Intense whistler-frequency emissions at the pedestal collapse in KSTAR H-mode plasmas

Abstract

The edge confinement barrier of high-confinement mode (H-mode) plasma involves a variety of plasma waves alongside with fluid instabilities and collective particle transport during the barrier collapse. We demonstrate a new method of resolving the plasma waves by measuring the modulations embedded in the second harmonic electron cyclotron emission (ECE). Utilizing mm-wave heterodyne detection and fast digitization technologies on the KSTAR tokamak, we resolve not only the frequency spectrum but the wavenumber as well. At the plasma boundary during the barrier collapse, we observe multiple bursts of broadband whistler-frequency (<8 GHz) waves, together with intense narrowband emissions. The narrowband emissions exhibit rapid rising and falling tones within a few microseconds. Bispectral analyses reveal the existence of nonlinear interactions between the broadband and the narrowband waves, confirming their concurrence in the barrier zone. We estimate that the vertical wavenumber of the narrowband waves is comparable to that of a whistler wave, utilizing multiple mm-wave mixer channels. Our work opens a new experimental way to study wave–wave and wave–particle interactions in magnetically confined plasmas.

Density dependence of ion cyclotron emission from deuterium plasmas in the large helical device

“…On LHD, the acquisition system of the ICE measured at a dipole antenna located in the 10-O port inside the vacuum vessel was developed in partnership with KSTAR [37][38][39][40]. A fast digitizer performs direct sampling of the radiofrequency measurements at a frequency of 1.25 GSa/s.…”

Formation of small-scale modes via ECCD injection into KSTAR plasma core

“…Therefore, sufficient data points to perform a signal correlation analysis can be gathered using the procedure described in section 2.2. In addition, the bicoherence given hereafter measures the degree of phase coupling between the fluctuating components, which also implies a nonlinear interaction between the fluctuating components [21,23,25,26].…”

“…Additionally, this study was conducted with a correlation analysis of the ECEI data. The implementation of channel correlation analysis for ECEI measurements [21,22] has enabled research on the interaction between turbulent fluctuation and magnetic islands [23,24], flow changes, coupling of turbulent eddies due to resonant magnetic perturbation [25], and whistler-frequency emission measurement based on the estimation of the vertical wavenumber [26]. Similarly, [27] investigated the change in fluctuations during sequences of sawtooth oscillations and suggested that the growth of fluctuations results from an increase in the T e gradient owing to the heat pulse stemming from the sawtooth crash.…”

Development of the ion cyclotron emission diagnostic on the HL-2A tokamak

“…fast ions from neutral beam injection (NBI), fusion reactions, acceleration by ICRH waves or during edge localized modes (ELMs) crash, and runaway electrons (REs) during low density discharge and major disruption. The instabilities driven by these energetic particles have been widely studied with ICE diagnostic in many devices including JET [8], TFTR [9,10], DIII-D [3,5,[11][12][13], ASDEX Upgrade [14,15], KSTAR [16][17][18] and EAST [4] tokamaks, NSTX-U [19] spherical tokamak and LHD [20] stellarator.…”