[pfdietz]

ITER doesn't use high temperature superconductors. It uses niobium-tin and niobium-titanium low temperature superconductors in its magnets.

ITER has been criticized since early days as a dead end, for example because of its enormous size relative to the power produced. A commercial follow-on would not be much better by that power density metric, certainly far worse than a fission reactor.

There is basically no chance than a fusion reactor operating in a regime similar to ITER could ever become an economical energy source. And this has been known since the beginning.

I call things like ITER "Blazing Saddles" projects. "We have to protect our phony baloney jobs, gentlemen!"

[cyberax]

> ITER doesn't use high temperature superconductors.

It does, for high-current buses that interface with regular resistive power distribution. They are also planned for some auxiliary components (like the neutral beam injectors).

> ITER has been criticized since early days as a dead end, for example because of its enormous size relative to the power produced.

ITER is NOT designed for power generation. It's essentially a lab experiment to see how plasma behaves in magnetic confinement and test various technologies.

That's why ITER was designed with a very conservative approach to reduce the technical risk. We don't need it to be compact, this can come later. We just need it to work.

And yes, it is necessary. Plasma behavior can't be simulated numerically or analytically. It always provides surprises, sometimes even good ones: https://en.wikipedia.org/wiki/High-confinement_mode

[pfdietz]

> ITER is NOT designed for power generation. It's essentially a lab experiment to see how plasma behaves in magnetic confinement and test various technologies.

That's the go-to excuse. But if you look at DEMO, it's power density is not enormously greater. ITER is so far out of the running that DEMO (or PROTO, etc.) will be too.

We're learning a great deal about something that's largely irrelevant.

[cyberax]

DEMO concept sketches are completely obsolete at this point. It's not going to look anything like this.

They're based on the state-of-the art from about 2005. Since then, a lot of improvements happened. A more realistic power plant design is going to use a thinner center column (because of better superconducting magnets), resulting in a smaller cryostat volume. Possibly high-TC magnets.

It can also be made more compact, if neutral beams can be used to suppress some plasma instabilities.

[Calwestjobs]

misunderstanding about ITER what you some people doing is that it is just one thing, it is not.

ITER is not only facility in france it is multitude of manufacturing capabilities all over the globe which build parts for ITER and all future power plants.

[pfdietz]

It's my understanding that neutron wall loading of DEMO concepts had been trending downward (due to materials limits), the opposite of the trend you're trying to portray there. And in no future world is the power density of DEMO going to be anywhere close to that of a fission reactor.

[cyberax]

Neutron loading is not the limiting factor (for now), it's the magnetic field pressure and its homogeneity. That's actually what is driving the humongous size of the ITER.

To solve the homogeneity problem, you need the central column to be as thin as possible. That's where a lot of the recent advancements can help.

Also, fission research and fusion are actually aligned in designing materials that can tolerate more displacements per atom.

> And in no future world is the power density of DEMO going to be anywhere close to that of a fission reactor.

That's for sure. Modern fission reactors are close to magic, with the amount of heat they produce for a given volume.

[pfdietz]

However, if neutron loading has gone down, and the reactor is the same size, the volumetric power density must also have gone down.

The comment about fission and neutron dpa is misleading. The neutron damage issue is much less bothersome in fission reactors.

Fission produces about 3% of its energy in neutrons, vs. 80% in the DT fusion reaction. The spectrum of fission neutrons is much softer, with a peak around 1 Mev, vs. 14 MeV for DT neutrons. The DT neutrons are above threshold for (n,2n) reactions in most materials, and have much higher cross section for (n,p) and (n,alpha) reactions. The latter is particularly troublesome, as helium accumulates inside materials, forming microscopic very high pressure bubbles that rip the materials apart.

But it's even comparatively worse for fusion than that. In a PWR (for example), the core is carefully designed so that the only parts exposed to unmoderated neutrons are the fuel rods and the replaceable parts of the fuel rod bundles. The latter provide structural support for the fuel rods and are removed along with the fuel rods when the fuel is spent. The actual core supports for the fuel bundles are well away from where the chain reaction is occurring, shielded by water. The mean free path of a fission neutron in water is just a few centimeters, so their energy is quickly dissipated before reaching these components.

So, exposure of permanent reactor components to fast neutrons is essentially a non-issue in PWRs. Even control rods are not exposed much; reactivity is controlled by boric acid dissolved in the water (BWRs do it somewhat differently.)

This same strategy cannot be used in a fusion reactor; the plasma facing surfaces are exposed to the full, unshielded brunt of the DT neutron flux. Maybe a few cm of liquid lithium could be flowed along some surfaces? This is a stretch, particularly in a toroidal reactor.

[adgjlsfhk1]

is a conservative approach useful if it is taking 30 years to build?

[myrmidon]

> I call things like ITER "Blazing Saddles" projects. "We have to protect our phony baloney jobs, gentlemen!"

I think this is overly harsh and somewhat unfair. You could make the same argument that anything operating in a regime similar to the Chicago Pile 1 could never be an economical reactor nor a bomb, but that does not mean skipping that particular development step is viable.

As far as fusion reporting goes, articles are at least somewhat consistent on the fact that ITER is a pure research project/reactor, while every 10-man fusion startup is being hyped up beyond all reason even if there is not even a credible roadmap towards an actual reactor in the 100MW range at all.

Personally I don't see fusion being a mainstream energy source (or helpful against climate change) in this century at all and maybe never, but ITER (even with all the delays) is at least an honest attempt at a credible size, and being stuck on older technology is an unfortunate side-effect of that.

[pfdietz]

I don't think it's unfair at all. And I don't see ITER as an "honest attempt", far from it.

The initial cost figures for ITER were obviously deliberate lies. When the true costs inevitably came out (after commitment had been made) this led to alternative approaches being canned. ITER has done grievous damage to fusion as a field, in a way eerily similar to how the Space Shuttle and ISS have done damage to NASA.

The true purpose of ITER wasn't to achieve fusion or push forward fusion; it was to preserve funding until those making the decisions had retired. If this required sacrificing long term goals, like actually delivering competitive energy (or, really, delivering anything at all), so be it.

[myrmidon]

As an engineer, the difference between "deliberate lies" and "overoptimistic estimates" is often just in the eye of the beholder; Hanlons Razor should be applied IMO.

Was ITER overambitious? Timeline and budget unrealistic from the start? Maybe. But I'm fairly confident that most people involved had perfectly defensible intentions.

I also think that if the goal is commercial fusion, small reactors (100MW and below) are nothing but a stepping stone and inherently commercially useless; I don't see the output (hundreds of termal megawatts) ever justifying the "fixed" overhead costs, and a scale at least close to GW scale seems completely inevitable to me.

If you agree with that premise, then building a reactor that size has a lot of utility already that you'd never achieve from building Wendelstein 7x equivalents or whatever at 50 different university campuses (or however else you'd want to spend the funds instead).

> The true purpose of ITER wasn't to achieve fusion or push forward fusion; it was to preserve funding until those making the decisions had retired. If this required sacrificing long term goals, like actually delivering competitive energy (or, really, delivering anything at all), so be it.

This is what I most disagree with; if commercial fusion is viable (I believe it really isn't) then I think ITER (or an equivalent of its size) is a very necessary, if expensive, step to make, and spending the money on dozens of smaller projects is not an "obviously better long term approach" at all in my view.

I also think that speaking about "true purpose" of the whole project is personifying the output of a complex process way too much, where individual actors in that scheme just want to make ITER happen (for very defensible reasons IMO).

[cobbzilla]

conceptually sure; but size-wise they are so different as to warrant valid questions about ROI.

Chicago Pile 1 ran for 12 years, ITER started ~12 years ago and plans to run into the 2030s at least. Budget and headcount would likely be vastly different too, I’d welcome any educated guesses. Sometimes quantity has a quality of its own, as they say.

[myrmidon]

Sure but those are not really equivalent/comparable in scale; just looking at power/size and conceptual distance from commercial viability, the Chicago pile does not even match up to something like SPARC or JET, much less ITER.

A more fitting comparison to ITER would be something like Fermi-1 or other prototype designs at almost commercial scale, IMO, and those were multi-year, large projects too (and fission is much simpler than fusion, which obviously also helps).

[pfdietz]

The X-10 reactor at Argonne went critical less than a year after CP-1, with a power of 500 kW, rising to 4 MW in 1944. The Hanford B reactor, with a power of 250 MW, was in operation less than two years after CP-1 went critical.

[pfdietz]

Correction: the X-10 reactor was at Oak Ridge, not Argonne.

[robocat]

> phony baloney jobs

I looked hopefully at the HR report https://www.iter.org/sites/default/files/media/2024-11/rh-20... to see if there was some sort of job categorisation - scientist, engineer, management. Disappointingly scant. PhD heavy. Perhaps the budget would be more insightful.

"Execution not ideas" is a common refrain for startups.

I wonder how much of the real engineering for ITER is occurring in subcontractors?

[whatshisface]

I wonder why a physics research facility would be PhD-heavy. ;-)