I don't know, For most fusion rockets there is the detonation point exhaust part. I thought it will look cool, so I just added that in. Deuterium Fusion engines will look very close to this. I left those filters just to increase the thickness so no neutrons leaks through, and funny enough, the game thinks that Deuterium is a fission fuel. Whatever.
Very cool indeed, but what is this photon beam doing here?