Assessment of pellet injection for net. Pt. 5

Results of ignition and continuous fuelling scenario calculations are presented that were obtained in the framework of an assessment performed for NET on the basis of the INTOR parameters. The results obtained with pellet injection are compared with results corresponding to gas puffing. Pellet injection transports fresh fuel to the reaction zone on a time scale that is much shorter than the diffusion time characterizing the gas puffing method, thus making the method flexible and readily adaptable to different situations. In the case of ignition by pellet injection, it may become possible to have deep NB penetration and maintain favourable heat deposition profiles up to the moment of density ramp-up, thus substantially relaxing the beam output requirements. Three beam energies (D0 particles) have been considered: 120 keV, 100 keV, and 80 keV. The importance of a proper match between the beam characteristics and the pellet parameters, specific for the transport scaling assumed (ALCATOR-INTOR), is shown. In the case of continuous fuelling of an already ignited discharge, the alpha power production notably increases if repetitive pellet injection, instead of gas puffing (at a fixed value of βsub(T)), is applied. The advantages of pellet injection are substantial even at moderate pellet velocities. (orig.)