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Comment by ck2 | Hacker News Reader

LHC didn't make me nervous and I laughed somewhat at the people who sued to keep it off for fear it might end the world.

This one however, I dunno. Sounds like things could go wrong with that much energy. When they made the first atomic bomb, they had theories about what might happen but not 100% sure and there were some surprises.

But I'll take death from this over death from fracking.

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It's actually a lot less energy than it sounds like. The temperatures will hit 10-100 times the temperature of the sun, but the density inside will be very very low. This thing couldn't vaporize a car.

Remember, this is only a 500 megawatt device, and the reaction is so unstable that if it somehow escapes the containment of the device it dies instantly. It can't "run away" like some fission reactions can.

edit: Not actually sure how much energy it takes to "vaporize a car in seconds." In terms of energy this thing is roughly equivalent to any other fairly large power plant.

Exactly right. Fusion is not at all like nuclear fission. It's so incredibly hard to maintain the reaction that any catastrophic failure stops everything.

There's no unrequested fission surplus situation possible here...

> but the density inside will be very very low

The density is not that low, but the total amount of ultra-hot matter is pretty small. If magnetic confinement is lost, the plasma will expand and cool; there is no sustained fusion without the confinement. The core would probably be wrecked, but that's about it.

"The density is not that low, but the total amount of ultra-hot matter is pretty small."

I'm sorry but I don't understand the distinction.

> I'm sorry but I don't understand the distinction.

While its contained, the density is not that low; if it loses containment, the density will become low as it expands. At least, that's my understanding of the distinction here.

It's more about containing it within the walls of the container than within a very small subsection of the container. The whole thing will be at a pretty serious vacuum throughout operation.

I should probably disclaim: I worked on a Tokamak in undergrad.

Loss of containment is expected, and is more or less trivial. The result is that the fusion plasma simply expands or runs into the side of the reactor wall. This may sound dramatic but it's not. We're talking about at most a few grams of hot gas/plasma. In reality it's not any more significant than running a welding torch or a plasma cutter. As for the fusion reactions, they require the high pressure and high temperature conditions of containment in order to operate. Once containment breaks down the fusion reactions stop.

Don't let ignorance fuel fear of technological advancement.

There's much less scope for catastrophic failure, because the 'bottle' is falling apart and being reconstructed repeatedly by design: There's not a lot of evidence it can be made completely stable but it only needs to be stable for long enough to be energy positive.

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