ELM pacing investigations at JET with the new pellet launcher

Lang, P. T.; Alonso, A.; Alper, B.; Belonohy, É.; Boboc, A.; Devaux, S.; Eich, T.; Frigione, D.; Gál, K.; Garzotti, L.; Géraud, A.; Kocsis, G.; Köchl, F.; Lackner, K.; Loarte, A.; Lomas, P. J.; Maraschek, M.; Müller, Hans; Neu, R.; Neuhäuser, J.; Petravich, G.; Saibene, G.; Schweinzer, J.; Thomsen, H.; Tsalas, M.; Wenninger, R.; Zohm, H.

doi:10.1088/0029-5515/51/3/033010

Cited by 52 publications

(70 citation statements)

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“…On ASDEX_Upgrade an increase of the ELM frequency by a factor of 2 was obtained with 83 Hz pellets from the high field side (HFS) that resulted in strong fueling due to an ExB major radius drift of the pellet cloud [12] and a subsequent decrease in confinement [6]. Similar HFS injection fueling and confinement observations were made on JET [11]. The DIII-D pellet injector [13] was configured to inject deuterium pellets from the LFS near the divertor X point (''R-2'') and outside midplane (''MID'') as shown in Fig.…”

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confidence: 72%

“…While the principle of on-demand ELM triggering by pellet injection has been previously observed on ASDEX-Upgrade [6], DIII-D [10], and JET [11], these new DIII-D experiments have demonstrated unprecedented ELM control with no deterioration in plasma performance and no net fueling from the injected pellets, which is due to the LFS injection location and triggering of an ELM-like event well before the pellets reach the edge pedestal top. On ASDEX_Upgrade an increase of the ELM frequency by a factor of 2 was obtained with 83 Hz pellets from the high field side (HFS) that resulted in strong fueling due to an ExB major radius drift of the pellet cloud [12] and a subsequent decrease in confinement [6].…”

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confidence: 93%

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Reduction of Edge-Localized Mode Intensity Using High-Repetition-Rate Pellet Injection in TokamakH-Mode Plasmas

et al. 2013

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High repetition rate injection of deuterium pellets from the low-field side (LFS) of the DIII-D tokamak is shown to trigger high-frequency edge-localized modes (ELMs) at up to 12× the low natural ELM frequency in H-mode deuterium plasmas designed to match the ITER baseline configuration in shape, normalized beta, and input power just above the H-mode threshold. The pellet size, velocity, and injection location were chosen to limit penetration to the outer 10% of the plasma. The resulting perturbations to the plasma density and energy confinement time are thus minimal (<10%). The triggered ELMs occur at much lower normalized pedestal pressure than the natural ELMs, suggesting that the pellet injection excites a localized high-n instability. Triggered ELMs produce up to 12× lower energy and particle fluxes to the divertor, and result in a strong decrease in plasma core impurity density. These results show for the first time that shallow, LFS pellet injection can dramatically accelerate the ELM cycle and reduce ELM energy fluxes on plasma facing components, and is a viable technique for real-time control of ELMs in ITER.

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confidence: 72%

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confidence: 93%

Reduction of Edge-Localized Mode Intensity Using High-Repetition-Rate Pellet Injection in TokamakH-Mode Plasmas

et al. 2013

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“…For pacing and ELM sustainment demonstration in plasmas at I P = 2.5 MA at low and high triangularity large pellets had to be used. The obtained results can be compared to recent findings from similar experiments performed with a C wall [15]. The pellets were produced by the HFPI, which was installed on JET at the end of 2007 and further improved during the shutdown by modifications of the extrusion nozzle assembly eliminating the ice extrusion instability causing a general degradation of performance [7].…”

Section: Setup and Experimental Boundary Conditionsmentioning

confidence: 92%

“…Penetration was modelled by the pellet ablation and deposition code HPI2 [18] assuming a linear relation between the recorded ablation radiation and the pellet mass and taking the pellet arrival speed to be 0.9 times the average speed in the final track. The analysis was performed the same way as a previous analysis for trigger investigations during experimental campaigns C20 -C27 while JET was operated with a carbon (C) wall [15,19].…”

Section: Triggering Investigationmentioning

confidence: 99%

ELM pacing and trigger investigations at JET with the new ITER-like wall

et al. 2013

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Abstract. During the installation of the new ITER-Like Wall at JET, the High Frequency Pellet Injector has been further improved. The launching system is now capable of delivering reliable fuelling size pellets from the magnetic outboard side up to 15 Hz repetition rate. Pacing size pellets can be produced at rates up to 50 Hz but pellet trains suffer some losses during the transfer to the plasma. A significant fraction of the pellet train can arrive at the plasma when launched from the outboard, while only a few pellets make it to the vessel inboard launching site. Stable and reliable ELM control was achieved when using outboard fuelling size pellets. This tool was successfully applied for scenario development purposes in the ITER baseline H-mode scenario at 2.5 MA. Employed for ELM sustainment and impurity control, pellets prevented the ELM frequency from becoming so low as to cause a radiative collapse of the discharge. Despite technical limitations, injecting outboard pacing size pellets resulted in a transient enhancement of the initial ELM frequency up to a factor 4.5. This could be achieved in cases where a continuous train of sufficiently large and fast pellets were arriving in the plasma at a frequency of up to 31 Hz. Pacing size pellets were also used to investigate the ELM trigger threshold. Three basic parameters could be identified for outboard pellet launch. The ELM triggering probability increased with: i) the time elapsed since the previous ELM occurred, ii) pellet mass and iii) pellet speed. An indication for dependence of the ELM trigger threshold on the poloidal pellet launch position has been found; inboard launched pellets seem to reveal a higher trigger capability than pellets launched from the outboard. Finally, we compared the pellet penetration depth required for ELM triggering in the actual JET configuration with plasmafacing components to similar previous experiments performed with a carbon wall. This comparison indicates that pellet ELM triggering requires deeper penetration in the ILW configuration. IntroductionControlling the ELM frequency is an important task for the development of high performance plasma scenarios. ELM control requirements in ITER [1] cover the limitation and mitigation of large heat fluxes to the divertor and the first wall expected during type-I ELMs for H-mode operational scenarios at high plasma current. Furthermore, the sustainment of a minimum ELM frequency, even in the low current regime, is required when operating with a W divertor at low density, to expel tungsten (W) from the plasma edge before it diffuses to the plasma core [2]. Following its first demonstration at ASDEX Upgrade [3,4,5] and the recent successful achievement of an ITER relevant 10x ELM frequency increase on DIII-D [6], pellet ELM pacing is considered as one of the most promising tools for ELM control in ITER. ELM triggering occurs most likely due to the local impact of the pellet ablation plasmoid in the edge barrier, which is expected to be effective even in high performance and high pl...

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“…JET [27] and AS-DEX Upgrade [28]. ELM control by pellet injection has been demonstrated on ASDEX Upgrade [29] and JET [30]. While many devices have demonstrated suppression or mitigation of ELMs with these and other methods a validated theoretical model to fully understand the phenomenon is still lacking and the final demonstration will be on ITER itself.…”

Section: Controlling Macroscopic Instabilitiesmentioning

confidence: 99%

Fusion Energy Research for ITER and Beyond

Romanelli

Laxåbäck²

2011

Green

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The achievement in the last two decades of controlled fusion in the laboratory environment is opening the way to the realization of fusion as a source of sustainable, safe and environmentally responsible energy. The next step towards this goal is the construction of the International Thermonuclear Experimental Reactor (ITER), which aims to demonstrate net fusion energy production on the reactor scale. This paper reviews the current status of magnetic confinement fusion research in view of the ITER project and provides an overview of the main remaining challenges on the way towards the realization of commercial fusion energy production in the second half of this century.

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ELM pacing investigations at JET with the new pellet launcher

Cited by 52 publications

References 27 publications

Reduction of Edge-Localized Mode Intensity Using High-Repetition-Rate Pellet Injection in TokamakH-Mode Plasmas

Reduction of Edge-Localized Mode Intensity Using High-Repetition-Rate Pellet Injection in TokamakH-Mode Plasmas

ELM pacing and trigger investigations at JET with the new ITER-like wall

Fusion Energy Research for ITER and Beyond

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