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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.

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.

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.

> 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.

> 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).

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

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)

> Theory dictates that with stronger magnets, the reactor can be scaled down (with the square/cube, can't remember exactly), and thus cost and time to develop

OTOH, in a tokamak, the plasma volume (and potential energy output) scales quadratically with the torus' aspect ratio (ratio of major to minus radius), so I'm not sure that tokamak-based fusion really is particularly suitable to miniaturization.

I had no idea, thanks for sharing.

Again, I'm very much a layman to this subject, but how does miniaturization necessarily affect that particular aspect ratio? Since it's literally a ratio of two dimensions of the torus, shouldn't this be invariant to the overall size? (Assuming all things being equal, which I have no idea whether holds.)

Wouldn't the aspect ratio remain constant as you scale down?

Unless you forget to hold the shift key as you drag.

This guy clearly does nuclear fusion.

You win HN for today...

Tokamak output scales with the square of reactor volume but the fourth power of magnetic field strength, so with sufficiently powerful magnets, scaling down the size can be an option.

This technical deep-dive by Dr. Dennis Whyte goes into the scaling considerations: https://www.youtube.com/watch?v=rY6U4wB-oYM

TLDR: Tokamak economics scale in size with 1/B^5 -- so doubling the magnet field strength reduces the physical size substantially. This factor dominates other scaling parameters by a substantial margin, and is entirely enabled by high-temperature superconductors. A host of other key fusion parameters also scale beneficially with B^x (for some value of x) -- most of which are discussed in first half the video.

However, you as you scale down, all the radiation damage effects per unit volume or unit surface area increase rapidly causing higher material activation and maintenance cost.

Miniaturization has never been realistic with tritium fusion anyway due to neutron production - you need several metres of material to stop them, otherwise your reactor is just kicking off radioactive oxygen into the atmosphere.

> Theory dictates that with stronger magnets, the reactor can be scaled down (with the square/cube, can't remember exactly), and thus cost and time to develop

Here's the quick summary:

B: magnetic field strength

R: length scale

Fusion rate ∝ (plasma pressure)^2 ∝ B^4

Energy gain (Q) ∝ R^1.3 B^3

Power density ∝ R B^4

Cost ∝ R^3

So, say for example you're targeting a fixed Q. Doubling the magnetic field strength results in R1 = R0 / 2^(3/1.3) = 0.2 R0. And 0.2 R0 translates to 1/(0.2)^3 = 0.008 = 0.8% the cost.

The scaling is absolutely insane, and a stronger magnetic field has other advantages (such as making plasma instability far less of a concern), though structural loads can be an issue (that, at least is a relatively straightforward engineering problem).

If you take 12T for ITER and 20T for SPARC, that's not actually 2x, it's 1.67, which translates to 30% the size and 3% the cost (and time). It should also be noted that this is just rough, order-of magnitude estimation, but it should be broadly accurate.

For a more detailed explanation: https://youtu.be/KkpqA8yG9T4

To be fair, the main reason instabilities are less of a concern is wrapped up in that B^4 scaling.

I understand there's a bit more to it than that.

Here's the section in Professor Whyte's talk: https://youtu.be/KkpqA8yG9T4?t=2215

> It's even more subtle than that, in fact this is really one of the things we've studies at MIT, is that there's other things that come in terms of benefits, particularly when you make the magnetic field very high, it basically starts to tame, just all of the whole suite of plasma instabilities that exist.

There's no such thing as a room temperature super-conducting magnet. You are talking about "high temperature" magnets, which are YBCO tape magnets. High temperature, in this case, means about -290 degrees F.

The next breakthrough that will come will be YBCO powder-in-tube wires, that will allow much stronger fields than currently. They'll be here within a decade, probably much less, as working prototypes exist now.

Anything that is warmer than liquid nitrogen is room temp for scientists.

It's easy to produce, handling is well understood and cheap.

> -290 degrees F

-273.15°C == −459.67°F

I think they were referring to the boiling point of liquid nitrogen, at around -196°C, not being cooled by nitrogen being what makes them "high temperature".

Yeah, you're right. That was a typo and now I can't correct it.

I'm not sure what "high room temperature" would even entail :)

I'd love to work at CFS. Cambridge, MA is right down the road from me and there is no greater cause right now than fusion energy in my opinion.

Why though, we already have Nuclear energy, we could easily build enough that it could power the world's energy needs. The issue is storage, until we have a revolutionary storage solution very little will change with fossil fuel usage.

However! fusion plants are much larger than fission cores, and the neutrons are an order of magnitude more energetic, so you wind up with both way more mass and way higher activation.

Storage is an issue for the other renewables due to intermittent peak power. Fusion should be able to operate like a traditional power station.

Did you mean power storage or waste storage?

At this point, I think fusion has the best chance of saving us from ourselves wrt to climate change, so long as the unforeseen consequences aren’t too bad.

It doesn't seem like it's quick enough. We're, at minimum, decades away from it even being built out commonly, and to _really_ save ourselves we should have already replaced a substantial portion of the world's energy generation decades ago.

Sure, it may be too little, too late.

You don't know that until the failure is complete, though, and "it may fail" is a terrible reason to not try the best shots we have.

I mean, it _will_ fail at stopping global warming, there's no "may" about it. It will probably have other positive effects though.

I'm very onboard for any potential fusion power generation, I just don't think it has any hope of saving us from global warming.

Can we use it to put the CO2 back in the ground?

I guess there are some irreversible effects once warming reaches a certain threshold however.

Yes, this is part of what would need to happen: using a super abundance of essentially carbon-free energy to do geo-engineering on a massive scale (including artificial carbon sequestration).

It might in the future turn out to be more efficient with a "few" reactors than, say, lots of batteries and wind turbines and solar panels, from a resource perspective. But I think not even that will come true, if we optimize stuff enough, which we will have a long time to do before fusion is here.

Fusion would "solve" the climate change issue, but do nothing in regard to all other crises affecting our environment right now (biodiversity collapse, various sources of chemical and particulate pollution, fertilizer runoff...).

On the contrary, unlimited energy would exacerbate the man-made crises we are having today by further pushing the potential impact of man on its environment.

I remember being nervous about CFS not being able to raise its 100 MUSD target a few years ago. I'm very excited for their results.

There are certainly some exciting projects happening in the fusion world coming up. It seems likely we will start seeing much higher energy outputs, I think for SPARC they are predicting >10x the energy produced as what it will consume (Q > 10).

My biggest question is with the crazy temperatures involved will we ever see one of these things able to run for hours at a time? With SPARC they are shooting for 10 second bursts, so that would double this breakthrough for the JET reactor. Even with the magnetic containment there are components in there exposed to millions of degrees Celsius right? That leaves us with some significant material science problems to solve.

Temperature is high but total heat isn't remarkable. The atoms are moving very fast but there aren't many of them.

Private companies have a big incentive to share the good news and hide the bad news.

What are the chances these guys have a pile of problems they can't solve with their approach, but rather than trying to approach it from another direction like an engineer would, instead they continue development because collecting more investor cash while the investors are unaware of the showstoppers is good employment.

I think at this point it's very likely that CFS will succeed. But economics could be a problem, which is why I'm more excited about Helion or ZAP.

>> Back in November 2021, they raised $1.8 billion from the likes of Bill Gates

<joke> I guess windows will be resetting the house energy provider on each update soon

</Joke>