Technicians Daniel Stevens and Scott Gifford stand inside PPPL’s National Spherical Torus Experiment-Upgrade (NSTX-U), a fusion device known as a tokamak.
Elle Starkman, PPPL Communications

For more than 70 years, Princeton University has been a major center of fusion energy research, pursuing one of the grandest challenges of science and engineering ever attempted: creating a clean, safe, and virtually limitless energy source on Earth by harnessing the nuclear reaction that powers the sun. 

The challenge is as fiendishly hard as it is audacious. Years can go by without prominent breakthroughs. But when the breakthroughs come, they fill us with awe at the potential for science to address the most complex problems in human history. 

Such a milestone happened in December at the Lawrence Livermore National Laboratory in California, where scientists for the first time demonstrated a fusion reaction that generated more energy than they put in to create it. The successful experiment is a step toward a fusion power plant, and it will accelerate research and investment in the field. 

For the Princeton Plasma Physics Laboratory (PPPL), the Department of Energy (DOE) national fusion lab managed by Princeton, the development means a burst of momentum at a time when the three engines of fusion science are running at full steam: government-funded research at universities and national labs such as PPPL; commercial fusion startups, including those incubated at PPPL; and international collaborations like the world’s largest fusion experiment under development in France, in which the United States is a partner. 

Fusion-generated electricity on our local grid is still decades away, but it should be ready in time to play its essential role in decarbonizing energy production and mitigating climate change. The international experiment, called ITER, aims to achieve self-sustaining fusion by the 2030s. The U.S. fusion community, in partnership with DOE, is working to create a pilot plant by the 2040s that will demonstrate commercial viability. Some startups hope to do it sooner. 

Princeton is doing its part by maintaining the scientific trajectory begun by astrophysics professor Lyman Spitzer in 1951 when he launched the U.S. search for fusion energy at the predecessor to PPPL. In addition to numerous scientific breakthroughs, Princeton has since produced more than 260 Ph.D.s in plasma physics, many of whom have become leaders in the field. We are preparing for the commercialization stage of fusion energy by forging industry partnerships and educating the workforce needed to sustain a viable fusion industry. 

The mechanics of fusion energy are easy to grasp. If you can fuse two types of hydrogen atoms into one helium atom, you will generate abundant energy. That’s because the merger results in a stable nucleus that is lighter than the two that combined to create it. The leftover mass is released as energy, along with a stray neutron. This is the same type of reaction that powers the sun and all the other stars. 

The hard part is engineering: generating a fusion reaction, keeping it going by recycling some of the excess energy back into the fusion machine, capturing the rest as usable energy — and doing it all cost efficiently. Fusion on earth can only happen at temperatures even hotter than the center of the sun, in a state of matter called a plasma, which makes it difficult to create, maintain, and manipulate. (Fortunately, that difficulty also makes fusion safe: turning down the heat and turning off the reaction is easy, so it cannot spiral out of control in the way that nuclear fission — the particle-splitting reaction behind nuclear weapons — can.) 

In New Jersey, this painstakingly hard work happens in an unassuming collection of mid-century buildings tucked in the woods across Route 1 on the James Forrestal Campus. There is no Collegiate Gothic here, no gargoyles, no picturesque spires. But as I reflect on PPPL’s role at this milestone in fusion history, I am struck by how quintessentially Princetonian the Lab is. 

The sheer ambition of PPPL epitomizes the spirit of “audacious bets” that is the theme of our Venture Forward campaign. It is multidisciplinary in the Princeton tradition, combining physics with engineering disciplines — and, increasingly, computer science and quantum information science. And when it fulfills its promise, this partnership with the Department of Energy may turn out to be the best example in our 276-year history of being in the nation’s service and the service of humanity. 

I hope the recent fusion breakthrough has captured your attention and imagination in recent weeks and enticed you to learn more about the science behind the headlines. (Check out this introductory video and timeline, or go deeper in this distillation by the Andlinger Center for Energy and the Environment.) I hope you also take special pride in Princeton’s role in this history, which is made possible by the support of alumni, by a nation committed to the scientific research enterprise, and by a spirit of international collaboration that recognizes we are all in this together.