Correlations between NBI blips and ELM triggers in Tokamaks

In tokamaks, the power injected with neutral beam injection (NBI) is often modulated at steady frequencies, providing 'blips' of power fueling the plasma core. Recent observations on DIII-D suggest these NBI power blips could play a role in triggering explosive instabilities called edge-localized modes (ELMs), which are responsible for intense transient heat fluxes on the machine walls and help to flush particles out of the core region. Here we examine a range of DIII-D discharges to identify correlations between NBI blips and ELMs under various plasma conditions. Statistical techniques identify the plasma regimes showing the strongest correlation between these two transients , demonstrating the sensitivity of NBI-ELM triggering on plasma density, rotation, power and shape. In cases with strong NBI and ELM frequency and time correlations, we examine the experimental pedestal profiles as a function of NBI and ELM phase to shed light on the triggering method itself. We can use this information to learn about the physics of ELM triggering, potentially leading to further optimization of ELMing H-mode plasmas.