Density profile control in a fusion reactor using pellet injection

The relationships between plasma parameters that are dependent on the density profile (fusion rate, core and edge densities and temperatures, density and temperature profile peaking), fuel particle pumping in the divertor (expressed as particle throughput) and pellet injection parameters (size, velocity and injection frequency) are examined for tokamak reactor plasmas. These relationships are illustrated with the results of transport simulations of steady state conditions for a nominal set of reactor parameters representative of the International Thermonuclear Experimental Reactor (ITER) using pellet parameters characteristic of both present and advanced injectors. The radial separation between the pellet source and the pumping in the divertor region, even with very modest pellet velocities, allows for the possibility of density profile control in the plasma edge. When matching both fusion power and edge density constraints, fuel particle throughput decreases with increasing pellet penetration. The sensitivity of the results to the details of the transport model and to the limit on the edge density is also examined