Various ideas, i don't know what Helion are planning: https://en.wikipedia.org/wiki/Direct_energy_conversion

Touched on here: https://www.euro-fusion.org/news/alternative-fusion-concepts...

The diagram from Helion on that page makes it look basically like a two-stroke petrol engine: a magnetic field compresses the plasma, which then fuses, and the energy pushes back against the field, doing work. I'm not sure my intuitions about lawnmower engines really carry over to fusion reactors like that, though.

Well, of course they do. If 20th century SciFi literature has taught me anything then that there is nothing in high-energy physics that cannot be explained by a metaphor to some good old combustion device or, in exceptional cases, a hydraulic system.

Back when I was looking at fusors (I still have ideas, but no time), there was a suggestion of converting the high-energy charged particles from the fusion into energy by decelerating them in an electric field and then collecting the charge as the speed approached zero; the exact reverse of a particle accelerator putting energy in.

Directly coupling the two processes like that would certainly have some interesting failure modes with regard to potential and phase. If this results in DC power distribution... elephants everywhere will rejoice as Westinghouse's reign of terror ends.

Power transfer from large scale Renewables projects have already precipited HVDC [0].

There isn't an absolutely AC/DC dicotomy as it was in Edison's feud. It all comes down to using the right solution for the right problem.

[0] https://en.wikipedia.org/wiki/High-voltage_direct_current#/m...

Well feeding an HVDC line with something that doesn't already naturally generate AC (like a wind turbine) would be a better fit. But it would be a little strange to not fully exploit the other thing that distinguished the DC system from AC: distributed generation vs centralized generation. What was once necessary due to transmission inefficiency is now desirable due to transmission inefficiency :) (among other things). I guess I'll have to wait a little longer for the breadbox sized fusion reactor, though I wouldn't turn up my nose to a residential fission option.

Yeah. This is something you can do only when the outputs of a fusion reaction are mostly charged particles moving quickly. If most of the energy comes out in neutrons, as in deuterium-tritium fusion which most fusion reactor attempts are using, you have to run the resulting energy through a heat engine to produce electricity.

Which is why Helion is going for direct conversion, given their mostly aneutronic design.

I don't think that idea can be made to practically work, due to space charge limits.

I don’t doubt something will cause problems, given this is 1-20 megavolts at (for a gigawatt reactor) 50-1000 amps, but I’m not sure what issue you’re describing here. Can you elaborate?

Space charge is the accumulated effect of the charge of ions or electrons altering the electric field. It limits current flow in vacuum tubes, and also limits the current density (and hence thrust density) of ion engines.

https://en.wikipedia.org/wiki/Space_charge#Space-charge-limi...

> (I still have ideas, but no time),

You do have the money?

Easily, fusors are Highschool-project cheap.

That's the headline, but you'd need about $10k of kit if you're handy at digging through trash to put one together.

> This releases energy, and the plasma expands, pushing back on the magnetic field. The change in field induces current and thus electricity to power electrical loads (Figure 1).

As I understand it, they inject two plasmoids into the central solenoid, then compress the merged plasma by increasing the magnetic field there. After a short burn, the magnetic field there is reduced, with the (now hotter) plasma pushing against it. In this last step energy can be withdraw from the magnet and recovered.

The last step is the one I'm wondering about. You can't just put an electric cable near a 7T magnetic field.

I think you use an opening switch to divert the current in the magnet into an external load. And yes all the conductors in the magnet experience strong forces; some 60% of the mass of ARC is the stainless steel support needed to resist JxB forces.