On the possibility of limit-cycle-state of peeling mode near stability boundary in the quiescent H-mode

Itoh, K.; Kamiya, K.; Aiba, N.; Itoh, Sanae–I.

doi:10.1088/1361-6587/abcab2

Cited by 4 publications

(1 citation statement)

References 41 publications

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“…Together with the fundamental mode of the EHO, the mean temperature gradient was measured to oscillate in a limit cycle with an LCO frequency about a factor 60 lower than the EHO frequency. A limit-cycle model for these oscillations in JT60-U was developed in [51]. With this model it was shown that a limit cycle solution exists near the stability boundary of peeling modes, in which the pressure gradient and peeling mode amplitude oscillate in time, quantitatively consistent with the JT60-U observations.…”

Section: Limit Cycle Oscillationssupporting

confidence: 54%

MHD simulations of formation, sustainment and loss of quiescent H-mode in the all-tungsten ASDEX Upgrade

et al. 2023

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Periodic edge localized modes (ELMs) are the non-linear consequences of pressure-gradient-driven ballooning modes and current-driven peeling modes becoming unstable in the pedestal region of high confinement fusion plasmas. In future tokamaks like ITER, large ELMs are foreseen to severely affect the lifetime of wall components as they transiently deposit large amounts of heat onto a narrow region at the divertor targets. Several strategies exist for avoidance, suppression, or mitigation of these instabilities, such as the naturally ELM-free quiescent H-mode (QH-mode). In the present article, an ASDEX Upgrade equilibrium that features a QH-mode is investigated through non-linear extended MHD simulations covering the dynamics over tens of milliseconds. The equilibrium is close to the ideal peeling limit and non-linearly develops saturated modes at the edge of the plasma. A dominant toroidal mode number of $n=1$ is found, for which the characteristic features of the edge harmonic oscillation are recovered.The saturated modes contribute to heat and particle transport preventing pedestal build-up to the ELM triggering threshold. The non-linear dynamics of the mode, in particular its interaction with the evolution of the edge safety factor is studied, which suggest a possible new saturation mechanism for the QH-mode.The simulations show good qualitative and quantitative agreement to experiments in AUG. In particular, the processes leading to the termination of QH-mode above a density threshold is studied, which results in the transition into an ELM regime. In the vicinity of this threshold, limit cycle oscillations are observed.

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Section: Limit Cycle Oscillationssupporting

confidence: 54%

MHD simulations of formation, sustainment and loss of quiescent H-mode in the all-tungsten ASDEX Upgrade

et al. 2023

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Unveiling the structure and dynamics of peeling mode in quiescent high-confinement tokamak plasmas

et al. 2021

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Quiescent high-confinement mode plasmas with edge-harmonic oscillations do not exhibit the explosive instabilities associated with edge-localized modes. Instead, an additional means of enhanced transport is considered to maintain the plasma edge under conditions just below the boundary of the peeling mode instability. Although the potential of the peeling mode has been widely recognized in plasma physics, no direct evidence for this mode has been revealed previously because decisive diagnostics were lacking. Herein, we report evidence of the structure and dynamical steady state of peeling mode in quiescent high-confinement mode. Edge-harmonic oscillations are dominated by fundamental mode at both the low- and high-field sides. Edge perturbations are confirmed to have kink parity and exhibit the frozen-in-condition predicted by linear stability analysis. The envelope signal of the fundamental mode exhibits repeated cycles of growth and damping in association with minor changes in the edge gradient. Results from this study are quantitatively consistent with limit-cycle-oscillation model.

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Structure and dynamical steady state of the peeling mode in edge-localized mode-free, high-confinement tokamak plasmas

Kamiya

Itoh

Aiba

et al. 2021

Preprint

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Explosive dynamical events in controlled-nuclear-fusion devices (known as edge-localized modes) display many similarities to solar-flare events on the sun, revealing a new connection between laboratory plasma physics and astronomy. However, to date there has been no direct evidence for the peeling mode structure, due to the lack of decisive diagnostics. Here we report the first evidence for the structure and dynamical steady state of a peeling mode for low-n edge-harmonic oscillations (EHOs) in the quiescent H-mode. EHOs are dominated by the fundamental mode (1fEHO) at both the low- and high-field sides. 1fEHO edge perturbations are confirmed to have kink parity and exhibit the frozen-in-condition predicted by a linear stability analysis. The envelope signal of the 1fEHO mode exhibits repeated cycles of growth and damping to the order of a few hundred Hz associated with small changes in an edge gradient, and results are quantitatively consistent with a limit-cycle-oscillation model.

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On the possibility of limit-cycle-state of peeling mode near stability boundary in the quiescent H-mode

Cited by 4 publications

References 41 publications

MHD simulations of formation, sustainment and loss of quiescent H-mode in the all-tungsten ASDEX Upgrade

MHD simulations of formation, sustainment and loss of quiescent H-mode in the all-tungsten ASDEX Upgrade

Unveiling the structure and dynamics of peeling mode in quiescent high-confinement tokamak plasmas

Structure and dynamical steady state of the peeling mode in edge-localized mode-free, high-confinement tokamak plasmas

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