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mynewaccount5 t1_j04s54a wrote

Besides being cool, and being another step forward, what is the scientific significance of net positive energy in fusion experiments?

What I mean to say, is generating 2.04 much easier than generating 2.06? Is there some barrier that makes crossing that net barrier so difficult?

In my mind, I am comparing this to a perpetual motion machine. The big barrier there of course are the laws of thermodynamics. The difference between 99% and 100% efficiency is huge because that would mean a fundamental law of the universe is not actually true.

Net positive energy on the other hand seems more arbitrary and perhaps more of an engineering achievement than a scientific achievement since the implications relate more to scale. I know nothing about fusion so am seeking to learn.

(Not to downplay anything, I am just wondering about the scientific implications)

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Shrike99 t1_j05098e wrote

Net positive energy is indeed kind of arbitrary. Hitting Q=1.1 is not substantially more difficult than hitting Q=0.9. There's no barrier or even minor bump to get over, it's a continuous scale of linearly increasing difficulty, and even that scale can vary a lot depending on the specifics.

A comparison I might make as an aircraft geek is that it's not substantially more difficult to make an engine that produces 1.1 tonnes of thrust than one that makes 0.9 tonnes of thrust. As it happens, that's pretty damn close to the thrust numbers of the first and second production models of the world's first fighter jet engine; the Jumo 004.

However, the reason it's significant is that if we suppose that the engine in question weighed exactly one tonne, then the first model would be incapable of lifting it's own weight off the ground, while the second model could. Increasing the thrust by that small amount is relatively trivial and mundane, but the consequences of crossing that 1:1 threshold are profound.

(As it happens the Jumo 004 actually only weighed about 0.75 tonnes, so both versions could in fact lift their own weight off the ground)

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FrickinLazerBeams t1_j06980c wrote

Hypothetically, if the reaction itself is net positive, it means there is is no longer a question of whether physics allows this to work; it becomes simply an engineering challenge to make it practically viable. That's not to say the engineering problem is easy, or is sure to be solvable; but it's a meaningful distinction.

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