ELM frequency control by continuous small pellet injection in ASDEX Upgrade

Lang, P. T.; Neuhäuser, J.; Horton, L. D.; Eich, T.; Fattorini, L.; Fuchs, Julien; Gehre, O.; Herrmann, A.; Ignácz, P. N.; Jakobi, Martin; Kálvin, S.; Kaufmann, Michael; Kocsis, G.; Kurzan, B.; Maggi, C. F.; Manso, M. E.; Maraschek, M.; Mertens, V.; Mück, A.; Mürmann, H.; Neu, R.; Nunes, I.; Reich, David J.; Reich, M.; Saarelma, S.; Sandmann, W.; Stöber, J.; Vogl, Ulrich

doi:10.1088/0029-5515/43/10/012

Cited by 123 publications

(104 citation statements)

References 25 publications

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“…As a monitor for the pellet ablation we adopt the diode recorded ablation radiation D α signal. This radiation intensity is known to represent fairly well the time-varying pellet particle ablation rate dmP dt ≡ṁ P [13]; this approximation was also well confirmed by our earlier pellet ELM pacing and fuelling studies [14]. For this study we simplify the picture assuming in the ELM case the Mirnov signal is stemming from the mode activity in the edge region closest to the coil.…”

Section: Resultssupporting

confidence: 74%

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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Section: Resultssupporting

confidence: 74%

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

et al. 2008

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“…A cascade of ELMs intensified in comparison to the earlier intrinsic train onset follows. This is likely due to strong fuelling resulting in a massive out flux of particles, documented as typical behaviour for the injection of large pellets in ASDEX Upgrade [7]. The ELM triggered shortly after an intrinsic one (right) turns out less pronounced but is followed by a fuelling-cascade as well.…”

Section: Reliable Elm Triggering By Pelletsmentioning

confidence: 90%

ELM triggering by local pellet perturbations in type-I ELMy H-mode plasma at JET

et al. 2007

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The pellet pacing ELM control concept developed at the mid sized tokamak ASDEX Upgrade is considered for the larger machines JET and ITER as well. By driving up the ELM frequency, the ELM size can be reduced and eventually suppressed below a dangerous level. An according pellet injection systems for JET is under construction, the ITER design includes one as well. However, it has still to be proven the concept will work also at bigger machine sizes. A step forward in this mission was achieved by re-analysing previous JET experiments dedicated to pellet particle fuelling. Although the experiments were performed in a parameter regime unsuitable for pellet ELM pacing both with respect to pellet frequency and size they demonstrate prompt triggering of ELMs takes place at JET as well. Prompt triggering, an indispensable premise for useful pacing, obviously can be achieved already with a pellet size sufficiently small to avoid unbearable side-effects by particle fuelling. An ELM released by the local perturbation imposed by the ablating pellet in the plasma edge region is detected when only a minor fraction (less than 1%) of the fuelling size pellets (containing about 4 × 10 21 D) was ablated and deposited yet. It is thus very likely JET will allow for investigations on the operational technique and the underlying physics of pellet pacing once the new system becomes operational.1

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“…The same system will be used for the triggering of ELMs with the aim of reduction of the ELM amplitude [498]. This concept is based on ASDEX Upgrade observations, which show that pellets can trigger high frequency Type-I ELMs with a lower energy loss per ELM relative to the naturally occurring ELMs, with no significant confinement degradation [148].…”

Section: Pellet Fuellingmentioning

confidence: 99%

Chapter 4: Power and particle control

Loarte¹,

et al. 2007

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Abstract.Progress, since the ITER Physics Basis publication, in understanding the processes that will determine the properties of the plasma edge and its interaction with material elements in ITER is described. Experimental areas where significant progress has taken place are : energy transport in the SOL in particular of the anomalous transport scaling, particle transport in the SOL that plays a major role in the interaction of diverted plasmas with the main chamber material elements, ELM energy deposition on material elements and the transport mechanism for the ELM energy from the main plasma to the plasma facing components, the physics of plasma detachment and neutral dynamics including the edge density profile structure and the control of plasma particle content and He removal, the erosion of low and high Z materials in fusion devices, their transport to the core plasma and their migration at the plasma edge including the formation of mixed materials, the processes determining the size and location of the retention of tritium in fusion devices and methods to remove it and the processes determining the efficiency of the various fuelling methods as well as their development towards the ITER requirements. This experimental progress has been accompanied by the development of modelling tools for the physical processes at the edge plasma and plasma-materials interaction and the further validation of these models by comparing their predictions with the new experimental results. Progress in the modelling development and validation has been mostly concentrated in the following areas : refinement of the predictions for ITER with plasma edge modelling codes by inclusion of detailed geometrical features of the divertor and the introduction of physical effects, which can play a 2 major role in determining the divertor parameters at the divertor for ITER conditions such as hydrogen radiation transport and neutral-neutral collisions, modelling of the ion orbits at the plasma edge, which can play a role in determining power deposition at the divertor target, models for plasma-materials and plasma dynamics interaction during ELMs and disruptions, models for the transport of impurities at the plasma edge to describe the core contamination by impurities and the migration of eroded materials at the edge plasma and its associated tritium retention and models for the turbulent processes that determine the anomalous transport of energy and particles across the SOL. The implications for the expected performance of the reference regimes in ITER, the operation of the ITER device and the lifetime of the plasma facing materials are discussed. Introduction.This chapter outlines the significant progress achieved since the ITER Physics Basis in understanding basic scrape-off layer (SOL) and divertor processes in a tokamak. The interaction of plasma with first-wall surfaces will have considerable impact on the performance of fusion plasmas, the lifetime of plasma facing components, and the retention of tritium in next step Burning Plasma E...

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ELM frequency control by continuous small pellet injection in ASDEX Upgrade

Cited by 123 publications

References 25 publications

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

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

ELM triggering by local pellet perturbations in type-I ELMy H-mode plasma at JET

Chapter 4: Power and particle control

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