First pellet injection experiments on the Tore Supra tokamak

Results of early pellet fueling experiments on the Tore Supra tokamak using a centrifuge pellet injector are reported. The pellet fueling injector developed by ORNL can produce and accelerate up to 100 deuterium pellets of variable size at a frequency up to 10 Hz and speeds of 600 to 900 m/s. The initial deposition and evolution of the plasma are followed by an array of diagnostics. In ohmic discharges the pellet penetration is just past midradius, producing a density rise and temperature drop consistent with the pellet size. Thomson scattering profiles indicate that the fueling process is locally almost adiabatic, i.e., there is no change in the pressure profile 30 ms after injection even though the density profile is peaked at midradius and hollow. With deuterium injection into discharges dominated by hydrogen evolution from the walls, a deuterium pellet plasma is produced and changes over to hydrogen on a time scale much shorter than the density decay. Pellets injected into a pump limiter discharge produce an initial drop in particle flux into the throat followed by a rise