topping cycle

noun1

1. •
   The high-temperature power cycle of a combined cycle power plant.

   • The very-high-temperature helium turbine, driven directly by the superheated coolant from the fission reactor, serves as the topping cycle for a mercury-vapor turbine powered by the heat given up by the helium; the mercury turbine itself serves as the topping cycle for the steam turbine that takes up most of the space of the turbine hall.