Influence of the low order rational q surfaces on the pellet deposition profile

Commaux, N.; Pégouriè, B.; Baylor, L. R.; Köchl, F.; Parks, P.B.; Jernigan, T. C.; Géraud, A.; Nehme, H.

doi:10.1088/0029-5515/50/2/025011

Cited by 19 publications

(31 citation statements)

References 15 publications

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“…A detailed description of (4) is given in [16]. In HPI2, the heat transfer from the background plasma to the plasmoid is governed by the following equations, which describe the change in electron and ion energy content of the plasmoid [13]: (5) The first term describes the heat exchange between the plasmoid and the background plasma in the magnetic flux surface shell, where the plasmoid is located.…”

Section: Jintracmentioning

confidence: 99%

Integrated simulation of ELM triggered by a pellet through energy absorption and transport enhancement

Hayashi¹,

Parail²,

Koechl³

et al. 2011

Nucl. Fusion

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Abstract. Two integrated core / scrape-off-layer (SOL) / divertor transport codes TOPICS-IB and JINTRAC with links to MHD stability codes have been coupled with models of pellet injection to clarify effects of pellet on the behavior of edge localized modes (ELMs). The energy absorption by pellet and its further displacement due to ExB drift as well as transport enhancement by the pellet were found to be able to trigger the ELM. The ablated cloud of pellet absorbs the background plasma energy and causes the radial redistribution of pressure due to the subsequent ExB drift. On the other hand, the sharp increase in local density and temperature gradients in the vicinity of ablated cloud could cause transient enhancement of heat and particle transport. Both mechanisms produce a region of an increased pressure gradient in the background plasma profile within the pedestal, which triggers the ELM. The mechanisms have the potential to explain a wide range of experimental observations.

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Section: Jintracmentioning

confidence: 99%

Integrated simulation of ELM triggered by a pellet through energy absorption and transport enhancement

Hayashi¹,

Parail²,

Koechl³

et al. 2011

Nucl. Fusion

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“…In addition, several mechanisms that either enhance [14] or reduce [13,15,16] such a drift have been proposed. These models can reproduce accurately the experimental results in tokamaks [3,17,18]. For instance, these drift effects are included in the Hydrogen Pellet Injection (HPI2) code, developed by Pégourié and Köchl [10,13,19].…”

Section: Introductionmentioning

confidence: 99%

Experimental studies and simulations of hydrogen pellet ablation in the stellarator TJ-II

Panadero¹,

McCarthy²,

Koechl

et al. 2018

Nucl. Fusion

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Plasma core fuelling is a key issue for the development of steady-state scenarios in large magnetically-confined fusion devices, in particular for helical-type machines. At present, cryogenic pellet injection is the most promising technique for efficient fuelling. Here, pellet ablation and fuelling efficiency experiments, using a compact pellet injector, are carried out in Electron Cyclotron Resonance and Neutral Beam Injection heated plasmas of the stellarator TJ-II. Ablation profiles are reconstructed from light emissions collected by silicon photodiodes and a fast-frame camera system, under the assumptions that such emissions are loosely related to the ablation rate and that pellet radial acceleration is negligible. In addition, pellet particle deposition and fuelling efficiency are determined using density profiles provided by a Thomson Scattering system. Furthermore, experimental results are compared with ablation and deposition profiles provided by the HPI2 pellet code, which is adapted here for the stellarators Wendelstein 7-X (W7-X) and TJ-II. Finally, the HPI2 code is used to simulate ablation and deposition profiles for pellets of different sizes and velocities injected into relevant W7-X plasma scenarios, while estimating the plasmoid drift and the fuelling efficiency of injections made from two W7-X ports.

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“…From pellet injection experiments in DIII-D and Tore Supra it is known that the maxima of the mass deposition profiles are close to the magnetic q = 2 and q = 3 surfaces. Low order rational surfaces appear to slow down or even stop the polarization drift of the density cloud towards the low field side of the plasma [29]. Since holes are regions of lower density than the ambient plasma the ∇B polarization and therefore the drift is in opposite direction to blobs or density clouds.…”

Section: Discussionmentioning

confidence: 99%

On the genesis and nature of Palm Tree Modes in the JET tokamak

Maszl¹,

Naulin²,

Schrittwieser³

2021

Preprint

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Long-lived, highly localized structures called palm tree modes (PTM) are observed in the edge plasma of the JET tokamak. Although PTMs are well documented, little is known about the mechanisms which produce these structures. In the case of the PTM, an ELM-postcursor, its genesis is usually explained by ergodisation of the magnetic field due to edge localized modes and the appearance of a seed magnetic island which evolves into a PTM later. In this study we try to invoke a creation mechanism based on the concepts and observations in edge plasma turbulence. An interesting aspect of plasma turbulence is the occurrence of coherent, long-lived structures in the scrape-off-layer (SOL). These localized and magnetic-field-aligned regions with higher or lower plasma densities are called blobs and holes. Measurements show that these filaments carry parallel currents. We thus here interpret ELM-filaments as massive blobs and the interspace between these filaments as holes. We demonstrate that a forward-modelled closed current filament on a q = 3 surface produces similar magnetic fluctuations as measured by the JET in-vessel magnetic pickup coils if a PTM is present. From that we deduce that if a hole is captured on a q = 3 surface after an ELM-crash, a PTM equivalent signature is generated. If the ELM-filament itself is captured on a q = 4 surface, a signature equivalent to an outer mode appears.

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Influence of the low order rational q surfaces on the pellet deposition profile

Cited by 19 publications

References 15 publications

Integrated simulation of ELM triggered by a pellet through energy absorption and transport enhancement

Integrated simulation of ELM triggered by a pellet through energy absorption and transport enhancement

Experimental studies and simulations of hydrogen pellet ablation in the stellarator TJ-II

On the genesis and nature of Palm Tree Modes in the JET tokamak

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