system
Given the following post, respond as if you're commenting on Reddit:
human
[The Expanse] Just how does the Epstein Drive work?

What is the nitty gritty of how the Epstein Drive works?
gpt
It's a fusion torch. It's similar in principle to a conventional rocket, but except instead of a combustion chamber, it's a fusion reactor. A high efficiency continuous fusion reaction produces a large quantity of high velocity plasma and radiation that's magnetically directed out the back of the ship.

But that design was created before epstien; his contribution was cracking the problem of reaction mass expulsion. Before, the reactors would spit out perfectly fusible hydrogen and helium along with the heavier exhaust plasma species due to limitations in the magnetic containment field technology. 

By stabilizing the reaction mass with cyclotronic superconducting coils that generate bidirectional electromagnetic vortices in the boundary layer between the actively fusing reaction mass and the "cold" exhaust, epstien dramatically increased the power output and efficiency of older fusion torch design.