Pedestals and feedback in fusion-plasma relevant sandpile models

Abstract

We present modifications to the sandpile model [Chapman, Phys. Rev. E 62, 1905 (2000)] (Classic Model). A feedback loop is added to the Classic Model, elements of which may have relevance to the behaviour of a fusion plasma. Those elements include variation of the total energy of the system in proportion to a proxy for the Larmor radius, ρ, and resulting variations in mass loss event (MLE) size and waiting times between MLEs. We also show other variants of the Classic Model which produce pedestals, without introducing feedback. The modifications produce a pedestal similar to that seen in a fusion plasma, as well as feedback effects. We observe that maximum MLE sizes, and maximum waiting times between MLEs, grow with pedestal size only in the presence of feedback. If, as we purport, the edge localised mode (ELM) process is captured by an MLE model with feedback, then a conclusion is that ELMs can be reduced if feedback effects are reduced.