Effect of time-varying flow-shear on the nonlinear stability of the boundary of magnetized toroidal plasmas

Abstract

We propose a phenomenological yet very general model in a form of generalized complex Ginzburg-Landau equation to understand the dynamics of the quasi-periodic fluid instabilities (called edge-localized modes) in the boundary of toroidal magnetized high-temperature plasmas. The model reproduces key dynamical features of the boundary instabilities observed in the high-confinement state plasmas on the KSTAR tokamak, including quasi-steady states characterized by field-aligned filamentary eigenmodes, transitions between different eigenmodes, and rapid transition to non-modal filamentary structure prior to the relaxation. It is found that the inclusion of time-varying perpendicular sheared flow is crucial for reproducing the observed dynamical features.

Direct evidence of E × B flow changes at the onset of resonant magnetic perturbation-driven edge-localized mode crash suppression

“…Figure 3(b) is the reversed process, which is the trans ition from the ELM-crash suppression to mitigation. Overall, the bifurcation of v ⊥ synchronizes with the transition into and out of ELM-crash suppression, strongly suggesting that the change of v ⊥ could be directly associated with the ELM-crash phase transition [30].…”

Phase-mixing v.s. phase synchronization in the dynamics of flow-shear induced edge transport barrier

“…In addition, nonlinear resistive-MHD simulations observed similar nonlinear oscillations [9]. In previous works [10,11], we proposed a Ginzburg-Landau like phenomenological model, to account for the quasi-periodic dynamics of these relaxations. In the present work, we give a more in-depth analysis of the mechanism of these nonlinear oscillations, associated to nonlinear phase synchronization, in an extended version of the model including random fluctuations modeled as white-noise.…”

“…We analyze the following extended Ginzburg-Landau model, a phenomenological model for transport barrier relaxations [10,11]:…”

“…The parameters used for the numerical calculations are: V ′ = 4×10 1 , h = 1 × 10 −2 , Q = 10 and Q c = 0.5, and χ ⊥ = 1 × 10 −2 . In a previous publication [11], sensitivity studies were undertaken to determine the sensitivity of the model to the value of several parameters of the model, namely the flow shear V ′ , the shear-layer width h, the distance to threshold Q − Q c and the heat diffusivity χ ⊥ . Depending on the values of Q − Q c and χ ⊥ (denoted γ L and η, c.f.…”

Machine-Learning enabled analysis of ELM filament dynamics in KSTAR

“…These types include violent, low-frequency Type-I ELMs, or more intermittent, burst-like Type-III ELMs, as well as a mixed regime [8,9,10]. While two-fold stability analysis of peelingballooning modes explains linear stability of ELMs [11,12], the actual ELM crash is a nonlinear magnetohydrodynamic phenomenon and an area of active research interest [13,3,14,15,12].…”