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Scientists at a federal nuclear weapons facility have made a potentially significant advance in fusion research that could lead to a source of bountiful energy in the future, according to a government official.
The advance is expected to be announced Tuesday by the Department of Energy, which said a “major scientific breakthrough” was made at Lawrence Livermore National Laboratory in California. Jennifer Granholm, the energy secretary, and White House and other Energy Department officials are expected to be in attendance. The Financial Times reported on Sunday that the scientific advance involves the National Ignition Facility, or NIF, which uses giant lasers to create conditions that briefly mimic the explosions of nuclear weapons.
The government official, who spoke anonymously to discuss results that are not yet public, said that the fusion experiment at NIF achieved what is known as ignition, where the fusion energy generated equals the laser energy that started the reaction. Ignition is also called energy gain of one.
Such a development would improve the ability of the United States to maintain its nuclear weapons without nuclear testing and could set the stage for future progress that could one day lead to the use of laser fusion as an energy source.
Although not yet publicly announced, the news has quickly bounced among physicists and other scientists who study fusion.
“Yesterday a scientist friend sent me a note stating that Livermore had exceeded energy gain of one just last week and would be announcing the result on Tuesday,” Stephen Bodner, a retired plasma physicist who has long been a critic of NIF, said in an email Monday morning. “They deserve commendations for reaching their goal.”
What is fusion?
Fusion is the thermonuclear reaction that powers the sun and other stars — the fusing of hydrogen atoms into helium. The mass of helium is slightly less than the original hydrogen atoms. Thus, by Einstein’s iconic E=mc² equation, that difference in mass is converted into a burst of energy.
Fusion that could be produced in a controlled fashion on Earth could mean an energy source that does not produce greenhouse gases like coal and oil, or dangerous, long-lived radioactive waste, as current nuclear power plants do.
How do you produce fusion without a star?
Most fusion efforts to date have employed doughnut-shaped reactors known as tokamaks. Within the reactors, hydrogen gas is heated to temperatures hot enough that the electrons are stripped away from the hydrogen nuclei, creating what is known as a plasma — clouds of positively charged nuclei and negatively charged electrons. Magnetic fields trap the plasma within the doughnut shape, and the nuclei fuse together, releasing energy in the form of neutrons flying outward.
Tuesday’s announcement, however, involves a different approach. NIF consists of 192 gigantic lasers, which fire simultaneously at a metal cylinder about the size of a pencil eraser. The cylinder, heated to some 5.4 million degrees Fahrenheit, vaporizes, generating an implosion of X-rays, which in turn heats and compresses a BB-size pellet of frozen deuterium and tritium, two heavier forms of hydrogen. The implosion fuses the hydrogen into helium, creating fusion.
What laser fusion advances have been made so far?
The main purpose of NIF, built at a cost of $3.5 billion, is to conduct experiments that help the United States maintain its nuclear weapons without nuclear test explosions. Proponents also said it could advance fusion research that could lead to viable commercial power plants.
However, NIF initially generated hardly any fusion at all. In 2014, Livermore scientists finally reported success, but the energy produced then was minuscule — the equivalent of what a 60-watt light bulb consumes in five minutes.
Last year, Livermore scientists reported a major leap, a burst of energy — 10 quadrillion watts of power — that was 70 percent as much as the energy of laser light hitting the hydrogen target.
But the burst — essentially a miniature hydrogen bomb — lasted only 100 trillionths of a second.
The report by the Financial Times on Sunday suggests Livermore will announce that in the latest experiment the fusion energy produced exceeded the amount of laser energy hitting the hydrogen target.
For that to occur, the fusion reaction had to be self-sustaining, meaning the torrent of particles flowing outward from the hot spot at the center of the pellet heated surrounding hydrogen atoms and caused them to fuse as well.
What are the obstacles to fusion power?
An important caveat is that the claim focuses on the laser energy hitting the hydrogen target. NIF’s lasers are extremely inefficient, meaning only a small fraction of the energy used to power the lasers actually makes it into the beams themselves.
More modern technology like solid-state lasers would be more efficient but still far from 100 percent fusion; for this to be practical, the fusion energy output must be at least several times greater than that of the incoming lasers.
Does Tuesday’s announcement mean we’ll have cheap fusion energy soon?
Even if scientists figure out how to generate bigger bursts of fusion, immense engineering hurdles would remain.
NIF’s experiments have studied one burst at a time.
A practical fusion power plant using this concept would require a machine-gun pace of laser bursts with new hydrogen targets sliding into place for each burst. Then the torrents of neutrons flying outward from the fusion reactions would have to be converted into electricity.
The laser complex fills a building with a footprint equal to three football fields — too big, too expensive, too inefficient for a commercial power plant.
A manufacturing process to mass-produce the precise hydrogen targets would have to be developed.