The National Ignition Facility (NIF) at Lawrence Livermore National Laboratory (LLNL) is a chandelier "holding a system of high-precision optics," according to a newly published book.
But unlike a delicate chandelier illuminating a room, NIF's thousands of optical components are able to resist or survive damage even under the enormous strain of amplifying and directing NIF's 192 high-power laser beams.
In the book, Optic Technologies Enabling Fusion Ignition, published by John Wiley & Sons, veteran LLNL optics and laser experts tell the comprehensive story of how they were able to push the performance of those optics beyond what many thought was possible - one of the key factors that enabled LLNL's remarkable scientific achievement of fusion ignition at NIF in 2022 and since repeated eight times.
The book is "the cumulation of many, many decades of work," said LLNL's Tayyab Suratwala, the book's principal author and editor. "And it wasn't just one thing. It took many enabling optic technologies to make the laser do what it does. This book shares this in a single resource."
Wiley published the 688-page book in August in print and digital form (see below for details). The book is the definitive reference textbook that details more than three decades of painstaking scientific research and innovation, creating a blueprint for current and upcoming generations of optics and lasers scientists and engineers.
Suratwala, program director for the Optics & Materials Science & Technology (OMST) division of LLNL's NIF & Photon Science Directorate, led the book project. He, Wren Carr, OMST group leader for science and technology, and Christopher Stolz, the former OMST Optics Supply group leader, served as the main editors. They joined with 23 of their Lab colleagues to write the chapters.
Much of the material was previously published in individual research papers. The book, however, "organizes that material and makes it a one-stop shop that tells the story in a coherent, logical manner, with a storyline and the strategies that we used to get to where we are today," Suratwala said. "We're excited to see it come out."
NIF is the only facility on earth to achieve ignition - producing more energy from a fusion reaction than the laser energy delivered to the target. NIF's mission supports the nation's science-based Stockpile Stewardship Program to maintain the reliability, security and safety of the country's nuclear deterrent without full-scale testing.
The world's most energetic laser system, within a facility the size of three football fields, uses thousands of specially designed optics to direct and amplify the laser beams to a target the size of a peppercorn. The lasers generate a bath of X-rays that forces hydrogen atoms inside that small target to fuse (see "How NIF Works").
The laser energies needed to achieve ignition, however, can damage those glass optics. The book examines in exacting detail how NIF's optics experts, with their partners in industry and academia, have developed innovative strategies and materials over the years to make that chandelier of high-precision optics "the most resistant to laser damage in the world."
The book's chapters explore the fundamental science of preventing or repairing laser-induced damage, including identifying mechanisms that cause damage and sources of contamination. Also covered are the development of automated damage repair and refurbishment techniques and novel damage-management technologies like the use of online "shadow blockers" to shield potential damage sites from laser light.
Other chapters are devoted to the manufacturing of optics especially for NIF, which has about 8,000 large and about 30,000 small optics, "perhaps the largest and most complex optical system constructed to date," the book says. These include amplifier slabs, turning mirrors, focusing lenses, vacuum windows, debris shields and crystalline nonlinear optics.
"When we talk about ignition and fusion and all the high energy density science," Suratwala said, "historically the emphasis is on those results, because that's what we're trying to enable. But it's amazing that underneath the hood of what makes NIF work - optics, targets, diagnostics, laser precision - there is a tremendous amount of innovation."
Carr, who wrote or co-wrote chapters on identifying, preventing, repairing and measuring laser-induced damage mechanisms, said the book project was quite a task, especially since the authors contributed to it in addition to performing their "day" jobs.
Carr's wife took a photo of him once while attending an air show at the busiest airport in the world, "and there are F-22s and F-15s and an A-10 Warthog flying over my shoulder, and I'm working on the book. I'm on vacation!"
"We all knew how important it was that we got it done," he said.
The book was a labor of love aimed at future generations of optics and laser experts who can build on both the advances and the setbacks NIF's scientists experienced over the years.
"There were so many times when we had to figure out how to do something for the first time," Carr said. "Sometimes we've had to reinvent wheels. What doesn't work is almost more important than what does work."
Carr hopes a future reader seeking to learn about ideas that were tried unsuccessfully in the past could be using new technologies that are not yet known , and then be able to say, "Oh, we know how to solve that one now."
"We have the story in one place," he said. "They can read a chapter, get a pretty good, solid overview and then there's a hundred references for the details."
Stolz has now retired from LLNL after a career spanning more than 30 years on NIF optics manufacturing and processing. He also frequently served as a NIF tour guide. Yet even he was surprised about how much he learned while helping to edit other chapters.
"The one area that I was least familiar with, and learned the most about, was all of the optics visualization technologies in chapter 16," Stolz said.
He called the book a critical "central repository of information for next-generation NIF employees" and a "tremendous resource" to help make sure the burgeoning private fusion power industry doesn't "waste valuable resources in their missions to build fusion power plants."
Chapters were also written by LLNL's Isaac Bass, Allison Browar, Liang-Yu Chen, David Cross, Paul Ehrmann, Eyal Feigenbaum, Colin Harthcock, Amanda Hope, Henry Hui, Laura Mascio Kegelmeyer, Stephen Mezyk, Christopher Miller, Raluca Negres, Todd Noste, Mike Nostrand, Rajesh Raman, Kathleen Schaffers, Scott Trummer, Vaughn Van Note, Diana VanBlarcom, Brian Welday, Pam Whitman and Lana Wong.
Optic Technologies Enabling Fusion Ignition is available for purchase as an e-book or hardcover book from Wiley.
The book is also available on Amazon in Kindle or hardcover form.
-Benny Evangelista
