Why exactly do you think fusion offers "nearly unlimited" power? In any design conceived today, it is in no way impressive in terms of power/plant, and fusion power plants will be the most expensive power plants ever designed (since they are at the extreme limits of materials science and several other branches of engineering).

Exactly - IF we can get it to work, we'll know much more.

And IF we can do it affordably (these are both big IFs), the amount of energy available is huge. I see 1 gallon of water to 300 gallons of gas numbers thrown about; that's huge.

https://www.energy.gov/science/doe-explainsdeuterium-tritium...

(Gotta love their optimism - "when").

As Hamlet says, "It's as easy as lying."

Not "unlimited", but "more than anything else".

We know the energy density is there, based on thermonuclear weapons.

Yes, the designs for a power plant that are similarly impressive don't exist today. That's where research and engineering can help.

Yes, any new thing is expensive. These points are not necessarily intrinsic to the process.

> Yes, any new thing is expensive. These points are not necessarily intrinsic to the process.

It's not expensive just because it's new, it's expensive because it's trying to do a very very difficult thing - using magnets to achieve what the entire mass of Jupiter can't achieve, compress hydrogen so much that it starts fusing, and then keeping it compressed while it's essentially violently exploding - and exploding in a rain of extremely fast heavy particles that don't interact with the magnets at all.

What part of it do you think is intrinsically expensive? The steel? The concrete? The magnets?

Yes, the steel required to withstand the force of the magnets, and to be dense enough to prevent hydrogen from leaking, magnets powerful enough to contain thebl fusion reaction, cooling systems to keep the superconducting magnets in close proximity to the neutron rain at extreme low temperatures.

These are all the parts we know about. Then, there are all the systems that no one has attempted yet that you will need to actually extract some energy from the whole thing, and to inject fuel into the running reactor, and to recycle tritium.

Overall the reactor vessel has to be built similarly to a high-pressure submarine, but it needs to withstand even higher forces. Not exactly something that can be done cheaply, even though we have been building submarines for a good 50 years.

All of that requires a lot of capital, but what makes it expensive is the neutron flux ruining it in just ~5 years.

Fusion is likely to be useful in situations where renewables are just not feasible. For instance, anything large that moves (large boats, spacecraft, or even aircraft) or has no limited to sunlight (bunkers, deep space outposts, etc).

Fusion, at least of the most commonly pursued DT variety, is terrible for mobile applications since its power density is so low. The ARC reactor concept (190MW(e)) weighs as much as several WW2 destroyers.

I'm going to go out on a limb and guess they modern fission plants that are not designed with portability in mind also have really low power densities. Just imagine the weight of the cooling towers. And yet, very different designs with different requirements can be made to fit in a submarine.

I'm not saying it's going to be possible to run container ships on fusion, just that using a fixed research reactor as a data point probably isn't very useful.

Actually, no, fission reactors have much higher volumetric power density. This is inherent in the technology -- in a fission reactor, coolant flows through the core, with large surface area for heat to transfer from the thin fuel elements. In a DT fusion reactor, the coolant has to flow in a blanket around the core, and all the power has to radiate through the surface of the reactor itself. The square-cube law comes into play.

Doesn't fusion still require vast amounts of water to turn to steam?

From my understanding this is almost entirely an engineering problem at this point. The physics behind it has been understood for decades so I'm not sure how much more we'll gain in terms of fundamental physics.

There is still a great deal to be learned about plasma fluid dynamics. Probably the only good that will come out of all the work is a few generations of plasma fluid dynamicists. Pray they can find something else to do when the whole project finally fizzles out.

Well, it's not as if any of them were going to work on solar or wind power anyway, so what does it matter to you?

They are not who is consuming the $billions.

Then why the pearl-clutching over the plasma fluid dynamicists?