EFDA-JET-CP(07)03/38
Pellet Drift Effect Studies at JET
Due to the B induced drift of the pellet ablated material, the pellet deposition profile and fuelling efficiency depend on the pellet injection location. The cloud of ablated material surrounding the pellet is displaced along the magnetic field gradient, leading to deeper penetration into the plasma for pellet injections from the High Field Side (HFS) of the torus, as compared to pellet fuelling from the Low Field Side (LFS). According to previous studies, this drift effect can be used in JET-sized plasmas to obtain superior core fuelling characteristics. To clarify this issue, a statistical analysis of pellet experiments at JET has been carried out with the objectives (a) to verify if the observed drift displacement is systematic, (b) to obtain an estimate of the typical displacement length, and (c) to study the influence of particle transport effects like diffusion on the measured pellet deposition profile. For this purpose a database of pellets injected in JET plasmas since 1999 has been set up and one well diagnosed shot featuring pellets from three different injection locations, has been analysed in detail. A comparison of the pellet drift displacement with simulation results is given in section 3, whereas the fuelling efficiency is analysed in section 4.