How long is the fuse on fusion?
Harnessing the energy of nuclear fusion remains a formidable and worthwhile challenge. Meeting it requires nurturing international cooperation and reinvigorating US leadership.
August 14, 2012Published: August 14, 2012
The Washington Post recently ran a cover story in its Science section on fusion energy, with a photo showing a physicist peering through the porthole of an experimental magnetic fusion device at the Princeton Plasma Physics Laboratory (PPPL). I began my scientific career at that Department of Energy lab in 1975—just two years after a national energy crisis resulted in gas rationing and four years before the accident at Three Mile Island. Those events were rallying cries for developing clean and renewable domestic energy sources.
At the time, fusion energy was little more than a pipe dream, and scientists had no expectations that it would be part of the nation's energy supply in the foreseeable future. Nevertheless, the prospect of the US leading the development of fusion energy—the same source that powers the Sun—helped expand national funding for fusion research during the next decade. Europe, the Soviet Union, and Japan also undertook massive billion-dollar-class demonstration experiments. By the time the US's flagship experiment, the Tokamak Fusion Test Reactor at PPPL, was shut down in 1997, DOE had spent $8 billion over 45 years on fusion research—more than expenditures on any other energy technology. What do we have to show for that investment? Are we any closer to the day when fusion can contribute to central power generation?
Yes, but there is still a long way to go. In my opinion, sustaining a fusion reaction in the laboratory remains one of our greatest scientific and engineering challenges. The science behind nuclear fusion is well understood; it's a fundamental principle in stellar dynamics and in thermonuclear weapons technology. But for a domestic energy source, that brief, destructive reaction evident in a hydrogen bomb has to be harnessed, contained, and sustained over a long period of time. When the reaction produces more energy than it takes in, the break-even point is achieved. Reaching that point involves taking enough hydrogen to roughly fill a balloon and heating it to about 100 million degrees for about a second.
When I began working at PPPL as a postdoctoral fellow in 1975, the energy produced in the lab was about a trillionth of the energy required to heat the gas. By 1995 the energy gain had been improved by a factor of 100 billion. And in the mid 1990s, the Tokamak Fusion Test Reactor at PPPL and the Joint European Torus Tokamak, a sister experiment in the UK, performed a series of experiments using the easiest hydrogen isotopes to fuse (a deuterium and tritium mixture) and came within 30–65% of the break-even point! That was a remarkable scientific achievement because it involved a continuous evolution of the design and implementation of solutions needed to better heat, contain, and fuel the hot gas.
I can point to only one other technical endeavor that has shown such a large improvement in key performance parameters. Most people know it as Moore's law. The continuous improvement of microprocessors is largely due to miniaturization of transistors. Advancements in microelectronics manufacturing technology have enabled the size of a transistor to decrease by about a factor of two every two years. Intel made the first microprocessor chip commercially available in 1971—the 4004 contained 2300 transistors. Today's chips contain more than 2.6 billion transistors.
What are the steps needed to achieve commercial fusion power? A laboratory demonstration of the energy break-even point is far from a demonstration of a continuously operating and commercially viable reactor—one engineered to generate electric power for decades but to need only minimal downtime and low-cost maintenance. The promise of fusion always appears on the horizon.
As I write this, ITER, a fusion facility that will cost more than $10 billion, is being built by an international consortium—the European Union, Japan, Russia, the US, South Korea, China, and India—in Cadarache, France. The device is scheduled to begin operation by 2019, and scientists plan to demonstrate 500 million watts of fusion power for several minutes' duration a decade later. That may sound like a slogging pace when considering the world's constantly growing demand for energy. But consider that DOE and numerous study groups must struggle in their periodic attempts to construct and advocate national and international long-term energy strategies. Those efforts must compete against the enormous influence of the entrenched trillion-dollar interests in hydrocarbon-based energy sources. Moreover, with the fiscal realities of energy production and global debt crises reining in research budgets, it's even more of a challenge to sustain robust annual progress toward a long-term solution like fusion research.
That creates a painful reality for DOE and the US fusion community. The present fusion budget cannot sustain the remaining domestic research program at PPPL, MIT, General Atomics, and several other major centers and also fulfill the US's international obligations for funding its 10% share of the ITER project. Yet I strongly believe that the US's 60-year investment in this "holy grail of energy sources" has allowed scientists to make tremendous progress, and they are positioned to take a major step forward. The nation should find a way to sustain a critical mass of both domestic and international investments. The ultimate goal is so attractive that the US should not lose the opportunity to be a leader in the international fusion program. Consider that energy is the heart of every society's infrastructure; two examples illustrate how a society's sustained, long-term investment in infrastructure ultimately produced abundant rewards.
Tunnels and cathedrals
In 1911 construction began on expansive tunnels to channel water from the Catskill Mountains to New York City. The first two were completed in 1917 and 1935, respectively. With those lifelines in place, the nation's largest city has continued to thrive. The population has topped 8.2 million, and the city will be able to support its growth only with the help of a third water tunnel, which was started in 1970 and scheduled for completion in 2020. At a projected cost of more than $6 billion, the project represents the city's most expensive capital improvement—an infrastructure project conducted under a vision that has been consistently sustained over the course of almost half a century.
Going further back in history, to European cities of the Middle Ages, construction of a cathedral often spanned several centuries. Like a major science project, it required imagination about, and faith in, the future. And like a major science project, it required sustaining over time a resolve for innovating and solving problems at the cutting edge of the technology of the day—a process that sometimes involved setbacks and always involved challenges. Many who toiled to create a cathedral would not live to see the fruit of their labor. But maybe they knew, as researchers in fusion energy know, that their work would benefit generations to follow.
Religion isn't science. The lofty aspirations symbolized in a cathedral centuries ago are not the same as the lofty aspirations of those seeking today to revolutionize energy production for a planet increasingly in need. And whereas a cathedral is objectively and obviously a beautiful artifact of human ingenuity, the ingenious beauty of a future fusion power plant will not likely show in outward appearances. Nevertheless, researchers who devote years to the cause of fusion research share the noble vision of the aqueduct and cathedral builders.
It is true that science has plenty of other problems that will require similar sustained efforts over many decades for better understanding and possible application. Indeed, 95% of the content of the universe remains a mystery to us. To mask our ignorance, we give names to unknowns—"dark energy" and "dark matter." We look to research in biology to further our understanding of how the brain functions, what stem cells can do for medicine, and how to treat and prevent cancer.
When I was involved with fusion research, I was often asked what motivated me to work on such a difficult problem, even though I would probably never see a satisfactory solution in my lifetime. I didn't have to ponder the question very long. The yearly progress from the 1970s into the 1990s was exciting enough. Furthermore, serendipitous discoveries made along the way led to new devices, materials, and techniques that turned out to be valuable to other fields. In fact, out of the research grew key developments in extreme high vacuum technology—the very science needed to give rise to the burgeoning growth of high-performance microprocessors and optoelectronics.
I was fortunate to cut my scientific teeth on the challenging problem of fusion research. I saw the enormous size of the challenge, but I also saw that over decades, the modern science enterprise can meet it. That's why, with faith in human ingenuity and in the future, I believe that such scientific endeavors need to be nurtured worldwide. With the scale of investments required for frontier research, the US needs to reinvigorate its leadership role.