Magnetic triggering of ELMs in TCV

Degeling, A. W.; Martin, Yves; Lister, J.B.; Villard, L.; Dokouka, V.; Lukash, V.E.; Khayrutdinov, R.R.

doi:10.1088/0741-3335/45/9/306

Cited by 124 publications

(150 citation statements)

References 9 publications

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“…when the plasma is moving upwards, away from the divertor coils. This is similar to the result in TCV [35], but is different from the cases in ASDEX-Upgrade [36] and JET [37], where ELMs are observed when the plasma moves downwards.…”

Section: Observation Of Elm Pacing and Triggeringsupporting

confidence: 79%

First observation of ELM pacing with vertical jogs in a spherical torus

et al. 2010

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Experiments in a number of conventional aspect ratio tokamaks have been successful in pacing edge localized modes (ELMs) by rapid vertical jogging of the plasma. This paper demonstrates the first pacing of ELMs in a spherical torus plasma. Applied 30 Hz vertical jogs synchronized the ELMs with the upward motion of the plasma. 45 Hz jogs also lead to an increase in the ELM frequency, though the synchronization of the ELMs and jogs was unclear. A reduction in the ELM energy was observed at the higher driven ELM frequencies.

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Section: Observation Of Elm Pacing and Triggeringsupporting

confidence: 79%

First observation of ELM pacing with vertical jogs in a spherical torus

et al. 2010

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“…As already mentioned this scheme for ELM control was first developed (and named ELM control by magnetic triggering) and demonstrated at the TCV tokamak [109]. Coils which were routinely used for vertical plasma position feedback stabilisation were driven by a short voltage pulse causing a small vertical excursion of the plasma column.…”

Section: Status Of Experimental and Modeling Investigationsmentioning

confidence: 99%

ELM control strategies and tools: status and potential for ITER

et al. 2013

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Operating ITER in the reference inductive scenario at the design values of I P = 15 MA and Q DT = 10 requires the achievement of good H-mode confinement that relies on the presence of an edge transport barrier whose pedestal pressure height is key to plasma performance. Strong gradients occur at the edge in such conditions that can drive MHD instabilities resulting in Edge Localized Modes (ELMs), which produce a rapid energy loss from the pedestal region to the plasma facing components. Without appropriate control, the heat loads on plasma facing components during ELMs in ITER are expected to become significant for operation in H-mode at I P = 6 -9 MA; operation at higher plasma currents would result in a very reduced life time of the plasma facing components. Currently, several options are being considered for the achievement of the required level of ELM control in ITER; this includes operation in plasma regimes which naturally have no or very small ELMs, decreasing the ELM energy loss by increasing their frequency by a factor of up to 30 and avoidance of ELMs by actively controlling the edge with magnetic perturbations. Small/no ELM regimes obtained by influencing the edge stability (by plasma shaping, rotational shear control, etc.) have shown in present experiments a significant reduction of the ELM heat fluxes compared to type-I ELMs. However, so far they have only been observed under a limited range of pedestal conditions depending on each specific device and their extrapolation to ITER remains uncertain. ELM control by increasing their frequency relies on the controlled triggering of the edge instability leading to the ELM. This has been 2 presently demonstrated with the injection of pellets and with plasma vertical movements; pellets having provided the results more promising for application in ITER conditions. ELM avoidance/suppression takes advantage of the fact that relatively small changes in the pedestal plasma and magnetic field parameters seem to have a large stabilizing effect on large ELMs. Application of edge magnetic field perturbation with non-axisymmetric fields is found to affect transport at the plasma edge and thus prevent the uncontrolled rise of the plasma pressure gradients and the occurrence of type-I ELMs. This paper compiles a brief overview of various ELM control approaches, summarizes their present achievements and briefly discusses the open issues regarding their application in ITER. IntroductionThe main goal of current research in the field of magnetically confined plasmas aiming for power generation by nuclear fusion is to optimize high confinement plasma regimes (Hmode) in order to achieve the maximum plasma energy for a given input heating power P in . Thus, in future fusion devices such as the ITER tokamak, which is expected to produce considerable amounts of fusion power P fus , the gain or amplification factor Q = P fus /P in requires to be maximized as well. High confinement H-mode plasmas are characterized by the existence of an Edge Transport Barrier (ETB) in a ...

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“…Of particular interest in this context are the observations in the QH-mode [27], which in the frame of our model should correspond to a particular class of plasma profiles (requiring for their attainment also special external measures) where the development into a nonlinearly strongly unstable state is prevented, ripple [40], edge ergodisation [41,42] or fast plasma motions [43,44]. And finally, the impact of pellet pacing on edge profiles and its self-consistent feedback achieving steady state conditions can provide valuable information on the trigger process and its limitations.…”

Section: The Quiescent H-modementioning

confidence: 99%

Investigation of pellet-triggered MHD events in ASDEX Upgrade and JET

et al. 2008

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To get deeper insight into the MHD activity triggered by pellets we extended our previous analyses of standard type-I ELMs to pellets injected into discharge phases of the following types: Ohmic, L-mode, type-III ELMy H-mode, ELM-free, radiative edge scenarios with type-I ELMs, the quiescent H (QH)-mode regime. It turns out that pellet injection generally creates a strong, local perturbation of the MHD equilibrium in the ablation region and even beyond. Regarding the triggering of ELMs, this initial perturbation can damp out, indicating that the plasma is stable in the corresponding regime even for finite-size perturbations. This behaviour is observed not only in Ohmic and L-mode phases but also in the QH-mode where the edge harmonic oscillations (EHO) appear to keep the edge within or at the boundary of a stable regime. In case the plasma is prone to ELM growth, the large amplitude of the pellet perturbation can trigger the event even in situations where modes appear to be still linearly stable.The non-linear character of the ELM trigger process is highlighted also by the subsequent explosive growth of these events. For edge plasma conditions characterised by higher resistivity the growth time of spontaneously occurring ELMs increases when the plasma changes from the type-I into the type-III regime. Pellet-triggered ELMs, however, maintain the fast rise times otherwise typical for the hot edge type-I regime. In the discussion section we attempt to relate these observations also to core mode activity like neoclassical tearing modes or snakes. Data were taken from ASDEX Upgrade and JET.Pellet triggering of mode activity can be shown to be a quite universal phenomenon, which, however, only for the case of ELMs can be unambiguously attributed to prompt direct excitation by the pellet.

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Magnetic triggering of ELMs in TCV

Cited by 124 publications

References 9 publications

First observation of ELM pacing with vertical jogs in a spherical torus

First observation of ELM pacing with vertical jogs in a spherical torus

ELM control strategies and tools: status and potential for ITER

Investigation of pellet-triggered MHD events in ASDEX Upgrade and JET

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