I am working on a science project on the Sun. I have found that in order for nuclear fusion to work, it needs both helium 3 and 4.
Why can't nuclear fusion be done with just helium 4?
How can we create nuclear fusion on Earth?
Can we even do so?
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$\begingroup$ Welcome to Physics.SE. Where have you looked? What have you found? You should add a few details to your question. $\endgroup$– phoCommented Oct 27, 2014 at 23:11
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$\begingroup$ I write a little bit about the p-p cylce in an answer to another question. The star makes the Helium-3 as it goes along and then uses it up again to make Helium-4. $\endgroup$– dmckee --- ex-moderator kittenCommented Oct 28, 2014 at 0:27
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$\begingroup$ There is a related discussion here. $\endgroup$– John RennieCommented Oct 28, 2014 at 15:25
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1 Answer
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Why can't nuclear fusion be done with just helium 4?
Helium-4 is the product of fusion, where protons are the fuel. The helium-3 is produced as an intermediate step.
As an analogy, think of wood in a fire: the wood turns to charcoal, then to ash. You can douse the fire and pull the charcoal out to burn later, but you can't burn the ashes any more.
How can we create nuclear fusion on Earth? Can we even do so?
To create nuclear fusion on Earth we need to push nuclei close together with enough energy that they overcome the electrical repulsion between them. It's actually not hard to do and happens all the time in research laboratories. What is hard is producing a sustained nuclear fusion reaction where you get more energy out than you put in.
As an analogy, imagine that I want to raise \$100 with a lemonade stand at \$1 per cup. (I know, what a price. It's really good lemonade and the cups are big.) I could set up my stand in a good location and sell lemonade to everybody who happens to pass by; it might take a few afternoons to meet my goal. I could have a big sign professionally printed, and hire a dancing girl to go up and down the street singing a song about how great my lemonade is, and take out an advertisement on the TV, and hire a skywriter. I'd sell out of my lemonade in no time! But I'd probably end up having spent more money than I made. Fusion for power generation is in the second state.
