I just realized it's THAT Helion. Their fusion experiments are not without controversy.

Here's a video on explaining how it works:

https://www.youtube.com/watch?v=_bDXXWQxK38

And here's a video explaining what's wrong with the scheme:

https://www.youtube.com/watch?v=3vUPhsFoniw

But the TLDW version is that environment required for fusing He3 with deuterium also leads to deuterium fusing with itself, a reaction that creates neutron radiation that irradiates its environment.