MAGNETOHYDRODYNAMIC EFFECTS ON PELLET INJECTION IN TOKAMAKS

The location at which pellets are injected into a plasma can have a si gnificant effect on what fraction of the pellet mass remains in the pl asma for refueling purposes. Magnetohydrodynamic (MHD) simulations pre sented here, confirm the results of pellet injection experiments: toro idal curvature makes it favorable to inject pellets from the inboard s ide or from the top or bottom, rather than from the outboard side. Suf ficiently large pellets injected at the inboard edge can reach the pla sma center, and in the process drive magnetic reconnection to produce negative central shear. Injection at the top (or bottom) of the tokama k causes relatively little displacement of the pellet. A scaling law i s obtained for pellet displacement which agrees well with the simulati ons. The MHD simulations were carried out with a new unstructured mesh finite element version of the MH3D full MHD code. (C) 1998 American I nstitute of Physics. [S1070-664X(98)03907-X].