Speaker
Description
For a reactor based on the Spherical Tokamak, it is very likely that the device will need to be completely non-inductive for the majority of the plasma ramp-up and steady-state phases, due to the limitations imposed on the central coil assemblies by the compact design. Efficiency gains from solenoid-driven current cannot be relied upon. What’s more, it’s critical that an electricity producing plant maximises the wall-plug efficiency of its heating and current drive system, as one of the largest users of recirculating power. The combination of these requirements necessitates an optimal design for the spherical tokamak heating and current drive system in order to meet goals of net electricity production. The UK’s Spherical Tokamak for Energy Production (STEP) reactor design program has recently taken the decision to use exclusively microwave-based heating and current drive actuators for its reactor concepts. We present the optimisation of a microwave current drive for a spherical tokamak reactor, based around the STEP concepts, arriving at a solution which overcomes the limitations imposed by the spherical tokamak for microwave access and high trapped particle fraction. Consideration is given to how the optimal configuration for the plasma flat-top operating point performs during the low density non-inductive current ramp phase and how this may impact the design choices for the STEP ECCD system.
