This seems to be p-11B fusion via electrically accelerating protons to collide with slow boron nuclei, producing three ballistic helium, or alpha particles, and gamma radiation. Under normal thermal conditions this would need to be many orders of magnitude hotter than e.g. D-D fusion attempted in earthbound projects. Guessing two alphas come out neutral and the third positive, with kinetic energy that can be extracted magnetically. If the boron were ionized, more of the alpha particles would be, too. It is not clear how they get thrust from it. Much of the gamma radiation can be converted directly to electrical energy to power the system.
They say the fusion boosts the thrust by 50% over a simple proton beam.