Distinct stages of radio frequency emission at the onset of pedestal collapse in KSTAR H-mode plasmas

Using a high-speed and broadband radio frequency (RF) (0.1-1 GHz) spectrum analyzer developed on the KSTAR tokamak, it is found that several distinct stages of RF emission appear at the pedestal collapse in high confinement discharges. Comparison with 2-D electron cyclotron emission (ECE) images has...

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Bibliographic Details
Published in:arXiv.org 2018-03
Main Authors: Kim, Minho, Thatipamula, Shekar G, Lee, Jieun, Choi, Minjun J, Park, Hyeon K, Akiyama, Tsuyoshi, Yun, Gunsu S
Format: Article
Language:English
Subjects:
Broadband
Bursting strength
Collapse
Cyclotrons
Dynamic stability
Emission
Frequency ranges
Ion dynamics
Plasma
Plasmas
Radio frequency
Tokamak devices
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Summary:Using a high-speed and broadband radio frequency (RF) (0.1-1 GHz) spectrum analyzer developed on the KSTAR tokamak, it is found that several distinct stages of RF emission appear at the pedestal collapse in high confinement discharges. Comparison with 2-D electron cyclotron emission (ECE) images has revealed that each stage is related to the instantaneous condition at the outboard mid-plane edge. First, high-harmonic ion cyclotron emissions (ICE) are intensified with the appearance of a non-modal filamentary perturbation in the edge within several tens of microseconds before the collapse. Then, the RF emission becomes broad toward high-frequency range (< 500 MHz) at the burst onset of the non-modal filament. During the pedestal collapse initiated by the filament burst, rapid chirping (1-3 {\mu}s) appear with additional filament bursts. The strong correlation between the RF spectra and the perturbation structure provides important clues on the stability of edge-localized modes and on the ion dynamics in the plasma boundary.
ISSN:2331-8422
DOI:10.48550/arxiv.1803.09376