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What is Fusion?

With its high energy yields, low nuclear waste production, and lack of air pollution, fusion, the same source that powers stars, could provide an alternative to conventional energy sources. But what drives this process?

What is fusion?

Fusion occurs when two light atoms bond together, or fuse, to make a heavier one. The total mass of the new atom is less than that of the two that formed it; the "missing" mass is given off as energy, as described by Albert Einstein's famous "E=mc2" equation.

In order for the nuclei of two atoms to overcome the aversion to one another caused their having the same charge, high temperatures and pressures are required. Temperatures must reach approximately six times those found in the core of the sun. At this heat, the hydrogen is no longer a gas but a plasma, an extremely high-energy state of matter where electrons are stripped from their atoms.

Fusion is the dominant source of energy for stars in the universe. It is also a potential energy source on Earth. When set off in an intentionally uncontrolled chain reaction, it drives the hydrogen bomb. Fusion is also being considered as a possibility to power crafts through space.

Fusion differs from fission, which splits atoms and results in substantial radioactive waste, which is hazardous.

Cooking up energy

There are several "recipes" for cooking up fusion, which rely on different atomic combinations.

Deuterium-Tritium fusion: The most promising combination for power on Earth today is the fusion of a deuterium atom with a tritium one. The process, which requires temperatures of approximately 72 million degrees F (39 million degrees Celsius), produces 17.6 million electron volts of energy.

Deuterium is a promising ingredient because it is an isotope of hydrogen, containing a single proton and neutron but no electron. In turn, hydrogen is a key part of water, which covers the Earth. A gallon of seawater (3.8 liters) could produce as much energy as 300 gallons (1,136 liters) of gasoline. Another hydrogen isotope, tritium contains one proton and two neutrons. It is more challenging to locate in large quantities, due to its 10-year half-life (half of the quantity decays every decade). Rather than attempting to find it naturally, the most reliable method is to bombard lithium, an element found in Earth's crust, with neutrons to create the element.

Deuterium-deuterium fusion: Theoretically more promising than deuterium-tritium because of the ease of obtaining the two deuterium atoms, this method is also more challenging because it requires temperatures too high to be feasible at present. However, the process yields more energy than deuterium-tritium fusion.

With their high heat and masses, stars utilize different combinations to power them.  [VIDEO: Sun to Sun – The Need for Fusion Energy]

Proton-proton fusion: The dominant driver for stars like the sun with core temperatures under 27 million degrees F (15 million degrees C), proton-proton fusion begins with two protons and ultimately yields high energy particles such as positrons, neutrinos, and gamma rays.

Carbon cycle: Stars with higher temperatures merge carbon rather than hydrogen atoms.

Triple alpha process: Stars such as red giants at the end of their phase, with temperatures exceeding 180 million degrees F (100 million degrees C) fuse helium atoms together rather than hydrogen and carbon.

— Nola Taylor Redd, LiveScience Contributor

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