Systems and methods utilizing successive, axially symmetric acceleration and adiabatic compression stages to heat and accelerate two compact tori towards each other and ultimately collide and compress the compact tori within a central chamber. Alternatively, systems and methods utilizing successive, axially asymmetric acceleration and adiabatic compression stages to heat and accelerate a first compact toroid towards and position within a central chamber and to heat and accelerate a second compact toroid towards the central chamber and ultimately collide and merge the first and second compact toroids and compress the compact merge tori within the central chamber.