Fusion is a nuclear reaction that combines two atoms to form one or more new atoms with a slightly lower total mass. The mass difference is released as energy, as described by Einstein’s famous equation, E = mc2, where energy is equal to mass times the speed of light squared. Because the speed of light is so high, converting only a small amount into energy—as in fusion—produces a correspondingly large amount of energy.

Researchers at the United States government’s National Ignition Facility in California have demonstrated for the first time what is called “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.

The technique used at the National Ignition Facility involved firing 192 lasers at a 0.04-inch (1 mm) pellet of fuel made of deuterium and tritium — two versions of the element hydrogen with extra neutrons — housed in a gold canister. .

When the lasers hit the canister, they produce X-rays that heat and compress the fuel pellet to about 20 times the density of lead and more than 5 million degrees Fahrenheit (3 million Celsius). The Sun If you can maintain these conditions long enough, the fuel will fuse and release energy.

During the experiment, the fuel and canister vaporize in a few billionths of a second. The researchers then hope that their equipment has survived the heat and accurately measured the energy released by the fusion reaction.

Recently, an American laboratory has demonstrated that fusion could be used as a power source in the future. But it still has a long way to go before it becomes viable…

So what did they achieve?

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To gauge the success of a fusion experiment, physicists look at the ratio between the energy released by the fusion process and the amount of energy contained within the lasers. This ratio is called profit.

Anything greater than one means that the fusion process released more energy than the lasers.

On December 5, 2022, the National Ignition Facility shot a fuel ball with 2 million joules of laser energy — about the same amount of energy it takes to run a hair dryer for 15 minutes — all in a few billionths of a second. Is. This triggered a fusion reaction that released 3 million joules. That’s an increase of nearly 1.5, breaking the previous record of 0.7 achieved by the facility in August 2021.

How big a deal is this result?

Fusion energy has been the “holy grail” of energy production for nearly half a century. While the 1.5 gain is, in my opinion, a truly historic scientific breakthrough, fusion still has a long way to go before it becomes a viable energy source.

While the laser energy of 2 million joules was less than the fusion yield of 3 million joules, it took about 300 million joules to produce the lasers used in this experiment. This result shows that fusion ignition is possible, but much work will be needed to improve the efficiency to the point where fusion can provide net positive energy considering the entire end-to-end system, not just A single interaction between lasers and fuel.

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The fuel is placed in a small container designed to keep the reaction as free of contaminants as possible. Lawrence Livermore National Laboratory

What needs to be improved?

There are many pieces of the fusion puzzle that scientists have been refining for decades to achieve this result, and more work could make the process more efficient.

First, lasers were only invented in the 1960s. When the US government completed construction of the National Ignition Facility in 2009, it was the most powerful laser facility in the world, capable of delivering 1 million joules of energy to a target.

The 2 million joules it produces today is 50 times more energetic than the next most powerful laser on Earth. More powerful lasers and lower-energy ways of generating those powerful lasers can greatly improve overall system performance.

Fusion conditions are very difficult to maintain, and any small flaw in the capsule or fuel can increase energy requirements and reduce efficiency. Scientists have made great strides in transferring the energy from the laser into the canister and the X-ray beam from the can into the fuel capsule more efficiently, but currently only 10 percent to 30 percent of the total laser energy is being transferred. Is. for canisters and fuel.

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Finally, while one of the fuel components, deuterium, is naturally abundant in seawater, tritium is much less abundant. Fusion itself actually produces tritium, so researchers are hoping to develop ways to harvest that tritium directly. In the meantime, other methods of producing the necessary fuel are available.

These and other scientific, technical and engineering hurdles will need to be overcome before fusion can power your home. Work will also need to be done to bring the cost of the fusion power plant down from the $3.5 billion National Ignition Facility. These initiatives will require significant investment from both the federal government and private industry.

It is worth noting that there is a global race around fusion, with many other labs around the world pursuing different techniques. But with the new results from the National Ignition Facility, the world has seen evidence for the first time that the dream of fusion is achievable.

The author is an Associate Professor of Nuclear Engineering at the University of Michigan, USA.

Reprinted from The Conversation.

Published in Dawn, EOS, January 29, 2023.


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