Experiments and simulation of edge turbulence and filaments in MAST

Dudson, B.; Ayed, N. Ben; Kirk, A.; Wilson, H. R.; Counsell, G.; Xu, X. Q.; Umansky, M.; Snyder, P. B.; Lloyd, B.

doi:10.1088/0741-3335/50/12/124012

Cited by 62 publications

(83 citation statements)

References 24 publications

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“…Interestingly, the filaments propagate in the radial direction with a relatively constant velocity, a result consistent with previous results in MAST [10,11,35] and in literature [27] (although this might not be a universal feature, see [7,[36][37][38]). Filament 1 and 2 move with average radial velocities of around 1.5 km s −1 and 0.6 km s −1 , respectively, in agreement with previous measurements in similar conditions [26,35]. The half width (i.e.…”

Section: Filaments Dynamics and Geometrysupporting

confidence: 90%

“…The camera resulution was such that sub centimeter filaments could be resolved, as tested using syntetic signals. In order to enhance the filamentary structures we used a background subtraction technique [26] which calculates in each pixel the minimum light intensity over 16 frames (current frame plus 15 others) and subtracts this from the frame of interest. It is observed that the background emission peaks in the region of the separatrix, where the neutral ionisation is maximum.…”

Section: Diagnostics and Analysis Techniquementioning

confidence: 99%

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Multi-code analysis of scrape-off layer filament dynamics in MAST

Militello

Walkden

Farley

et al. 2016

Plasma Phys. Control. Fusion

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Section: Filaments Dynamics and Geometrysupporting

confidence: 90%

Section: Diagnostics and Analysis Techniquementioning

confidence: 99%

Multi-code analysis of scrape-off layer filament dynamics in MAST

Militello

Walkden

Farley

et al. 2016

Plasma Phys. Control. Fusion

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“…8 left). The characteristics of these filaments as deduced from the visible imaging are listed in Table 1 [34]. This comparison suggests that the sporadic inter-ELM filaments are more closely related to L- mode filaments than to ELM filaments (e.g.…”

Section: Sol Modelling and Edge Filamentsmentioning

confidence: 94%

Overview of physics results from MAST

Raman¹,

Ahn²,

Allain³

et al. 2011

Nucl. Fusion

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Several improvements to the MAST plant and diagnostics have facilitated new studies advancing the physics basis for ITER and DEMO, as well as for future spherical tokamaks. Using the increased heating capabilities P NBI ≤ 3.8 MW H-mode at I p = 1.2 MA was accessed showing that the energy confinement on MAST scales more weakly with I p and more strongly with B t than in the ITER IPB98(y,2) scaling. Measurements of the fuel retention of shallow pellets extrapolate to an ITER particle throughput of 70% of its original design value. The anomalous momentum diffusion, χ φ , is linked to the ion diffusion, χ i , with a Prandtl number close to P φ ≈ χ φ /χ i ≈ 1, although χ i approaches neoclassical values. New high spatially resolved measurements of the edge radial electric field, E r , show that the position of steepest gradients in electron pressure and E r are coincident, but their magnitudes are not linked. The T e pedestal width on MAST scales with the β pol rather than ρ pol . The ELM frequency for type-IV ELMs, new in MAST, was almost doubled using n = 2 resonant magnetic perturbations from a set of 4 external coils (n = 1, 2). A new internal 12 coil set (n ≤ 3) has been commissioned. The filaments in the inter-ELM and L-mode phase are different from ELM filaments, and the characteristics in L-mode agree well with turbulence calculations. A variety of fast particle driven instabilities were studied from 10 kHz saturated fishbone like activity up to 3.8 MHz compressional Alfvén eigenmodes (CAE). The damping rate of ellipticityinduced AE was measured to be 4% using the new internal coils as antennae. Fast particle instabilities also affect the off-axis NBI current drive and lead to fast ion diffusion of the order of 0.5 m 2 /s and reduce the driven current fraction from 40% to 30%. EBW current drive start-up is demonstrated for the first time in a spherical tokamak generating plasma currents up to 55 kA. Many of these studies contributed to the physics basis of a planned upgrade to MAST. Introduction: MAST [1]is one of the two leading tight aspect ratio (A = ε −1 = R/a = 0.85 m/0.65 m ∼ 1.3, I p ≤ 1.5 MA) tokamaks in the world. The hot T ≤ 3 keV, dense n e = (0.1 − 1) × 10 20 m −3 and highly shaped (δ ≤ 0.5, 1.6 ≤ κ ≤ 2.5) plasmas are accessed at moderate toroidal field B t (R = 0.7 m) ≤ 0.62 T and show many similarities to conventional aspect ratio tokamaks. Detailed physics studies using the extensive array of state of the art diagnostics and access to different physics regimes help to consolidate the physics basis for ITER and DEMO [2,3], and explore the viability of future devices based on the spherical tokamak (ST) concept such as a component test facility (CTF) [4] or an advanced power plant [5]. The challenge for today's experiments is to find an integrated scenario that extrapolates to these future devices, in particular to develop plasmas with reduced power load on plasma facing components, notably from edge localised modes (ELM), but high confinement facilitated by internal or edge transport ba...

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“…93,100 3D simulations have been used to make comparisons of blob size (or poloidal correlation length), 74,88 parallel filament structure, 74,88,140 and blob velocity. 74,91 Typically, the agreement was reasonable (factor of 2) for some quantities but poor for others. In some cases, it was impossible to compare the same quantities in both simulation and experiment; in other papers, the simulation parameters were not varied over a large enough range to optimize the comparison.…”

Section: -39mentioning

confidence: 99%

Convective transport by intermittent blob-filaments: Comparison of theory and experiment

2011

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A blob-filament (or simply “blob”) is a magnetic-field-aligned plasma structure which is considerably denser than the surrounding background plasma and highly localized in the directions perpendicular to the equilibrium magnetic field B. In experiments and simulations, these intermittent filaments are often formed near the boundary between open and closed field lines, and seem to arise in theory from the saturation process for the dominant edge instabilities and turbulence. Blobs become charge-polarized under the action of an external force which causes unequal drifts on ions and electrons; the resulting polarization-induced E × B drift moves the blobs radially outwards across the scrape-off-layer (SOL). Since confined plasmas generally are subject to radial or outwards expansion forces (e.g., curvature and ∇B forces in toroidal plasmas), blob transport is a general phenomenon occurring in nearly all plasmas. This paper reviews the relationship between the experimental and theoretical results on blob formation, dynamics and transport and assesses the degree to which blob theory and simulations can be compared and validated against experiments.

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Experiments and simulation of edge turbulence and filaments in MAST

Cited by 62 publications

References 24 publications

Multi-code analysis of scrape-off layer filament dynamics in MAST

Multi-code analysis of scrape-off layer filament dynamics in MAST

Overview of physics results from MAST

Convective transport by intermittent blob-filaments: Comparison of theory and experiment

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