Variation of ELM Frequency with NBI Heating Delay in DIII-D

The impact of increase in heating power with respect to the current ramp-up and flat top on the pedestal structure is not yet understood. In DIII-D we observe that if the NBI heating time is altered with respect to reaching the $I_{p}$ flat-top, ELM frequency ($f_{ELM})$ can vary by a factor of 2 from \textasciitilde 30Hz to \textasciitilde 60Hz while the pedestal width and height are similar prior to the first ELM. Fueling is same (20 Torrl/s) prior to L-H transition and onwards. While all discharges show low frequency quasi-coherent magnetic fluctuations (\textless 100 kHz), discharges with low $f_{ELM}$ show broadband fluctuations at high frequency (300-400 kHz) in the magnetic spectrogram, whereas for those with higher $f_{ELM}$ a quasi-coherent mode is observed at 220 kHz. Magnetic fluctuations characteristics and role of the L-H mode transition time with respect to the $I_{p}$ flat top and its effects on the pedestal formation will be investigated to address the differences in $f_{ELM}$. We will investigate time-dependent evolution of the pedestal values before onset of the first ELM and pedestal stability during the ELMing regime. Understanding the impact of the heating onset with respect to the $I_{p}$ ramp-up on the pedestal and confinement might open opportunities for accessing similar confinement regimes with potentially smaller or no ELMs.