Dynamics of filaments during the edge-localized mode crash on NSTX

Lampert, M.; Diallo, A.; Myra, J. R.; Zweben, S. J.

doi:10.1063/5.0031322

Cited by 8 publications

(4 citation statements)

References 47 publications

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“…Measurements on ELM radial velocities in the literature have shown values ranging from ∼0.07 km s −1 in K-STAR [50] to 2-3 km s −1 in ASDEX-Upgrade [51], NSTX [52] and MAST [53], and intermediate values (0.2-0.7 km s −1 ) observed in JET [15] and DIII-D [33]. The velocity profiles input to the model and examined in this work, shown in figure 9(a), are obtained by fitting the peak radial velocities of the ELMs (typically 2-3 ELMs per case, as shown in red for the partially detached case), measured through the SOL with FRP, with an exponential function, as discussed in section 3, except for the attached case (in black) which is measured with reflectometry and whose decay length is extracted from a sensitivity study that will be discussed in section 5.1.…”

Section: Radial Velocity Of Elm Filaments For Various Divertor Condit...mentioning

confidence: 99%

Measurements and modeling of type-I and type-II ELMs heat flux to the DIII-D divertor

Perillo,

Boedo,

Lasnier

et al. 2023

Nucl. Fusion

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Type-I and type-II Edge-Localized-Modes (ELMs) heat flux profiles measured at the DIII-D divertor feature a peak in the vicinity of the strike-point and a plateau in the scrape-off-layer (SOL), which extends to the first wall. The plateau is present in attached and detached divertors and it is found to originate with plasma bursts upstream in the SOL. The integrated ELM heat flux is distributed at ~65% in the peak and ~35% in this plateau. The Parallel Loss Model (PLM), currently used at ITER to predict power loads to the walls, is benchmarked using these results in the primary and secondary divertors with unprecedented constraints using experimental input data for ELM size, radial velocity, energy, electron temperature and density, heat flux footprints and number of filaments. The model can reproduce the experimental near-SOL peak within ~20%, but cannot match the SOL plateau. Employing a two-component approach for the ELM radial velocity, as guided by intermittent data, the full radial heat flux profile can be well matched. The ELM-averaged radial velocity at the separatrix, which explains profile widening, increases from ~0.2 km/s in attached to ~0.8 km/s in detached scenarios, as the ELM filaments’ path becomes electrically disconnected from the sheath at the target.The results presented here indicate filaments fragmentation as a possible mechanism for ELM transport to the far-SOL and provide evidence on the beneficial role of detachment to mitigate ELM flux in the divertor far-SOL. However, these findings imply that wall regions far from the strike points in future machines should be designed to withstand significant heat flux, even for small-ELM regimes. 

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Section: Radial Velocity Of Elm Filaments For Various Divertor Condit...mentioning

confidence: 99%

Measurements and modeling of type-I and type-II ELMs heat flux to the DIII-D divertor

Perillo,

Boedo,

Lasnier

et al. 2023

Nucl. Fusion

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“…The time-to-ELM crash is given by the colorbar. Reprinted from [108], with the permission of AIP Publishing. edge current and pressure gradient (figure 10(b)).…”

Section: Transport and Pedestal Structurementioning

confidence: 99%

“…First, the characteristic behavior of SOL filaments observed before, during and after ELM crashes was analyzed exploiting the high temporal (2.5 μs) and spatial resolution (10 mm) of the GPI system [108]. A database of 159 ELM events (including type I, III and V ELMs) was generated from the 2010 NSTX measurement campaign.…”

Section: Boundary and Pmimentioning

confidence: 99%

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NSTX-U theory, modeling and analysis results

Guttenfelder¹,

Battaglia²,

Белова³

et al. 2022

Nucl. Fusion

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The mission of the low aspect ratio spherical tokamak NSTX-U is to advance the physics basis and technical solutions required for optimizing the configuration of next-step steady-state tokamak fusion devices. NSTX-U will ultimately operate at up to 2 MA of plasma current and 1 T toroidal field on axis for 5 seconds, and has available up to 15 MW of Neutral Beam Injection (NBI) power at different tangency radii and 6 MW of High Harmonic Fast Wave (HHFW) heating. With these capabilities NSTX-U will develop the physics understanding and control tools to ramp-up and sustain high performance fully non-inductive plasmas with large bootstrap fraction and enhanced confinement enabled via the low aspect ratio, high beta configuration. With its unique capabilities, NSTX-U research also supports ITER and other critical fusion development needs. Super-Alfvénic ions in beam-heated NSTX-U plasmas access energetic particle parameter space that is relevant for both -heated conventional and low aspect ratio burning plasmas. NSTX-U can also generate very large target heat fluxes to test conventional and innovative plasma exhaust and plasma facing component (PFC) solutions. This paper summarizes recent analysis, theory and modelling progress to advance the tokamak physics basis in the areas of macrostability and 3D fields, energetic particle stability and fast ion transport, thermal transport and pedestal structure, boundary and plasma material interaction, RF heating, scenario optimization and real-time control.

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Novel 2D velocity estimation method for large transient events in plasmas

Lampert

Diallo

Zweben

2021

Review of Scientific Instruments

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Dynamics of fast transient events are challenging to be analyzed with high time resolution. Such events can occur in fusion plasmas such as the filaments during edge-localized modes (ELMs). In this paper, we present a robust method—the spatial displacement estimation—for estimating the displacements of structures with fast dynamics from high spatial and time resolution imaging diagnostics [e.g., gas-puff imaging (GPI)] with sampling time temporal resolution. First, a background suppression method is shown, which suppresses the slowly time-evolving and spatially non-uniform background in the signal. In the second step, a two-dimensional polynomial trend subtraction method is presented to tackle the remaining polynomial order trend in the signal. After performing these pre-processing steps, the spatial displacement of the propagating structure is estimated from the two-dimensional spatial cross-correlation coefficient function calculated between consecutive frames. The method is tested for its robustness and accuracy by simulated Gaussian events and spatially displaced random noise. An example application of the method is presented on propagating ELM filaments measured by the GPI system on the National Spherical Torus Experiment spherical tokamak.

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Dynamics of filaments during the edge-localized mode crash on NSTX

Cited by 8 publications

References 47 publications

Measurements and modeling of type-I and type-II ELMs heat flux to the DIII-D divertor

Measurements and modeling of type-I and type-II ELMs heat flux to the DIII-D divertor

NSTX-U theory, modeling and analysis results

Novel 2D velocity estimation method for large transient events in plasmas

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