Yes, it does. This follows from the fact that structural mass is proportional to stored magnetic energy, just as the mass of a pressure vessel is proportional to volume x pressure (for materials of a given strength).
Viewed another way: if we double B, we quadruple the forces on each segment of conductor, and therefore must quadruple the strength of the supports.
I explicitly said "support structure", the structure that is resisting the force of the magnets. There are other parts that scale more slowly, but I don't need to show that all components scale poorly to show that overall there are diseconomies of scale.
Note that this is NOT like in a fission reactor. In a fission reactor, everything scales just about linearly with power.
> I don't need to show that all components scale poorly to show that overall there are diseconomies of scale.
Yes you do. If A represents 0.001% of the cost then increasing it by 20x doesn’t matter and the support structure is cheap.
Same deal with a fission reactor there’s several diseconomies of scale for example around the length of control rods passive cooling after an accident etc, most of them just don’t matter much.
You do realize that almost all the mass of a PWR reactor is steel, right? The steel pressure vessel, steel supports for the fuel bundles. So the argument you are making there is that the mass discrepancy between fusion reactors and PWRs grossly understates the difference in cost.
In a separate line of inquiry, this is what I’ve been thinking about wrt fusion lately. Even if the “fusion” part were free, how much would the electricity cost just based on the steam generator turbine part? (More generally, the sum of all the non-fusion parts of a fusion power plant)
Further, if electricity from a fusion plant were effectively free (like it didnt need turbines or something) what would large-scale desalination cost even if it did use truly free energy? This is what I’d be excited for from fusion power, because potable water scarcity is a huge upcoming/ongoing problem in some developing nations with very large populations.
Nuclear fission and fusion power plants can use sea water for most of their needs no need for desalination when you just want thermal mass. Remember nuclear subs operate under the ocean.
Deuterium requires processing a great deal of water, but can be moved around the world cheaply at the levels needed for fuel.
As to the costs of fusion or fission power if the nuclear bits were free, it’s roughly half the cost of coal.
I meant the economic effects of using fusion as a cheap energy source to provide drinking water to ~1 billion people or so (some part of the population who live in places which currently cannot afford to provide their citizens with proper potable water). Desalination uses a ton of electricity. It's a very significant portion of the cost (~50%). But even if the energy from fusion was magically absolutely free, it would "only" reduce the cost of desalination by about 50%. This might not be enough for those who need it.
It's a parallel to how with a fusion power plant, even if the reactor only cost $50,000 (some comically small amount near zero), the electricity from the overall power plant connected to the reactor might still be fairly expensive. Like - if you have access to free steam, is turbine generation actually cheaper than solar? Even assuming absolute best-case, fusion's place might not be "lowest cost source of energy" but rather "a notably cleaner and lower-cost base load" which can provide electricity when weather causes the solar and wind farms to underproduce. In 30 years in developed nations, its competition will be batteries, pumped hydro, and other energy storage farms.
Ops accidentally removed: Compared to PV free energy might reduce the cost of desalination by 1/3, but fusion isn’t going to be free.
The core issues is drinking water is isn’t generally a lack of water. People in rainforests still have issues getting clean water because maintaining a distribution system requires a functioning society/government which simply isn’t available in extremely poor countries.
Similarly keeping water supplies drinkable requires pollution controls which is basically non existent in such countries.
Yep - so it's kind of a check for "Am I overexcited about fusion energy?". Seems like it would be nice to have the fusion option if it works out but we can maybe get the same benefits promised by fusion from wind + solar + a few days of energy storage. Either way it doesn't seem like it will be truly revolutionary at this point - as you showed, our problems are bigger than just cheap/clean energy, and we do have seemingly viable options for that on the near horizon anyways without fusion.
I'm pro-fusion, I'd like to see more resources allocated towards its development, but my outlook on its potential impact is very tempered.
Again that would be more relevant if that was the only fission specific cost. That giant concrete building designed to survive an aircraft strike etc isn’t cheap. The equipment for handling spent fuel including the cooling pond and safety systems is more expensive than the reactor.
Fuel rods end up 0.6c/kWh and on top of that requires weeks of downtime for refueling etc. People hear nuclear reactor and think that’s the most expensive bit, but it’s really not.
I personally doubt fusion will be cost effective vs renewables + storage, but there’s reasons to suspect it could beat fission at scale.
Viewed another way: if we double B, we quadruple the forces on each segment of conductor, and therefore must quadruple the strength of the supports.
I explicitly said "support structure", the structure that is resisting the force of the magnets. There are other parts that scale more slowly, but I don't need to show that all components scale poorly to show that overall there are diseconomies of scale.
Note that this is NOT like in a fission reactor. In a fission reactor, everything scales just about linearly with power.