eli5: To make fusion energy viable, we need to get out more energy than it takes to actually run the process. But doesn’t that contradict the laws of thermodynamics (getting more energy out then you put in)?
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No, because E=MCC (C squared). It’s that trick of squatting the speed of light that makes converting mass into energy so appealing. Once we get the physics right to contain the plasma in a fusion reactor, we’ll have boundless energy available with minimum radioactive byproducts to deal with.
There was a podcast last week on BBC that explained this and why it doesn’t Curious Cases of Rutherford and Fry
You’re neglecting the fuel that’s consumed. In the case of fusion the fuel is hydrogen, and mass of the fuel is consumed. Energy input is needed to maintain pressure and to start it up in the first place, and that’s what is being talked about when talking about energy input.
Think of like a regular fire. You need to put energy in to start with a match, you need to recycle some of that energy to keep it warm (which is why blowing a fire puts it out, it blows away the residual heat which is needed to gassify the solid fuel and maintain the fire) and you get energy out.
It’s like with a fire: You put in fuel and you get heat out which you can then use to make electricity or whatever. All of the energy was already present in the fuel, so we are not violating any laws. But we are getting more *usable* energy out than we put in.
Technically, we aren’t getting more energy out. We are just getting energy out in a different form.
That energy starts stored in fuel, and (ideally) ends up as electrical energy. Fusion is the process we use to convert it from fuel to electricity. We’ve got loads of fuel, and want electricity instead.
Fusion produces energy from the interaction of the bonds between the particles in an atomic nucelli. Each atomic nucleus is a bundle of protons and neutrons which is overall has a positive charge.
To get fusion to happen, we have to shove those atomic nuclei together close enough for them to react. Because of electromagnetism, where like charges repel each other, it takes a massive amount of energy to get the two nucelli close enough together to interact reliably. In the sun, the energy comes from the gravity of the star, but outside of a star, we have to provide it in the form of heat and magnetic fields.
That’s the energy we’re putting into the system.
When the two nucelli do end up interacting and combining, however, the change in the bonds between the protons and neutrons of the two nucelli becoming one atomic nucleus and some byproducts that fly off results in a massive amount of energy being released.
That’s the energy we get out of the reaction.
For fusion to be a viable source of energy, we need to get more energy out from the nuclear reaction than we’re putting in to get the reaction to happen.
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