Fuelling and density control for DEMO

Plasma fuelling and density control are an open issue regarding EU DEMO studies and solutions may be different from present day experiments. The present paper addresses through JINTRAC core transport code simulations the feasibility of different fuelling methods such as gas puff and pellet injection and the influence of neoclassical and anomalous inward pinch in the edge transport barrier in order to achieve and control the target DEMO density. Given the expected high fusion power production, He accumulation in the plasma core is a critical issue, and an estimation of the influence of impurities (He, Ar, and W) on core fuelling and plasma dilution is given together with a discussion on D-T core balance. The DEMO reference scenario investigated in this work is characterized by a peaked density profile, which requires a careful core fuelling. Due to the large pedestal temperature gradient, gas puff may not be a feasible option for core density control, unless assuming a large anomalous inward pinch in the edge transport barrier of more than ∼2 m s-1. Pellet injection from the high field side of the torus, on the contrary, may represent a viable solution for core fuelling and D-T ratio control. The effect of pellet mass, speed, and injection geometry is also discussed in the present paper. Regardless, core fuelling efficiency with pellet injection is almost entirely determined by the presence of E × B drift.