THE 192-beam National Ignition Facility (NIF), the world’s largest and most energetic laser, is also one of the most productive scientific research facilities in existence. NIF experiments create temperatures of 100 million degrees and pressures 100 billion times that of the Earth’s atmosphere. Every experiment requires a millimeter-scale target made of various precision, fragile components. Each target has been carefully designed by teams of scientists and engineers, manufactured to extraordinary tolerances by talented technicians, assembled in clean rooms rivaling those in semiconductor plants, and inspected with microscopes and other fine-scale tools.
The feature article, A Growing Family of Targets for the National Ignition Facility, describes the challenging materials science and engineering associated with fabricating NIF targets. Five different targets are discussed that illustrate the Laboratory’s wide-ranging experimental physics program conducted at NIF in the areas of inertial confinement fusion (ICF), materials’ strength, materials’ structure, radiation transport, and astrophysics. These five examples represent the culmination of more than three decades of laser target design and fabrication at Livermore.
All of these targets are designed to re-create the physics regimes our investigators require to probe matter in extreme environments. Indeed, NIF’s suite of capabilities, including diagnostics, laser attributes, staff expertise, as well as targets, have evolved in response to the extreme physics necessary for our investigators’ research. As experiments at NIF have matured over the past several years so have the complexities of target components and the advanced materials of which they are made. Target materials include metals, polymers, gases, and low-density aerogel foams. We depend on a team of highly skilled engineers, scientists, machinists, and technicians to develop the means to fabricate and assemble them into exquisite, minuscule objects.
The intense temperature and pressure conditions targets encounter during experiments make results highly susceptible to any manufacturing imperfections. All targets must meet precise specifications for such attributes as dimensions, density, and surface finish. For example, some components must be machined to an accuracy of 1 micrometer with surface features no larger than approximately 10 nanometers. As our experimental diagnostics improve, greater demand exists for precision in target fabrication, assembly, and metrology.
Cryogenic ICF targets are among the most complicated in current use. At their core is a 2-millimeter-diameter plastic or diamond capsule that is filled with the hydrogen isotopes deuterium and tritium. The capsule is centered inside an approximately 10-millimeter-high by 5-millimeter-wide hohlraum cylinder. An extremely thin polymer “tent” holds the fuel capsule in place. We are working on innovative methods to replace this tent because experiments have shown it interferes with the smooth compression of the fuel capsule by the x rays generated when laser beams strike the hohlraum’s inner walls.
A completely different type of target, designed to re-create the young cluster of stars called the Eagle Nebula, is particularly illustrative of NIF’s extraordinary capabilities. The Eagle Nebula stretches light years across in deep space. And yet, we can reproduce the same physics regimes with a target measuring a few centimeters across. I find our ability to duplicate celestial phenomena thousands of light years away using NIF an impressive feat of science. By microencapsulating the physics of the life and death of stars, planets, and galaxies, we learn more about the physical processes driving our universe.
We have established an ambitious production goal of nearly 500 targets for the 2016 fiscal year to meet an ever-increasing shot rate. Along with this rise in production, we are striving to become more agile so that we can respond faster to the demands of new target design concepts and the novel materials they may require. Together with our partners, General Atomics and Schafer Corporation, we continue to improve production processes. For example, we are automating some manufacturing, assembly, and inspection activities. In this way, we can manufacture multiple copies of the same target design more consistently, which is critical to building experimental data sets. Toward boosting efficiency, we are also consolidating the footprint of our target assembly areas. With these improvements and further advances in target design, we look forward to the important scientific discoveries that may be possible using NIF.