Role of EHO-like modes in Inter-ELM Particle Transport during type-I ELMy DIII-D H-mode Discharges

Edge harmonic oscillation (EHO)-like modes, observed during the inter-ELM period of regular type-I ELMing H-mode discharges of the DIII-D tokamak, are investigated for the role they may play in the inter-ELM particle transport. The appearance of the EHO-like modes correlates with higher D_α levels while their disappearance correlates with a sharp decrease in D_α. ELITE calculations show that the MHD stability is close to the peeling boundary in the inter-ELM period. These pedestal localized modes (~10 kHz and its harmonics) are observed in the measurement of flow oscillations by Doppler backscattering (DBS), density fluctuations by beam emission spectroscopy (BES), and magnetic fluctuations by magnetic probes. They are also observed in the ion saturation current measurements by Langmuir probes, which suggests their role in inter-ELM particle transport. BES measurements show that the modes rotate in ion diamagnetic direction in lab frame and have k_θ~0.1–0.3 cm^-1. Linear CGYRO simulation indicates that kinetic ballooning modes are most unstable in the region where EHO-like modes are measured which might explain the inter-ELM particle transport.

This work was supported by the US Department of Energy under grants DE-SC0019352 and DE-FC02-04ER54698.