Sandpile modeling of pellet pacing in fusion plasmas.

Sandpile models have been used to provide simple phenomenological models without incorporating the detailed features of a fully featured model. The Chapman sandpile model [Chapman et al., Phys. Rev. Lett. 86, 2814 (2001)PRLTAO0031-900710.1103/PhysRevLett.86.2814] has been used as an analog for the behavior of a plasma edge, with mass loss events being used as analogs for edge-localized modes (ELMs). In this work we modify the Chapman sandpile model by providing for both increased and intermittent driving. We show that the behavior of the sandpile, when continuously fuelled at very high driving, can be determined analytically by a simple algorithm. We observe that the size of the largest avalanches is better reduced by increasing constant driving than by the intermittent introduction of "pellets" of sand. Using the sandpile model as a reduced model of ELMing behavior, we conject that ELM control in a fusion plasma may similarly prove more effective with increased total fuelling than with pellet addition.