David Kirtley

And that's the temperature that traditional fusion folks have really focused on getting to.

That's the threshold.

When you get to 100 million degrees, you're at the operating point of fusion and you know it works, colloquially anyway.

Helium-3 requires higher temperatures.

That's not enough.

Yes, fusion happens for helium deuterium and helium three at 100 million degrees, but it's not its optimal temperature.

And in fact, in a high beta system, the optimal temperature is higher 200, even sometimes 300 million degrees.

So you have to get to even higher temperatures.

Temperature's hard.

And so you have to push to even higher temperatures than you had before.

And so that's one of the downsides.

The other downside can be as you get to those higher temperatures,

We talked about B squared is in T. B squared is density times temperature.

Well, for a given magnetic field, density and temperature are now inverse.

So as I increase temperature, density decreases.

And so now you have an issue of you may have less particles to do fusion, which means your fusion system has to get bigger than it was before.

So for the same reaction rates, a helium three system compared to deuterium tritium has to operate at higher temperature and be bigger.

However, the flip side is, is if you can now recover energy at three times the energy efficiency, at 80-some percent versus 30-some percent, and recover all your input energy, then now it's actually about the same size.

Because for the same electricity output, not energy, it's not energy that we're worried about.

It's electricity we're worried about.