Effects of Internal Disruptions on Impurity Transport in Tokamaks

Séguin, F.H.; Petrasso, R. D.; Marmar, E.

doi:10.1103/physrevlett.51.455

Cited by 87 publications

(77 citation statements)

References 6 publications

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“…In contrast, χ 2 -minimization methods evaluate the transport coefficients through a direct comparison of a simulation to the measured spectroscopic data, but the result will be intrinsically dependent on the sawtooth crash model used. The one used for this work has its foundations on the theory from Kadomtsev [31] and on observations performed on "standard" sawtooth crashes [28]. Also based on Kadomtsev's model is [25], whose predicted change in sawtooth behaviour with on ECRH deposition position is in good agreement with the results shown here.…”

Section: # 24648supporting

confidence: 78%

“…Sawtooth crashes have been modelled as a complete flattening of the total impurity density within the mixing radius r mix = r inv · √ 2, where r inv is the position of the q = 1 surface [28,29]. The quality of the fit is defined by the total χ 2 considering lines of sight of camera I within the diagnostic sensitivity range.…”

Section: Benchmarking Against χ 2 -Minimization Methodsmentioning

confidence: 99%

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Local effects of ECRH on argon transport in L-mode discharges at ASDEX Upgrade

Sertoli

Angioni

Dux

et al. 2011

Plasma Phys. Control. Fusion

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Abstract. The transport of argon as trace impurity has been investigated in electron cyclotron resonance heated L-mode discharges at ASDEX Upgrade to test recent theories predicting the rise of an outward impurity convection. The profiles of the argon transport coefficients for r/a < 0.65 have been determined by analysing the linear flux-gradient dependency of the total argon ion density evolution after the puff. A new methodology to experimentally obtain the total impurity ion density from the integrated use of two spectroscopic diagnostic and the 1D impurity transport code STRAHL has been developed. Results confirm the enhancement in diffusivity and the rise of the positive convection observed in previous studies, but show for the first time how these effects are strongly localized around the electron cyclotron resonance heating deposition radius. These experimental results are found in promising qualitative agreement with a set of quasi-linear gyrokinetic simulations with the code GS2.

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Section: # 24648supporting

confidence: 78%

Section: Benchmarking Against χ 2 -Minimization Methodsmentioning

confidence: 99%

Local effects of ECRH on argon transport in L-mode discharges at ASDEX Upgrade

Sertoli

Angioni

Dux

et al. 2011

Plasma Phys. Control. Fusion

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“…inward neo-classical impurity pinch, which leads to long impurity confinement times. This implies that the large inward impurity convection at the edge dominates the core impurity confinement times [75]. Similar behavior is seen in the core of plasmas with ITBs.…”

Section: Discussionsupporting

confidence: 60%

Core impurity transport in Alcator C-Mod L-, I- and H-mode plasmas

Rice¹,

Reinke

Gao³

et al. 2015

Nucl. Fusion

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Core impurity transport has been investigated for a variety of confinement regimes in Alcator C-Mod plasmas from x-ray emission following injection of medium and high Z materials. In Ohmic L-mode discharges, impurity transport is anomalous (D eff ≫ D nc ) and changes very little across the LOC/SOC boundary. In ICRF heated Lmode plasmas, the core impurity confinement time decreases with increasing ICRF input power (and subsequent increasing electron temperature) and increases with plasma current. Nearly identical impurity confinement characteristics are observed in I-mode plasmas. In EDA H-mode discharges the core impurity confinement times are much longer. There is a strong connection between core impurity confinement time and the edge density gradient across all confinement regimes studied here. Deduced central impurity density profiles in stationary plasmas are generally flat, in spite of large amplitude sawtooth oscillations, and there is little evidence of impurity convection inside of r/a = 0.3 when averaged over sawteeth.

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“…For these discharges, however, the momentum seems to be expelled from the plasma center, rather than having increased confinement. From a fit to the hollow ITB velocity profile in Fig.6, a value of −2.3 is found for the peaking factor S. From the decay time of the core velocity in the ITB phase, D φ is determined [41] to be ∼0.05 m 2 /s, if the ITB foot radius is used, and v c is ∼−2 m/s. The reason that the momentum transport in ITB discharges doesn't follow the behavior of particle and energy confinement may be because these plasmas have a negative E r well in the core, and may be influenced by the fact that momentum is an odd moment of the distribution function, with directionality.…”

Section: Discussionmentioning

confidence: 99%

Observations of anomalous momentum transport in Alcator C-Mod plasmas with no momentum input

Lee²,

et al. 2004

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Anomalous momentum transport has been observed in Alcator C-Mod tokamak plasmas. The time evolution of core impurity toroidal rotation velocity profiles has been measured with a tangentially viewing crystal x-ray spectrometer array. Following the L-mode to EDA (enhanced D α ) H-mode transition in both Ohmic and ICRF heated discharges, the ensuing co-current toroidal rotation velocity, which is generated in the absence of any external momentum source, is observed to propagate in from the edge plasma to the core with a time scale of order of the observed energy confinement time, but much less than the neo-classical momentum confinement time. The ensuing steady state toroidal rotation velocity profiles in EDA H-mode plasmas are relatively flat, with V φ ∼ 50 km/s, and the momentum transport can be simulated with a simple diffusion model. Assuming the L-H transition produces an instantaneous edge source of toroidal torque (which disappears at the H-to L-mode transition), the momentum transport may be characterized by a diffusivity, with values of ∼ 0.07 m 2 /s during EDA H-mode and ∼ 0.2 m 2 /s in L-mode. These values are large compared to the calculated neoclassical momentum diffusivities, which are of order 0.003 m 2 /s. Velocity profiles of ELM-free H-mode plasmas are centrally peaked (with V φ (0) exceeding 100 km/s in some cases), which suggests the workings of an inward momentum pinch; the observed profiles are consistent with simulations including an edge inward convection velocity of ∼ 10 m/s. In EDA H-mode discharges which develop internal transport barriers, the velocity profiles become hollow in the center, indicating the presence of a negative radial electric field well in the vicinity of the barrier foot. Upper single null diverted and inner wall limited L-mode discharges exhibit strong counter-current rotation (with V φ (0) ∼ −60 km/s in some cases), which may be related to the observed higher Hmode power threshold in these configurations. For plasmas with locked modes, the toroidal rotation is observed to stop (V φ ≤5 km/s). 1

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Effects of Internal Disruptions on Impurity Transport in Tokamaks

Cited by 87 publications

References 6 publications

Local effects of ECRH on argon transport in L-mode discharges at ASDEX Upgrade

Local effects of ECRH on argon transport in L-mode discharges at ASDEX Upgrade

Core impurity transport in Alcator C-Mod L-, I- and H-mode plasmas

Observations of anomalous momentum transport in Alcator C-Mod plasmas with no momentum input

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