I know for conventional fission reactors the heat of fission is basically used to run a steam turbine. Given the extreme heat of the plasma, and that it must be magnetically suspended so that it doesn't even touch the sides of the containment, how is that heat transferred to some other medium to generate electricity?
The energy of the reaction is mostly carried away as high-energy neutrons. So, the way to get energy back is to "capture" those neutrons. Since neutrons are not electrically charged, you can't use them to directly create electricity, so all you're left with is using them for heat.
Unfortunately, since they are electrically neutral, they're also relatively hard to catch. You need a dense material where they will have a good chance to hit some nucleus. The proposed designs are typically some kind of liquid metal blanket being circulated around the reactor and onto a place where it can boil water to produce steam to spin a turbine. Lithium is the metal most proposed for this, since it also has the advantage that it can produce tritium when bombarded with neutrons (tritium being the super rare half of the fuel that goes into the reaction).
https://www.helionenergy.com/faq/
(See "How does Helion generate electricity from fusion?" question)
To entirely skip the steam cycle portion is to intentionally make a much less efficient design.
For space-constrained, high-value, applications where economics don't matter that much, such as a submarine, that would make sense, but otherwise...
(I'm still not convinced of their explanations, but a fast proton may be easy to catch by the magnetic field and create the effect they want.)
See the diagram here: https://undsci.berkeley.edu/teach-resources/products-of-deut...
With fuel costs insignificant, your cost per kWh is mainly capital cost. Let's say it's all capital just to keep it simple. I don't know how much the input energy will be but if your choice is between, say, generating net energy of 50MW without a turbine or 54MW with a turbine, then you would skip the turbine if it adds more than 8% to the capital cost. I suspect Helion has done this calculation in detail.
Helion's other fuel is helium-3 which they'll make themselves by fusing deuterium. So the helium-3 cost will directly depend on the capital cost of the reactor producing it.
(This may be the same reactor, both generating electricity and breeding He3. Or they may use dedicated He3 breeders, and minimize the D-D reactions in the generators.)
However, D+T fusion is the only type of fusion that we have been able to sustain for any significant amount of time with reasonable energy inputs. What Helion is planning to do is completely unexplored and requires some major scientific advances.
Still, it seems very indirect. Like generating solar power by using a parabolic mirror to heat water instead of photovoltaic panels... but of course I just found an example of doing that too: https://en.wikipedia.org/wiki/Parabolic_trough
Usually the liquid is some sort of oil that csn reach higher temperature and then the oil is used to heat water
Another design uses hundreds of mirror centered around a high tower with molten salts as the heat medium
The really good part of this design is that the molted salts can produce energy for 3-4h after the sun is set.
The 90% efficiency quoted in the comments is 90% of theoretical maximum efficiency. This theoretical maximum is about 50% for the best systems.
For the German-speaking crowd here, the Alternativlos podcast guys were there twice and had lengtly conversations with the researchers there. Like, between nerds. Really cool, if you understand the language.
https://alternativlos.org/36/ (from 2016)
https://alternativlos.org/51/ (most recent, from may 2023)
https://omegataupodcast.net/312-the-wendelstein-7-x-fusion-e... (from 2019, 3Hrs, English)
This one in particular isn't setup to do that, and as far as I know, none are yet. It's a pretty simple engineering problem, and, until we can maintain fusion for months at a time, it's not really something that needs to be built.
There is, however, one fusion concept that shows some promise that doesn't require all that that helion energy is developing (helionenergy.com) they're yet to create net-power, but, their idea has some promise, and avoids the common problems with other forms of fusion power. I don't really see it as the be-all to end-all in the space, but from what I can tell they very well might be the stopgap that is needed between large scale stellerators and fission.
That doesn't entirely follow. 2 particles whizzing past each other at relativistic speeds have extreme temperatures but don't offer much energy. Mass is in this equation.
Jumpjng back up the stack: photon radiation is mostly considered a loss since it transfers energy out of confinement and does not impart it on other fuel. You nominally extract your heat via neutrons: same as fission reactors. Some designs (Helion) aim for reactions with charged byproducts. The reaction produces a current that can be coupled by a surrounding coil, much like a transformer but powered by current induced by plasma rather than another copper wire.
But it sure is fun to dream!