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Comment by px43 | Hacker News Reader

The insane thing that people should realize about the 20T CFS test back in September was that it was them completing the first of 18 coils, and it performed incredibly well.

The secret sauce is better high temperature superconductors, and the ridiculous magnets you can build with them. They're pretty much putting these coils together as quickly as they can accumulate the HTSC wiring, and once they have all 18, they basically just need to put them all in a ring and light it up, and in theory they'll be generating over 10x the amount of power that they're putting into it.

This is the kind of tangible progress that gets me really excited. I wish there was a tracker on the CFS site to see how many coils they've completed so far, similar to tracking the progress of the JWST. Last I checked they were estimating completion around 2025, and at this pace that actually seems reasonable.

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ReBCO tape is the specific high-temperature superconducting material they're using.

Another important material is FLiBe, which is a liquid that I think absorbs the energy from the fusion reactor. I don't really understand the properties that make it particularly well suited to the task, but I gather it's important.

https://en.wikipedia.org/wiki/Rare-earth_barium_copper_oxide

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

According to the article, FLiBe has the same heat capacity of water, but a boiling point over 14x higher (1430 °C according to the article). Melting point is 359 °C, 3.5x higher. I will speculate that its basically used as a water coolant with the phase shifts shifted up and out. I bet the heat exchangers are exotic, too, having to operate at such high temps! In fact I'd expect to see a pretty sophisticated cascade of exchangers.

Nitpick, ratios of °C do not make physical sense. For ratios of temperatures you should first convert them to Kelvin, Rankine, or something similar.

Accordingly, the ratio of 1430°C to 100°C is roughly 1703/373=4.6.

The ratio between waters melting and boiling point is amazingly high at 100°C/0°C!

Higher temperatures in the coolant loop are normally desirable for efficiency. In a heat engine, the hotter the hot side, and cooler the cold side, the more energy you can extract after all.

I don't really see why it's important for a fusion reactor though, where efficiency isn't really a concern at this point.

Efficiency is the main concern for a fusion reactor!

We've known how to produce fusion reactions for a long time, the difficult part is to generate net energy.

Well, the energy output of the reactor is limited by the amount of energy you can get out, which is limited by how much coolant you can move through it and how much energy the coolant can absorb without boiling/exploding. The MIT SPARC/ARC reactor designs are physically rather small, so it's possible that heat exchange could be the limiting factor in power output of an individual reactor.

typo, I guess: the melting point is 459 °C, 359 degrees higher than water but 4.5x higher.

It captures neutrons and breeds tritium, which will be separated out and used to fuel the fusion reaction.

https://www.sciencedirect.com/topics/engineering/breeding-bl...

The relevant breeder equations, since I was wondering how to create tritium by neutron capture without deuterium:

n + ⁷Li → T + ⁴He + n′

n′ + ⁶Li → T + ⁴He

(and ⁴He + n → D + T)

It didn't help that I was scanning the equations for ²H and ³H, not D or T.

> they basically just need to put them all in a ring and light it up

Well, if that's not under understatement... There are surely many more challenges in the high-field line of research, probably more than we know of, since they're kind of pioneering this field. Large size tokamaks, depsite their huge costs, have some considerable benefits like longer timescales for MHD instabilities and smaller stresses (both thermal and mechanical).

> in theory they'll be generating over 10x the amount of power that they're putting into it

Does this mean 9/10ths of the power can be sold and the other 1/10th can be re-used to power the reactor endlessly?

How much power does this produce compared to a nuclear reactor?

> Does this mean 9/10ths of the power can be sold and the other 1/10th can be re-used to power the reactor endlessly?

In theory, yes, but in practice it doesn't. But it does mean that they'll've proven the concept sound, and we can start making real fusion reactors.

> Does this mean 9/10ths of the power can be sold and the other 1/10th can be re-used to power the reactor endlessly?

No: https://youtu.be/LJ4W1g-6JiY

That video's a bit confusing because it purely talks about watts and not everything is continuous.

Anyway, the important part: In addition to the output being thermal, with losses from conversion, only the energy going into the plasma is being counted. So measuring the entire system, this reactor might still be a little short of break-even.

So they arent counting magnets/magnetism as a source of energy like a battery then? However I'm sure these newer stronger possibly more directional/controllable batteries will have an effect in electric motors in the future.

I think the newer higher temperature super conductors helps, but then I wonder if the cooling facilities of the older generation of super conductors might have been a potential future safety feature on earth but not in space.

Shows how much progress begets progress.

There was alot of debate about spending so much money on the large hydron collider when there was other social programs the money could be spent on instead of probing the fundamental nature of the universe.

LHC actually paved the way for commercial production of novel superconductors and magnets, leading in some way to helping fusion become a reality. In my opinion, Fusion and solving death should be my generations guiding star. (i'm 26)

yea, just "draw the rest of the owl" :-D

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