The first computers were massive Rube Goldberg machines the size of industrial buildings which cost a fortune and were useful only for the militaries of nation states. Now machines with a billion times the number of transistors fit in our pockets.
Projects like ITER and NIF are monstrously complex because they are science experiments where lots of things need to be varied and we don't even know what it is we need to do. An economical reactor designed by people who knew how to make such a reactor would look remarkably different.
With old and new computers, the physics are different - what makes the principles still work is that logics are the same, both have gates, memory etc.
With fusion you still have the same physical substrate you need to affect.
Also you have something backwards in your reasoning. Real production systems are usually much more complicated because they need to stay up all the time, witness real nuclear power plants with their little armies of engineers, operators etc. versus the simple research reactors of old times.
I was not reasoning by analogy, I presented an example that contradicts the claim that machines meant for widespread adoption must resemble their experimental form.
The laws of physics are unchanged, computers improved because of clever workarounds that allowed us to accomplish the same tasks in easier ways. Practical fusion reactors need to produce power via fusion, but beyond that the how is irrelevant. Swap out different lasers, different magnets, different power supplies, hell even the fuels might be different, it's frankly ignorant to claim that these changes are the same physics but "use a shorter wavelength in your fab" isn't.
A modern computer in terms of number of logic gates is astronomically more complex than ENIAC, however what matters for practicality is not complexity but cost. The cost of complexity decreases as you learn what you're doing. Chicago Pile 1 cost $17 million in today's dollars to produce about half a watt of thermal power, or $34,000,000/Wth. A modern nuclear plant costs about $2/Wth. ITER will cost $45 Billion to generate 500 MW. If fusion sees 0.001% of the economic improvement that fission experienced, that's $0.52/Wth.
The conclusion that DT fusion reactors will be expensive follows from basic engineering considerations on heat transfer, not from specifics of any design. The volumetric power density will be lousy, so cost will be high.
> A modern nuclear plant costs about $2/Wth
This may have been the projection before the AP1000 and the EPR flamed out. In practice, the cost can escalate well above that. Their complexity made them difficult to build. And yet, these designs have reactor power densities orders of magnitude better than ITER, and are far simpler (and more fault tolerant) than a fusion reactor would be.
The cost is not a function of volumetric power density. I believe we have had this conversation before.
The most expensive nuclear plant projected to be constructed is the Hinkley Point C reactor. With all its overruns, it's projected that the cost will be £23 Billion, which works out to $3.37/Wth. $2/Wth is a $6 billion 1000 MWe plant, quite typical. Note that this is for reactors in the west, in China, where non-technical issues like NIMBYism aren't a concern, the cost is closer to $1/Wth.
> The cost is not a function of volumetric power density. I believe we have had this conversation before.
Yes, and you failed to make the case that larger things aren't more expensive than smaller things (all else being equal, but note that fission reactors are made of steel, not the complex sophisticated equipment of fusion reactors). We can continue the argument here, if you can come up with any argument for your position that makes any sense.
We have simple research "fusion reactors", to the point where we know a lot about fusion. That's not the hard part. Making the real production system is the hard part.
Projects like ITER and NIF are monstrously complex because they are science experiments where lots of things need to be varied and we don't even know what it is we need to do. An economical reactor designed by people who knew how to make such a reactor would look remarkably different.