Particle Deposition, Transport and Fuelling in Pellet Injection Experiments at JET
Pellet ablation and particle deposition have been extensively studied at JET giving a clear evidence of B drift effects in hot plasmas and its impact on fuelling efficiency. This result confirms observations made on smaller devices. In L-mode or moderately heated H-mode this effect seems to be weak while at high temperature, injection from the VHFS has proven to be much more effective than from LFS in depositing particles beyond the pedestal. In the latter case ablated particles are quickly lost due to a combination of B drift and edge instabilities. The fuelling performance, although investigated only in a limited range of plasma and pellet parameters, seems to be promising for the capability of pellets to raise the density without increasing the neutral pressure in the main chamber. This latter feature is important for ITER, because it confirms that pellets are less demanding in terms of required pumping speed. Experiments of pellet fuelling in combination with ELM mitigation techniques using Error Field Correction Coils (EFCC) have also given encouraging results and are also reported.