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Comment by elondaits | Hacker News Reader

According to the NY Times:

"The government official, who spoke anonymously to discuss results that are not yet public, said that the fusion experiment at NIF achieved what is known as ignition, where the fusion energy generated equals the laser energy that started the reaction. Ignition is also called energy gain of one."

https://www.nytimes.com/2022/12/12/science/nuclear-fusion-en...

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That's not ignition https://en.wikipedia.org/wiki/Fusion_ignition . They are redefining ignition to make the current improvement more trendy, but they are very far away from true ignition.

The lasers at NIF provide both the startup energy and confinement. They can't just shut them off because then they would lose confinement.

Does the laser radiation really contribute [significantly] to the confinement? I always assumed once the energy has been deposited into the outer layer of the target, it is the material of the target doing all the work, i.e. heating and confining the fuel.

The laser energy is converted to x-rays by the gold cylinder. But the cylinder only has a conversion ratio of 10~20 percent, so the amount of energy that gets deposited on the capsule is much lower.

Can they harvest the (electrical?) power to keep the laser running from whatver form of energy the fusion provides (radiation, heat?)?

No. They are not near a power plant yet.

This is not how it works at all. The confinement is produced for a tiny fraction of a second by the inertia of the fuel pellet casing which is driven inward by ablation from a powerful pulse of light. It’s the same basic mechanism as an H-bomb, except unlike an H-bomb, this uses lasers instead of a fission (A-bomb) trigger. And is MUCH smaller.

You left out a whole step. The X-rays.

Because NIF can also potentially use the UV lasers directly, without converting to X-rays in the Hohlraum. Direct drive would be more practical for an actual power plant version: https://en.wikipedia.org/wiki/Laser_Inertial_Fusion_Energy#M...

So instead of “x-rays” I left it as the more general “light.”

It's amazing how people even in hacker news just say whatever they want with absolute certainty.

This is ignition but ignition was achieved by their August 2021 shot. See this paper for the details: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.12...

The reason why it's a big deal is because they surpassed scientific breakeven.

And based on how NIF is set up, ignition and scientific breakeven occur at around the same spot.

ICF isn't MCF, but yes, they already had ignition earlier. This is net energy gain if you draw the line at the energy in the lasers (even before the conversion to UV, much less x-rays).

https://archive.vn/vteLJ

Related Wikipedia on Fusion Ignition:

- https://wikipedia.org/wiki/Fusion_ignition

And additional news source:

- https://www.theguardian.com/environment/2022/dec/12/breakthr...

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