Could also be that it doesn't make economic sense yet, they're still pretty new compared to classical superconductors.

MRIs are a more mature market, i.e. > 1 units, and need to justify component switches not just for feasibility, but for profitability. Swapping out a known-good for something in such short supply isn't feasible, it's more expensive than liquid helium.

Source: https://spectrum.ieee.org/fusion-2662267312 "Over two years, the team managed to buy up most of the world’s supply of 4-millimeter-wide HTS tape"

I would also say the reason CFS has been getting funding is not because of fusion (although, hey, why not take that longshot bet), but because of the value of being able to make these magnets for non-fusion applications.

REBCO tapes are still very brittle, and MRI machines are notorious for the amount of banging they produce when active.

the gradient coils make the noise, and due to field homogeneity requirements, it is safe to assume the superconducting coil is not moved by the gradient coils

Your mass-energy conversion number is within error of mine, but your estimate of how much power we use is much lower.

https://www.wolframalpha.com/input?i=%2810+TWh%29+%2F+%2817....

Much greater conductivity than what? I assume there are other non-REBCO layers in the tape, but the article neglects to mention them.

If you have two resistors in parallel, the current in each is proportional to the ratio of the resistances. But what if one of the resistances is zero? Then all the current goes through that resistor. So if you have a superconductor in parallel with another resistor, all the current goes through the superconductor! Doesn't matter if the other resistance is very, very low, but still nonzero.

Reportedly some undergrad thought of this.

So the superconducting layer is bonded to stainless steel tape, which is strong, not brittle, and will go down to cyrogenic temperatures without problems. Most previous superconducting "wires" had brittle ceramic insulation, which was hard to wind into magnets.

This is really clever.

Here, since you're using a much higher Tc material, if Tc is lowered by a few K you still have plenty of thermal budget, allowing you to take the hit from the proximity effect but be able to save on insulation.

The article outlines a plate design that incorporates steel/REBCO windings and cooling channels for liquid helium that seems to be modular and easily serviced.

REBCO is actually listed as a high-Tc material in the wiki below, but requires liquid helium.

If this were reworked into a liquid nitrogen design, could it reach 20 Tesla?

https://en.m.wikipedia.org/wiki/High-temperature_superconduc...

https://www.nature.com/articles/s41598-021-81559-z/figures/6

https://ieeexplore.ieee.org/document/10316632

He goes through a lot of the interesting design details, including why REBCO is such a huge difference and will make their commercial reactor design possible:

https://www.youtube.com/watch?v=KkpqA8yG9T4

I'd be curious if MIT / Commenwealth Fusion have made any progress on their "remountable magnets" approach.

The problem is that if you have to replace parts of the reactor, the magnets get in the way. I think they found that you could just solder the ends of REBCO film to each other and even though the solder isn't superconducting, the layer can be thin enough that it doesn't matter. So, they were looking at technology to take a tokomak apart by desoldering the REBCO, then they can replace whatever parts are inside, then solder it back together when they're done.

That seemed like a pretty hard problem, and not one they're trying to solve with SPARC (which is only meant to be a cheap prototype reactor, not something designed for a long service lifetime).

You at least have to give the poor guy credit :). Wankel engines can be found all sorts of places including planes!

https://en.m.wikipedia.org/wiki/Wankel_engine

The fact that it took 3 years is a positive, as it means multiple parties rigorously reviewed and approved the material.

(Normally we prefer the best third-party article to a press release but the balance of information here points the other way.)

Edit: I should say that if there's a more informative third-party article, we can switch to that.

A benefit of stronger magnets is that you can make it a lot smaller, and presumably cheaper -- which is what MIT has been working on with SPARC.

I don't know if it's practical to upgrade the magnets on ITER, but I'd expect it to be really expensive -- especially if they've already manufactured/installed the old magnets.

In the high Tc high field designs, the mass of the metal supports for the magnets dominates the reactor mass.

Why does JxB scale quadratically? Because a stronger field can contain (linearly) more current?

But the JxB force is now quadrupled, because you doubled both J and B.

ITER is not a prototype of a commercial fusion reactor, it's a burning plasma laboratory. Its main goal is to study the plasma confinement technology.

Newer designs will have a much thinner central column and stronger magnets, resulting in much better confinement. And high-temperature superconductors will an order of magnitude cheaper.

Right now, ITER is still needed to get information on plasma properties at the temperatures required for fusion.

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

Check out figure 5 here. The relevant bit is the vertical slice along the left edge. Crtical current density and internal magnetic field both go way up when you go below LN2 temps. You could make an LN2 HTS magnet, it just wouldn't be in the 1T+ class.

https://cds.cern.ch/record/2277484/files/Bruker%20HTS%20Fit....

I dimly recall a graph showing progress on how they were able to fire up the thing and the energy out compared to energy in. That graph had quite a decay on it initially but a really long tail. That long tail is where the always 25 years off meme comes from.

Nuclear fusion as an energy source is a massively complicated beast. You might like to note, say, that building for Hinkley Point C (a fission plant, Somerset, UK - just up the road from here) was started late 2018 and was due to be commissioned in 2023 and now is due in 2030. You might also note that aircraft and the like tend to take 20+ years to go from concept to service. A nuclear fusion plant will take quite a while to commission once a concept has been thrashed out.

Perhaps CF have got it sorted but there is a damn good reason for the always 25 years off "joke" - I was told it over 30 years ago by physicists working and already long time served at the coal face.

Interesting, so what is their timeline for commercial fusion?

Ah, found this: - https://cfs.energy/news-and-media/commonwealth-fusion-system...

from broader context I remember, the 2025 "commercially relevant net energy" means "net positive, and not trivially so, i.e. not for 2 femtonanopicofemtoseconds for 1 of 30 trials if we had a better laser"

Some of it does, the decay chains are wildly variable. Fortunately, the longer the half life, the lower the power output. If Cobalt-60 and Plutonium-242 released the same energy per decay event and you had the same number of atoms at the start, the radiation from the cobalt would be 72,000 times as intense to start with, but equal after 84 years.

But the main point, all things nuclear are so energy dense that in practice there's (relatively speaking) so little of the waste it basically doesn't matter. I've been in single rooms large enough to contain all the world's high level nuclear waste.

> The original bomb scientists really wanted to go with thorium as it has several safety features. One it needs to be pushed to criticality so it can't go runaway. Two its waste is much safer in its duration.

That seems like a flaw for a bomb, which is specifically it going runaway.

But also, it's quite hard to crush uranium or plutonium hard enough to do that. Even with Chernobyl, the fuel was surrounded by stuff designed to make it more energetic (although not as energetic as the actual accident, obviously).

Here's another graph of the same thing, but updated with the actual rather than predicted value for one year after your link was published — and the price decline is back: https://www.statista.com/statistics/883118/global-lithium-io...

> The allegedly low cost of solar energy comes from ignoring battery cost.

Can also solve the same issues with other storage options, hedge with other renewables that are also cheap, and electricity transport is a political issue rather than an economic or engineering problem.

> And the relatively high cost of fission comes largely from overregulation.

The low cost of fission is it being subsidised by the military value.

The regulations exist because even though the mean cost of accidents per TWh is tiny, the upper bound of the damage when they do happen is sufficient to bankrupt superpowers.

Also see https://www.nrc.gov/docs/ML2325/ML23258A145.pdf "Fusion Systems Rulemaking: United States Nuclear Regulatory Commission Preliminary Proposed Rule Language". The NRC are already proposing to regulate fusion reactors much more like particle accelerators (which can produce medical radioisotopes, for example), and less like fission reactors.

Hydrogen is not used yet, because we don't have enough renewables to have significant overproduction. For now storage is not needed.

Truly this is a topic where everyone feels comfortable to throw in strong opinions without having even the slightest idea of how any of it works.

There is no causal relationship between high share of renewables and high electricity prices in Germany. If you have any argument or evidence that supports the causal link, please share. If not please acknowledge that you are operating on gut feeling without a factual basis.

Wholesale prices for electricity have been higher in France than in Germany, they have been much lower in Sweden, which has more renewables than Germany in the system already.

hydrogen isn’t exactly the safest element. not that any element is truly safe if used in the wrong way.

Why would anyone make a plan to use it as a fuel without a plan to generate it? They don't. You breed it in the blanket that collects the energy. The energy balance is quite positive.

https://www.tecaccessories.com/collections/tritium-isotope-f...

Where did he push tritium?

Is the word tritium in the article? (Chrome can't find it.)

Is hydrogen more common than uranium?

Is hydrogen more common than plutonium?

What quote demonstrates "accuse", as in, "they had the nerve to accuse"?

These are honest questions, I hope you don't take offense.

Full disclosure: I live in Cambridge, MA, where MIT is located.

Deuterium and Tritium are the fuels, they have to be. There are lots of other pathways, but they all require even higher temperatures/pressure than D-T, and we can't really sustain even D-T for any useful length of time.

Unfortunately, as we don't have any commercially viable fusion reactors yet, we can't even guess if we can afford to make T in the future.

If you didn't know this you need to pay much more attention to them. IMO, they are the least dubious of all the fusion efforts at reaching a practical reactor, and that includes the DT efforts.

Helion is also going to produce prodigious amounts of excess tritium if their scheme works, which is good news for others trying the DT path (although how they compete against a workable advanced fuel reactor is not clear.)

most elements are safe if you handle them properly. that assumes nothing outside of your control. and no one.

Tesla alone could provide material for nine such reactors annually.

And then there's the beryllium. A single one of those ARC reactors would use something like 40% of the current world annual beryllium production.