ELM behavior in ASDEX Upgrade with and without nitrogen seeding

Frassinetti, L.; Dunne, M.; Beurskens, M.; Wolfrum, E.; Bogomolov, A.; Carralero, D.; Cavedon, M.; Fischer, R.; Laggner, F. M.; McDermott, R. M.; Meyer, H.; Tardini, G.; Viezzer, E.

doi:10.1088/0029-5515/57/2/022004

Cited by 12 publications

(17 citation statements)

References 44 publications

(79 reference statements)

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“…The high‐pressure fingers in the SOL are partly sheared off by plasma flows induced during the crash by Maxwell stress, leading to the formation of filaments elongated along the magnetic field lines as shown in Figure . Several such bursts are observed, which is in line with experimental observations for long type‐I ELMs . The high‐pressure structures expelled into the SOL quickly lose energy towards the divertor by parallel heat conduction, whereas the heat flux onto the main walls is typically low since the time scale for parallel conduction to the divertors is usually much shorter than the time scale for the filament convection to the wall.…”

Section: Type‐i Elmssupporting

confidence: 85%

“…A proper treatment of the heat flux limit will be implemented for future simulations. The ELM duration defined by the time during which significant losses and divertor heat fluxes are observed is about 2 ms both in the experiment and simulations, corresponding to the so‐called long ELMs …”

Section: Type‐i Elmsmentioning

confidence: 98%

“…The simulations shown in the following are based on a typical ASDEX Upgrade H‐mode equilibrium with an edge safety factor q 95 = 5.9. The experimentally observed type‐I ELM crashes take about 2 ms corresponding to the so‐called long ELMs . A pre‐ELM equilibrium reconstruction (ASDEX Upgrade discharge #33616 at 7.2 s) performed by the CLISTE code is used for initial conditions, which is already unstable such that the simulations only allow the investigation of the ELM crash itself but not the inter‐ELM phase.…”

Section: Type‐i Elmsmentioning

confidence: 99%

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Insights into type‐I edge localized modes and edge localized mode control from JOREK non‐linear magneto‐hydrodynamic simulations

Hoelzl

Huijsmans

Orain

et al. 2018

Contributions to Plasma Physics

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Edge localized modes (ELMs) are repetitive instabilities driven by the large pressure gradients and current densities in the edge of H‐mode plasmas. Type‐I ELMs lead to a fast collapse of the H‐mode pedestal within several hundred microseconds to a few milliseconds. Localized transient heat fluxes to divertor targets are expected to exceed tolerable limits for ITER, requiring advanced insights into ELM physics and applicable mitigation methods. This paper describes how non‐linear magneto‐hydrodynamic (MHD) simulations can contribute to this effort. The JOREK code is introduced, which allows the study of large‐scale plasma instabilities in tokamak X‐point plasmas covering the main plasma, the scrape‐off layer, and the divertor region with its finite element grid. We review key physics relevant for type‐I ELMs and show to what extent JOREK simulations agree with experiments and help reveal the underlying mechanisms. Simulations and experimental findings are compared in many respects for type‐I ELMs in ASDEX Upgrade. The role of plasma flows and non‐linear mode coupling for the spatial and temporal structure of ELMs is emphasized, and the loss mechanisms are discussed. An overview of recent ELM‐related research using JOREK is given, including ELM crashes, ELM‐free regimes, ELM pacing by pellets and magnetic kicks, and mitigation or suppression by resonant magnetic perturbation coils (RMPs). Simulations of ELMs and ELM control methods agree in many respects with experimental observations from various tokamak experiments. On this basis, predictive simulations become more and more feasible. A brief outlook is given, showing the main priorities for further research in the field of ELM physics and further developments necessary.

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Section: Type‐i Elmssupporting

confidence: 85%

Section: Type‐i Elmsmentioning

confidence: 98%

Section: Type‐i Elmsmentioning

confidence: 99%

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Insights into type‐I edge localized modes and edge localized mode control from JOREK non‐linear magneto‐hydrodynamic simulations

Hoelzl

Huijsmans

Orain

et al. 2018

Contributions to Plasma Physics

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“…Second, granule injections at a frequency greater than what is required for mitigation could lead to a sharp increase in overall Z eff . While there are instances of improved plasma performance as a result elevated impurity concentration within the pedestal [12], an overaggressive injection size or frequency could dilute the main ion concentration within the burning plasma, thus decreasing the fusion power. To measure ELM triggering characteristics, lithium granules of multiple sizes were injected into EAST H-mode discharges to ascertain their likelihood of triggering an ELM.…”

Section: Introductionmentioning

confidence: 99%

Injected mass deposition thresholds for lithium granule instigated triggering of edge localized modes on EAST

et al. 2018

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The ability of an injected lithium granule to promptly trigger an edge localized mode (ELM) has been established in multiple experiments. By horizontally injecting granules ranging in diameter from 200 microns to 1mm in diameter into the low field side of EAST H-mode discharges we have determined that granules with diameter > 600 microns are successful in triggering ELMs more than 95% of the time. It was also demonstrated that below 600 microns the triggering efficiency decreased roughly with granule size. Granules were radially injected from the outer midplane with velocities ~ 80 m/s into EAST upper single null discharges with an ITER like tungsten monoblock divertor. These granules were individually tracked throughout their injection cycle in order to determine their efficacy at triggering an ELM. For those granules of sufficient size, ELM triggering was a prompt response to granule injection. By simulating the granule injection with an experimentally benchmarked neutral gas shielding (NGS) model, the ablatant mass deposition required to promptly trigger an ELM is calculated and the fractional mass deposition is determined.

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“…JET ITER-like wall ELMs are sometimes followed by an extended collapse phase, called the slow transport event (STE) [22], the presence of which has been proposed to be related to divertor/scrape-off layer (SOL) conditions [23] [24] and to a change in recycling behavior in a W divertor [25] [26] . These STEs are analogous to the second phase of ELM collapse observed at ASDEX Upgrade (AUG) [24].…”

Section: Elm Duration and Slow Transport Eventsmentioning

confidence: 99%

Correlation analysis for energy losses, waiting times and durations of type I edge-localized modes in the Joint European Torus

et al. 2017

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Abstract. Several important ELM control techniques are in large part motivated by the empirically observed inverse relationship between average ELM energy loss and ELM frequency in a plasma. However, to ensure a reliable effect on the energy released by the ELMs, it is important that this relation is verified for individual ELM events. Therefore, in this work the relation between ELM energy loss (W ELM ) and waiting time (∆t ELM ) is investigated for individual ELMs in a set of ITER-like wall plasmas in JET. A comparison is made with the results from a set of carbon-wall and nitrogenseeded ITER-like wall JET plasmas. It is found that the correlation between W ELM and ∆t ELM for individual ELMs varies from strongly positive to zero. Furthermore, the effect of the extended collapse phase often accompanying ELMs from unseeded JET ILW plasmas and referred to as the slow transport event (STE) is studied on the distribution of ELM durations, and on the correlation between W ELM and ∆t ELM . A high correlation between W ELM and ∆t ELM , comparable to CW plasmas is only found in nitrogen-seeded ILW plasmas. Finally, a regression analysis is performed using plasma engineering parameters as predictors for determining the region of the plasma operational space with a high correlation between W ELM and ∆t ELM .

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ELM behavior in ASDEX Upgrade with and without nitrogen seeding

Cited by 12 publications

References 44 publications

Insights into type‐I edge localized modes and edge localized mode control from JOREK non‐linear magneto‐hydrodynamic simulations

Insights into type‐I edge localized modes and edge localized mode control from JOREK non‐linear magneto‐hydrodynamic simulations

Injected mass deposition thresholds for lithium granule instigated triggering of edge localized modes on EAST

Correlation analysis for energy losses, waiting times and durations of type I edge-localized modes in the Joint European Torus

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