ELM pace making and mitigation by pellet injection in ASDEX Upgrade

Lang, P. T.; Conway, G. D.; Eich, T.; Fattorini, L.; Gruber, O.; Günter, S.; Horton, L. D.; Kálvin, S.; Kallenbach, A.; Kaufmann, Michael; Kocsis, G.; Lorenz, A.; Manso, M. E.; Maraschek, M.; Mertens, V.; Neuhäuser, J.; Nunes, I.; Schneider, W.; Suttrop, W.; Urano, H.

doi:10.1088/0029-5515/44/5/010

Cited by 209 publications

(210 citation statements)

References 47 publications

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“…A first proof-of-principle demonstration of ELM pacing and ELM control was carried out at ASDEX Upgrade [90]. By injecting pellets with a frequency a factor of 2-3 times higher than the natural, or uncontrolled, ELM frequency full control of the ELMs was achieved with the pellet rate f PEL determining the ELM frequency f ELM .…”

Section: Pacing Scenario 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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Section: Pacing Scenario Investigationsmentioning

confidence: 99%

ELM control strategies and tools: status and potential for ITER

et al. 2013

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“…The scaling of ELM loss energy is not known, but present data suggests an unfavourable dependence on pedestal collisionality ν * [2]. Techniques to avoid large ELMs are therefore being investigated, for example ELM loss reduction by injection of cryogenic pellets [3], small ELM regimes [4][5][6] and stationary ELM-free regimes [7,8]. It has been observed early on in COMPASS-D that non-axisymmetric error fields can reduce the size of ELMs [9].…”

Section: Introductionmentioning

confidence: 95%

In-vessel saddle coils for MHD control in ASDEX Upgrade

Suttrop

Gruber

Günter

et al. 2009

Fusion Engineering and Design

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A set of 24 in-vessel saddle coils is planned for MHD control experiments in ASDEX Upgrade. These coils can produce static and alternating error fields for suppression of Edge Localised Modes, locked mode rotation control and, together with additional conducting wall elements, resistive wall mode excitation and feedback stabilisation experiments. All of these applications address critical physics issues for the operation of ITER. This extension is implemented in several stages, starting with two poloidally separated rings of eight toroidally distributed saddle coils above and below the outer midplane. In stages 2 and 3, eight midplane coils around the large vessel access ports and 12 AC power converters are added, respectively. Finally (stage 4), the existing passive stabilising loop (PSL), a passive conductor for vertical growth rate reduction, will be complemented by wall elements that allow helical current patterns to reduce the RWM growth rate for active control within the accessible bandwidth. The system is capable of producing error fields with toroidal mode number n = 4 for plasma edge ergodisation with core island width well below the neoclassical tearing mode seed island width even without rotational shielding. Phase variation between the three toroidal coil rings allows to create or avoid resonances with the plasma safety factor profile, in order to test the importance of resonances for ELM suppression.

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“…The first consists of driving non-linearly saturated modes at the edge that, being coupled to the most unstable peeling-ballooning mode, prevent the onset of type-I ELMs; techniques based on this approach are the Quiescent High (QH) mode regime [8] and the Resonant Magnetic Perturbation (RMP) [9]. The second approach is based on triggering ELMs when the pedestal has lower energy than that at the peeling-balloning limit, so that the resulting heat fluxes are below the damage threshold of PFCs; such techniques, known as ELM pacing, generate small and frequent ELMs and are routinely executed via pellet [10] and gas [11] injection, vertical stabilization control [12], or by means of modulated Electron Cyclotron Heating absorbed near the plasma edge [13]. A third technique aims at developing confinement scenarios that inherently provide necessary energy confinement without the presence of a particle confinement barrier, and thus avoiding the necessity for ELMs for impurity control while simultaneously keeping plasma edge below the peelingballooning stability limits.…”

Section: Introductionmentioning

confidence: 99%

Characterization of density fluctuations during the search for an I-mode regime on the DIII-D tokamak

et al. 2015

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Abstract. The I-mode regime, routinely observed on the Alcator C-Mod tokamak, is characterized by an edge energy transport barrier without an accompanying particle barrier and with broadband instabilities, known as Weakly Coherent Modes (WCM), believed to regulate particle transport at the edge. Recent experiments on the DIII-D tokamak exhibit I-mode characteristics in various physical quantities. These DIII-D plasmas evolve over long periods, lasting several energy confinement times, during which the edge electron temperature slowly evolves towards an H-modelike profile, while maintaining a typical L-mode edge density profile. During these periods, referred to as I-mode phases, the radial electric field at the edge also gradually reaches values typically observed in H-mode. Density fluctuations measured with the Phase Contrast Imaging diagnostic during Imode phases exhibit three features typically observed in H-mode on DIII-D, although they develop progressively with time and without a sharp transition: the intensity of the fluctuations is reduced; the frequency spectrum is broadened and becomes nonmonotonic; two dimensional space-time spectra appear to approach those in H-mode, showing phase velocities of density fluctuations at the edge increasing to about 10 km/s. However, in DIII-D there is no clear evidence of the WCM. Preliminary linear gyro-kinetic simulations are performed in the pedestal region with the GS2 code and its recently upgraded model collision operator that conserves particles, energy and momentum. The increased bootstrap current and flow shear generated by the temperature pedestal are shown to decrease growth rates, thus possibly generating a feedback mechanism that progressively stabilizes fluctuations.

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ELM pace making and mitigation by pellet injection in ASDEX Upgrade

Cited by 209 publications

References 47 publications

ELM control strategies and tools: status and potential for ITER

ELM control strategies and tools: status and potential for ITER

In-vessel saddle coils for MHD control in ASDEX Upgrade

Characterization of density fluctuations during the search for an I-mode regime on the DIII-D tokamak

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