Optimization of CFETR confinement by controlling rotation shear and pedestal collisionality

Optimization of a CFETR baseline scenario (Chan et al 2015 Nucl. Fusion. 55) with EC and NB H{\&}CD is performed using a multi-dimensional code suite. Rotation shear is controlled using NB, with injection angle being constrained to avoid edge heating and to maintain q\textunderscore min \textgreater 2. The NB power is adjusted to keep the plasma fully non-inductive. The NB energy that maximize the fusion gain Q is identified. Trade-off between the pedestal density and temperature is performed with the pedestal pressure fixed. It is found that Q increases with pedestal density, while the density peaking factor (DPF) remains unchanged. Linear analysis shows that the transport is dominated by TEM and ITG turbulence. Collisionality affects these turbulences in such a way that the induced changes in DPF cancel out. A weaker dependence of DPF makes higher density operation more favorable for fusion gain.