Multimode excitation during the inter-ELM-crash periods in KSTAR H-mode plasma

Kim, M.; Lee, J.; Park, H.K.; Yun, Gunsu; Lee, W.; Domier, Calvin; Luhmann, Neville C.; Team, Kstar

doi:10.1088/0029-5515/55/7/073001

Cited by 13 publications

(11 citation statements)

References 27 publications

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“…Experimental findings that support this theory have already been reported on different machines. Significant modification of the mode structure due to the nonlinear coupling has been reported on TCV [25] and similar amplitude modulation has been observed in KSTAR [26] and explained by a superposition of two modes with Figure 11. Shot # 33616 at t=7.5 s. (a) Density profile of the steep gradient edge region shown as a black solid line; radial electric field E r estimated from the poloidal flow of impurities is presented as a dashed grey line.…”

Section: Summary and Discussionsupporting

confidence: 75%

Effects of density gradients and fluctuations at the plasma edge on ECEI measurements at ASDEX Upgrade

Vanovac

Wolfrum

Denk

et al. 2018

Plasma Phys. Control. Fusion

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Electron cyclotron emission imaging (ECEI) provides measurements of electron temperature (T e) and its fluctuations (δT e). However, when measuring at the plasma edge, in the steep gradient region, radiation transport effects must be taken into account. It is shown that due to these effects, the scrape-off layer region is not accessible to the ECEI measurements in steady state conditions and that the signal is dominated by the shine-through emission. Transient effects, such as filaments, can change the radiation transport locally, but cannot be distinguished from the shine-through. Local density measurements are essential for the correct interpretation of the electron cyclotron emission, since the density fluctuations influence the temperature measurements at the plasma edge. As an example, a low frequency 8 kHz mode, which causes 10%-15% fluctuations in the signal level of the ECEI, is analysed. The same mode has been measured with the lithium beam emission spectroscopy density diagnostic, and is very well correlated in time with high frequency magnetic fluctuations. With radiation transport modelling of the electron cyclotron radiation in the ECEI geometry, it is shown that the density contributes significantly to the radiation temperature (T rad) and the experimental observations have shown the amplitude modulation in both density and temperature measurements. The poloidal velocity of the low frequency mode measured by the ECEI is 3 km s-1. The calculated velocity of the high frequency mode measured with the magnetic pickup coils is about 25 km s-1. Velocities are compared with the E×B background flow velocity and possible explanations for the origin of the low frequency mode are discussed.

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Section: Summary and Discussionsupporting

confidence: 75%

Effects of density gradients and fluctuations at the plasma edge on ECEI measurements at ASDEX Upgrade

Vanovac

Wolfrum

Denk

et al. 2018

Plasma Phys. Control. Fusion

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“…Both frequency branches were measured with magnetic pick-up coils. The Electron Cyclotron Emission Imaging (ECEI) diagnostic also measures the inter-ELM modes in the pedestal, in the low-frequency part of the spectrum at ASDEX Upgrade [18,19], and KSTAR [20]. With a careful analysis at the plasma edge, it is possible to distinguish between the different modes appearing in the narrow pedestal.…”

Section: Introductionmentioning

confidence: 99%

Characterization of low-frequency inter-ELM modes of H-mode discharges at ASDEX Upgrade

et al. 2018

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The steep edge gradient region of tokamak plasmas in the high confinement regime is known to drive instabilities, which cause transport. Several diagnostics are used to allow for a high degree of characterization of low-frequency modes appearing in between type-I Edge Localizes Modes (ELMs). These modes are dominantly observed in Electron Cyclotron Emission (ECE) and ECE Imaging measurements as the modulation of radiation temperature (δT rad). In the radial magnetic field (Ḃ r) measurements, the frequency range of 4 kHz to 12 kHz is observed. The position of the mode is determined to be at the upper part of the steep gradient region, the poloidal mode velocity is changing from 1.5 ± 0.5 km/s to 2.5 ± 0.5 km/s and the toroidal mode number is 13 to 14. A comparison with the measured E × B velocity leads to the conclusion that the phase velocity of the mode is smaller than 3 km/s or zero. The poloidal structure of the modes is found to be in agreement with the poloidal structure size associated with n = 13 as estimated from the equilibrium calculations. The modes are compared between two different heating phases during one discharge, and are found to differ in duration, velocity, frequency and toroidal mode number. The possibility of non-linear interaction between these modes and other, high frequency modes existing in the narrow pedestal, is assessed via bicoherence. The presented analysis gives an unprecedented picture of the mode, its position, its structure and its velocity, calling for comparison with non-linear modelling.

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“…[5,6] and shown to be stabilizing. Moreover, there is a large body of experimental evidence and simulations pointing to the non-linear nature of the dynamics of ELM cycles and ELM burst [7][8][9][10][11]. Ref.…”

mentioning

confidence: 99%

“…Eqs. (8,9) have two limiting cases: i) without flow-shear V E = 0, the second term on the r.h.s. of Eq.…”

mentioning

confidence: 99%

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ExB flow-induced shearing-merging of filaments: a Ginzburg-Landau model of Edge-Localized Mode cycles

Leconte¹,

Yun²,

Jeon³

2016

Preprint

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We derive and study a simple 1D nonlinear model for Edge Localized Mode (ELM) cycles. The nonlinear dynamics of a resistive ballooning mode is modeled via a single nonlinear equation of the Ginzburg-Landau type with a radial frequency-gradient due to a prescribed E × B shear layer of finite extent. The nonlinearity is due to the feedback of the mode on the profile. We identify a novel mechanism, whereby the ELM only crosses the linear stability boundary once, and subsequently stays in the nonlinear regime for the full duration of the cycles. This is made possible by the shearing and merging of filaments by the E × B flow, which forces the system to oscillate between a radially-uniform solution and a non-uniform solitary-wave like solution. The model predicts a 'phase-jump' correlated with the ELM bursts.

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Multimode excitation during the inter-ELM-crash periods in KSTAR H-mode plasma

Cited by 13 publications

References 27 publications

Effects of density gradients and fluctuations at the plasma edge on ECEI measurements at ASDEX Upgrade

Effects of density gradients and fluctuations at the plasma edge on ECEI measurements at ASDEX Upgrade

Characterization of low-frequency inter-ELM modes of H-mode discharges at ASDEX Upgrade

ExB flow-induced shearing-merging of filaments: a Ginzburg-Landau model of Edge-Localized Mode cycles

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