News this Week

Science  28 Oct 2011:
Vol. 334, Issue 6055, pp. 438

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  1. Around the World

    1 - Jerusalem
    Museum of Tolerance Under Fire for Intolerance
    2 - Berlin
    European Research Heads Get New Body
    3 - Kourou, French Guiana
    First Two Galileo Satellites Lift Off
    4 - New York, New York
    Genomics X PRIZE Revamped
    5 - Wageningen, The Netherlands
    Three Glasses of Milk a Day? Maybe Not
    6 - Gran Sasso, Italy
    Superfast Neutrinos Announced Too Quickly?


    Museum of Tolerance Under Fire for Intolerance

    In design.

    Jerusalem's planned Museum of Tolerance.


    In a 20 October letter, leading archaeologists spoke out against plans to break ground for a museum—the Simon Wiesenthal Center's Museum of Tolerance—on and adjacent to the ancient Muslim cemetery of Mamilla in Jerusalem. Mentioned in 11th century C.E. documents, the cemetery was the resting place for early Muslims as well as Christian crusaders, and was used as a burial ground until the mid-20th century.

    In a letter addressed to center board members, Jerusalem's mayor, and the director of the Israeli Antiquities Authority, 84 respected archaeologists spoke out against the project, which is scheduled to begin construction next month. The letter says that the project involved “surreptitious and unscientific removal of hundreds of human burials,” and broke Israeli laws requiring that all human remains be turned over to the Ministry of Religious Affairs for reburial. Such lapses, the letter says, “would not have occurred with a Jewish burial site.” Center officials did not return requests for comment, but on its Web site, the center maintains that no one complained about the location during years of public hearings.


    European Research Heads Get New Body

    Fifty funding and research organizations from 23 countries joined in the founding assembly on 21 October of Science Europe, an organization its members hope will give research funders a stronger voice in policymaking at the European Commission in Brussels and across the region. The assembly also elected a board for Science Europe and adopted bylaws and membership criteria. Eligible members are national organizations that fund or carry out research in countries that are part of the 47-member Council of Europe.

    The new body will work together with the to-be-dissolved European Science Foundation (ESF) to coordinate ESF's “responsible wind-down” in the next few years, said Paul Boyle, who was elected Science Europe president at the assembly this morning. Boyle, a geographer who is chief executive of the U.K. Economic and Social Research Council, says that priorities for the organization will be to find ways for European scientists to enjoy open access to data and publications and freedom of movement—both of money and researchers—across national borders.

    Kourou, French Guiana

    First Two Galileo Satellites Lift Off


    The first pair of operational Galileo satellites, part of Europe's counterpart to the U.S. Global Positioning System (GPS), blasted off atop Russia's Soyuz rocket on 21 October from the European Spaceport in French Guiana. The launch was the first that Soyuz has made from the European space base.

    The Galileo system, which will ultimately consist of 30 satellites (Science, 23 December 2005, p. 1893), will “position our continent as a world-class player in the strategic domain of satellite navigation,” said Jean-Jacques Dordain, the director general of the European Space Agency (ESA), in a press release. The first two satellites are part of the In-Orbit Validation (IOV) phase that will test the Galileo system; two more IOV satellites are scheduled for launch in summer 2012.

    New York, New York

    Genomics X PRIZE Revamped

    Five years ago, the X PRIZE Foundation set up a $10 million prize for the first sequencer to decipher 100 human genomes in 10 days for less than $10,000 apiece. The intent was to push for the eventual routine use of sequence data in medical practice. As predicted (Science, 13 October 2006, p. 232), no one stepped up to the plate.

    But in Nature Genetics this week, the foundation announced new rules and an updated contest: Starting on 3 January 2013, contestants can compete to sequence the genomes of 100 healthy centenarians. The winner takes all only if the cost is $1000 per genome. Participants will have up to 30 days to finish the job, which will be evaluated and compared with multiply sequenced subsets of the genomes, says X PRIZE Foundation adviser Larry Kedes. The foundation decided that it would be biomedically useful to sequence subjects who have lived to be over 100 years old rather than just a random sampling of individuals, with the sequenced genomes becoming part of a scientific database.

    Not just anyone can compete. The foundation will have a vetting process to make sure would-be contestants are up to the task, says Kedes.

    Wageningen, The Netherlands

    Three Glasses of Milk a Day? Maybe Not

    Does drinking lots of milk keep you healthy? Yes, according to a 2010 press release by Wageningen University and Research Centre (WUR) in the Netherlands about a study of milk consumption and cardio vascular disease in The American Journal of Clinical Nutrition. But on 18 October, the university appeared to withdraw the claim after one of the study's authors, Harvard University epidemiologist Walter Willett, called it “misleading” and “an extreme distortion” of the results.

    WUR nutrition scientist Sabita Soedamah-Muthu said in 2010 that the study, which was supported by a grant from the Dutch Dairy Association, found that drinking three glasses of milk a day reduced the risk of cardiovascular disease by 18%. The release suggested a milk-touting cartoon character spokesperson for the Dutch dairy industry in the '60s and '70s “was right after all.” Willett, however, says that the majority of the evidence from the study “did not support a benefit for cardiovascular disease.”

    The university now says the press release was based on four European studies with a limited number of cases, and that broader analysis showed that heart attacks and strokes, the two most important forms of cardio vascular disease, “were not significantly associated with milk consumption.”

    Gran Sasso, Italy

    Superfast Neutrinos Announced Too Quickly?


    Last month, the OPERA (Oscillation Project with Emulsion-Tracking Apparatus) collaboration announced that it had apparently observed neutrinos traveling faster than the speed of light. In the wake of heated disagreements between collaboration members about both the solidity of the claim and the speed with which it was announced, OPERA has now decided to delay submitting its controversial result to a peer-reviewed journal while it checks the result with a new set of very precise measurements.

    OPERA's detector under the Gran Sasso mountain in central Italy studies the properties of neutrinos traveling 730 kilometers through Earth's crust from the CERN laboratory in Geneva. The new measurements will involve a change in the CERN neutrino beam that will make it possible to more precisely measure the time it takes neutrinos to travel between the labs.

    Sources suggest the collaboration will carry out the measurements over a period of 10 days, probably starting this week, and that in that time it should intercept around 12 neutrinos—possibly generating enough data to either disprove the announced result or confirm an important part of the analysis behind the result.

  2. Random Sample


    The Royal Society announced 26 October that its historical journal archive, including more than 8000 historical scientific papers, is now open-access (for papers older than 70 years). The society's Philosophical Transactions, which debuted in 1665, is the world's oldest peer-reviewed journal.

    They Said It

    “I've been recommending to all my colleagues here in the wine district that they should also go for a Nobel Prize, because I promise, it does a lot for your business.”

    —Winemaker Brian Schmidt, who also won the 2011 Nobel Prize in physics for discovering that the expansion of the universe is speeding up.

    World on Fire


    Individual local wildfires tend to stand out in the news: California's deadly 2009 Station Fire, fires in Russia sparked by a 2010 summer heat wave, and blazes raging across Texas since November 2010. But at any given time, thousands more wildfires are burning around the world—some wild and deadly, some intentional and controlled for land clearing. Now, scientists using data from the Moderate Resolution Imaging Spectroradiometer (MODIS) instruments on NASA's Terra and Aqua satellites have pieced together a decadelong global tour of the world's fires, from waves of grassland fire sweeping across Africa, “the fire continent,” to agricultural fires in Asia and catastrophic wildfires in the western United States. Since Terra launched in 1999 and Aqua in 2002, the MODIS instruments have mapped more than 40 million actively burning fires around the world. This long-term record, scientists say, is particularly important for understanding how fires respond to climate change and changing human populations.

    By the Numbers

    $33.57 billion — The total economic value of Hawaii's coral reef ecosystems per year, according to a survey of U.S. residents commissioned by National Oceanic and Atmospheric Administration.

    About 21,000 — Number of humpback whales in the North Pacific Ocean, up from 1400 in 1966. An international whaling ban helped the whales come back, according to a Marine Mammal Science study.

    Moving Images


    Life and death were the bookend themes at New York's fourth Imagine Science Film Festival, a weeklong showcase of 80 films linking science and storytelling that concluded on 21 October. The festival opened with Mr. Nobody, a sci-fidrama by filmmaker Jaco Von Dormael that explores the blur of memories and alternate realities in the mind of the last earthling in 2092. In the 30-minute documentary Until, which closed the festival, neurologist-turned-filmmaker Barry Gibb asked children, the elderly, and gerontologists questions like, “How long would you like to live, and why?” Until earned Gibb the Nature People's Choice Award.

    A jury of four filmmakers, writers, and scientists selected three other award winners. The Scientist Award, sponsored by AAAS (which publishes Science), went to Chasing Birds in Beringia, field biologist Stephani Gordon's 10-minute documentary about pilot-biologists studying migrating swans north of the Arctic Circle. One judge praised the film's “vivid portrayal of the intrinsic beauty and difficulty of such remote work.” Director Michael Please won the Nature Scientific Merit Award for best short for Eagleman Stag, a 9-minute stop-motion film about an aged entomologist who tries to slow the pace of time. A judge lauded the work as a “beautifully made short about the passion of science, life, and memory.” And Breast Stem Cells, a 3-minute film by biologist-animators Drew Berry and Etsuko Uno of the Walter and Eliza Hall Institute of Medical Research in Australia, won the Visual Science Award.

  3. Newsmakers

    New Chief for NIH's Basic Research Institute


    Massachusetts Institute of Technology (MIT) cell biologist Chris Kaiser will take the helm of the $2 billion National Institute of General Medical Sciences (NIGMS) next spring. Kaiser, 54, uses yeast to study how proteins fold and transport molecules within cells. He is currently chair of MIT's department of biology and will join NIH's fourth-largest institute at a time of ever-tighter budgets.

    Kaiser says maintaining NIGMS's investigator-initiated research grants is his top priority. He also expects to carry out NIGMS's strategic plan for training programs, drawing on lessons he learned from attracting minority graduate students in biology to MIT.

    Kaiser says he plans to continue predecessor Jeremy Berg's practice of blogging about how NIGMS makes funding decisions. “It's really important even if times get tougher for stakeholders to understand how the money is being deployed.”

  4. Inertial Confinement Fusion

    Fusion Power's Road Not Yet Taken

    1. Daniel Clery

    Billed as a way of simulating tests of nuclear weapons, a dark-horse technique called inertial confinement fusion might outstrip mainstream fusion projects in producing commercial energy.

    Shock treatment.

    Could fusion be triggered by intense current pulses like those from Sandia's Z machine?


    If nature smiles on the researchers at Lawrence Livermore National Laboratory, sometime in the next year or two they will fire a high-energy laser pulse at a tiny target containing frozen hydrogen isotopes, and BANG! A small explosion will take place—not big enough to damage anything much, but big enough to prove that after more than 6 decades of trying, scientists can make fusion happen in a laboratory and create an excess of energy.

    Fusion, the melding together of nuclei as opposed to the splitting apart that occurs in fission, sounds like the perfect energy source: Its fuel is cheap and plentiful (it comes from seawater), and it emits no carbon and minimal radioactive waste. What it does have is a credibility gap. Despite the enormous progress in understanding fusion and proving its viability, a genuine fusion power station always seems tantalizingly out of reach. Although researchers can cause fusion reactions in the lab, it takes more energy to make them happen than is produced. A major proof-of-principle step would be ignition: a self-sustaining fusion reaction that produces an excess of energy. As the name implies, Livermore's $3.5 billion laser center, the National Ignition Facility (NIF), has that goal in its sights (p. 449).

    NIF's main goal is not energy production but stockpile stewardship: validating computer simulations of nuclear explosions. Nevertheless, fusion researchers are hoping that that small explosion will be a huge boost to their field. “A sea change could come after ignition at NIF,” says Robert McCrory, director of the Laboratory for Laser Energetics (LLE) at the University of Rochester in New York state. Fusion energy research in the United States has been starved of funds over the past couple of decades, leading to the cancellation of many projects. And those involved in inertial confinement fusion (ICF), crushing pellets of fuel to cause small explosions, have been the poor relations compared with their colleagues in magnetic confinement fusion, who aim to confine much larger and less dense plasma using powerful magnets. Magnetic fusion researchers have pinned their hopes on ITER, a huge international reactor currently being built in France, which aims to prove the feasibility of magnetic fusion energy. The United States is committed to spend more than $1 billion on ITER, which is putting a severe strain on the Department of Energy's fusion budget (Science, 16 September, p. 1556).

    In contrast, ICF hasn't been treated as energy research at all. It gets most of its funding through the National Nuclear Security Administration because of its ability to mimic nuclear weapons. But with the twin threats of climate change and declining oil stocks, interest in alternative sources of energy is growing. So ICF researchers across the country have been drawing up plans for research that would be needed to take their techniques out of the lab and into prototype power plants. They want to be ready in the event that ignition at NIF leads to a surge of interest in ICF and new money. “The whole field is on the brink of some amazing physics,” says Michael Cuneo of Sandia National Laboratories in Albuquerque, New Mexico.

    Politicians, too, are aware of the possibilities. Secretary of Energy Steven Chu and his Under Secretary for Science Steven Koonin have been following NIF's efforts and know the impact it may have. As a result, in 2010, Koonin asked the National Academy of Sciences (NAS) to carry out a study of ICF to explore—assuming that ignition is achieved—the prospects for an ICF power plant, identify the science and engineering challenges, and sketch out an R&D road map. Throughout this year, the NAS panel has been visiting labs and listening to dozens of presentations about ICF. Its interim report is expected to be published any time now. The question for ICF researchers is: What sort of research program will it recommend? No one is expecting a flood of money straightaway, but if nature does smile on NIF, could ICF become a genuine contender capable of putting electricity in the grid before ITER and its successors do?

    Frantic pace

    Even if NIF achieves its goals in full, there's still a very long way to go before ICF can produce power commercially, and a future power station may look nothing like NIF. Likening ignition to the first flight by the Wright brothers, Glen Wurden of Los Alamos National Laboratory in New Mexico says: “We're still at the wood, cloth, and wire stage, and it looks nothing like a 747.”

    Certain elements are common to all ICF approaches. First, you need a target. This is a small container filled with deuterium and tritium, two isotopes of hydrogen that will fuse if you heat them to more than 100 million kelvin. That temperature is reached by squeezing the target very rapidly. So the next thing you need is a driver, some impulsive force to crush the target. The most common driver is an array of lasers. NIF's vast laser bays produce the most energetic laser pulse in the world, at 1.8 million joules (MJ). But other ICF researchers use different drivers, including particle beams and intense electrical pulses.

    An ICF power plant will also need a reaction chamber, sealed to contain the radioactive tritium and strong enough to withstand repeated explosions. Its walls have to absorb the intense neutron bombardment that carries most of the energy from the fusion and whisk that energy away as heat to boil water, make steam, drive a turbine, and generate electricity. The chamber walls have another role, too: breeding more fuel. Tritium doesn't exist naturally on Earth, but it can be made by bombarding lithium (from seawater) with neutrons. All fusion power schemes include plans to have lithium embedded in the walls in some fashion so that some of the neutrons from fusion can breed more tritium.

    Coming soon?

    Researchers at NIF say their fusion reactor design, dubbed LIFE (for Laser Inertial Fusion Energy), could be built in 12 years by using replaceable off-the-shelf components and avoiding advanced materials.


    Perhaps the biggest challenge facing all ICF fusion schemes is repetition rate. Current research facilities do their shots in no particular hurry. They want hours, days, or even weeks to analyze their results. But because the energy from each shot is not high, a power station would need to do lots of them, anywhere from one every 10 seconds to 16 times per second—nearly 1.4 million shots a day. A high repetition rate is hard to achieve because the driver has to power up and produce a high-energy pulse very fast; the chamber has to be cleared of debris after each shot so it doesn't interfere with the next one; and targets must be manufactured at a high rate and placed precisely in the chamber.

    Nothing fancy

    The most ambitious plans for an ICF power plant come from NIF itself. Researchers there set out to find the quickest route to generating power. They talked to electrical utilities about what sort of plant they would want and then designed one that filled their needs using the lowest risk approach. “It was a mindset change for us. What do end users want?” says Mike Dunne, director of NIF's laser fusion energy program. “We decided to make use of existing technology as much as possible. No advanced materials; only use what comes out of NIF. That's good enough.” As a result, Dunne estimates that with ignition as a starting gun they could have a pilot plant—dubbed LIFE, for Laser Inertial Fusion Energy—running in 12 years.

    Others are skeptical about the pace. McCrory says he won't believe that's possible “until they make a prototype beamline and do many shots.” Nevertheless, they admire Livermore's ambition. “Livermore is in the vanguard of getting industry involved,” McCrory says. “They're way ahead, the leading candidate.”

    NIF's current laser system is entirely unsuitable for a high-repetition driver. Its neodymium-doped glass laser amplifiers are pumped with energy by xenon flash lamps that are big, expensive, and take a long time to power up. For LIFE, solid-state diodes would take the place of the flash lamps. Suitable diodes exist today; they're very expensive, but like most semiconductors, their cost is expected to drop. Instead of NIF's single giant laser split into 192 beamlets, LIFE would have twice as many beamlets, each produced by a replaceable 8-kilojoule (kJ) laser unit. The laser units, each housed in a box big enough to accommodate a torpedo or two, would be built in a factory and delivered to the plant ready to use. If one or two of them failed, they could be replaced without stopping the power plant.

    LIFE's reaction chamber would use liquid lithium as its coolant, filling the dual role of extracting heat for power generation and breeding tritium. In line with LIFE's “no advanced materials” approach, the chamber would be built from steel. The problem with steel is that the constant bombardment by neutrons slowly weakens it and makes it radioactive. Dunne says the solution is to make the chamber a replaceable item. After 2 years, LIFE's chamber would be disconnected from the lithium circuit (its only connection) and wheeled out on rails to an adjacent building to “cool off,” and a fresh chamber would be wheeled in. After a few months the level of activation would drop enough for the chamber to be dismantled and disposed of by shallow burial.

    Rapid fire.

    Any inertial fusion plant will need a driver, such as lasers; a large chamber to absorb the heat from neutrons with a lithium blanket to breed tritium fuel; and a way to make targets and drop them into place. Each component poses technical challenges.


    Dunne estimates that an initial 400-megawatt plant would produce electricity at 12 cents per kilowatt-hour. That's on the expensive side, but, Dunne says, “it's not about the ultimate cost performance. We need to show availability and reliability.”

    Shooting for simplicity

    McCrory faults LIFE engineers' decision to use NIF's indirect drive technique. With indirect drive, the laser beams don't hit the target directly. Instead, the target sits inside a small gold cylinder called a hohlraum. The beams shine in through the ends of the hohlraum and heat the inside of its walls so intensely that they emit x-rays; the x-rays cause the capsule coating to explode, forcing the fuel inward. The hohlraum helps smooth out unevenness in the laser beams, which could make a target implode asymmetrically, causing the core of the fuel to break up without igniting fusion (see diagram, p. 450). Such an indirect approach, however, inevitably leads to a loss of efficiency. The peak energy of NIF's beams is 1.8 MJ, but the hohlraum is only 25% efficient at converting the ultraviolet beams into x-rays, so at most 450 kJ reaches the target capsule.

    Since NIF's experiments were designed, researchers have developed ways to overcome the unevenness in laser beams. McCrory believes that direct drive is a better bet for a power plant because the target is simpler—there is no need for a hohlraum, and without it there is a huge gain in efficiency. The team at the LLE in Rochester has been working on a direct drive scheme that could be used at NIF if the indirect drive fails to achieve ignition. “Having a robust alternative approach is fiscally prudent,” he says.

    Researchers at the Naval Research Laboratory (NRL) in Washington, D.C., also favor direct drive, and they've been developing a different laser system to do it: the krypton-fluoride gas laser. KrF lasers have one big advantage over the neodymium glass lasers of NIF and LLE: They naturally produce ultraviolet beams. Early ICF researchers found that compression works better the higher the frequency of the laser beam; UV interacts with plasma less and causes a better implosion of the target. In 1980, LLE researchers found crystals that could boost the frequency of glass lasers' infrared output first to green light and then to UV. NIF uses such crystals, but they, too, have an efficiency penalty. The peak energy of NIF's laser system is actually 6 MJ, but passing the beams through crystals before they enter the chamber knocks that down to 1.8 MJ.

    If a fusion power plant could do without frequency converters, it wouldn't need such a high-energy laser. NRL researchers have been working for years to demonstrate that KrF lasers—which are pumped with electron beams—are suitable for fusion. They've built ones that can operate for hundreds of millions of shots but have low power, and single-shot ones with higher power. The challenge now is to combine those techniques into a single, fusion-ready laser. They've also been grappling with the problem of unevenness in the beam. “We tried to make perfect beams, but it turned out to be very difficult,” says NRL's John Sethian. One problem common to all beam wavefronts is a speckled pattern of high- and low-intensity regions. The researchers developed a way to make the pattern change more quickly than the target can react to it, causing the target to “see” a kind of average intensity.

    Researchers at Sandia believe they can improve efficiency further still by dispensing with laser beams altogether. Their technique relies on a phenomenon called the pinch effect. If you pass a strong current through a conductor, it produces a magnetic field looping around itself. That magnetic field then interacts with the current to produce a force that pushes the current in toward the center of the conductor. If the conductor is a metal cylinder and the current is strong enough, the force will crush the cylinder. To use this as a fusion device, simply fill the cylinder with deuterium and tritium.

    The key technology here is the pulsed current source. Sandia has a huge device called the Z machine, which stores up enormous amounts of electrical energy and then produces intense current pulses. Researchers use these pulses—up to 27 mega-amps (MA) for 100 nanoseconds—to produce x-rays and for other experiments. Although the Z machine can be used to test the feasibility of doing fusion with such pulsed power, Sandia's Cuneo says a new machine able to generate 60 MA will be needed to really put the theory to the test.

    As with other drivers, the key challenge is repetition rate. Researchers at Sandia are testing a new technology called linear transformer drivers (LTDs). They have a couple of LTD modules rigged up, and each is producing 1-MA pulses at a rate of 1 every 10 seconds.

    Sandia's plan calls for a circular array of LTDs feeding current via a central transmission line into a reaction chamber where the target is. Because of its slow repetition rate, a pulsed power fusion plant would need to have larger explosions. This would mean that the reaction chamber and other equipment would need to be stronger to withstand the blasts, and the cone-shaped transmission line as well as the cylindrical target would be destroyed in each shot. But the engineering of replacing a target every 10 seconds is a lot easier than that for 10 times a second.

    Cuneo thinks the Sandia scheme's simple current pulses and low repetition rate give it a big advantage in simplicity. “A fusion power plant has to be as simple as you can imagine,” he says. “After all, it's competing with plants that rely on shoveling coal into a boiler.”

    Another driver that claims the advantage of simplicity and efficiency is ion beams. Most particle accelerators concentrate on boosting a small number of particles to very high energy. These wouldn't work as fusion drivers because the particles would just shoot straight through the target without depositing any energy. Heating a target, which would be similar to those on NIF, requires heavy particles with moderate energy and lots of them. Researchers at Lawrence Berkeley National Laboratory (LBNL) are putting the finishing touches on a linear accelerator that will produce just that sort of beam. The LBNL team put together the Neutralized Drift Compression Experiment II (NDCX-II) with just $11 million of stimulus money by recycling parts from an earlier accelerator at Livermore. NDCX-II will spend some of its time studying warm dense matter—the stuff in the core of giant planets—and will also aim to make the sort of high-current, short-duration pulses that fusion needs and test its effects on target materials.


    The target station of NRL's Nike laser; krypton-fluoride lasers like those under development at NRL hold the promise of high repetition rate and ultraviolet output.


    LBNL's Joe Kwan says ion beams offer an advantage: There is no need to place delicate optical elements close to a nuclear explosion. “Focusing is not done with lenses but with magnetic fields, so there are no lenses prone to damage,” he says. “And ion acceleration is efficient, and there is no repetition rate problem.”

    Another way to make ICF easier, says Los Alamos's Wurden, is to poach some ideas from magnetic fusion. His team has been experimenting with a technique called magneto-inertial fusion (MIF, sometimes known as magnetized target fusion), which uses a magnetic field to help contain the plasma of deuterium and tritium in the target and stop heat from escaping. As a result, the driver does not need to be as strong or as fast. “You can use drivers that are 20 to 30 years old, on the $50-[million]-to-100-million scale,” Wurden says.

    In experiments at Los Alamos, researchers make a target from a metal can (roughly the size of a tall beer can) filled with plasma and apply a magnetic field of about 2 to 3 tesla to hold the plasma in the middle of the can. They use an explosive to compress the can to around 1 centimeter across in less than 20 microseconds. This is a pretty sedate compression by ICF standards, but the magnetic field inside the can gets boosted 100 times, to as much as 300 tesla—a field strength “so huge that it is not known in this corner of the galaxy,” Wurden says. At the moment, the Los Alamos team is refining the compression technique, but its explosive driver is not practical for energy production.

    The beauty of MIF, Wurden says, is that you can use almost any sort of driver. Sandia researchers have done experiments with magnetized targets on the Z machine, and LLE researchers have done the same with their OMEGA laser. A private company, General Fusion in Vancouver, Canada, is designing a fusion energy demonstrator using pneumatic pistons to crush an MIF target with an acoustic shock wave.

    Which way to go?

    No one is expecting the NAS panel to recommend, or the government to approve, lavish funding for ICF research. But if a convincing demonstration of ignition at NIF does raise the field's profile, the panel, confronted with this smorgasbord of different approaches, faces a dilemma: Should it pick the most promising candidate and fund it handsomely, or spread the bounty and hope the best one rises to the top? “The question facing the NAS panel is how to ensure the community remains healthy while still moving forward,” NIF's Dunne says.

    LIFE will be a tantalizing prospect for the panel, as the most ambitious and advanced design from the biggest ICF lab. But other researchers say a crash program to develop LIFE, to the exclusion of all else, is not the best way to go. They don't want to see ICF research starved in the way magnetic fusion is suffering at the hands of ITER's ever-increasing costs. “We should not go with one pony. We need lots of ponies in the field, and I hope the academy report will reflect that,” Wurden says.

    NRL's Steve Obenschain agrees. “We advocate competition: See which approach works better and choose in 5 to 10 years,” he says. “You've got to have that competition. You don't want to end up doing the wrong thing extremely well.”

    All told, fusion researchers are cautiously optimistic that ICF's moment may be about to arrive; too bad it had to come in such a time of austerity. “People won't get all the money they need,” McCrory says. “But if there's enough enthusiasm, we could go faster than people think.”

  5. Inertial Confinement Fusion

    Step by Step, NIF Researchers Trek Toward the Light

    1. Daniel Clery

    Like wilderness explorers, physicists at the National Ignition Facility seek the most direct path to their goal: an implosion that releases more energy than it consumes.

    Dead center.

    A positioner arm holds the target at the heart of NIF's chamber.


    LIVERMORE, CALIFORNIA—Ever since the razzmatazz of its official opening 2 years ago, there hasn't been a lot of news coming out of the National Ignition Facility (NIF), the huge laser fusion machine here at Lawrence Livermore National Laboratory. That doesn't mean researchers at the $3.5 billion facility haven't been busy. Some have been simulating what goes on in a supernova explosion, and others gauging the equation of state of materials at the heart of a giant planet. Nuclear weapons researchers have also been using NIF's enormous lasers to verify their computer models of nuclear explosions. But that's not the news most people are waiting for. They're waiting for the one thing important enough to be encapsulated in its name: ignition.

    Ignition is the moment when a pulse of light from NIF's 192 laser beams heats a target containing a tiny capsule of fusion fuel and causes it to implode, heating the fuel enough for a large fraction of its nuclei to fuse together and release a burst of energy larger than the energy of the light pulse that created it. Fusion researchers have been trying to achieve ignition with lasers for more than 40 years; if NIF can reach the goal, it will finally show that, in principle, fusion could produce copious amounts of electricity from easily obtainable fuels, with no carbon emissions and minimal radioactive waste (Science, 17 April 2009, p. 326).

    As the delays in starting up the Large Hadron Collider at the CERN particle physics lab in Switzerland underscore, however, getting a big, complex machine up and running takes skill and patience. “We have to find the path through the thicket that's the easiest way through,” says NIF director Edward Moses.

    Easier said than done. Back in 2009 when NIF was completed, Moses predicted his team would achieve ignition in 2010. That time is long gone, and ignition still doesn't look imminent. Last month, at the Inertial Fusion Sciences and Applications conference in Bordeaux, France, the U.S. Department of Energy's Under Secretary for Science, Steven Koonin, acknowledged that “ignition is proving more elusive than hoped.” He added, “Some science discovery may be required” to make it a reality. The NIF team, however, maintains it is making steady progress toward the goal. “The potential is there, but it's so much harder when no one has done it before,” NIF's chief scientist, John Lindl, says.

    One potential Achilles' heel—NIF's vast laser system—has proved less of a problem than some had expected. No other machine had ever produced such high-energy beams: 1.8 megajoules (MJ) per 20-nanosecond pulse. Some researchers thought the energy would cause the glass optics to crack or explode, that optical elements would need constant replacement or repair, and that it would be impossible to achieve the required beam quality.

    Instead, NIF's lasers are widely hailed as triumphs of engineering. The building that houses the fiber lasers that produce the initial beams, the hundreds of slabs of neodymiumdoped glass that amplify them, the thousands of flash lamps that pump the glass full of energy, and all their associated paraphernalia is the size of three football fields and 10 stories high. The place hums with a clean, quiet efficiency, like a cross between a semiconductor plant and the lair of a James Bond villain bent on world domination. NIF researchers have their sledgehammer; now they just have to figure out how to crack the nut.

    The devil, as always, is in the details: the exact speed, shape, temperature, and composition of the fuel as it implodes. Long experience with earlier laser fusion experiments has taught researchers that brute force alone is not enough: Ignition requires finesse too. The target in such experiments is a tiny plastic sphere just a millimeter or two across. Inside this capsule is a 50-50 mixture of the hydrogen isotopes deuterium and tritium—the fusion fuel. Before a laser shot, the capsule is cooled to a chilly 18 kelvin so that the fuel condenses as a smooth ice layer on the inside of the sphere. The laser beams do not physically crush the capsule, but they heat the plastic material so fast and to such a high temperature that it explodes and, like a spherical rocket, drives the fusion fuel toward the center.

    If all goes as planned, this implosion will compress the fuel into a spherical blob some 30 micrometers across in which the very center reaches high temperature while most of the surrounding fuel remains cool. When the central hot spot reaches more than 100 million kelvin, deuterium and tritium nuclei will start to fuse, producing high-energy alpha particles (helium nuclei) and neutrons. “The aim is to get the alpha particles to deposit their energy in the dense fuel shell,” says NIF's plasma physics group leader, Siegfried Glenzer, raising the surrounding fuel to high temperatures so that the fusion burn propagates outward, rapidly consuming about a quarter of the fuel in an explosion of up to 18 MJ.

    Canned heat.

    In NIF's “indirect drive” system, a cylindrical capsule (hohlraum) makes an x-ray oven to heat the tiny spherical fusion target.


    In earlier experiments, researchers found that it was almost impossible to get the lasers to heat the capsule evenly from all directions at once. The laser beams just weren't smooth enough, so compression wasn't symmetrical, and fuel escaped. They developed a different technique known as indirect drive: The capsule is placed in the center of a small gold cylinder called a hohlraum, about the size of a pencil eraser. The beams shine through the ends of the hohlraum and onto its inside walls. The walls get so hot they emit x-rays, and it is this bath of radiation that causes the capsule to explode, driving the fuel inward. “What indirect drive gives you is a good oven. It pushes uniformly,” Moses says.

    One potential problem is that the oven is dirty: When the beams hit the inside walls, they kick up debris that fills the hohlraum with a plasma that can scatter photons, reducing beam power and possibly causing uneven implosion. Fortunately, such laser-plasma interactions (LPI) have been less of a stumbling block than many feared. “Some aspects mystify us, but we can control it even though we don't understand the details,” Moses says.

    NIF researchers have even managed to turn LPI to their advantage (Science, 29 January 2010, p. 514). The pattern of laser beams coming into the hohlraum nudges the plasma into a regular pattern, which can be coaxed to act like a diffraction grating. The team has been able to manipulate that grating to steer the power of the incoming beams as needed to correct the shape of the implosion. “LPI has turned out to be a really controllable tool,” Lindl says.

    Such control is key. Scientists think four conditions must achieve critical values before fusion will happen: The imploding fuel must maintain its spherical shape; it must achieve a certain speed; the amount of mixing between the fuel and the capsule material must be kept low; and the entropy of the system must be kept down—in other words, the energy applied needs to be focused on compressing the fuel and not raising its temperature, which would impede compression.

    To move toward ignition values, the NIF team has been focusing on a particular condition for a few months at a time, trying to improve its value without losing ground on the other three. They've identified 14 key parameters of the laser and three of the target: 17 knobs they can adjust to make fusion work. Earlier this year they focused on final density of the fuel just before ignition, which was far from its required value. By tweaking the shape of the laser pulses that spark implosion, they managed to double its value. “It's now 65% to 70% of where we're heading,” Moses says.

    Since early summer they've had velocity in their sights. The aim is to up the implosion speed from its current 300 kilometers per second to 370 km/s: the speed thought necessary for ignition. Here again, the shape of the laser pulse—actually a series of bursts, four short ones to put pressure on the capsule material followed by a big one to trigger the implosion—was key. At the beginning of the velocity campaign, the final shock was 50 times the energy of the initial ones, but the researchers planned to increase that figure to 300 times. “We're pushing the laser people a lot,” Glenzer says.

    Researchers also tweaked the design of the hohlraum, making it shorter and stubbier to help the incoming laser beams avoid interference from material blowing off the capsule surface from the early laser bursts. The new hohlraum “gives us more flexibility in shaping the implosion,” Lindl says. And they've also replaced the germanium dopant in the capsule material with silicon, which explodes as well as germanium but doesn't heat the fuel as much, leading to better compression. Their efforts netted a velocity increase of 30 to 40 km/s. “We're still 30 kilometers per second low, but there is a straightforward path to get there,” Lindl says. “The challenge is to get there while controlling the mixing [of capsule with fuel].”

    “Playing around with mixing and velocity is the place you want to be,” Moses says. “We're at the end of the beginning.” Moses likens the group's efforts to the expedition of Lewis and Clark, the first explorers to cross North America. To find a way to the Pacific, he explains, they didn't explore every pass and tributary; they sought the path of least resistance. “This facility has everything you need to get there: the laser, the diagnostics, the targets,” Moses says. “We don't have to understand all LPIs. We're staying away from complex environments, avoiding complexity at every choice.”

    Fusion researchers on the outside acknowledge the tough task NIF has ahead. “There's a good bit of work still to do,” Glen Wurden of Los Alamos National Laboratory in New Mexico says. Robert McCrory, director of the Laboratory for Laser Energetics at the University of Rochester in New York state, agrees. “It's just hard, it really is hard,” he says. “But once it's done, we can rewrite the script.”