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SPIE Professional July 2009 | Open Access Article

Giant Lasers at NIF

The National Ignition Facility, with 192 laser beams, is the world's largest and highest-energy pulsed laser system.

By Rich Donnelly

The National Ignition Facility (NIF), dedicated on 29 May at Lawrence Livermore National Laboratory in California, represents exciting new capabilities in the world of lasers and clean energy.

While researchers joked in the 1960s that the laser was "a solution looking for a problem," the world's largest high-energy pulsed laser system at NIF is aimed at solving twin problems in physics and global energy demand by harnessing the power of nuclear fusion as a source of electricity.

Federal and state dignitaries and international scientists who attended the NIF dedication lauded the new facility's potential to revolutionize the world's energy system and the feat of optical engineering that will allow NIF to create conditions and conduct a wide range of experiments never before possible on Earth.

The target positioner and target alignment system precisely locate a target in the NIF target chamber. The target is positioned with an accuracy of less than the thickness of a human hair. (Photos courtesy of LLNL and DOE.)

The guests included many current and former staff of the LLNL laser program and international scientists who have and will continue to collaborate on the new user facility.

NIF "promises to blaze a new trail toward sustainable, carbon-free energy independence," U.S. Sen. Dianne Feinstein of California said.

"A successful demonstration of ignition and energy gain at NIF would be a transforming event that would solidify fusion's potential as an important energy source," added Steven Koonin, Under Secretary for Science at the U.S. Department of Energy. Koonin called the dedication of NIF a milestone "in an exciting scientific journey that will create a lasting legacy of discovery, innovation, and security and allow the nation to reap the benefits of this visionary investment in its future."

SPIE CEO Eugene Arthurs called NIF "the most massive optical engineering project ever" and echoed the sentiments of many who look forward to discoveries in plasma physics, astrophysics, and extreme matter conditions that will change and better the world.

Arthurs, who also attended the dedication, said NIF's lasers "will open the way to practical fusion sources, just as Ted Maiman's ruby laser opened the way for lasers to revolutionize our world."

SPIE CEO Eugene Arthurs outside the target chamber.

NIF Project Director and SPIE Fellow Ed Moses is also excited about what the future holds for the giant lasers at NIF. "NIF's success will be a scientific breakthrough of historic significance — the first demonstration of fusion ignition in a laboratory setting, duplicating on Earth the processes that power the stars," he said.

NIF has 192 laser beams, each one the most energetic UV and IR laser yet constructed.

"They all put out around 10 kilojoules at the third harmonic of neodymium glass, which is at 351 nanometers. Ten kilojoules in approximately 10 nanoseconds," Moses says. "You put all that together and you get a lot of energy on targets in a very short time. And it all works."

NIF will replicate the extreme conditions needed to achieve the long-sought goals of fusion ignition and burn as well as energy gain, creating and igniting a small, man-made star with laser light. It will also be the first facility to demonstrate both phenomena in a lab, a major step towards building a nuclear fusion power station that could be a source of safe, limitless, and carbon-free electricity.

Challenging Construction With Thousands of Optics

With more than 7000 large optics with apertures up to 40 cm and 30,000 small optics under 10 cm apertures, the NIF project posed some significant challenges in tolerancing, stability, and coatings.

NIF's Laser Bay 2, where half of the 192 beamlines are housed. (Photos courtesy of LLNL and DOE.)

"We have to have all the beams hit the targets within 50 microns RMS," Moses said in an interview earlier this year, "not a trivial challenge" considering the size of the building, more than 200 meters long.

"We have over 60,000 control points on the NIF, and they're very smart in that each one of the beams sort of works on its own when you're aligning it. It's an autonomous alignment system. They go work on their own to bring themselves to target chamber center during around a three-hour countdown. At around T-minus 100 seconds, a master clock takes over, queries all the laser beams and starts charging the power supply, and at T-minus 1 second, all our loops close, lock, and then the system fires."

Moses says that maintaining uniformity of the laser beams was one of the big challenges of NIF. "The specifications of the near-field and far-field intensity distribution are very demanding," he says. "In the near field, in the peak to mean, you can only have a variation of 12% or less. Across a big aperture like that, that's hard.

"The reason you have that challenge is because we try to run at the highest fluence possible that doesn't damage the optics. So if you have a lot of variation in the beams in the near field, you will have places where you damage the optics for no particular reason. And what we have done through not only our very sophisticated optical design but through development of incredibly good surface characteristics of the glass and the mirrors, we have reached that, and actually exceeded that capability."

With a deformable mirror and an interferometer on each laser beam, during the very last few seconds the beam is brought into "very exquisite control of the phase front, so as it propagates we get good beam quality throughout the system," Moses says.

Stability is maintained through a nested series of controls from the most low tech - concrete in the floor so it's seismically stable and isolated from other machinery - to a temperature control for the air conditioning of the system, to "local control loops that are near the optics, through very sophisticated optical design, relay imaging design that takes a lot of pressure off of the systems, and finally to pointing and centering systems and phase control systems that manage each beam independently of the other."

The coating challenge was addressed by communicating with vendors about the specifications that would be required for the extremely high power of NIF --in the IR section around 20 joules per square centimeter, and the UV section up to 10 joules per square centimeter, Moses says.

"This is kind of a place where people have never worked before, in the sense that we have gigawatts per square centimeter peak power also. If you look at historical legacy glass slab lasers such as Nova (at LLNL) and Omega (at the University of Rochester), they generally run under a joule per square centimeter. So we had to figure out ways to get these surfaces to take around 10 times the performance that had ever been done before."

The facility conducted target experiments as far back as 2001 with just a few laser beams, and in January of this year with 96 beams. On 26 February, the first 192-beam system test shot was fired, marking the unofficial completion of the NIF construction project. The Department of Energy certified NIF's completion in March.

NIF's Laser Applications

In addition to energy for the future, the NIF's primary missions include national security and understanding the universe. Moses noted that there are many benefits to being able to create conditions to study fusion reactions in lieu of weapons testing. The NIF target chamber will also allow study of the cosmos, for example.

A hohlraum cylinder, which contains the NIF fusion fuel capsule, is just a few millimeters wide, about the size of a pencil eraser, with beam entrance holes at either end. The fuel capsule is the size of a small pea. (Photo courtesy of LLNL and DOE.)

"Some pretty far out stuff can be done on the NIF," he says. "So instead of having to look through our beautiful telescopes and inferring what's going on, we'll be able to assemble a very small supernova inside the target chamber on schedule, have all your diagnostics in place, and fire it away and study it."

Perhaps NIF's greatest potential, however, is the possibility of verifying the potential for fusion-fission energy, from a concept called LIFE (laser inertial fusion engine).

According to the NIF Web site, LIFE power plants could generate gigawatts of power 24 hours a day for as long as 50 years without refueling while avoiding carbon dioxide emissions, easing proliferation concerns, and minimizing the problems of long-term nuclear waste disposal.

"The energy mission is extremely interesting to us; people have considered that the long pole in the tent for a long time," Moses says. "You make the fusion process easier, you take advantage of all the energy in the fission fuel, and you get rid of the waste. The remarkable thought is that you make your own fusion fuel, your own fission fuel, you get the maximum use of the energy that's available, and get rid of the waste products, all in situ, all in one space.

"We've had this reviewed by a lot of people, both scientific and policy people," he adds, "and there's a lot of interest in the community about it."

Moses credits the nearly 3000 partners in the construction of NIF with achieving the goal of completing the facility. From construction companies to lens manufacturers, they all played an important role in the project. "They deserve as much credit as we do for what we have here," Moses says.

Fact File From the National Ignition Facility

• NIF'S 192 giant lasers are housed in a 10-story building in Livermore, CA, the size of three U.S. football fields.

• Experiments leading to controlled, self-sustaining nuclear fusion and energy gain will begin in 2010.

• The energy of all 192 laser beams will be focused on a pea-sized target filled with deuterium and tritium fuel, creating temperatures and pressures found only in the core of stars and giant planets and inside nuclear weapons.

• The resulting reaction will "ignite" the hydrogen atoms' nuclei in the same fusion energy process that provides the life-giving energy of the sun.

• This fusion reaction will release many times more energy than the laser energy that was required to initiate the reaction, serving as the "proof of principle" of inertial confinement fusion.

• Take a virtual tour of the facility at https://lasers.llnl.gov/

NIF Will Help With Global Energy Needs

NIF will not itself be used to generate electricity. But NIF's laser experiments, with fusion ignition and burn and energy gain in the lab, should bring fusion energy a major step closer to becoming a viable source of virtually limitless energy.

Fusion, nuclear fission, and solar-produced energy (including biofuels) are the only energy sources capable of satisfying the Earth's need for power for the next century and beyond without the negative environmental impacts of fossil fuels.

Energy experts estimate that over the next 75 years, the demand for energy could grow to as much as three times what it is today, while affordable and accessible supplies of petroleum and natural gas will decline steadily and may well be exhausted by the turn of the century.

-Source: NIF

SPIE Laser Damage symposium, 21-23 September 2009

Lawrence Livermore National Lab is one of the international sponsors of SPIE Laser Damage in Boulder, CO (USA), in September.

Sen. Dianne Feinstein discusses the future energy possibilities of NIF as NIF director Ed Moses, to her right, and George Miller (far right), LLNL director, look on.
NIF Chief Ed Moses

SPIE Fellow Edward Moses, who was recently inducted into the National Academy of Engineering, says his career experience was ideally suited to bring him to his current position overseeing the creation of the NIF.

SPIE Fellow Ed Moses, director of the NIF"I have the lucky combination of backgrounds in that I grew up in construction, went to college in engineering, and even though I got my PhD in electrical engineering at Cornell, I really did all my work in applied physics-laser physics in particular, and quantum electronics," he says.

"When I came to Lawrence Livermore Laboratory in 1980, I worked on the atomic vapor laser isotope separation program and built a lot of laser systems."

He then worked in industry for five years before returning to Livermore to work on the NIF.

He calls his skill set "very apropos" for putting together a multidisciplinary team. "It's quite a gamut that's been working on it, and they're all around the country and around the world. This has been a great team that has put this together, and we're very excited about the work we're about to do."

A podcast of Ed Moses discussing the challenges and possibilities for the NIF can be found on the SPIE Newsroom.

Rich Donnelly is managing editor of SPIE Newsroom. 

Have a question or comment about this article? Write to us at spieprofessional@spie.org.

DOI: 10.1117/2.4200907.12

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