By Harry Keller
Editor, Science Education
Last February, Conrad Farnsworth achieved nuclear fusion in his father’s shed in Wyoming*. This would be a big deal were it not for fourteen other high school students who had done this previously. You can find a YouTube video of his accomplishment and will note that the poverty-stricken need not apply. The equipment I see there would cost a few thousand dollars new and over a thousand even if you scrounged quite a bit. You even have to have a cylinder of deuterium, the stable heavier isotope of hydrogen. It has an atomic mass of two instead of hydrogen’s one due to an added neutron in its nucleus.
“First Neutrons,” uploaded to YouTube by Conrad Farnsworth on 2 Dec. 2011.
He achieved fusion by confining the deuterium in an extremely hot plasma, hundreds of millions of degrees hot. That’s hot!
Plasma is the fourth state of matter after solid, liquid, and gas. A plasma is like a glowing hot gas. Its molecules have disintegrated into atoms, and those have lost electrons to become ionized. Ionized gases can conduct electricity just like your fluorescent lights (today’s energy-saving CFLs for example) do. The ionized gas in those lights causes the fluorescent material lining the inside of the glass to glow.
Gases like to expand when they’re heated up. This expansion cools them down. To achieve enormous temperatures and fusion, you must confine the gas to prevent expansion. The problem you’ll face is that no known substance can survive those high temperatures. You cannot make a bottle to hold your super-hot plasma out of any material in the universe.
In a plasma, the deuterium atoms lose their single electrons to become bare atomic nuclei consisting of just one positively charged proton and one neutron. Like charges repel, making it very difficult to get two deuterium nuclei close enough to react. That’s why such a high temperature is used. The speed of the nuclei doubles when the absolute temperature increases fourfold.
When two deuterium nuclei combine, they have lots of excess energy, so-called “binding” energy. The combination of two deuterium nuclei forms helium-4, the most common form and a very stable atom. However, all of the excess energy must be released, and the helium emits either a neutron to form helium-3 or a proton to form tritium, hydrogen-3, which is unstable and decays.
Nuclear fusion means combining nuclei, while nuclear fission means splitting them. Today’s nuclear reactors use the latter process and produce lots of radioactive by-products, especially plutonium, the most deadly element on Earth. Fusion produces no such radioactive products, but its neutrons can make containing materials radioactive.
Farnsworth knew he had achieved fusion when he measured neutrons coming out of his reactor.
Both nuclear fission and nuclear fusion end with products that have slightly less mass than the reactants had. Thus, mass has been converted to energy by Einstein’s famous equation, E=mc2. The “c” in the equation is the speed of light, a very large number. The devastating nuclear bombs dropped during World War II converted about one gram of mass into energy when they exploded, a testimony to the power of this equation.
The path to nuclear fusion power is costing governments billions of dollars. They use hyper-powerful lasers or ultra-powerful, specially shaped, toroidal (donut-shaped) magnetic fields for confinement. Farnsworth used an easier electrostatic method. Think of sparks from rubbing our feet as you cross a wool rug on a dry day and then touch a doorknob. This method will never produce more power than it uses.
Farnsworth’s achievement in a regional science fair meant he was on his way to the International Science and Engineering Fair. The story is that he was disqualified on a technicality having nothing to do with his work. It had to do with him entering two regional science fairs, something that his high school has done routinely for years.
Note that Farnsworth’s accomplishment is an engineering feat more than a science investigation. It had been done before. He was duplicating previous attempts and seeing if he could improve on them. Pure engineering, a highly creative endeavor. After four years of hard work and lots of perspiration, he was on his way only to be stopped at the last moment by a bureaucrat.
Hopefully, he’ll take his ingenuity and persistence with him into his future life and do wonderful things for our society. Hopefully, he will find a place with less bureaucracy than the state science fairs.
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* AP, “Wyoming Teen Who Built Fusion Reactor Disqualified from Science Fair on Technicality,” Washington Post, 5.31.13.
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For those who care about details, that fusion of two deuterium nuclei to form a highly excited helium nucleus and can decay to make helium-3 or tritium (hydrogen-3) sets up another step. Any tritium formed will quickly react with another deuterium nucleus, a much more favorable reaction that deuterium-deuterium. Then, a neutron is ejected to leave behind a nicely stable helium-4 nucleus. Lots of heat results from these reactions.
If we could just find a way to contain them and extract the heat, we could power the world inexpensively without using any more fossil fuels.
It’s truly awesome to see in your own garage or shed one of the reactions that powers the Sun.
If anyone out there is thinking past the fun of nuclear fusion, you might ask where the Sun gets it deuterium. It gets it from protons (hydrogen-1 nuclei) colliding and emitting a positron (the electron’s antimatter partner with a positive charge) to create deuterium nuclei.
The next obvious question regards what happens when the hydrogen is used up. That depends on the size of the star. It does mean that the best source of star energy will be gone. It’s happening to stars all over the Milky Way all of the time. Some stars just collapse. Some explode. In the case of the Sun, it will expand to the diameter of the Earth’s orbit, more or less, before contracting to a small size and gradually darkening.
How long do we have?
The Sun has been burning hydrogen for around 4.5 billion years and should continue on for another 4 billions years, although some scientists have suggested shorter times.
Those who have been following the various Mars settlement activities know that making Mars habitable is an important step to securing the long-term future of the human race — and I do mean really, really long!!
This will actually redound to his benefit. In a sense, the Science Fair Community has “graduated” this young man from the Science Fair Culture and declared him a fully fledged professional grade world class Nuclear Engineer.
Nice take on the event, Barry. I’d question the “full-fledged” part, but agree with the sentiment.