Variation of ELM Frequency with NBI Heating Delay in DIII-D
Abstract
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 Ip flat-top, ELM frequency (fELM) can vary by a factor of 2 from ~30Hz to ~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 (<100 kHz), discharges with low fELM show broadband fluctuations at high frequency (300-400 kHz) in the magnetic spectrogram, whereas for those with higher fELM 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 Ip flat top and its effects on the pedestal formation will be investigated to address the differences in fELM. 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 Ip ramp-up on the pedestal and confinement might open opportunities for accessing similar confinement regimes with potentially smaller or no ELMs.
This work is supported by US DOE under DE-SC0019302, DE-FG02-04ER54761 and DE-FC02-04ER54698.- Publication:
-
APS Division of Plasma Physics Meeting Abstracts
- Pub Date:
- 2020
- Bibcode:
- 2020APS..DPPP15016B