Analysis & Opinions - Belfer Center for Science and International Affairs, Harvard Kennedy School

Fusion Breakthroughs in Context: Professors Holdren and Bunn Reflect on Fusion Ignition Announcement

| Dec. 14, 2022

Editor’s Note: The Belfer Center Communications Team reached out to policy experts John P. Holdren and Matthew Bunn to reflect on the recent achievement of fusion ignition at the Lawrence Livermore National Laboratory

John Holdren, the Teresa and John Heinz Research Professor of Environmental Policy and Co-Director of the Belfer Center's Science, Technology, and Public Policy Program, served as President Obama’s Science Advisor and Director of the White House Office of Science and Technology Policy from 2009 - 2017. A plasma physicist who worked in the Magnetic Fusion Energy Division of the Livermore Lab in 1970-72 and served as a consultant on both magnetic and inertial confinement fusion to that Lab and the Department of Energy from 1974 to 1994, Holdren led the study of the future of the U.S. fusion-energy program produced by President Clinton’s Council of Advisors on Science and Technology in 1995.

Matthew Bunn is the James R. Schlesinger Professor of the Practice of Energy, National Security, and Foreign Policy and Co-Principal Investigator for the Belfer Center’s Project on Managing the Atom. Before joining the Kennedy School in January 1997, Bunn served for three years as an advisor to the White House Office of Science and Technology Policy, where he played a major role in U.S. policies related to the control and disposition of weapons-usable nuclear materials in the United States and the former Soviet Union. He also directed a special study for President Clinton on security for nuclear materials in Russia. 

Below, Holdren and Bunn provide context for this breakthrough and its implications for national security, clean energy, and climate change. 


Matthew Bunn

The scientists at Lawrence Livermore National Laboratory should be applauded for their success in getting more energy out of a fusion reaction than it took to make the reaction go.  Fusion – slamming the smallest atoms together so they form larger ones, releasing energy – has been a daunting scientific and engineering quest for decades.  Achieving “ignition” – more energy out than in – is a worthy scientific achievement, though it comes many years and billions of dollars later than originally expected.

The National Ignition Facility (NIF), where the work was done, targets enormous high-powered lasers on tiny pellets with hydrogen at their center, bringing them to incredible temperatures and pressures.  Now that more energy is coming out of each experiment, the conditions will be more like those at the heart of a thermonuclear bomb, contributing to NIF’s main mission, helping the United States use experiments and simulations rather than nuclear testing to maintain its nuclear weapons stockpile.

On the energy side, this fiendishly complex multi-billion-dollar experimental facility is a long, long way from anything a utility might buy to generate power.  As Livermore Director Kimberly Budil pointed out, commercially viable energy from fusion is probably still decades away.  Some startup companies hope to achieve it much faster (with very different approaches to achieving fusion from those used at NIF), but the engineering challenges in the path of building cheap, reliable fusion power plants are huge.  If those challenges can someday be met, fusion could be quite an important energy source in the second half of this century, as fusion greatly reduces the safety, security, waste, and proliferation concerns that have limited the growth of traditional nuclear power based on splitting big atoms (fission), rather than putting little atoms together (fusion).


John P. Holdren

Tuesday’s announcement of a breakthrough in fusion energy research at the Department of Energy’s Livermore Lab was just the latest in a recent flurry of fusion-breakthrough announcements at labs around the world.  What is going on?  After seven decades of increasingly costly research—including an unprecedented degree of cooperation across nations -- are safe, clean, affordable fusion reactors now just around the corner?

Fusion reactions power the stars, and they have allowed the building of thermonuclear bombs of unlimited explosive power.  But, aside from capturing energy from the sun, harnessing these reactions on Earth’s surface to help meet society’s energy needs has proven to be incredibly challenging.   No technology devised for this purpose so far has been able to produce as much energy as needed to operate it. 

This energy gap has gotten more or less steadily smaller over the years, however, for both of the main approaches to meeting the fusion challenge;  “Magnetic fusion”, using a cage of magnetic fields to confine the immensely hot fusion fuel; and “Inertial- confinement fusion”, using powerful, pulsed lasers or particle beams to compress and heat tiny fuel pellets essentially instantaneously, producing a series of fusion micro-explosions.

The Livermore breakthrough used the world’s most powerful laser, bigger than three football fields, to create a single micro-explosion that, for the first time anywhere, yielded a bit more fusion energy than the laser energy arriving at the target.  That fusion yield, however, was about 250 times smaller than the amount of electrical energy supplied to the laser for the “shot”.   A practical fusion reactor based on this approach would need 10-20 times more fusion yield per shot than the electricity supplied to the laser, hence 2500-5000 times the yield of the Livermore experiment, and it would need to operate at rate of about 10 shots per second.  The current Livermore device can manage 2 shots per day. 

Thus, while the Livermore result represents real progress, it is miles short of the performance needed for a practical fusion reactor. The daunting energy gap just mentioned, moreover, takes no account of other, as yet unsolved problems relating to structural damage by fusion neutrons, efficient and secure breeding and recycling of the radioactive tritium needed for an adequate reaction rate, and more.  The current Livermore laser-fusion system, however, is quite useful for the less-advertised, national-defense function that has paid most of the facility’s bills:  studying the physics of thermonuclear explosions without blowing up real bombs.

The magnetic approach to controlled fusion, around which a number of physics and technology breakthroughs have also been announced in recent months, is actually considerably closer than laser fusion to achieving reactor-relevant yield. (Beneficially for arms-control purposes, it also has little relevance to thermonuclear-weapon physics.)  Even so, the additional hurdles that need to be surmounted in order to arrive at a practical magnetic-fusion reactor are formidable.  It seems very unlikely that fusion reactors of any type will be contributing significant electricity to the power grid before the second half of this century; and, even on that timescale, it is not obvious that they can be made both reliable and inexpensive enough to compete with other options.

Is it worth the continuing effort and expense needed to find out?  I believe the answer is yes. Uncertainties relating to the adequacy of other carbon-free energy technologies for meeting all of society’s energy needs for the long term are large, and the potential attractions of fusion are considerable: practically inexhaustible fuel from sea water, less polluting than fossil fuels, safer and less proliferation-prone than fission energy systems, free of the intermittency and land requirements of wind and solar. It is also the only known energy source potentially powerful enough to carry humans beyond the solar system, should society want or need to go there.                

For additional information or to request an interview, contact Liz Hanlon at or Matthew Parent at

Statements and views expressed in this commentary are solely those of the author and do not imply endorsement by Harvard University, the Harvard Kennedy School, or the Belfer Center for Science and International Affairs.

For more information on this publication: Belfer Communications Office
For Academic Citation: Holdren, John and Matthew Bunn.“Fusion Breakthroughs in Context: Professors Holdren and Bunn Reflect on Fusion Ignition Announcement .” Edited by Elizabeth Hanlon and Matthew Parent. Belfer Center for Science and International Affairs, Harvard Kennedy School, December 14, 2022.

The Authors

John P. Holdren

The Editors