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US scientists repeat fusion power breakthrough (www.afr.com)

submitted 1 year ago by [email protected] to c/[email protected]

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[-] [email protected] 25 points 1 year ago* (last edited 1 year ago)

https://archive.is/pM7Q0

tl;dr: net positive fusion, though only if you count just the laser energy, not the total power used to run the system

[-] [email protected] 4 points 1 year ago* (last edited 1 year ago)

I don't think that that's necessarily a huge issue, though, because their aim wasn't to address that.

That experiment briefly achieved what’s known as fusion ignition by generating 3.15 megajoules of energy output after the laser delivered 2.05 megajoules to the target, the Energy Department said.

In other words, it produced more energy from fusion than the laser energy used to drive it, the department said.

A 2020 article, before the current success or the prior one at the same facility:

https://www.powermag.com/fusion-energy-is-coming-and-maybe-sooner-than-you-think/

No current device has been able to generate more fusion power than the heating energy required to start the reaction. Scientists measure this assessment with a value known as fusion gain (expressed as the symbol Q), which is the ratio of fusion power to the input power required to maintain the reaction. Q = 1 represents the breakeven point, but because of heat losses, burning plasmas are not reached until about Q = 5. Current tokamaks have achieved around Q = 0.6 with DT reactions. Fusion power plants will need to achieve Q values well above 10 to be economic.

So if I understand this aright, on the specific thing they're working on, they're at 1.54 as of OP's article, that is (3.15/2.05), up from 0.6 in 2020. The target is somewhere "well above 10" for a commercially-viable fusion power plant. Still other problems to solve, but for the specific thing they're working on, that maybe gives some idea of where they are.

[+] [email protected] 2 points 1 year ago* (last edited 9 months ago)

[deleted]

[-] [email protected] 4 points 1 year ago* (last edited 1 year ago)

To my understanding, here they use lasers to create fusion and the 2 megajoules are emitted by the lasers.

Yes.

Hence they need waaay more power than is generated to drive their lasers.

googles

It sounds like the additional power is due to energy exiting the system:

https://en.wikipedia.org/wiki/Fusion_energy_gain_factor

Most fusion reactions release at least some of their energy in a form that cannot be captured within the plasma, so a system at Q = 1 will cool without external heating. With typical fuels, self-heating in fusion reactors is not expected to match the external sources until at least Q ≈ 5. If Q increases past this point, increasing self-heating eventually removes the need for external heating. At this point the reaction becomes self-sustaining, a condition called ignition, and is generally regarded as highly desirable for practical reactor designs. Ignition corresponds to infinite Q.

So it sounds like additional power requirements effectively means getting from their current 1.54 to 5.

That is also why this research is not actually aiming at power geration, but at fusion weapons.

I am confident that that is not the case. The US knows how to do fusion weapons and has for decades -- that's what a thermonuclear bomb is, the second stage. That's a much simpler problem than fusion power generation. You don't involve lasers or magnets or other things that you use in fusion power generation if you just want a fusion weapon; you only need to force the material together with a great deal of force for a very brief period of time, and then you're done.

this post was submitted on 07 Aug 2023

221 points (97.4% liked)

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