Particle confinement of pellet-fuelled tokamak plasma

Valovič, M.; Axon, K.B.; Garzotti, L.; Saarelma, S.; Thyagaraja, A.; Akers, R.; Gurl, C.; Kirk, A.; Lloyd, B.; Maddison, G.; Morris, A.W.; Patel, A.; Shibaev, S.; Scannell, R.; Taylor, D.; Walsh, M. J.

doi:10.1088/0029-5515/48/7/075006

Cited by 48 publications

(54 citation statements)

References 21 publications

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“…This leads to an increased turbulence level in this region according to calculations with the GS2 [26] and CUTIE [27] codes. This increased turbulence leads to OV/3-2 an increased inwards particle flux which is needed to understand the pellet retention time [24]. As can be seen from the square in Fig.…”

Section: Pellet Fuellingmentioning

confidence: 95%

“…Typical pellet speeds between 250 m/s ≤ v pellet ≤ 400 m/s from the high field side (HFS) top of the machine result in shallow pellet injection between 0.6 ≤ ρ pel = √ ψ N,pel ≤ 0.9 The pellet trajectory has been observed using unfiltered high speed visible imaging as well as time averaged narrow band filtered visible imaging in a line free region at λ = (523.44 ± 0.32) nm to measure bremsstrahlung. These data are used to establish the pellet deposition radius ρ pel [24]. High resolution TS measurements with the single time Ruby system event triggered from the pellet system itself are used to determine the pellet retention time τ pel [24,25].…”

Section: Pellet Fuellingmentioning

confidence: 99%

“…These data are used to establish the pellet deposition radius ρ pel [24]. High resolution TS measurements with the single time Ruby system event triggered from the pellet system itself are used to determine the pellet retention time τ pel [24,25]. [2] of n e = 10 20 m −3 , S = 683 m 2 and τ E = 3.7 s. Comparisons with predictive pellet ablation codes show that the ∇B-drift as well as the plasma precooling due to the drift is needed in order to understand the post pellet n e profiles on MAST.…”

Section: Pellet Fuellingmentioning

confidence: 99%

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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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Section: Pellet Fuellingmentioning

confidence: 95%

Section: Pellet Fuellingmentioning

confidence: 99%

Section: Pellet Fuellingmentioning

confidence: 99%

See 1 more Smart Citation

Overview of physics results from MAST

Raman¹,

Ahn²,

Allain³

et al. 2011

Nucl. Fusion

Self Cite

View full text Add to dashboard Cite

show abstract

“…We have repeated the microstability analysis of an older MAST pellet shot presented in [14], where density and temperature profiles were measured with the previous Thomson scattering system, which had a lower temporal and spatial resolution than the current system. In that shot the pellet mass was 0.7·10 20 deuterium atoms (i. e. ∼ 60% smaller than the pellet considered in the present study) and the analysis was limited to one radial flux surface (corresponding to the maximum R/L Te surface inside the pellet ablation peak) at one time slice (5 ms after pellet injection) and considered only the region of the spectrum 0.08 < k y ρ i < 0.5.…”

Section: Comparison With Previous Analysismentioning

confidence: 99%

Microstability analysis of pellet fuelled discharges in MAST

Garzotti

Figueiredo²,

Roach

et al. 2014

Plasma Phys. Control. Fusion

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Abstract. Reactor grade plasmas are likely to be fuelled by pellet injection. This technique transiently perturbs the profiles, driving the density profile hollow and flattening the edge temperature profile. After the pellet perturbation, the density and temperature profiles relax towards their quasi-steady-state shape. Microinstabilities influence plasma confinement and will play a role in determining the evolution of the profiles in pellet fuelled plasmas. In this paper we present the microstability analysis of pellet fuelled H-mode MAST plasmas. Taking advantage of the unique capabilities of the MAST Thomson scattering system and the possibility of synchronizing the eight lasers with the pellet injection, we were able to measure the evolution of the post-pellet electron density and temperature profiles with high temporal and spatial resolution. These profiles, together with ion temperature profiles measured using a charge exchange diagnostic, were used to produce equilibria suitable for microstability analysis of the equilibrium changes induced by pellet injection. This analysis, carried out using the local gyrokinetic code GS2, reveals that the microstability properties are extremely sensitive to the rapid and large transient excursions of the density and temperature profiles, which also change collisionality and βe significantly in the region most strongly affected by the pellet ablation.

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“…Such plasmas are an excellent test bed for exploration of anomalous electron transport and electron temperature gradient driven fluctuations have recently been identified in NSTX by coherent scattering of electromagnetic waves [23]. Particle confinement of pellet fuelled plasmas has been studied in MAST [24]. Grad-B effects and turbulent transport can both enhance pellet penetration.…”

Section: Recent Advancesmentioning

confidence: 99%