National Ignition Facility

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NIF's basic layout. The laser pulse is generated in the room just right of center, and is sent into the beamlines (blue) on either side. After several passes through the beamlines the light is sent into the "switchyard" (red) where it is aimed into the target chamber (silver). Three football fields could fit inside NIF.

The National Ignition Facility, or NIF, is a laser-based inertial confinement fusion (ICF) research device located at the Lawrence Livermore National Laboratory in Livermore, California, United States (a lab funded by the U.S. Dept. of Energy). NIF uses powerful lasers to heat and compress a small amount of hydrogen fuel to the point where nuclear fusion reactions take place. NIF is the largest and most energetic ICF device built to date, and the first that is expected to reach the long-sought goal of "ignition" (more energy coming out than is put in).

Construction began in 1997 but was fraught with problems and ran into a series of delays that greatly slowed progress into the early 2000s. Progress since then has been much smoother, but compared to initial estimates, NIF is five years behind schedule and almost four times more expensive than budgeted. The construction of the National Ignition Facility was certified complete on 31 March 2009 by the U.S. Dept. of Energy.[1] The first target experiments with all 192 lasers are expected in May 2009, and a dedication ceremony is scheduled for May 29.[2] Ignition is expected by 2010.[3]


[edit] Description

[edit] Background

Inertial confinement fusion (ICF) devices use "drivers" to rapidly heat the outer layers of a "target" in order to compress it. The target is a small spherical pellet containing a few milligrams of fusion fuel, typically a mix of deuterium and tritium. The heat of the laser burns the surface of the pellet into a plasma, which explodes off the surface. The remaining portion of the target is driven inwards due to Newton's Third Law, eventually collapsing into a small point of very high density. The rapid blowoff also creates a shock wave that travels towards the center of the compressed fuel from all sides. When it reaches the center of the fuel, a small volume is further heated and compressed to a great degree. If the temperature and density of that small spot can be raised high enough, fusion reactions will occur.[4]

The fusion reactions release high-energy particles, some of which (primarily alpha particles) collide with the high density fuel around it and slow down. This heats the fuel further, and can potentially cause that fuel to undergo fusion as well. Given the right overall conditions of the compressed fuel—high enough density and temperature—this heating process can result in a chain reaction, burning outward from the center where the shock wave started the reaction. This is a condition known as "ignition", which can lead to a significant portion of the fuel in the target undergoing fusion, and the release of significant amounts of energy.[5]

To date most ICF experiments have used lasers to heat the targets. Calculations show that the energy must be delivered quickly in order to compress the core before it disassembles, as well as creating a suitable shock wave. The energy must also be focused extremely evenly across the target's outer surface in order to collapse the fuel into a symmetric core. Although other "drivers" have been suggested, notably heavy ions driven in particle accelerators, lasers are currently the only devices with the right combination of features.[6][7]

[edit] Driver laser

NIF aims to create a single 500 terawatt (TW) flash of light that reaches the target from numerous directions at the same time, within a few picoseconds. The design uses 192 individual "beamlets", which are amplified in 48 beamlines containing 16 laser amplifiers per line, each one amplifying four of the beamlets.[4]

To ensure that the output of the beamlines is uniform, the initial laser light is amplified from a single source in the Injection Laser System (ILS). This starts with a low-power flash of 1053 nanometers (nm) infra-red light generated in an ytterbium-doped optical fiber laser known as the Master Oscillator.[8] The light from the Master Oscillator is split and directed into 48 Preamplifier Modules (PAMs). The PAMs pass the light four times through a circuit containing a neodymium glass amplifier similar to (but much smaller than) the ones used in the main beamlines, boosting the nanojoules of light created in the Master Oscillator to about 6 joules. According to LLNL, the design of the PAMs was one of the major stumbling blocks during construction. Improvements to the design since then have allowed them to surpass their initial design goals.[9]

Simplified diagram of the beampath of a NIF laser beam, one of 48 similar beamlines. On the left are the amplifiers and optical switch, and on the right is the final spatial filter, switchyard and optical frequency converter.

The main amplification takes place in a series of glass amplifiers located at one end of the beamlines. Before "firing", the amplifiers are first optically pumped by a total of 7,680 xenon flash lamps (the PAMs have their own smaller flash lamps as well). The lamps are powered by a capacitor bank which stores a total of 400 megajoules (MJ) of electrical energy. When the wavefront passes through them, the amplifiers release some of the light energy stored in them into the beam. This is not a particularly efficient process and less than a quarter of the stored energy is transferred into the beam as it passes through; to improve the energy transfer the beams are sent though the main amplifier section four times, using an optical switch located in a mirrored cavity. In total these amplifiers boost the original 6 J provided by the PAMs to a nominal 4 MJ.[4] Given the time scale of a few billionths of a second, the power is correspondingly very high, 500 TW.

After the amplification is complete the light is "switched" back into the beamline, where it runs to the far end of the building to the Target Chamber. The total length of the laser from one end to the other is about 1,000 feet (305 meters). A considerable amount of this length is taken up by "spatial filters", small telescopes that focus the laser beam down to a tiny point, with a mask cutting off any stray light outside the focal point. The filters ensure that the image of the beam when it reaches the target is extremely uniform, removing any light that was mis-focussed by imperfections in the optics upstream. Spatial filters were a major step forward in ICF work when they were introduced in the Cyclops laser, an earlier LLNL experiment. The various optical elements in the beamlines are generally packaged into Line Replaceable Units (LRUs), standardized boxes about the size of a small car that can be dropped out of the beamline for replacement from below.[10]

Just before reaching the Target Chamber the light is reflected off various mirrors in the switchyard in order to impinge on the target from different directions. Since the length of the overall path from the Master Oscillator to the target is different for each of the beamlines, optics are used to "slow" the light in order to ensure all of them reach the center within a few picoseconds of each other.[11] As can be seen in the layout diagram above, NIF normally directs the laser into the chamber from the top and bottom. The target area and switchyard system can be reconfigured by moving half of the 48 beamlines to alternate positions closer to the equator of the target chamber.

A large KDP crystal grown at LLNL to be cut into slices and used on NIF for frequency conversion from the IR fundamental line at 1053 nm to UV at 351 nm.

One of the last steps in the process before reaching the target chamber is to convert the infrared light at 1053 nm into the ultraviolet (UV) at 351 nm in a device known as a frequency converter.[12] These are made of thin sheets cut from a single crystal of potassium dihydrogen phosphate. When the 1053 nm (IR) light passes through the first of two of these sheets, frequency addition converts a large fraction of the light into 527 nm light (green). On passing through the second sheet, frequency combination converts much of the 527 nm light and the remaining 1053 nm light into 351 nm (UV) light. IR light is much less effective than UV at heating the targets, because IR couples more strongly with hot electrons which will absorb a considerable amount of energy and interfere with compressing the target. The conversion process is about 50% efficient, reducing delivered energy to a nominal 1.8 MJ.[13]

One important aspect of any ICF research project is ensuring that experiments can actually be carried out on a timely basis. Previous devices generally had to cool down for hours to allow the flashlamps and laser glass to regain their shapes after firing-caused thermal expansion, limiting use to one or fewer firings a day. One of the goals for NIF is to reduce this time to 5 hours, in order to allow 700 firings a year.[14]

[edit] NIF and ICF

Laser energy to hohlraum x-ray to target capsule energy coupling efficiency. Note the "laser energy" is after conversion to UV, which loses about 50% of the original IR power.

The name "National Ignition Facility" refers to the goal of "igniting" the fusion fuel, a long-sought threshold in fusion research. In existing (non-weapon) fusion experiments the heat produced by the fusion reactions rapidly escapes from the plasma, meaning that external heating must be applied continually in order to keep the reactions going. "Ignition" refers to the point at which the energy given off in the fusion reactions currently underway is high enough to cause fusion reactions in the surrounding fuel. This causes a chain-reaction that allows the majority of the fuel to undergo a nuclear "burn". Ignition is considered a key requirement if fusion power is to ever become practical.[5]

NIF is designed primarily to use the indirect drive method of operation, in which the laser heats a small metal cylinder instead of the capsule inside it. The heat causes the cylinder, known as a hohlraum (German for "hollow room", or cavity), to re-emit the energy as intense X-rays, which are more evenly distributed and symmetrical than the original laser beams. Experimental systems, including the OMEGA and Nova lasers, validated this approach through the late 1980s.[15] In the case of the NIF, the large delivered power allows for the use of a much larger target; the baseline pellet design is about 2 mm in diameter, chilled to about 18 degrees above absolute zero and lined with a layer of solid deuterium-tritium (DT) fuel. The hollow interior also contains a small amount of DT gas.

This conversion process is fairly efficient; of the original ~4 MJ of laser energy created in the beamlines, 1.8 MJ is left after conversion to UV, and about half of the remainder is lost in the x-ray conversion in the hohlraum. Of the rest, perhaps 10 to 20% of the resulting x-rays will be absorbed by the outer layers of the target (see image below).[16] The shockwave created by this heating absorbs about 140 kJ, which is expected to compress the fuel in the center of the target to a density of about 1,000 g/mL (or 1,000,000 kg/m³);[17] for comparison, lead has a normal density of about 11 g/mL (11,340 kg/m³). It is expected this will cause about 20 MJ of fusion energy to be released.[16] Improvements in both the laser system and hohlraum design are expected to improve the shockwave to about 420 kJ, in turn improving the fusion energy to about 100 MJ.[17] However, the baseline design allows for a maximum of about 45 MJ of fusion energy release, due to the design of the target chamber.[2] This is the equivalent of about 7 kg of TNT exploding.

The gold-plated hohlraum designed for the NIF.
NIF's fuel "target", filled with either D-T gas or D-T ice. The capsule is held in the hohlraum using thin plastic webbing.

NIF is also exploring new types of targets. Previous experiments generally used plastic ablators, typically polystyrene (CH). NIF's targets are constructed by coating a plastic form in a layer of sputtered beryllium or beryllium-copper alloys, and then oxidizing the plastic out of the center.[18][19] In comparison to traditional plastic targets, beryllium targets offer higher density, high transparency to x-rays, and high thermal conductivity. All of these are advantageous in the indirect-drive mode where the incoming energy is in the form of x-rays. They also have a higher leftover ablative mass compared to the fuel inside, which has the benefit of being less sensitive to instability growth from the roughness of the DT ice (although plastic targets of the same mass also show this effect). A more practical benefit is that the mechanical strength of a Be target is high enough to contain the fuel in gaseous form at room temperature. This could allow the targets to be filled with fuel and stored for periods before being chilled to freeze the DT just before firing. In practice, however, the ice has to be carefully grown from an initial seed.[20]

Although NIF was primarily designed as an indirect drive device, the energy in the laser is high enough to be used as a direct drive system as well, where the laser shines directly on the target. Even at UV wavelengths the power delivered by NIF is estimated to be more than enough to cause ignition, resulting in fusion energy gains of about forty times,[21] somewhat higher than the indirect drive system. In this case the value of the Be target is reduced and more traditional plastic targets are more appropriate. A more uniform beam layout suitable for direct drive experiments can be arranged through changes in the switchyard that move half of the beamlines to locations closer to the middle of the target chamber.

It has been shown, using scaled implosions on the OMEGA laser and computer simulations, that NIF should also be capable of igniting a capsule using the so-called polar direct drive (PDD) configuration where the target is irradiated directly by the laser, but only from the top and bottom.[22] In this configuration the target suffers either a "pancake" or "cigar" anisotropy on implosion, reducing the maximum temperature at the core. However, the amount of energy being dumped into the target by the laser is so high that it ignites anyway. Fusion gains in this configuration are estimated to be anywhere between ten and thirty times; less than the symmetrical direct-drive approach, but obtainable with no changes to the NIF beamline layout.

Other targets, called saturn targets, are specifically designed to reduce the anisotropy and improve the implosion.[23] They feature a small plastic ring around the "equator" of the target, which quickly vaporizes into a plasma when hit by the laser. Some of the laser light is refracted through this plasma back towards the equator of the target, evening out the heating. Ignition with gains of just over thirty-five times are thought to be possible using these targets at NIF,[22] producing results almost as good as the fully symmetric direct drive approach.

[edit] History

[edit] Impetus

LLNL's history with the ICF program starts with physicist John Nuckolls, who predicted in 1972 that ignition could be achieved with laser energies about 1 kJ, while "high gain" would require energies around 1 MJ.[24][25] Although this sounds very low powered compared to modern machines, at the time it was just beyond the state of the art, and led to a number of programs to produce lasers in this power range. LLNL decided early on to concentrate on glass lasers, while other facilities studied gas lasers using carbon dioxide (e.g. Antares laser, Los Alamos National Laboratory) or KrF (e.g. Nike laser, Naval Research Laboratory). By the 1980s the advantage of shorter wavelengths in terms of delivering energy to the interior of the targets had been conclusively demonstrated in LLNL's highly successful Shiva laser. This put the glass laser approach pioneered at LLNL in the lead for future development.

After the Shiva project, LLNL turned to the 20-beam 200 kJ Nova laser design which was expected to reach ignition conditions. During the initial construction phase, Nuckolls found an error in his calculations, and a October 1979 review chaired by John Foster Jr. of TRW confirmed that there was no way Nova would reach ignition. The Nova design was then modified into a smaller 10-beam design that added frequency conversion to 351 nm light, which would increase coupling efficiency.[26] In operation, Nova was able to deliver about 20 to 30 kJ of laser energy, about half of what was initially expected, due to various nonlinear optical effects.

Throughout these efforts, the amount of energy needed to reach ignition had continually risen and it was unclear whether the current 200 kJ estimate was more reliable than earlier ones. The Department of Energy (DOE) decided that direct experimentation was the best way to settle the issue, and between 1978 and 1988 ran a series of underground experiments at the Nevada Test Site that used small nuclear bombs to directly illuminate ICF fuel components with high-energy X-rays; LLNL ran their program under the name "Halite", while LANL ran theirs as "Centurion".[27] Initial data were available by mid-1984, and the testing ceased in 1988. Although there is little publicly available data from the Halite-Centurion series, it appears the experiments suggested that an implosion energy of about 20 MJ was required, and that given that about 1/5th of the laser energy is delivered as X-rays, drivers on the order of 100 MJ would be needed.[28]

[edit] LMF and Nova Upgrade

Nova's partial success, combined with the Halite-Centurion numbers, prompted DOE to request a custom military ICF facility they called the "Laboratory Microfusion Facility" (LMF) that could achieve fusion yields of between 100 and 1,000 MJ. Based on the LASNEX computer models, it was estimated that LMF would require a driver of about 10 MJ,[26] in spite of the Halite-Centurion test that suggested a higher power. Building such a device was within the state of the art, but would be expensive, on the order of $1 billion.[29] LLNL submitted a design with a 5 MJ 350 nm (UV) driver laser that would be able to reach about 200 MJ yield, which was enough to attain the majority of the LMF goals. The program was estimated to cost about $600 million FY 1989 dollars, and an additional $250 million to upgrade it to a full 1,000 MJ if needed, and would grow to well over $1 billion if LMF was to meet all of the goals the DOE asked for.[29] Other labs also proposed their own LMF designs using other technologies.

Faced with this enormous project, in 1989/90 the National Academy of Sciences conducted a second review of the US ICF efforts on behalf of the US Congress. The report concluded that "considering the extrapolations required in target physics and driver performance, as well as the likely $1 billion cost, the committee believes that an LMF [i.e., a Laser Microfusion Facility with yields to one gigajoule] is too large a step to take directly from the present program." Their report suggested that the primary goal of the program in the short term should be resolving the various issues related to ignition, and that a full-scale LMF should not be attempted until these problems were resolved.[30] The report was also critical of the gas laser experiments being carried out at LANL, and suggested they, and similar projects at other labs, be dropped. The report accepted the LASNEX numbers and continued to approve an approach with laser energy around 10 MJ. Nevertheless, the authors were aware of the potential for higher energy requirements, and noted "Indeed, if it did turn out that a 100-MJ driver were required for ignition and gain, one would have to rethink the entire approach to, and rationale for, ICF."[30]

In July 1992 LLNL responded to these suggestions with the Nova Upgrade, which would reuse the majority of the existing Nova facility, along with the adjacent Shiva facility. The resulting system would be much lower power than the LMF concept, with a driver of about 1 to 2 MJ.[31] The new design included a number of features that advanced the state of the art in the driver section, including the multi-pass design in the main amplifiers, and 18 beamlines (up from 10) that were split into 288 "beamlets" as they entered the target area in order to improve the uniformity of illumination. The plans called for the installation of two main banks of laser beamlines, one in the existing Nova beamline room, and the other in the older Shiva building next door, extending through its laser bay and target area into an upgraded Nova target area. The lasers would deliver about 500 TW in a 4 ns pulse. The upgrades were expected to allow the new Nova to produce fusion yields of between 2 and 20 MJ[29] The initial estimates from 1992 estimated construction costs around $400 million, with construction taking place from 1995 to 1999.

[edit] NIF emerges

Throughout this period the ending of the Cold War led to dramatic changes in defense funding and priorities. As the need for nuclear weapons was greatly reduced and various arms limitation agreements led to a reduction in warhead count, the US was faced with the prospect of losing a generation of nuclear weapon designers able to maintain the existing stockpiles, or design new weapons.[32] At the same time, progress was being made on what would become the Comprehensive Nuclear-Test-Ban Treaty, which would ban all criticality testing. This would make the reliable development of newer generations of nuclear weapons much more difficult.

Out of these changes came the Stockpile Stewardship and Management Program, which, among other things, included funds for the development of methods to design and build nuclear weapons that would work without having to be explosively tested. In a series of meetings that started in 1995, an agreement formed between the labs to divide up the SSMP efforts. An important part of this would be confirmation of computer models using low-yield ICF experiments. The Nova Upgrade was too small to use for these experiments,[33] and a redesign emerged as NIF in 1994. The estimated cost of the project was just over $1 billion,[34] with completion in 2002. Physicist Richard Garwin described the outcome this way, "Sandia got the microelectronics research center [MESA], which had minimal relevance to the CTBT. Los Alamos got the Dual-Axis Radiographic Hydrodynamic Test facility. Livermore got the National Ignition Facility — the white elephant eating us out of house and home. They all maintained these were essential to stockpile stewardship, which they are not."[35]

In spite of the "agreement", the large project cost combined with the ending of similar projects at other labs resulted in several highly critical comments by other weapons labs, Sandia National Laboratories in particular. In May 1997, Sandia fusion scientist Rick Spielman publicly stated that NIF had "virtually no internal peer review on the technical issues" and that "Livermore essentially picked the panel to review themselves".[36] Similar complaints about the makeup of the "oversight" committees, consisting largely of LLNL contractors, led to a lawsuit being filed by the Natural Resources Defense Council.[37] A retired Sandia manager, Bob Puerifoy, was even more blunt; "NIF is worthless ... it can't be used to maintain the stockpile, period."[38]

[edit] Early construction problems

Work on the NIF started with a single beamline demonstrator, Beamlet. Beamlet operated between 1994 and 1997 and was entirely successful. It was then sent to Sandia National Laboratories as a light source in their Z machine. A full-sized demonstrator then followed, in AMPLAB, which started operations in 1997.[39] The official groundbreaking on the main NIF site was in June 1997.

At the time, the DOE was estimating that the NIF would cost approximately $1.1 billion and another $1 billion for related research, and would be complete as early as 2002.[40] Later in 1997 the DOE approved an additional $100 million in funding and pushed the operational date back to 2004. As late as 1998 LNLL's public documents stated the overall price was $1.2 billion, with the first eight lasers coming online in 2001 and full completion in 2003.[41]

Sandia, with extensive experience in pulsed power delivery, designed the capacitor banks used to feed the flash lamps, completing the first unit in October 1998. To everyone's surprise, the Pulsed Power Conditioning Modules (PCMs) suffered capacitor failures that led to explosions. This required a redesign of the module to contain the debris, but since the buildings holding them had already been poured, this left the new modules so tightly packed that there was no way to do maintenance in-place. Yet another redesign followed, this time allowing the modules to be removed from the bays for servicing.[26] Continuing problems of this sort further delayed the operational start of the project, and in September 1999 an updated DOE report stated that NIF would require up to $350 million more and completion would be pushed back to 2006.[40]

Throughout this period the problems with NIF were not being reported up the management chain. In 1999 then Secretary of Energy Bill Richardson reported to Congress that the NIF project was on time and budget, following the information that had been passed onto him by E. Michael Campbell, NIF's director. In August that year it was revealed that Campbell had misled Richardson, and in fact neither claim was close to the truth.[42] As the GAO would later note, "Furthermore, the Laboratory's former laser director, who oversaw NIF and all other laser activities, assured Laboratory managers, DOE, the university, and the Congress that the NIF project was adequately funded and staffed and was continuing on cost and schedule, even while he was briefed on clear and growing evidence that NIF had serious problems."[40] Richardson later commented "I have been very concerned about the management of this facility… bad management has overtaken good science. I don't want this to ever happen again." A DOE Task Force reporting to Richardson late in January 2000 summarized that "organizations of the NIF project failed to implement program and project management procedures and processes commensurate with a major research and development project… [and that] …no one gets a passing grade on NIF Management: not the DOE's office of Defense Programs, not the Lawrence Livermore National Laboratory and not the University of California."[43] Campbell resigned from the project in September 1999, when it was disclosed that he never completed a doctorate from Princeton that he had allowed the laboratory to believe he held.[44]

[edit] Re-baseline and GAO report

In the wake of these revelations the DOE started a comprehensive "Rebaseline Validation Review of the National Ignition Facility Project" in 2000, which took a critical look at the project, identifying areas of concern and adjusting the schedule and budget to ensure completion. John Gordon, National Nuclear Security Administrator, stated "We have prepared a detailed bottom-up cost and schedule to complete the NIF project… The independent review supports our position that the NIF management team has made significant progress and resolved earlier problems."[45] The report revised their budget estimate to $2.25 billion, not including related R&D which pushed it to $3.3 billion total, and pushed back the completion date to 2006 with the first lines coming online in 2004.[46][47]

Given the budget problems, the US Congress requested an independent review by the General Accounting Office (GAO). They returned a highly critical report in August 2000 stating that the budget was likely $3.9 billion, including R&D, and that the facility was unlikely to be completed anywhere near on time.[40][48] The report, "Management and Oversight Failures Caused Major Cost Overruns and Schedule Delays," identified management problems for the overruns, and also criticized the program for failing to include a considerable amount of money dedicated to target fabrication in the budget, including it in operational costs instead of development.[42] A follow-up report the next year included all of these items, pushing the budget to $4.2 billion, and the completion date to around 2008.

The public fighting between the various Department of Energy laboratories soon started anew. Los Alamos publicly attacked the facility as ill-conceived.[49] On 25 May Sandia vice president Tom Hunter told the Albuquerque Tribune that the NIF should be downsized so that it would not "disrupt the investment needed" in other labs.[49] Criticism of the project also came from politicians, government officials and review panels, some going so far as to refer to the project as being "out of control".[50]

[edit] Progress

Laser Bay 2 was commissioned in July 2007

LRU installation started in 2005, and has continued at an increasing pace since then. In May 2003, the NIF achieved "first light" on a bundle of four beams, producing a 10.4kJ pulse of IR light in a single beamline.[14] In 2005 the first eight beams (a full bundle) were fired producing 153 kJ of infrared light, thus eclipsing OMEGA as the highest energy laser (per pulse) on the planet. By January 2007 all of the LRUs in the Master Oscillator Room (MOOR) were complete, and the computer room had been installed. By August 2007 96 laser lines were completed and commissioned, and "A total infrared energy of more than 2.5 megajoules has now been fired. This is more than 40 times what the Nova laser typically operated at the time it was the world's largest laser."[51] As of February 2009, construction was unofficially completed. [52] The first target experiments with all 192 lasers are expected in May 2009, and a dedication ceremony is scheduled for May 29.[2] Ignition (more energy coming out than is put in) is expected by 2010.[3]

Recent reviews of the project have been positive, generally in keeping with the post-GAO Rebaseline schedules and budgets. However, there are lingering concerns about the NIF's ability to reach ignition, at least in the short term. An independent review by the JASON Defense Advisory Group was generally positive about NIF's prospects over the long term, but concludes that "The scientific and technical challenges in such a complex activity suggest that success in the early attempts at ignition in 2010, while possible, is unlikely."[53] The group suggested a number of changes to the completion timeline to bring NIF to its full design power as soon as possible, skipping over a testing period at lower powers that they felt had little value.

The delays in NIF construction have led to something of a race with the French Laser Mégajoule, which has very similar energies as NIF. Mégajoule started construction later than NIF but has a shorter planned building time, originally estimated to be complete in 2008. Mégajoule has run into problems of its own, however, and has been pushed back to 2010.[54]

[edit] Completion

On January 26, 2009, the final line replaceable unit (LRU) was installed, completing one of the final major milestones of the NIF construction project.[55] On February 26, 2009, for the first time NIF fired all 192 laser beams into the target chamber.[56] On March 10, 2009, NIF became the first laser to break the megajoule barrier, firing all 192 beams and delivering 1.1 MJ of ultraviolet light, known as 3ω, to the target chamber center in a shaped ignition pulse.[57] The main laser delivered 1.952 MJ.

It is hoped that the main experiments will start in June 2009, when the theory of nuclear fusion will be tested.[58]

[edit] Criticisms

Outside of the problems with the project itself, criticism of NIF has been focused on its role in the Stockpile Stewardship and Management Program (SSP). This program is an umbrella effort to study the long-term storage of the nuclear stockpile, and a variety of groups have been highly critical of the effort, dismissing it as a program of "scientific welfare" that has little to do with science and much to do with keeping a nuclear industry alive. The Federation of American Scientists noted that "Some claim that the experiments were politically essential; only with the promise of huge, expensive projects would the laboratory management publicly endorse a testing moratorium."[59] NIF is singled out as a particularly weak portion of the SSP, with questions about its capability to generate information that is actually useful to the project.

However, in 2001 it was learned that LLNL was pursuing a method to allow the use of plutonium and uranium in experiments on NIF;[60] this would allow a direct examination of equation of state parameters for these materials at extremely high pressures and densities not currently allowed by subcritical experiments which compress the fissile material using conventional explosives. The decision to proceed with the use of plutonium, other fissile materials, fissionable materials, and lithium hydride in experiments conducted at the NIF was finalized by the National Nuclear Security Administration in November 2005.[61][62] A 2007 report by the National Research Council's Plasma Science Committee concluded that "NIF is crucial to the NNSA Stockpile Stewardship Program because it will be able to create the extreme conditions of temperature and pressure that exist on Earth only in exploding nuclear weapons and that are therefore relevant to understanding the operation of our modern nuclear weapons."[63]

[edit] Pictures

[edit] References

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  2. ^ a b c Lasers & Sources (2009-03-24). "NIF project director Moses says facility is ready to go". SPIE. Retrieved on 2009-03-23. 
  3. ^ a b Trimble, Tyghe (2008-06-25). "The Laser to End All Lasers". Discover. Retrieved on 2008-07-03. 
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  6. ^ Per F. Peterson, How IFE Targets Work, University of California, Berkeley, 1998. Retrieved on May 8, 2008.
  7. ^ Per F. Peterson, Drivers for Inertial Fusion Energy, University of California, Berkeley, 1998. Retrieved on May 8, 2008.
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  9. ^ Keeping Laser Development on Target for the NIF, Lawrence Livermore National Laboratory. Retrieved on October 2, 2007
  10. ^ Larson, Doug W. (2004). NIF laser line-replaceable units (LRUs), Optical Engineering at the Lawrence Livermore National Laboratory II: The National Ignition Facility. DOI:10.1117/12.538467. Retrieved on May 7, 2008
  11. ^ Arnie Heller, Orchestrating the World's Most Powerful Laser, Science & Technology Review, July/August 2005. Retrieved on May 7, 2008
  12. ^ P.J. Wegner et al.,NIF final optics system: frequency conversion and beam conditioning, Proceedings of SPIE 5341, May 2004, pages 180–189.
  13. ^ Bibeau, Camille; Paul J. Wegner, Ruth Hawley-Fedder (June 1, 2006). "UV SOURCES: World’s largest laser to generate powerful ultraviolet beams". Laser Focus World. Retrieved on May 7, 2008.
  14. ^ a b NIF Project Sets Record for Laser Performance, Lawrence Livermore National Laboratory, June 5, 2003. Retrieved on May 7, 2008.
  15. ^ J.D. Lindl et al., The physics basis for ignition using indirect-drive targets on the National Ignition Facility, Physics of Plasmas, Vol. 11, February 2004, page 339. Retrieved on May 7, 2008.
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