Behind The Science Powering The Sun

[psycopk]

Updated Feb. 13, 2014 10:38 a.m. ET

Scientists in California achieved a short-lived fusion reaction by bombarding with lasers a small gold can, as shown, containing a hydrogen isotope fuel. Researchers are considering altering the shape of the container from a cylinder to something more akin to a rugby ball. AFP/Getty Images. Lawrence Livermore National Laboratory/Agence France-Presse/Getty Images

What is fusion?

It is the process that powers the Sun. At the Sun's core, powerful gravitational forces generate enormous heat and pressure, causing a reaction whereby two light-hydrogen atoms collide and bond into a heavier helium atom. But the mass of the helium atom is slightly less than the total mass of the original hydrogen atoms. The difference is converted to energy, as described by Einstein's equation E=MC2. We see this released energy as light and feel it as the Sun's warmth.

Why is it so hard to achieve a fusion reaction in a lab?

Because scientists can't replicate the tremendous gravitational forces feeding the Sun and stars, they must find other ways to generate the intense heat and pressure needed to fuse the hydrogen atoms. Sustainable success has been elusive.

How is it done?

Further Reading

• A Star Is Born: U.S. Scores Fusion-Power Breakthrough

There are several techniques. One popular approach is to fire powerful lasers at a nuclear material in tightly confined space. Another is to use powerful magnets to confine the material.

What raw materials are needed?

Researchers have found that the reaction between two hydrogen isotopes—deuterium and tritium—can provide the highest energy gain at the lowest temperature. Even then, it requires temperatures of 150 million degrees Celsius for fusion to take place in a lab setting. That is 10 times as great as the temperature powering the reaction at the sun's core.

Are the fusion materials easy to obtain compared with the uranium used in today's nuclear fission plants?

Deuterium can be easily extracted from seawater. Tritium can be produced from lithium, which is found in the Earth's crust.

What are some of the biggest practical hurdles?

It's expensive and complicated to generate the tremendous temperatures and pressures needed to achieve a sustained fusion reaction that feeds on itself. And that's crucial to ensure that the energy released in the process is more than what's used to fire it up in the first place.

—Gautam Naik

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