EVALUATION OF PUMPING AND FUELING REQUIREMENTS FOR THE ITER EDA

The relationships between fueling (gas injection and pellets of variou s sizes and velocities), pumping in the divertor chamber (constrained by fuel processing and divertor design), core density (constrained by the desired fusion power and helium ash accumulation), separatrix dens ity (constrained by divertor operation and density Limits) and plasma confinement models are examined for the International Engineering Toka mak Reactor (ITER) Engineering Design Activity (EDA) for guidance in t he definition of design requirements for the pumping and fueling syste ms. Various combinations of gas and pellet injection are found to meet the constraints for operation at 1500 MW of fusion power and 1 bar.l/ s (5.3 x 10(22) atoms/s) of DT pumping. Very low pumping reduces fuel processing requirements, but can lead to excessive helium accumulation depending on the particle transport properties. Isotopic tailoring of the fuel sources, e.g., 20-30% of the input fuel stream as tritium pe llets and the rest as deuterium gas, can maintain the core fuel specie s mixture in the optimum range for fusion production (at least a 40-60 mixture) while reducing the tritium concentration in the edge region to 20-30%. This should reduce the tritium inventory in the plasma faci ng components, since that is typically governed by the fuel density mi x near the plasma edge. A high density, low temperature ignited regime supported by deep pellet injection is shown to exist under some low c onfinement conditions.