A nuclear physicist explains why fusion ignition is being hailed as a major breakthrough in fusion

US scientists have announced what they describe as a major breakthrough in the elusive goal of generating energy from nuclear fusion.

The US Department of Energy said on December 13, 2022 that for the first time — and after several decades of trying — scientists had been able to get more energy out of the process than they otherwise had to.

But how important is development? And how far is the long-awaited dream of fusion providing clean and abundant energy? Carolyn Curransan assistant professor of nuclear engineering at the University of Michigan who worked at the facility that just broke the fusion record, helps explain this new finding.

What happened in the fusion chamber?

Fusion is a nuclear reaction that brings two atoms together to form one or more new atoms with a slightly lesser total mass. The difference in mass is released as energy, as shown by Einstein’s famous equation, E=mc2, where energy equals mass times the speed of light squared. Because the speed of light is enormous, converting a very small amount of mass into energy – such as what happens in fusion – produces an equally enormous amount of energy.

Researchers in the US government National Ignition Facility In California, for the first time, what is known as “fusion ignition”. Ignition occurs when a fusion reaction produces more energy than is put into the reaction from an external source and becomes self-sustaining.

Gold and plastic box.

The fuel is kept in a small canister designed to keep the reaction as free of contaminants as possible. US Department of Energy/Lawrence Livermore National Laboratory

The technology used at the National Ignition Facility involved firing 192 lasers at a 0.04 in (1 mm) of fuel Made of deuterium and tritium – two versions of the element hydrogen with extra neutrons – housed in a gold case. When the lasers hit the canister, they produce X-rays that heat and compress the fuel grains to about 20 times the density of lead and more than 5 million degrees Fahrenheit (3 million degrees Celsius) — about 100 times hotter than the surface of the Sun. If you can maintain these conditions long enough, then… The fuel will fuse and release energy.

The fuel and canister vaporize within a few billionths of a second during the experiment. The researchers then hope that their instrument escaped the heat and accurately measured the energy released by the fusion reaction.

So what have they accomplished?

To assess the success of a fusion experiment, physicists look at the ratio between the energy released by the fusion process and the amount of energy inside the laser. This ratio called gain.

Anything over a gain of 1 means the fusion process releases more energy than the laser being delivered.

On December 5th, 2022, the National Ignition Facility fired a pellet of fuel with two million joules of laser energy—roughly the amount of energy needed to power a hair dryer for 15 minutes—all contained within a few billionths of a second. This triggered a fusion reaction 3 million joules released. This is a gain of about 1.5%, breaking the previous record of gain 0.7 achieved by the facility in August 2021.

How big is this score?

Fusion energy was the “holy grail” of energy production Almost half a century. While a gain of 1.5 is, I believe, a truly historic scientific breakthrough, there is still a long way to go before fusion is a viable energy source.

While the laser’s energy of 2 million joules was less than the fusion yield of 3 million joules, the facility took nearly 300 million joules to produce a laser used in this experiment. This result showed that fusion ignition is possible, but that it will take a lot of work to improve efficiency to the point where fusion can provide a net positive energy return when considering the entire system, not just a single laser-fuel interaction.

Arcade full of pipes, tubes and electronics.

The machines used to create powerful lasers, such as these pre-amplifiers, require much more power than the lasers themselves produce. Lawrence Livermore National LaboratoryAnd the CC BY-SA

What does he need to get better?

There are a number of pieces of the fusion puzzle that scientists have been steadily improving on for decades to achieve this result, and more work could make this process more efficient.

First, it was just the laser Invented in 1960. When the US government Completion of building the National Ignition Facility in 2009It was the world’s most powerful laser facility, capable of delivering 1 million joules of energy to hit the target. The two million joules you produce today is fifty times more energy than the The second most powerful laser on Earth. More powerful lasers and less energy-intensive methods of producing those powerful lasers can greatly improve the overall efficiency of the system.

fusion conditions It is very difficult to maintainand any A small defect in the capsule or fuel It can increase energy requirements and reduce efficiency. Scientists have made a lot of progress More efficient transfer of energy from the laser to the enclosure and the X-ray radiation from the canister into the fuel capsulebut for now only about 10% to 30% Of the total laser energy is transferred to the canister and to the fuel.

Finally, while only one part of the fuel, deuterium, is normal Tritium is much rarer in seawater. The merger itself actually produces tritium, so the researchers hope to develop ways to harvest this tritium directly. Meanwhile, there Other methods are available to produce the required fuel.

These and other scientific, technological, and engineering hurdles must be overcome before fusion can produce electricity for your home. Work must also be done to reduce the cost of the fusion power plant well from $3.5 billion from the National Ignition Facility. These steps will require significant investment from both the federal government and the private sector.

It should be noted that there is a global race on fusion, with many other labs around the world Follow different techniques. But with the new result from the National Ignition Facility, the world saw, for the first time, evidence that The merger dream is achievable.


Carolyn CurransAssociate Professor of Nuclear Engineering, University of Michigan

This article has been republished from Conversation Under Creative Commons Licence. Read the The original article.

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