A high field side pellet penetration depth scaling derived for ASDEX Upgrade

Belonohy, É.; Kardaun, O.; Fehér, Tamás; Gál, K.; Kálvin, S.; Kocsis, G.; Lackner, K.; Lang, P. T.; Neuhäuser, J.

doi:10.1088/0029-5515/48/6/065009

Cited by 12 publications

(10 citation statements)

References 23 publications

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“…A preliminary investigation however indicates that in purely NBI heated H-mode discharges strong ablation radiation sets in also only significantly beyond the separatrix while additional electron cyclotron heating causes a corresponding onset already a few mm outside the separatrix. A more detailed study covering a broader range of pellet and plasma parameters by taking data from the HFS-PAD database [16] is now launched and under way. Nevertheless the D α ablation monitor can still be used as relative measure whose reliability for the subsequent major part of the pellet trajectory was confirmed by the still observed correlation D α ∼ ṁ P ∼ m P ∼ ∆N plasma ( m P estimated pellet mass arriving in plasma taking into account tube transfer losses [17], ∆N plasma plasma particle inventory enhancement by injection).…”

Section: Resultsmentioning

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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Section: Resultsmentioning

confidence: 99%

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

et al. 2008

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“…Since we assume, that the ablation rate is important in determining the cloud size, we also look for the scaling in this form. This idea is also strengthened by an investigation of statistical significance of the different pellet-and plasma parameters at the HFS pellet penetration depth scaling [4], where the outcome of the investigation gave similar parameters.…”

Section: The Pellet Cloud Scalingmentioning

confidence: 97%

“…To optimise fuelling efficiency, it is important to determine, how deep the pellet penetrated into the plasma, before the material has fully ablated (pellet penetration depth), how this material is deposited along the pellet path (deposition profile), and how these two quantities depend on the different pellet-and plasma parameters. Experimental scaling at axially symmetric divertor experiment (ASDEX) Upgrade (AUG) tokamak for H-mode plasmas on high field side (HFS) pellet injection [3] shows, that the main parameters determining the pellet penetration depth are the pellet speed, size, plasma density and temperature and the applied magnetic field [4]. These findings are in fair agreement (despite the lack of magnetic field effect) with the results of the hybrid pellet simulation code (combination of the LLP (Lajos Lengyel's Pellet ablation simulation code) [5] and the neutral gas shielding (NGS) model [6]-see later), which takes into account shielding of the spherical cloud, channel flow and electrostatical double potential [7].…”

Section: Introductionmentioning

confidence: 99%

Pellet cloud characterisation, scaling and estimation of the material- and temperature distribution inside the cloud

et al. 2016

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Using spatially calibrated images of fast visible cameras, a database was established containing pellet cloud images and the related pellet-and plasma parameters. Using this database, two scalings were derived for the cloud size along the magnetic field lines as a function of pellet speed and ablation rate (first case) and pellet speed, pellet volume, plasma temperature and plasma density (second case). Using the images-based on the number of radiation maxima-the four main cloud shapes were also categorized. The isotope effect (the effect of hydrogen pellets in hydrogen or helium plasma) was also investigated with particular attention devoted to the cloud characteristics. Finally, a synthetic diagnostic-which simulates the measurement system and produces a synthetic pellet cloud image based on the output of the pellet cloud simulation-was developed to reveal the underlying densityand temperature distributions of the observed pellet cloud images. Using this synthetic diagnostic, one of the main identified cloud shapes was reconstructed. Our goal is to derive a scaling law for the toroidal extension of the pellet cloud at different pellet-and plasma conditions, to give a more reliable input for the pellet ELM triggering simulations and using these two results-a better understanding of the pellet-caused pressure perturbation.

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“…Pellet fuelling relies on the injection of mm-sized bodies of solid ice formed from hydrogen isotopes. For the sake of high fuelling efficiency, it is believed the launch has to be made at velocities of at least 1 km/s through guiding tubes from the torus inboard side [41]. Acceleration takes place using conventional pellet launchers; these are blower guns, gas guns (single or multi stage) and mechanical centrifuge devices.…”

Section: Matter Injection Technology Reviewmentioning

confidence: 99%

Consequences of the technology survey and gap analysis on the EU DEMO R&D programme in tritium, matter injection and vacuum

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Giegerich

et al. 2016

Fusion Engineering and Design

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In the framework of the EUROfusion Programme, EU is preparing the conceptual design of the inner fuel cycle of a pulsed tokamak DEMO. This paper illustrates a quantified process to shape a R&D programme that exploits as much as possible previous R&D. In an initial step, the high-level requirements are collected and a novel DEMO inner fuel cycle architecture with its three subsystems vacuum pumping, matter injection (fuelling and injection of plasma enhancement gases) and tritium systems (tritium plant and breeder coolant purification) is delineated, driven by the DEMO key challenge to reduce tritium inventory. Then, a technology survey is carried out to review potential existing solutions for the required process functions and to assess their maturity and risks. Finally, a decision-making scheme is applied to select the most promising candidates. ITER technology is exploited where possible. As a primary result, a fuel cycle architecture is suggested with an advanced tritium plant that avoids full isotope separation in the main loop and with a Direct Internal Recycling path in the vacuum systems to shorten cycle times. For core fuelling, classical inboard pellet injection technology is selected, in principle similar to that proposed for ITER but aiming for higher launch speeds to achieve deep fuelling of the DEMO plasma. Based on these findings, a tailored R&D programme is shaped that tackles the key questions until 2020.

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A high field side pellet penetration depth scaling derived for ASDEX Upgrade

Cited by 12 publications

References 23 publications

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

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

Pellet cloud characterisation, scaling and estimation of the material- and temperature distribution inside the cloud

Consequences of the technology survey and gap analysis on the EU DEMO R&D programme in tritium, matter injection and vacuum

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