Nuclear fusion research took a big step forward recently with the stunning announcement by the Department of Energy (DOE) that on August 8, the National Ignition Facility (NIF) – a powerful laser that fills a building the size of three football fields at the Lawrence Livermore National Laboratory – had fired an intense pulse of light to heat and compress a bit of hydrogen weighing less than a grain of sand. The resulting fusion reactions, in which hydrogen nuclei combine to form helium, produced about two-thirds of the energy in the laser pulse. That's triple what researchers expected and eight times the previous record set in February.
Scientists in the coming months will strive to repeat this result and to further increase the fusion energy produced. Fusion is sensitive to small changes and there are many aspects of the laser and the hydrogen target that can be fine-tuned. It is thus plausible to expect that experiments will soon produce more energy than the laser delivers. Achieving that elusive goal of "ignition" in laser fusion would open the door to tapping the energy stored in our planet's most abundant resource, ordinary water, from which the hydrogen is derived. This would put the US far ahead of efforts in China, Russia, and France.
The backstory of laser fusion deserves as much attention as the latest achievement because it illustrates what it takes to foster transformational innovation. The story begins more than fifty years ago with the notion of using a laser to drive hydrogen fuel to ignition. Classified underground nuclear experiments through the 1980s tested the way ignition would be achieved. By 1990, these program results, together with unclassified work using the most powerful laser available at the time, provided scientists with enough understanding to envisage a driver powerful enough to achieve ignition. Construction of the NIF laser began in 1997 as the research program's goal meshed with the need to ensure the continued safety and reliability of the nuclear stockpile without underground testing.
To have a good chance of achieving ignition, the 192-beam NIF had to be at least 50 times more powerful than its 10-beam predecessor. The new manufacturing technologies that had to be developed were not without risk, and many things didn't go as smoothly as planned as the NIF was being built. But finally in 2009, having met its specifications, the laser began its operations along with a program of non-ignition experiments. Today, the program continues to provide important scientific and stockpile insights.
The initial campaign of ignition experiments began in 2011. Unfortunately, it was too aggressive, and pushed too fast and too hard toward ignition without adequate instruments to "see" what was happening during the laser pulse. Nor was it possible to accurately model the experiments. That campaign was terminated several years later, and efforts were then diverted to better understanding the science needed for success. A more deliberate march toward ignition resumed in 2014, enabled by improved hydrogen targets, and better tools to measure and model the experiments. The fusion energy produced in each shot increased slowly in the following years before dramatically increasing this past year because of a growing understanding of the experiments.
One takeaway here is that the DOE national laboratories are uniquely suited to such focused, long-term efforts on important national problems. Their researchers are organized for multidisciplinary work – because laser fusion requires coordinated expertise in fields such as materials, optics, precision fabrication, instrumentation, and simulation – and for productive partnerships with other laboratories, universities, and the private sector. Contributions from that extended fusion community were critical to this latest success. Another takeaway is the importance of support by the Department of Energy and Congress. These efforts were sustained over decades and informed by rigorous and frank independent assessments of progress and prospects.
Americans should build on this success and not be timid. Reliable ignition experiments on the NIF laser will enable novel research. These experiments will improve understanding of our nuclear weapons without the need to explode them (a key component in DOE's program to maintain a safe and reliable nuclear deterrent without underground tests). Other important research will study materials under the extreme conditions found inside stars. And in the long term, these ignition experiments could well show the way to a new source of carbon-free energy.
Steven E. Koonin, a physicist at New York University, chaired the 1990 and 1997 National Academies' panels that recommended construction of the National Ignition Facility. He later served as Under Secretary of Energy for Science in the Obama administration.