ToughSF wrote a nice blog post trying to design a functional Epstein drive. He ended up choosing Deuterium and Helium-3 fusion reactions (which create little neutrons but lots of protons) happening far behind the ship to prevent overheating, picked up by a very strong magnetic field to provide thrust.

http://toughsf.blogspot.com/2019/10/the-expanses-epstein-dri...