On December 13, 2022, Secretary of Energy, Jennifer Granholm, announced a historic scientific achievement; President Biden would call it a “BFD” she said. Eight days before, the National Ignition Facility (NIF) at the Department’s Lawrence Livermore National Laboratory had aimed its 192 lasers at a single tiny capsule of deuterium and tritium and achieved “ignition”; that meant the nuclear fusion reactions had released more energy than was in the lasers that “ignited” the pellet. Net positive energy from fusion reactions has never before been accomplished in a laboratory. The explosion at Livermore on December 5, 2022 was 3.15 megajoules, equivalent to about three sticks of dynamite.
Several details in this blog are from the December 13, 2022 Livermore technical panel video.
Thermonuclear fusion, which powers the sun and stars, was first accomplished on Earth on November 1, 1952, when the United States exploded a 10.5-megaton thermonuclear blast, code named “Mike”; it was about 14 billion times greater than the laboratory explosion at Livermore. The Mike explosion evaporated the island of Elugelab (part of Enewetak Atoll in the Marshall Islands) where the test was done. The 2022 Livermore experiment would have shattered the pencil-eraser-sized gold cavity called a “hohlraum”; inside it was a little diamond shell containing the deuterium-tritium (D-T) fuel. Science magazine noted that the “diamond capsule turned out to be the key.”
The laser fusion dream was born at Livermore 60 years ago. The 1954 multi-megaton BRAVO test at Bikini Atoll had made nuclear weapons testing infamous, raining intense radioactive fallout on Rongelap Atoll (among others) and on a Japanese fishing boat, the Daigo Fukuryū Maru – the Lucky Dragon No. 5. Global calls for an end to nuclear testing, and even nuclear disarmament, became loud and insistent. A U.S.-Soviet nuclear test moratorium followed in the late 1950s. Laser fusion raised the possibility of smaller, “clean” bombs without radioactive fallout. The radioactivity in fallout is almost entirely due to the fission products that result from the splitting of uranium and plutonium nuclei in atomic and thermonuclear weapons.
John Nuckolls, a former director of the Livermore Laboratory described the laser effort as being located in the “hectoton group [a hundred tons of TNT equivalent] instead of the megaton group.” “I heard,” he reminisced on the 70th anniversary of the founding of the laboratory in September 1952 (minutes 38 and 39 of the recording) that the object was to make “a fusion explosion without a fission explosion; pure fusion they called it.”
Though there would be some induced radioactivity in soil and building materials and carbon-14 in the air, smaller pure fusion bombs would be much more usable; indeed, it was difficult even to imagine militarily sensible targets for multi-megaton bombs. Pure fusion bombs would also make it possible to occupy the bombed territory without the kinds of radiation exposure and controversy about cancer that came to dog the nuclear weapons program, including among the U.S. troops who occupied Hiroshima and Nagasaki in the wake of the atomic destruction of those cities. The problem of marching troops into ground zero would be much simplified.
A new twist was added to Livermore’s laser fusion program in the 1990s, when nuclear testing was stopped. The National Ignition Facility would allow the study of physics of thermonuclear explosions without having to explode bombs in the Nevada desert to keep the US nuclear arsenal “safe, secure, and effective” as Livermore’s Director Kim Budil put it, celebrating the achievement on December 13, 2022 (minute 21 of the event video). It was part of an elaborate and costly “Stockpile Stewardship Program.” Scientists on the technical panel that day also mentioned weapons modernization as a goal. To their credit, the primacy of the weapons functions was clearly noted.
As the years wore on and the National Ignition Facility’s complexity delayed the achievement of ignition, there was more talk of the device being useful as an energy source and as an instrument for the study of the stars. The funds kept flowing.
Despite the achievement of ignition, the Livermore approach, known technically as “indirect drive” inertial confinement fusion because of the use of the hohlraum, has little chance of becoming a viable, economical power source. It needs to go from one explosion a day to perhaps ten per second. Even with much better lasers, energy output per unit of energy input must increase by 500 times or more to account for the energy to make the laser light and have significant energy left over to power something else, like a light bulb. These two factors alone require a combined performance improvement by hundreds of millions of times.
The huge performance increase must be accomplished with less-than-ideal materials from a physics point of view. Gold hohlraums must be replaced by lead ones (the most likely cheap material), each perfectly positioned to yield a blast; diamond shells, which took months of labor to make, will not be affordable.
Then there are housekeeping practicalities. Each explosion will shatter the lead hohlraum – creating debris, shrapnel, and lead dust. The lasers must stand the heat of hundreds of millions of shots per year (there are 31.5 million seconds in a year) without being damaged by shrapnel. The lead debris and dust from must be cleaned up safely, recovered, and (one hopes) recycled. All that without even speaking of how the energy of the explosions – mostly in neutrons – will be captured and converted to electricity.
Finally, there is the tritium problem. The Livermore shot only used four percent of the D-T fuel. Even with improvement, there will be plenty of unused tritium, some of which lodge in plentiful available metal surfaces and form metal hydrides – since, chemically, tritium is just elemental hydrogen. Most of the unused tritium must be recovered; the consumed and lost tritium must be entirely produced economically inside the device itself (from the more difficult D-D reactions or lithium-6 + neutron reactions). On the market, tritium costs around $30,000 per gram or more, hundreds of times more expensive than gold per unit weight. Just the tritium cost element could render any D-T fusion approach to electricity production uneconomical if a significant fraction of tritium had to be procured commercially.
While its prospects as an energy source are dim, the National Ignition Facility could play a significant part in reviving the old dream of pure fusion nuclear weapons. Being the size of three football fields, it is far too large to be a weapon; but its physics and engineering insights can play a part in the creation of pure fusion weapons.
Smaller fusion devices, like “magnetized target fusion,” which is being studied at Los Alamos, could play a role. The concept was invented in 1951 by the famed Soviet scientist and human rights activist Andrei Sakharov, who led the development of the Soviet thermonuclear bomb; it was brought to Los Alamos during the post-Cold War heyday of US-Russian collaboration in the 1990s. Research on it continues at Los Alamos, though US-Russian collaboration has fallen by the wayside.
IEER’s 1998 report, Dangerous Thermonuclear Quest (by Hisham Zerriffi and myself), analyzed the various fusion programs in the “Stockpile Stewardship Program”; we concluded that one result of the combination of programs could be the development of pure fusion weapons. Then whole idea of “inertial confinement fusion,” of which laser fusion is one variant, was that the plutonium trigger that ignites fusion in thermonuclear bombs be replaced by a non-nuclear energy source. Until December 5, 2022 that was only theory; for decades it seemed a distant dream. No longer. The reality is here.
The possible weapons angle also makes the question of whether the explosions at NIF comply with the Comprehensive Test Ban Treaty more immediate. The treaty bans all nuclear explosions, with no exceptions. In response to an October 28, 1999 letter from then-Senator Tom Harkin, the Department of Energy flatly stated that “NIF experiments are not nuclear explosions”; but the experiments then were far from achieving ignition. The Department avoided answering whether planned experiments with energy release of ten pounds of TNT equivalent would be explosions. (The correspondence is available in Rule of Power or Rule of Law?, Appendix B, pp. 161-168). Would three sticks of dynamite (about 1.6 pounds of TNT equivalent) be an explosion? What about the much larger ones releasing hundreds of megajoules (hundreds of sticks of dynamite) of energy?
John Nuckolls, who once led the Livermore laser fusion program and later led the whole laboratory, conceptualized fusion ignition without plutonium even before lasers were invented. He recounted that in 1957 Edward Teller, who led the founding of the Livermore lab and the development of thermonuclear weapons, had proposed using megaton-size underground nuclear explosions in a huge cavity to generate electricity. That idea inspired Nuckolls to examine the prospect of fission-free inertial confinement fusion; he had no hesitation in calling the phenomena, including from laser-driven fusion, “explosions” in his 1998 recapitulation of the early history of the inertial confinement fusion program.
The matter of Comprehensive Test Ban Treaty compliance remains unresolved. It may be moot from a U.S. domestic point of view since the U.S. Senate rejected ratification of the Treaty in 1999. But the Treaty still matters a great deal; indeed, it is central to the global non-proliferation regime.
The insights from ignition at NIF may well help other fusion energy programs, a matter I will discuss another day. For now, the celebration of the immense scientific achievement must surely be tempered by reflection on the serious nuclear weapons and proliferation questions that are now more real and pressing than they were before December 5, 2022.