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Comment by elihu | Hacker News Reader

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

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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.

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.

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!

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.

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