For magnetic torus (Tokamak) type fusion, there's a few challenges.
1. Getting the magnetic confinement perfect so the plasma does not touch the walls. As that will cool/kill the plasma stopping the reaction. Then keeping the plasma stable for long periods of time to continuously generate energy.
2. The Plasma has to be heated to an ungodly high temperature, several times higher than the core of the sun, because the plasma in the reactor is something like only 2x atmospheric pressure. The Sun can do it a lot cooler than that because the Hydrogen "plasma" there is at an average density much higher than lead because of all the umpteen thousand miles of the Sun's mass squeezing it down. So lacking pressure we can't reach even at the center of the Earth, the temperature needs to be higher to compensate and get the Hydrogen nuclei ramming into each other fast enough and hard enough to fuse.
https://news.mit.edu/2016/alcator-c-mod-tokamak-nuclear-fusion-world-record-1014#:~:text=On%20Friday%2C%20Sept.,Mod%20tokamak%20nuclear%20fusion%20reactor.
I think the record for a Tokamak to contain fusion plasma is something like 6 minutes and change. (ITER in Europe) But there's other issues like temperature, pressure, and time (I guess 24/7 is what's needed?) so other fusion reactors have done better pressures, at higher temperatures but for less time. So the record for "best" is probably really some combination of all three factors.
3. Capturing the energy. The energy from Fusion comes off in heat, photons, and other particles like Neutrons (depending on the fusion reaction being done about 80% of the energy is in Neutrons). Generally speaking, the idea to capture the energy is to have some sort of blanket (Water) around the reactor that catches the neutrons and converts their passage/impact into heat which can then drive a turbine. The trick is that neutrons are slippery, being neutral, so you can't guide them or anything with magnetic fields, and getting them to hit other atoms for heat capture can be difficult. And there's other issues because there's neutrons produced at different speeds. Fast neutrons that can zip through several meters of any kind of blanket or shielding, and interact with nothing, and slow "Thermal" neutrons that are easier to stop and convert their energy into heat.
My completely wild-ass guess-idea to make a fusion reactor work is to instead make a kind of "fusion jet engine" that rather than a torus/Tokamak, it uses a magnetic pinch point kind of like a garden hose sprayer that squeezes the hydrogen plasma down to a narrow point, and that spot is also lit by lasers crossing through the pinch-point that add more energy to get the fusion reaction going. Because it neglects the neutrons produced, this might be an unworkable idea, but then the energy produced may be so much it's okay that it's already "80% inefficient" dunno, maybe a secondary thermal blanket that catches the Neutrons can still be used to run turbines.
But my idea would then be to run that hot plasma jet through Magneto Hydrodynamic Coils to generate electricity. Because you can take coils and charge them and move a conductive fluid or plasma through them, or vice-versa, run a conductive fluid or plasma through the coils and generate a charge. The nice thing is, if it can even work, is there's no moving parts other than the plasma. And it's directly taking that plasma's energy and converting it into electricity, so in theory, there may be fewer losses due to conversion.
The trick if this is workable at all, would be how and if the fusion at the pinch point adds enough energy and movement to the plasma that the MHD coils could pick up electricity from it. Or do the magnets that confine the plasma take more electricity than the MHD coils would get? Or does doing that "kill" the plasma too fast?
No clue. Not Birdman.
