asnuclear explosives, conventional high

explosives, and laser fusion, as well as forour collaborative efforts in planetaryscience research. For more than twodecades, we have been helping improvethat understanding through shock-compression studies using our two-stagelight-gas gun (see the box on p. 15).

The gas gun permits us to firehypervelocity projectiles into highlyinstrumented targets (Figure 1), shockingmatter to extreme conditions for a millionthof a second or less. These experimentscreate pressures of a million-plusatmospheres, temperatures up to thousandsof degrees depending upon the materialbeing shocked, and densities several timesthat of a material’s solid state.

In addition to hydrogen, we haveperformed shock compression experimentson other liquefied gases such as nitrogen,water, carbon dioxide, oxygen, carbonmonoxide, deuterium (an isotope ofhydrogen), helium, and argon, and onsolids such as aluminum, copper, tantalum,and carbon (graphite). Data from suchexperiments are used to determine amaterial’s equation of state (EOS expressesthe relationship between pressure, density,and temperature), to validate theories, andto generate reliable computational modelsof a material’s behavior under a wide rangeof thermodynamic variables.

Quest for Metallic Hydrogen

Under normal conditions on our planet,molecular hydrogen functions as aninsulator, blocking electrical flow. Applysufficient pressure, theory said, andhydrogen turns metallic, becoming anexceptional conductor of electricity.Theory predicted that metallization wouldoccur when the insulating molecular solidwould transform to a metallic monatomicsolid at absolute zero—0 degrees kelvin (K)or –460°F. For early metallic hydrogentheorists, “sufficient pressure” was thoughtto be 0.2 megabars (1 bar is atmosphericpressure at sea level; a megabar, or Mbar,is a million times atmospheric pressure atsea level). Subsequent predictions pushed

metallization pressure to as high as 20 Mbar. At the time our experimentswere conducted, the prevailing theorypredicted 3 Mbar for solid hydrogen at 0 K.

For 35 years after Wigner proposed histheory, studies on metallic hydrogen wererelegated to the theoretical realm becausethere was no way to approach the subjectexperimentally. By the 1970s, however,the tools of science had reached a pointwhere it became possible to constructexperiments aimed at creating conditionsthat theory said were required formetallization. At Lawrence Livermore, forexample, one research approach2 used anexplosively driven system thatcompressed a magnetic field and, in turn,a small sample of hydrogen to megabarpressures without shocking the hydrogen,and thus the temperature of the samplewas kept very low. The early Livermoreexperiments generated pressures similar tothose we recently reached (about 2 Mbar).While electrical conductivity wasmeasured, the approach did not providenecessary evidence of metallization; themeasurement system was only sensitive toconductivity values much less than that ofa metal.

In recent years, researchers at otherlaboratories have attempted to achievemetallization by crushing micrometer-sized samples of crystalline hydrogen in adiamond anvil cell. This small mechanicalpress creates very high pressures in ananogram-sized sample when the smallflat faces of two flawless diamonds areforced together, exerting megabarpressure on the sample trapped betweenthem.3 While diamond anvil studies ofhydrogen resulted in an initial claim ofoptical evidence for metallization, thisclaim was later found to not hold up.4Significantly, there was no establishmentof metallic character using optical probes.Metallic character is most directlyestablished by electrical conductivitymeasurements, which are not yet possiblein diamond anvil cells with hydrogensamples at any pressure.

13Metallic Hydrogen12

M e t a l l i c H y d r o g e nM e t a l l i c H y d r o g e n

A 1935 theory predicted that hydrogen

becomes metallic when enormously intense

pressure is applied. But the theory remained

unproved for some 60 years until a Lawrence

Livermore team tried a “shocking” idea.

H


The Laboratory’stwo-stage light-gasgun wasinstrumental in theshock compressionexperiments thatmetallized hydrogen.

JUMPIN’ JUPITER!JUMPIN’ JUPITER!JUMPIN’ JUPITER!

deuterium) in a suitable target containerthat separated it from the vacuum of thetarget chamber. (Refer to Figure 1b.)The target walls had the required flatimpact surface and were made of amaterial for which we have an accurateequation of state (aluminum) so that wecould compute the pressures, densities,and temperatures reached during theexperiments. The liquid hydrogen (ordeuterium) was a half millimeter thick,and the target was cryogenically cooled.

We sandwiched the target betweentwo single-crystal sapphire anvils thatprovide stiffness and electrical

insulation for the four steel electrodesimplanted at the surface of the liquidhydrogen inside the target. Theseelectrodes are used to measure thechanges in the sample’s electricalresistivity/conductivity during shocktests. Two of the electrodes introducecurrent to the inertially confinedhydrogen sample, and two measurevoltage across the sample. A trigger pinin the target produces an electricalsignal when struck by the initial shockwave, turning on the data recordingsystem (Figure 1c) at the propermoment. The conductivity of the

shocked hydrogen is thus measuredbefore the pressure wave reaches anyexternal surface, that is, before thesample holder blows up when the shockreaches its external surface.

We mounted the anvils onaluminum plates that serve as the frontand rear walls of the target, initially at20 K. At that low temperature, thealuminum remains strong and ductile.Finally, we carefully wrapped thetarget with 50 layers of aluminizedmylar to reduce the heat losses thatwould boil away the liquid hydrogenand cause our sample to literally

15


Metallic Hydrogen

Our Approach

In 1991, we began a series ofexperiments to determine howcompression affected the electricalproperties of diatomic or molecularhydrogen and deuterium both of whichare insulators at ambient temperaturesand pressures. Our specific objectivewas to advance fundamentalunderstanding of the way hydrogentransitions from an insulator to aconductor at shock-test pressures andtemperatures. Evidence of actualmetallization was an unanticipatedresult of our experiments. It wasunexpected for several reasons: (1) weused liquid hydrogen, rather than solidhydrogen that conventional wisdomindicated was required; (2) we applieda methodology—shock compression—that had never before been tried inorder to metallize hydrogen; and (3) we were working at higher

temperatures (3,000 K) thanmetallization theory specified.

For our experiments, we used liquidhydrogen at an initial temperature of20 K (–423°F) because: (1) it is easierto liquefy hydrogen than it is to solidifyit in our experiments, (2) shockcompression dramatically increasestemperatures and turns solid hydrogeninto liquid, so it made sense to beginwith a liquid, and (3) only fluidhydrogen, not solid, is present in high-pressure and high-temperature systemsthat matter to the “real world”—insuperhot, hydrogen-rich planets likeJupiter and Saturn and in fusion energyexperiments like those conducted atLivermore where laser beams compresstiny spherical targets of liquiddeuterium and tritium, both isotopicforms of hydrogen.

As in any shock-wave experimentinvolving liquids, we confined theliquid hydrogen (or in some cases liquid

14


Metallic Hydrogen

Liquid hydrogen

Impactor

Sapphire insulator disk

Aluminum target

Metal impactor

Electrodes for conductivity measurements

Trigger pinResistors

Rowgowski coil

Battery power source, 200 volts

Circuit switch

Capacitor

Pump tube Target assembly

Target chamber

Second stage barrel

Piston

Hydrogen gas

Differential digital oscilloscope with 1-nanosecond resolution

Target containing liquid hydrogen

(a)

(b)

(c)

Rupture valve

Figure 1. Our success in metallizinghydrogen came during a series ofexperiments to understand the electricalproperties of shocked liquid hydrogen. (a) Our two-stage light-gas gun acceleratesplastic-encased aluminum and copperimpactor plates to velocities of up to8 kilometers per second (18,000 mph),sending a shock wave into (b) the targetassembly containing a 0.5-millimeter-thicksample of liquid hydrogen. Electricalresistivity/conductivity is measured using(c) a four-probe constant-current circuit.Trigger pins turn on the data-recordingequipment when hit by the initial shock wave,and a Rowgowski coil measures current. Thecircuit is connected to a differential digitaloscilloscope, which instantaneously recordsthe electrical quantities during the test.

Our shock compression studies use a 20-meter-long, two-stage light-gas gun built by General Motors in the mid-1960sfor ballistic missile studies; the gun has been in operation atthe Laboratory since 1972.

The gun consists of a first-stage breech containing up to3.5 kilograms of gunpowder and a pump tube filled with 60 grams of hydrogen, helium, or nitrogen gas; and a second-stage evacuated barrel for guiding the high-velocity impactorto its target.

Hot gases from the burning gunpowder drive a heavy (4.5-to 6.8-kilograms) piston down the pump tube, compressing thegas. At sufficiently high pressures, the gas eventually breaks arupture valve and enters the narrow barrel, propelling a20-gram impactor housed in the barrel toward the target.

When the impactor hits the target, it produces a high-pressure shock wave. In a fraction of a microsecond, the

Hot gases

Hot gases

Breech Pump tubeImpactor

Rupture valve closed

Barrel

Rupture valve open

Hydrogen gas

Impactor

Target

Target

Piston

Piston Hydrogen gas(a)

(b)

How Our Gas Gun Works

shock wave reverberates through the target. Diagnosticequipment, triggered by the initial wave, measures theproperties of the shocked material inside the target during thisextremely brief period.

Projectile velocity can range from 1 to 8 kilometers persecond (up to 18,000 mph). The preferred velocity is achievedby selecting the appropriate type and amount of gunpowder,driving gas (hydrogen for velocities at or above 4 kilometersper second, helium and nitrogen for lower velocities),pressure required to open the rupture valve, diameter of thebarrel, and the metal and mass of the impactor.

The velocity of the shock wave, when combined with theinitial conditions (impactor velocity, known densities,equation of state of the projectile and target materials) yieldsa precise measure of the pressure, density, and energyattained.

(a) In the first stage of thegas gun (blue shading),hot-burning gases fromgunpowder drive a piston,which in turn compresseshydrogen gas. (b) In thesecond stage (pinkshading), the high-pressure gas eventuallyruptures a second-stagevalve, accelerating theimpactor down the barreltoward its target.

transparent insulator, like glass. Theorysaid that when hydrogen is squeezed bytremendous pressure, the gap wouldclose to zero (the band-gap of metals,which are nontransparent conductors).Our studies show that when shockedmultiple times in a very cold liquid state,hydrogen becomes first a semiconductorand then a fluid metal when, as itsdensity increases, its temperaturebecomes equal to the band-gap at about0.3 electron volts (Figure 3). At thispoint, all the electrons that can beexcited by the shock to conductelectricity have been excited. Insensitiveto further decreases in band-gap, theconductivity stops changing. Ourconductivity data for hydrogen areessentially the same as those for theliquid metals cesium and rubidium at2,000 K undergoing the same transitionfrom a semiconducting to metallic fluid.The comparison is shown in Figure 4.

Implications/Future Research

Our gas-gun experiments enhancecollective knowledge about the interiorsof giant planets. Our earlier studies of

temperature measurements of shock-compressed liquid hydrogen led us toconclude that Jupiter’s molecularenvelope is cooler and has much lesstemperature variation than previouslybelieved. Further interpretation of thosedata suggests that there may be nodistinct boundary between Jupiter’s coreand mantle, as there is on Earth.6

Jupiter, which is almost 90%hydrogen, is not the only planet rich inmetallic hydrogen. Hot metallichydrogen is believed to make up theinterior of Saturn and may be present inother large planets discovered recentlyoutside our solar system. The presence ofmetallic hydrogen in these planets has apronounced effect on their behavior. OnJupiter, given its extreme internalpressures, the bulk of hydrogen is mostlikely in the fluid metallic state; in fact,given the pressure at which hydrogenmetallizes, much more metallichydrogen—the equivalent of 50 times themass of Earth—exists in Jupiter thanpreviously believed. We also assume thismetallic hydrogen is the source ofJupiter’s very strong magnetic field, thelargest of any planet in our solar system.

The results of our experiments lendcredence to the theory that Jupiter’smagnetic field is produced not in the core,but close to the Jovian surface (Figure 5).Based on our data, it appears that the bandof conductivity producing the magneticfield is much closer to the planet’s surfacethan was thought to be the case.7

We anticipate that laser fusionscientists, who use the compressibility ofhydrogen to tune laser pulses, also willfind the results of our metallic hydrogenexperiments extremely useful. Ourexperiments provide new insight into thebehavior of deuterium and tritium, isotopicforms of hydrogen used in laser fusiontargets. Higher fusion-energy yields couldresult from an improved understanding ofthe temperature–pressure relationship inhydrogen and its isotopes. Indeed, ourhydrogen metallization studies suggeststrongly that the revised computation ofthe equation of state of hydrogen atintense pressures will help in perfectingthe hydrogen-isotope-filled targets beingdesigned for the National IgnitionFacility, making their performance rangebroader and more flexible. This is alsoencouraging news for the science-based

17


Metallic Hydrogen

disappear. The impactors aimed at thesetarget samples were made of aluminumand copper embedded in plastic.

Using these impactors in the gas gun,we shocked the hydrogen samples topressures ranging from 0.9 to 1.8 Mbarand temperatures from 2,000 to 4,000 K.We designed our conductivityexperiments to consist of an initial weakshock in the hydrogen followed by aseries of very weak shocks reverberatingbetween sapphire anvils, between whichour hydrogen sample was sandwiched.In this way, the temperature was keptabout ten times lower than it would befor a single sharp shock to the same finalpressure. Each data point we recordedusing the diagnostics illustrated inFigure 1c represents a measurementtaken in about one ten-millionth of asecond, which is more than sufficient forthe sample to come into equilibrium,that is, reach a stable pressure, density,and temperature. Electrical signal levelsof a few hundredths of a volt andcurrents of about 1 ampere lasted about200 nanoseconds (200 ¥ 10–9 seconds),indicating that, indeed, metallization had occurred.

Our Results

As shown in Figure 2, we found thatfrom 0.9 to 1.4 Mbar, resistivity in theshocked fluid decreases almost fourorders of magnitude (i.e., conductivityincreases); from 1.4 to 1.8 Mbar,resistivity is essentially constant at avalue typical of that of liquid metals. Ourdata indicate a continuous transitionfrom a semiconducting to metallicdiatomic fluid at 1.4 Mbar, nine-foldcompression of initial liquid density, and3,000 K.

Some theorists have speculated thatmetallic hydrogen produced underlaboratory conditions might remain inthat state after the enormous pressuresrequired to create it are removed.However, metallization in ourexperiments occurred for such a briefperiod of time, and in such a manner,that questions about hydrogen’ssuperconducting properties and retentionof metallic form could not be answered.

At the relatively low temperature, thefluid hydrogen remained almostessentially molecular, rather thanbreaking into individual atoms. As a

result, electrons in the sample freelyflowed from molecule to molecule in afashion that is characteristic of metals. Atmetallization, we calculate that onlyabout 5% of the original molecules haveseparated into individual atoms ofhydrogen, which means that our metallichydrogen is primarily a molecular fluid.(Observation of this molecular metallicstate in our experiments was unexpected.Only the monatomic metallic state waspredicted by theory.)

In looking at the insulator-to-metaltransition, we focused on the changes inelectronic energy band-gap (measured inelectron volts) in hydrogen under shockcompression. The value of the electronicband-gap is the energy that must beabsorbed by an electron in order for it tocontribute to electrical conduction. Azero band-gap is characteristic of a metal;a positive, nonzero band-gap ischaracteristic of an insulator. Thus, themagnitude of the band-gap of aninsulator is a measure of how far awaythe insulator is from being a metal.

At ambient pressure, condensedmolecular hydrogen has a wide band-gap(about 15 electron volts), making it a

16


Metallic Hydrogen

DeuteriumHydrogen

Metallization occurs here

0.0001

0.001

0.01

0.1

Res

istiv

ity, o

hm-c

entim

eter

0.80 1.0 1.2 1.4Pressure, megabars

1.6 1.8 2.0

1

10Figure 2. As shockcompression increasespressure, liquid molecularhydrogen’s electricalresistivity falls dramatically, adecrease of almost fourorders of magnitude from 0.9 to 1.4 megabars beforeplateauing between 1.4 and1.8 megabars whereresistivity (and conversely,conductivity) is essentiallyconstant at a value typical ofthat of a liquid metal. Ourexperiments used molecularhydrogen and deuterium,which have differentdensities.

Figure 3. We examined electronicband-gap changes as molecularhydrogen makes the transition frominsulator to conductor. At ambientpressure, condensed molecularhydrogen has an electronic energyband-gap of 15 electron volts (eV),making it an excellent insulator. Inprevious single-shot shockcompression experiments (at up to0.2 megabars pressures and4,600 degrees kelvin), measurementsyielded an energy gap of 11.7 eV.5 Theresults of our new shock compressionstudies (shown by the solid part of thecurve) indicate that molecularhydrogen becomes metallized whenthe band-gap is reduced to about0.3 eV.

Figure 4. At2,000 degreeskelvin,conductivity forhydrogen isabout the sameas that of themetals cesiumand rubidium.Liquid molecularhydrogenbecomesconducting at ahigher densitythan do thosemetals.

0

4

6

2

10

Single shock

Electronic energy band-gap

Multiple shock

Molecular dissociation

Temperature

8

12

14

Ene

rgy,

ele

ctro

n vo

lts

0.0 0.1 0.2Density, moles per cubic centimeter

0.3

16

0

1

10

100

Con

duct

ivity

, ohm

–1-c

entim

eter

–1

0 0.005 0.01 0.7 0.90.5Atomic density, moles per cubic centimeter

1000

Cesium

Rubidium Hydrogen

10,000

NIKE3D modeling code, for example, whichwas developed at the Laboratory to address

engineering problems involving dynamicdeformations, such as the response of bridges to largeearthquakes,2 is now being used as part of our collaborativejoint modeling work.

Each person’s bones differ in shape and size. Our models arebased on the detailed anatomy of individual people. We startwith high-resolution data obtained from computed tomographyor magnetic resonance imaging, as shown in the illustrations onpp. 20–21. Images from a single hand scan involve severalgigabytes of raw data, and the models developed from them arehighly complex—thus the need for powerful computers.

Focusing on the Hand and KneeWe focused our initial attention on a few joints in the hand.

One joint of considerable clinical interest is the thumb carpo-metacarpal (CMC) joint, which connects the long bone at thebase of the thumb with the wrist. During routine graspingactivities, CMC joint surfaces are subjected to total forcesgreater than 200 kilograms (440 pounds), so it is not surprisingthat injuries are common. The thumb is also often involved inrepetitive motion injuries, and the CMC joint is the structuremost affected in osteoarthritis, which strikes 8% of the U.S.population. Other joints of considerable interest are the kneeand the proximal interphalangeal joint and the metacarpo-phalangeal joint in the index finger, which have some of thestrongest ligaments in the hand.

EPETITIVE motion injuries are one of the fastest growingcauses of lost time to business and industry, not to mention

their impact on worker health and morale. The orthopedicsurgery these injuries sometimes necessitate is costly andpainful. The therapy and orthopedic implantsassociated with degenerative bone and musclediseases and acute injuries are also costly, and inthe case of implants, the initial cost may not bethe final cost if and when the implant needs tobe replaced.

Computational models of joint anatomy andfunction can help doctors and physical therapistsunderstand trauma from repetitive stress, degenerativediseases such as osteoarthritis, and acute injuries. Models ofprosthetic joint implants can provide surgeons andbiomechanical engineers with the analytical tools to improvethe life-span of implants and increase patient comfort.1

With such purposes in mind, the Laboratory embarkedabout three years ago on a mission to model the whole humanhand at high resolution. The challenge is that most biologicalstructures are dauntingly complex, and the hand is noexception. The human wrist alone has eight bones, and the restof the hand has 19 more, to say nothing of soft tissues—ligaments, tendons, muscles, and nerves—and the interactionsamong them.

More recently, the Laboratory’s ComputationalBiomechanics Group within the Institute for ScientificComputing Research (ISCR) narrowed the mission to acomputational model focusing on the dynamics of specificbones and joints that are often associated with injury ordamage. The group also undertook a closely related endeavor:creating a computational model of prosthetic joint implants,initially for the thumb.

In light of the complexity of these models and the need forvery high accuracy, it is appropriate that a facility like LLNL—which offers powerful computational resources, anunderstanding of complex engineering systems, andmultidisciplinary expertise—take on these tasks. It is alsosignificant that the work is being done collaboratively throughthe ISCR and draws on experts from the Laboratory(particularly the Mechanical Engineering Department),academia, medicine, and industry (see the box on p. 20). The

19


stockpile stewardship research that willeventually be performed on NIF.

Future experiments will focus on (1) using various hydrogen isotopes—molecular hydrogen, deuterium, andhydrogen–deuterium—to determine thetemperature dependence of theelectronic energy gap, (2) exploringhigher pressures up to 3 Mbar, and (3) probing effects in similar liquidssuch as molecular nitrogen and argon.

Key Words: gas gun; hydrogen—fluid,liquid, metallic; Jupiter; National IgnitionFacility; shock compression tests; stockpilestewardship.

References1. S. T. Weir, A. C. Mitchell, and W. J.

Nellis, “Metallization of Fluid MolecularHydrogen,” Physical Review Letters 76,1860 (1996).

2. R. S. Hawke, et al., “Observation ofElectrical Conductivity of IsentropicallyCompressed Hydrogen at MbarPressures,” Physical Review Letters 41,994 (1978).

3. “The Diamond Anvil Cell: Probing theBehavior of Metals under UltrahighPressures,” Science & Technology

Review, UCRL-52000-3-96 (March1996), pp. 17–27.

4. R. J. Hemley, et al., “SynchrontronInfrared Spectroscopy to 0.15 eV of H2and D2 at Megabar Pressures,” PhysicalReview Letters 76, 1667 (1996) and H. N. Chen, et al., “Extended InfraredStudies of High Pressure Hydrogen,”Physical Review Letters 76, 1663 (1996).

5. W. J. Nellis, et al., “Electronic EnergyGap of Molecular Hydrogen fromElectrical Conductivity Measurements atHigh Shock Pressures,” Physical ReviewLetters 68, 2937 (1992).

18


Metallic Hydrogen

Physicist WILLIAM NELLIS joined the Laboratory in 1973. Hisspecialty is the investigation of condensed matter both during andafter high-pressure shock compression. The highlight of thiswork is the observation of the metallization of fluid hydrogen at1.4 megabars pressure and nine-fold compression. He hasdelivered invited talks at 44 professional conferences since 1979and is the author or co-author of more than 100 papers. A fellowof the American Physical Society’s Division of Condensed

Matter Physics, Nellis holds M.S. and Ph.D. degrees in physics from Iowa StateUniversity. He received his B.S. in physics from Loyola University of Chicago.

Figure 5. Our work has allowed us to calculate the electrical conductivity in the outer region of Jupiter. The planet’s magnetic field iscaused by convective dynamo motion of electrically conducting metallic hydrogen. Our results indicate that in Jupiter, the magnetic field isproduced much closer to the planet’s surface (b) than was thought previously (a).

Fluid molecular hydrogen mantle—electrical insulator

(a) Previous theory

3 megabars 10,000 degrees kelvin

Fluid metallic hydrogen core—source of magnetic field


Molecular hydrogen mantle


Moleculer metallic hydrogen—source of magnetic field

Fluid metallic hydrogen core


(b) Revised theory

About the Scientist

6. W. J. Nellis, M. Ross, and N. C. Holmes,“Temperature Measurements of Shock-Compressed Liquid Hydrogen:Implications for the Interior of Jupiter,”Science 269, 1249 (1995).

7. W. J. Nellis, S. T. Weir, and A. C. Mitchell, “Metallization andElectrical Conductivity of Hydrogen inJupiter,” Science (in press).

For further information contact William Nellis (510) 422-7200([email protected]).

19

R

Modeling Human Joints andProsthetic ImplantsModeling Human Joints andProsthetic Implants

Research Highlight

A new prosthetic implantdesign for the thumbjoint. We model thebehavior of each designwith physiological loadsapplied. Our techniqueuniquely reveals regionsof high stress (shown inred) versus relatively lowstress (blue).

21Joint ModelingJoint Modeling20

Science & Technology Review August 1996 Science & Technology Review September 1996

Collaborators in BiomechanicsModeling

ISCR biomechanics research is collaborative in thebroadest sense. At Livermore, we work with experts incomputer vision, mechanical and electrical engineering,nondestructive evaluation, health care technology, healthservices, and with visiting scholars and students. Partnersoutside the Laboratory include:

Academic institutionsUniversity of California, BerkeleyUniversity of California, San FranciscoUniversity of California, DavisUniversity of California, Santa CruzUniversity of New MexicoInstitute for Math and Computer Science, Hamburg, Germany

Medical facilitiesKaiser PermanenteG. W. Long Hansen’s Disease CenterLouisiana State University Medical CenterMassachusetts General HospitalChildren’s Hospital, San Diego

IndustryArthroMotion/Avanta Orthopedics, Inc.ExacTechOrthopedic Biomechanics InstituteNational Highway Traffic Safety AdministrationWright Medical, Inc.XYZ Scientific Applications, Inc.Zimmer, Inc.

5 to 15 years. The initial implant can cost about $20,000;revision implants are more expensive. Our methods caneventually be applied to any human joint for whichprosthetic implants have been designed. Our models areleading to better designs for prosthetic implants, resulting inlonger life spans and fewer costly followup operations.Finally, our work can help the automobile industry todevelop safety features that will protect against injury to thehead, chest, and lower extremities.

Key Words: biomechanical modeling, finite-element modeling,Institute for Scientific Computing Research (ISCR), NIKE3D,prosthetic point implants.

References1. Modeling the Biomechanics of Human Joints and Prosthetic

Implants, UCRL-TB-118601 Rev. 1, Lawrence LivermoreNational Laboratory, Livermore, CA (1995).

2. Energy & Technology Review, UCRL-52000-95-9/10(September/October 1995) is devoted to a series of articles oncomputational mechanical modeling, including NIKE3D.

3. For more information on finite-element modeling usingmassively parallel processors, see “Frontiers of Research inAdvanced Computations,” Science & Technology Review,UCRL-52000-96-7 (July 1996), pp. 4–11.

For further information contactKarin Hollerbach (510) 422-9111([email protected]).

Previous analyses of joint function (for example, rigid-body kinematic analyses) have typically provided lessinformation than is possible through finite-element methods.On the other hand, most finite-element analyses of biologicalsystems have been linear and two dimensional. We areapplying three-dimensional, nonlinear, finite-element codesthat assign material properties to bone and the soft-tissuestructures associated with joints.

For example, using the NIKE3D modeling code to look atbiological problems for the first time, we can model bones asmaterials that are more rigid than tendons, but less rigid than ametal implant. Soft tissues are inhomogeneous, undergo

deformation, and some showelastic behavior. Our methodssimulate tissue behavior undervarious loads, and jointmovement with and withoutprosthetic implants, andthey can assess injuryfollowing trauma, such asthat caused by a car crash.Because we can assigndifferent material propertiesto the tissues and examine arange of loads that areexperienced in real life, ourmethods allow us to seeinteractions between tissue types forthe first time, and we can identifyregions of high stress. Our high-qualityvisualizations, such as the one shown in the illustration on p. 19, display complex results in easy-to-understand form.

Two main issues are the computer time needed to run afinite-element code and the labor needed to develop a modelfrom each new scanned data set. We are addressing the firstproblem by working on powerful supercomputers and bypreliminary research in partitioning biological finite-elementmodels to run on massively parallel machines.3 To address thesecond problem, we are automating as much of the modelingprocess as possible.

Other 3D Visualization ToolsWe are also designing three-dimensional computational

tools to interactively move tissues so we can simulate surgicalprocedures. In the future, we plan to extend our modeling toinclude additional joints and perhaps internal organs, such asthe heart, lungs, and liver.

How can our computational tool benefit the clinicalcommunity and ordinary individuals? Our models providedata on internal joint stresses and strains that are not otherwiseobtainable. They can be used by surgeons to help plantreatment and to assess outcome following a traumatic orrepetitive motion injury. They can help a surgeon predictresults, such as strength, range of motion, and other indicatorsof function after an operation.

Orthopedic implants are a multibillion-dollar U.S. andworldwide industry; however, today’s prosthetic jointimplants have high failure rates. They often loosen, wear, andfail before the end of a recipient’s life, necessitating painfuland costly replacement. Orthopedic implants last on average

Computer tomography or

magnetic resonance imaging

Processed image

Finite-element mesh

Starting with (a) an individual human hand, we obtain (b) rawmagnetic resonance imaging or computed tomography scans. Thescan shown here is a cross section of bones and surroundingtissues proximal to the knuckles. From many cross sections, we (c) process the images and then generate (d) a high-quality, three-dimensional mesh that is suitable for finite-element analysis.

(b)

(c)

(d)

Human hand

(a)

Built of alternating layers of thin magnetic materials andnonmagnetic materials, this giant GMR sensor uses thin-filmtechnologies previously developed at Lawrence Livermore.Because the manufacturing process devised for the CPP-GMRdoes not require expensive fabrication tools, mass productioncosts can be kept low.

Because of the sensor’s unique properties (it actuallybecomes more sensitive at the higher device densities neededfor next-generation storage systems) and because of the simplemanufacturing process employed, Laboratory scientists expectthat magnetic heads using this sensor will enable theinformation storage industry to continue to develop higherdensity magnetic storage devices at reduced costs.Contact: Andrew Hawryluk (510) 422-5885 ([email protected]).

Tiny optical amplifier offers big boost to signal speedA dime-sized optical amplifier developed by the Laboratory

has the potential for delivering a big boost to signals whizzingthrough 21st century data communications systems. Thissemiconductor optoelectronic device is designed to amplifyoptical signals at ultrahigh (terabit-per-second) rates. Suchsignal amplification or regeneration is essential in fiber opticcommunication systems where signals must be distributed overgreat distances and to a large number of customers.

The Laboratory’s approach yields a component that is100 times less costly, 1,000 times more compact, and morereliable than competing fiber amplifier technology. Whenproduced in volume using present-day technologies, cost perunit is estimated to be as low as $500. As low-costmanufacturing techniques are developed, the cost is estimatedto drop to about $50 per unit.

Essentially an optical analog of the electronic amplifier,which is ubiquitous in the electronic world, the Lab’s miniaturesignal booster uses a tiny built-in laser system to eliminatecrosstalk problems that have prevented deployment of moreconventional semiconductor optical amplifiers.

Relying upon standard integrated circuit and optoelectronicfabrication technology, this device can be incorporated intomany types of photonic integrated circuits. Potentialapplications include wide-area and local-area informationnetworks, cable TV distribution, and computer interconnects.Contact: Mark Lowry (510) 423-2924 ([email protected]), Sol DiJaili(510) 424-4584 ([email protected]), or Frank Patterson (510) 423-9688([email protected]).

Lithography system proves boon for FEDsThe Laboratory has made a significant advance in the effort

to fabricate field emission display (FED) flat panels efficientlyand cost effectively by demonstrating large-area laser

interference lithography. Laser interference lithography is away to precisely and uniformly produce regular arrays ofextremely small (less than 100 atoms wide) electron-generating field emitter tips that are at the heart of FED flatpanel screens.

FEDs represent an advance over conventional flat paneldisplay technology used in a wide range of consumer andmilitary products—from digital watches to portable computers.

Field emission display panels consume less power thandevices using competing active matrix liquid crystal displaytechnology, a field dominated by Japanese companies.Compared to liquid crystal-based devices, field emissiondisplay panels can also be made thinner, brighter, lighter, andlarger, and they have a wider field of view.

FEDs, however, have not been much of a player in the $8-billion-a-year international flat panel market (projected tomore than double by the end of the decade). Their primarydrawback: expensive and complex micromachiningtechnology needed for their fabrication.

The Laboratory’s cost-effective fabrication technique,however, has potential to assure successful commercializationof large-area, high-performance FEDs. Potential applicationsrange from more efficient and energy-conserving portablecomputers to virtual reality headsets and wall-hugging TV screens.Contact: Michael Perry (510) 423-4915 ([email protected]).

23

Science & Technology Review August 1996

The Laboratory in the News

The electronic dipstick is impervious to condensation,corrosion, or grime on the sensor element, a simple metal stripor dipstick-like wire several inches to dozens of feet long,depending upon the application. The system’s electronics arebased on low-cost components that fit on a small circuit board.Cost is so low that one licensee of our technology plans toretail gas-cap-mounted dipsticks at $6 each.

Since development of MIR, initially invented as adiagnostic sensor for use by our Laser Programs, 30 patentshave been applied for, 16 of these have been granted to date,and hundreds of commercial applications have been identified.The Laboratory has been following the dual paths of licensingthe technology to qualified manufacturers and developingprograms that use the technology in support of our missions.

Like conventional radar, MIR works by sending out a pulseand measuring its return. In MIR, however, each microwavepulse is less than 5 billionths of a second in duration; an MIRunit emits about two million of these pulses per second.Because current is only drawn during this short pulse time,power requirements are extremely low. One type of MIR unitcan operate for years on a single AA battery.Contact: Tom McEwan (510) 422-1621 ([email protected]).

SixDOF sensor provides manufacturing flexibilityA small, noncontact optical sensor developed by the

Laboratory will increase flexibility in manufacturing processesthat employ robots. This invention does so by eliminating thetime-consuming and expensive process of “teaching” roboticmachinery new motions every time manufacturing changes are required.

Mounted on the tool head of a multi-axis robot arm, our six-degrees-of-freedom device (dubbed SixDOF) can sense itsposition relative to a workpiece, allowing the robot toautonomously follow a predescribed machining ormanufacturing path. As the device’s name indicates, SixDOFsenses its position in all six degrees of freedom (the x, y, and zaxes as well as the turning motion around those axes).

SixDOF is 250 times faster, 25 times more accurate, andone-sixth less expensive than its nearest competitor, which candetect only three degrees of freedom. The sensor works byemitting a laser beam and detecting the reflection off referencepoints mounted on the workpiece. Inside SixDOF, the beam issplit and directed onto three photo diodes. The analog signalsfrom the diodes are digitized and fed into a computer that caninstruct corrective action or provide position readings.

The sensor could be used to control a six-degrees-of-freedom computer mouse, to assemble large and complex partsautomatically, or to perform dangerous tasks remotely.Contact: Charles Vann (510) 423-8201 ([email protected]).

Optical crystal delivers tunable ultraviolet laserThrough an industrial partnership forged with II-VI

Corporation of Tarpon Springs, Florida (formerly LightningOptical Corporation), Lab scientists have developed andcommercialized a new optical crystal—Ce:LiSAF—that, for thefirst time, makes an all-solid-state, directly tunable ultraviolet(UV) laser commercially viable.

The crystal consists of lithium–strontium–aluminum–fluorite (LiSrAlF6) doped with cerium (Ce), a rare-earth metal.Before the availability of this lasing medium, generatingtunable UV light required multiple complex and sensitivenonlinear optical conversion steps. Ce:LiSAF eliminates these deficiencies.

Coupled with a compact solid-state laser, Ce:LiSAF yields apractical, robust laser system. Producing UV light directly andefficiently, it greatly expands laser applications; directlygenerating such light in a wide enough color band to providestraightforward “tunability” extends laser uses even more.

Ce:LiSAF lasers are particularly well suited to remotesensing applications. For example, a Ce:LiSAF laser could beused remotely to detect ozone and sulfur dioxide in theenvironment. Additionally, Ce:LiSAF lasers could be used tolocate biological weapons remotely by detecting the presenceof tryptophan, a common component of such weapons. Theultraviolet tunability provided by Ce:LiSAF also could be thebasis for development of a UV differential absorption Lidar(laser radar) system. Another potential application is securewireless communication links between infantry units in the battlefield.Contact: Christopher Marshall (510) 422-9781 ([email protected]).

Sensor offers greater performance, reduced costTeaming with the Read-Rite Corp. of Fremont, California,

Laboratory scientists have developed an advanced magneticsensor, a critical component in magnetic storage devices suchas hard disk drives in computers. A typical disk drive in acomputer would use 1 to 10 magnetic sensors.

Called the CPP-GMR (current-perpendicular-to-the-plane,magnetoresistance) sensor, this new invention offers greatersensitivity and 100 times greater storage densities than currentcommercial products. In fact, CPP-GMR storage densityranges from the current state of the art (about 1 gigabit persquare inch) upward to the projected limit of magnetic diskdrive technology (about 100 gigabits per square inch).

22


The Laboratory in the News

(continued from page 2)

24


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

Thomas E. McEwan

Hugh R. GreggMichael P. Meltzer

Thomas E. McEwan

Leonard C. Haselman,Jr.

Patent title, number, and date of issue

Phase Coded, Micro-Power Impulse Radar Motion Sensor

U.S. Patent 5,519,400May 21, 1996

Contamination Analysis Unit

U.S. Patent 5,521,381May 28, 1996

Range-Gated Field Disturbance Sensor with Range-Sensitivity Compensation

U.S. Patent 5,521,600May 28, 1996

Free Form Hemispherical Shaped Charge

U.S. Patent 5,522,319June 4, 1996

Summary of disclosure

A device for detecting a characteristic, such as motion, of objects within arange-gated field. A transmitter transmits a sequence of shortelectromagnetic pulses in response to a transmit timing signal at anominal pulse repetition frequency. A receiver samples echoes of thesequence of pulses from objects within the field with controlled timing (inresponse to a receive timing signal) and generates a sample signal. Therelative timing of the transmit-and-receive timing signals is modulatedbetween first and second relative delays at an intermediate frequency.

A unit that measures trace quantities of surface contamination in realtime. The detector head of the portable contamination analysis unit hasan opening with an O-ring seal, one or more vacuum valves, and a smallmass spectrometer. With the valve closed, the mass spectrometer isevacuated with one or more pumps. The O-ring seal is placed against asurface to be tested, and the vacuum valve is opened. Data are collectedfrom the mass spectrometer, and a portable computer providescontamination analysis.

A low-power, low-cost, close-range sensor that transmits a sequence ofbursts of electromagnetic energy to produce a sensor field. Thetransmitter frequency is modulated at an intermediate frequency. Thesensor receives electromagnetic energy at the transmitter frequency. Atransmitted burst is mixed with reflections of the same transmitted burstto produce an intermediate frequency signal, which indicates adisturbance in the sensor field and defines the sensor range.

A charge that has been modified such that the liner is aspherical andallows an aspherical wall thickness variation. The liner has a thick wall atits pole and a thin wall at the equator with a continually decreasing wallthickness from the pole to the equator. The ratio of the wall thicknessfrom the pole to the equator varies depending on the liner material andthe desired jet properties. By redesign of the basic liner thicknesses, thejet properties of coherence, stability, and mass distribution have beensignificantly improved.

Patents

AwardsBill Hogan has been awarded the 1996 Outstanding AchievementAward by the Fusion Energy Division of the American Nuclear Societyfor his pioneering work in inertial fusion energy. Hogan has been a keyplayer in the development of the field of inertial fusion energy as arespected branch of fusion research. A Laboratory physicist since1966, he is well known as a spokesman for the National IgnitionFacility and a proponent for inertial fusion energy applications beyondNIF. He is also an advocate of fusion energy internationally, and since1992, he has served as chairman of the Vienna-based InternationalAtomic Energy Agency’s advisory committee on fusion energy. Hewas recently elected vice chair/chairman-elect of the 1,000-memberANS fusion division.

Peter Fiske was recently awarded the prestigious White HouseFellowship by President Clinton. One of eight men and ten women toreceive the award, Fiske is a post-doctoral research associate in theLaboratory’s Institute of Geophysics and Planetary Physics. Herecently published a book, To Boldly Go. . .A Practical Career Guidefor Scientists, which is about the future of scientific research anddevelopment in the post-Cold War era and the career crisis he andother post-doctoral fellows face in today’s job market.

Laboratory employee Bart Hacker was the recipient of the 1996Richard W. Leopold Prize from the Organization of AmericanHistorians for his book Elements of Controversy: The Atomic Energy

Commission and Radiation Safety in Nuclear Weapons Testing,1947–1974. Established in 1984, the biennial Leopold Prize recognizessignificant historical work being done by historians outside academia.Hacker joined the Laboratory in 1992 as a science and technologyhistorian and is currently the editor of National Security Science andTechnology Review, the Laboratory’s classified quarterly journal.

David Zalk has been awarded the John J. Bloomfield Award by theAmerican Conference of Governmental Industrial Hygienists for hispioneering work in custodial ergonomics and asbestos handlingprocedures. The Bloomfield award is presented annually to a hygienistwith less than ten years’ experience “who pursues problems ofoccupational health hazards primarily via field work, and demonstratessignificant contribution to the profession.” Zalk has been employed bythe Laboratory’s Hazards Control Department as an industrial hygienistfor three years.

Two Laboratory Scientists—Rick Ryerson, of the Institute ofGeophysics and Planetary Physics, and Luiz Da Silva, from the LaserPrograms Directorate—have been selected as DistinguishedLecturers for Associated Western Universities for the 1996–97academic year. Ryerson and Da Silva join a list of Laboratory colleagueswho have received this honor since 1989. Ryerson is currentlyspecializing in using different dating methods for rocks to determine theslip rates along faults associated with the Indo–Asian collision and theuplift of Tibet. Da Silva is an expert in the uses of optical lasers formedical applications.

Taking Lasers beyond the National IgnitionFacility

High-energy solid-state lasers have been shown to be usefulfor studying the plasma physics of fusion, the nationalobjectives of stockpile stewardship, and possibly future energyproduction. Solid-state lasers based on flashlamp pump sourceswill achieve ignition and explore weapons issues during thebeginning of the next century. Diode-pumped solid-state lasersrepresent a next step in continuing to pursue laser fusion afterstartup and operation of the National Ignition Facility. Inaddition to offering us a pathway to future inertial fusionstudies and stockpile stewardship applications near-term usesfor advanced high-repetition-rate lasers also abound. Oursmall-scale experiments at Lawrence Livermore attest to thescientific viability of diode-pumped solid-state lasers forfusion, as do the synergistic laser development efforts insupport of numerous military, governmental, and civilianapplications.■ Contact: Steve Payne (510) 423-0570 ([email protected]) or Chris Marshall (510) 422-9781 ([email protected]).

Jumpin’ Jupiter! Metallic Hydrogen

The most abundant element in the universe, hydrogenplays a significant role in our defense and laser fusionprograms. As a result, we have a continuing interest in betterunderstanding hydrogen’s behavior at high temperature andpressure. Recently we succeeded in achieving a long-soughtgoal of high-pressure physics—converting hydrogen to ametal. The prediction that hydrogen would turn metallic atextremely high pressures was first theorized in 1935, buttangible evidence eluded scientists during the interveningdecades. We approached metallization differently fromothers, applying a series of relatively weak shockcompressions to targets of liquid, rather than solid, hydrogen.■ Contact: William Nellis (510) 422-7200 ([email protected]).

Abstracts

© 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: 1996/784-071-30019

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