March 5, 2009 Lasers, is there anything they can’t do? If they’re not shooting down UAVs, they’re fighting AIDS or bringing us the next generation of HDTVs. That’s all well and good, but when it comes to lasers there’s none bigger than the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory (LLNL) in California which is now nearing completion. Its myriad uses will include providing fusion data for nuclear weapons simulations, probing the secrets of extrasolar planets and could even lead to the holy grail of energy production - practical fusion energy.
NIF's 192 giant lasers, housed in a ten-story building the size of three football fields, will deliver at least 60 times more energy than any previous laser system. When all of its beams are operational later this year, NIF will focus about two million joules of ultraviolet laser energy on a tiny target in the center of its target chamber. When all that energy slams into millimeter-sized targets, it can generate unprecedented temperatures and pressures in the target materials – temperatures of more than 100 million degrees and pressures more than 100 billion times Earth's atmosphere - conditions similar to those that exist only in the cores of stars and giant planets and inside a nuclear weapon. The resulting fusion reaction will also release many times more energy than the laser energy required to initiate the reaction. These qualities will allow the NIF Project and related NIF & Photon Science programs to pursue their three complementary missions of future energy, national security and unlocking the secrets of the universe.
The idea for the NIF grew out of the decades-long effort to generate fusion burn and gain in the laboratory. While nuclear power plants, which use fission, have been splitting atoms to produce electricity (and radioactive waste) for more than 50 years, achieving nuclear fusion burn and gain has remained in the realm of science fiction and has not yet been demonstrated to be viable for electricity production. It is the gain part that is important because while a self-sustaining fusion burn has been achieved for brief periods under experimental conditions, the amount of energy that went into creating it was greater than the amount of energy it generated. There was no energy gain, which is essential if fusion energy is ever to supply a continuous stream of electricity. For fusion burn and gain to occur, a special fuel consisting of the hydrogen isotopes deuterium and tritium must first "ignite" so a primary goal for NIF is to achieve fusion ignition, in which more energy is generated from the reaction than went into creating it.
For the fusion process to occur extraordinarily high temperatures and pressures – tens of millions of degrees and pressures many billion times greater than Earth's atmosphere – are required. These conditions currently exist only in the cores of stars and planets and in nuclear weapons, and it is precisely these extreme conditions that the NIF seeks to replicate. By taking a hollow, spherical plastic capsule about the size of a small pea, filling it with 150 micrograms of a mixture of deuterium and tritium, the two heavy isotopes of hydrogen and focusing a laser that can generate 500 trillion watts for about 20 billionths of a second onto its surface the project hopes to create a miniature star that lasts for a tiny fraction of a second. In this process the capsule and its deuterium-tritium fuel will be compressed to a density 100 times that of solid lead, and heated to more than 100 million degrees Celsius – hotter than the center of the sun. During its brief lifetime this miniature star will produce ten to 100 times more energy than was used to ignite it by producing energy the way the stars and the sun do, by nuclear fusion.
Although the NIF will not be used to generate electricity, if successful it will be the first inertial confinement fusion facility to demonstrate ignition and a self-sustaining fusion burn, which could lead to Inertial Fusion Energy (IFE) power plants that would produce no greenhouse gas emissions, operate continuously to meet demand, and produce shorter-lived and less hazardous radioactive byproducts than current fission power plants. IFE power plants would also present no danger of a meltdown and, because nuclear fusion offers the potential for virtually unlimited safe and environmentally benign energy, the U.S. Department of Energy (DOE) has made fusion a key element in the nation's long-term energy plans.
The ability of the NIF to replicate conditions that exist naturally only in the interiors of stars, supernovae and giant planets, will also enable the NIF in its second mission to help in the understanding how the universe began, how it works, and how it will end. The project aims to provide new insights into what happened in the first nanoseconds of creation – the Big Bang – and to help give an understanding of how the fundamental particles of matter coalesced into the stars, the planets and the elements that make life possible. The Board on Physics and Astronomy of the National Research Council has recognized the study of the physics of materials under extreme pressures and temperatures, known as high energy density physics as one of the keys to unlocking the secrets of the universe and it is the NIF’s achievement of thermonuclear burn in the laboratory that will hopefully make such study a possibility.
Research at the NIF could help answer questions related to the nature of dark energy, what is going on in the matter that surrounds a black hole and how cosmic rays in the universe achieve energies many orders of magnitude greater than the highest energies that can be achieved in modern particle accelerators. Also, since NIF will provide the highest temperatures and densities that have ever been created in a laboratory environment, it will possible to carry out experiments to produce states of matter unlike any previously achieved to improve our understanding of materials in extreme conditions, and may also further our knowledge of stellar evolution, as well as of the inner structure of the largest planets such as Jupiter and Saturn. The project may also be able to shed some light on the stellar processes that synthesize, or create, the different isotopes of the heavy elements from iron to uranium.
On the national security front the NIF will provide data for sophisticated supercomputer simulations used to determine the effects of aging on nuclear weapons components as part of the National Nuclear Security Administration's Stockpile Stewardship Program (SSP). Since no new nuclear (newclear? – sorry, couldn’t resist) weapons are currently being built, however, and the existing weapons cannot be tested under a nuclear testing moratorium established by President George H.W. Bush in 1992, data is needed that replicates the conditions that exist inside a thermonuclear weapon to ensure the continuing reliability of the nuclear stockpile. When all of its 192 laser beams are complete, NIF will be the only facility that can provide data by performing controlled, experimental studies of thermonuclear burn, the phenomenon that gives rise to the immense energy of modern nuclear weapons. In effect, NIF allows scientists to separate the pieces of the physics of a nuclear weapon and examine each piece in isolation.
Not only will NIF create controlled thermonuclear burn in a laboratory setting, but NIF beams can also be used to create conditions of extremely high energy density in materials. One example is using various arrangements of beams to shock materials and demonstrate how they behave at high temperatures and pressures. High energy density physics plays a critical role in nuclear weapons and understanding how the many different kinds of materials used in nuclear weapons behave – especially as they age beyond their intended lifetimes – under the extreme environments produced in a thermonuclear reaction is a key part of the SSP mission.
While the NIF offers the possibility of a range of scientific breakthroughs, the realization of the facility required a few breakthroughs as well. Among them the development of a new method of glass production that continuously melts and pours the glass to meet construction schedules for the laser system’s 3,070 large plates of laser glass, each about three feet long and about half as wide. Fulfilling NIF's promise also requires one of the most sophisticated computer control systems in government service or private industry so it can facilitate the coordination of complex laser equipment that must strike within 50 micrometers of their assigned spot on a target measuring less than one centimeter long – an accuracy comparable to throwing a pitch over the strike zone from 350 miles away.
If you build it...
Naturally the building of the world’s biggest laser didn’t happen overnight. The ground was broken on the building of the facility over a decade ago on May 27, 1997 when then-Energy Secretary Federico Peña joined then-LLNL Director Bruce Tarter and Congresswoman Ellen Tauscher in the groundbreaking ceremonies saying, "NIF will unleash the power of the heavens to make Earth a better place.” On June 2001, one of the largest cranes in the world hoisted the 264,000-pound, 10-meter-diameter target chamber out of its silo before the seven-story walls and roof of the target bay were completed. The USD$196-million NIF conventional facility including the concrete foundations and monolithic mat floor slabs for the switchyards and target bay (six feet thick) and the foundations for the laser building; the Optics Assembly Building and the laser building's envelope were completed on September 28, 2001.
December 2002 saw a major milestone for the NIF when the first four of its 192 laser beams were commissioned and fired at high energy. It then took only until April 2003 for the full 192-beam precision-cleaned and aligned beampath to be completed in both laser bays. In June 2003, the Experimental Systems Integrated Team began demonstrating capability for target positioning, target alignment and diagnostics for the initial NIF experiments. In August 2003, while construction continued, the first experiment studying the propagation of energetic NIF laser beams through plasmas created during laser shots into small gas-filled targets was carried out with the first hydrodynamics experiments following in January 2004. On December 7, 2006, Cluster 3 in Laser Bay 2 was the first to become operationally qualified.
2007 saw the completion of the flashlamp installation and main laser utility completion in February, the performance qualification of four main laser bundles in April and May, and the progress continued to the end of July, when the 12th bundle was fired, completing the commissioning of the main laser in Laser Bay 2. More than 4,200, or 68 percent, of all line replaceable units were installed by the end of July 2007. At a recent celebration commemorating the installation of the final NIF line replaceable unit (LRU), NIF & Photon Science Principal Associate Director Ed Moses noted that NIF has met all of its project completion criteria and is essentially complete, having demonstrated energy levels 20 times higher than any other laser. "NIF is the most precise laser of its kind ever built," Moses said, "and because of that, we're going to be able to start experiments this spring and in 2010, to begin our first ignition experiments.
The three main missions examined above are far from the only areas of interest for the project. Other NIF programs promise breakthroughs in the use of lasers in medicine, radioactive and hazardous waste treatment, particle physics and X-ray and neutron science. With such a wide range of breakthroughs promised by the project, expect to hear much more news out of the NIF in the future.
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