There is one variant called Magnetized Target Fusion that kinda-sorta works like this, where the “cylinders” are made of liquid Lithium. On each “stroke” of the engine:
A rotating chamber of liquid Lithium is spun to make a cylinder of liquid metal
500 pistons situated at the site of each spinning Li pool are precisely synchronized to push the liquid metal inward, turning it into a sphere
Fusion fuel (H plasma) is injected into the middle
The intense pressure forces the fuel to undergo fusion, pushing the pistons back out and distorting the Lithium back into a cylinder
There is one variant called Magnetized Target Fusion that kinda-sorta works like this, where the “cylinders” are made of liquid Lithium. On each “stroke” of the engine: