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World's largest laser switches on to research

01 Apr 2005

The National Ignition Facility is capturing the hearts and minds of the scientific community as researchers grapple with a whole 'bundle' of data. James Tyrrell finds out the latest from physicist and NIF project manager Ed Moses.

Due for completion in 2008, the National Ignition Facility (NIF) - the world's largest laser - will be a 192-beam experimental resource that can mimic conditions at the centre of the sun. It is an incredible tool for the scientific community, and NIF project manager Ed Moses has some good news for researchers worried about the facility's status. Engineers have not only successfully tested the NIF beamline design, but in the process generated valuable scientific data.

"We have had our first paper accepted in Physical Review Letters: 'Experimental investigation of high mach number 3D hydro-dynamic jets'," Moses told OLE. "Actually, we have around 15 papers in various states of publication on the physics, and many more on the laser itself."

The last 18 months have been busy for the NIF team. "We built the whole facility, put in the infrastructure and then installed engineering prototypes for all the equipment," said Moses. "The beamline infrastructure, target chamber and all the utilities are in place." Formed from a total of 192 beams, the NIF's basic building block is called a bundle - a collection of eight beamlines. "If you build one bundle and repeat it 24 times, you have NIF," explained Moses. "We built and operated a bundle of NIF and ran it through its full paces. In about 400 shots, we showed that it met all of its performance specs."

More than just a manufacturing milestone, this testing phase was also an opportunity to do some real science. "Of those 400 shots, half were for laser-performance testing and around 200 were for physics tests," said Moses. "We had a series of different targets and we did hydrodynamic experiments, laser-plasma interaction experiments, very-high-temperature hohlraum experiments and equation-of-state experiments."

With scientific data now entering the public domain, it is tempting to say that the NIF facility is on-line - the building certainly appears complete to visitors. "It was working and generating real science, [but] now it isn't," clarified Moses. "The reason is that now we are satisfied everything we've built will work, we've gone back to filling out the other 23 bundles."

During the course of its construction, NIF has awarded around $1.3 bn (€1 bn) in contracts. "93% of those contracts are either in place or the work is completed. This includes the facility, beampath, utilities, assembly and installation equipment, and the optics," said Moses. "The only thing that has not been placed at this point is a very small number of line-replaceable units [NIF's modular optical mounts] that will come in at the end of the project."

NIF has several hundred vendors and has attracted the attention of big players in the optics world such as Hoya, Schott, Kodak, Zygo and Tinsley. "We look at these vendors as partners. Through the entire development and pilot-programming period we did a lot of technology development with them and shared the risk so that they could get into a production capability," explained Moses. "Generally, once they reach that capability we have a cost basis for their production, and then we go on to regular contracts." The scale of the project makes it a daunting task for vendors. NIF features more than 7000 large (80 x 40 cm) glass objects and 30,000 smaller optical pieces (under 10 cm) for the front-end diagnostics. According to Moses, the facility contains around 50 times the amount of high-quality optics found in what used to be the world's largest optical systems: the 10 m giant telescopes in Hawaii (WM Keck observatory) or the European Southern Observatory's Very Large Telescope project in Chile.

To overcome such high hurdles, NIF and its vendors worked as a team, focusing not only on production rates and quality, but also looking at ways of driving down component cost. "Previously, we had made the laser's gain medium, a phosphate neodymium glass, in a batch mode for around $5000 per litre," said Moses. "Now Schott and Hoyer make it for less than $1000 per litre."

Moses can cite other examples of where NIF was able to push forward the boundaries of technology. "If you look at the mirror blanks, between Corning, Heraeus, Tinsley, and Zygo, we are making glass that has the highest surface-quality and the highest reflectivity," commented Moses. "[With Cleveland Crystals] we learned how to rapidly grow very large crystals, and by that I mean 300 kg, in a couple of months, which usually take years to grow."

Along with its talented workforce, NIF's other catalyst for innovation was cash. With an investment of over $200 m in suppliers worldwide, NIF has stimulated significant growth in the industry. "Since we started, we have actually increased the large-scale optics production capability in the world by a factor of five," said Moses. "I think that an unexpected spin-off of the NIF is that all telescopes that will be built [in the future] will use facilities and capabilities that we have developed on the NIF [project]."

Moses admits that the NIF team actually surprised itself with the facility's performance to date, especially when it began analysing the initial test results. "First of all, NIF, even operating at 2% of its capability, could provide data in far fewer shots than had ever been done on any laser of its kind because of the high quality, reproducibility and reliability of the system," explained Moses. "We were doing experiments in laser-plasma interactions, hydrodynamics and equations of state that had never been done before. We were breaking new ground in physics right off the bat."

NIF's early experimental breakthroughs can be attributed to the foresight of its design team. "We can get 30 or 40 kJ from four beams coming in at a very low angle, which means that you can drive shocks and do those kinds of experiments much more effectively," said Moses. "Also, the beams are extremely uniform - we have less than 8% variation across the beam, which is by far the best that anyone has ever done."

The NIF facility also benefits from a sophisticated control system that includes beam pointing, centering, wavefront and timing control. "The beams themselves are only a few times diffraction-limited," said Moses. "We can get the beams to target chamber centre within 6 ps RMS, which is quite amazing."

Advances in information technology have pushed the NIF's systems to a new level. "Our control system is database-driven and we have a very accurate model for how the facility operates," revealed Moses. "You can dial in what the physicists require [for example, pulse shape and energy] and out it comes."

The high quality of the NIF's early experimental data has created a dilemma for the team in terms of project management. Officially, the goal is to be fully operational at the end of 2008. However, there are some differences in opinion about which route to take.

"The internal debate is whether we should come back on-line at some [midway] point so that people can do more experiments," said Moses. "The trade-off is that if you want to turn on a few bundles in the middle, it might benefit the early science, but it might also delay the end of the project [by six months to a year]."

NIF is a huge undertaking that has survived many twists and turns, and Moses is confident that NIF's management team will reach a resolution by the end of the spring.

"When I talk about NIF, it is a project of scales - you have to think about what is going on in the nucleus, in atoms and on a kilometre scale, which relates to the size of the facility," said Moses. "You have to think from picoseconds to years, and you have to think about all of this, all of the time when you are putting it [NIF] together to make it successful."

Bristol Instruments, Inc.Changchun Jiu Tian  Optoelectric Co.,Ltd.AlluxaEKSMA OpticsHÜBNER PhotonicsLASEROPTIK GmbHCHROMA TECHNOLOGY CORP.
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