Pedestal Structure Model

Callen, J. D.; Canik, J.; Smith, S. P.

doi:10.1103/physrevlett.108.245003

Cited by 12 publications

(22 citation statements)

References 24 publications

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“…Integrating this result for electrons from a reference radius ρ ref to ρ yields [10] (for regions II and III in Fig. 1)…”

Section: Motivation and Introductionmentioning

confidence: 96%

“…Neglecting again the typically negligibleṄ contribution (here < ∼ 3 % for the DIII-D pedestal in Fig. 1 [9]) yields the predictions [10,23] (for regions II and III in Fig. 1):…”

Section: Motivation and Introductionmentioning

confidence: 98%

“…A similar radial integration of the electron energy balance assuming paleoclassical electron heat transport dominates yields [10] − V D η n e (3/2)(dT e /dρ) + (3/2)Ṅ e T e = P e in which P e (ρ) is the effective conductive heat flow (W) through the ρ flux surface. Neglecting again the typically negligibleṄ contribution (here < ∼ 3 % for the DIII-D pedestal in Fig.…”

Section: Motivation and Introductionmentioning

confidence: 98%

“…1. The boxed equation in (5) indicates the effective electron thermal diffusivity χ pc e eff is D η times some geometric coefficients (χ pc e eff 1.2D η [10] for the DIII-D pedestal in Fig. 1).…”

Section: Motivation and Introductionmentioning

confidence: 99%

“…1. Thus, a pedestal structure model [10] based on paleoclassical transport has been developed recently and validation studies undertaken [10]- [12].…”

Section: Motivation and Introductionmentioning

confidence: 99%

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Pedestal Structure without and with 3D Fields

Callen

2014

Contrib. Plasma Phys.

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Achieving high pedestal pressures in H(high)-mode plasmas confined in tokamaks is critical for obtaining fusion burning plasmas in ITER. Recent characterizations of quasi-equilibrium plasma parameter profiles in low collisionality H-mode pedestals in the DIII-D tokamak are briefly summarized. Critical plasma transport properties (large radial electron heat flow, density pinch) that establish the transport barrier structure of the pedestal profiles are identified. The paleoclassical transport model, which naturally includes a density pinch, is shown to provide the minimum electron heat and density transport in the pedestal. Microinstabilities can provide additional plasma transport within and especially at the top of pedestals. Macroscopic peeling-ballooning (P-B) instabilities cause periodic edge localized modes (ELMs) that limit the temporal and spatial growth of the pedestal initially and between ELMs. Externally imposed 3D resonant magnetic perturbations (RMPs) in the pedestal have been used to stabilize P-B modes and suppress ELMs. A magnetic flutter model of plasma transport induced by the 3D RMPs has been developed for low collisionality DIII-D pedestals. Comparisons of it with data on ELM suppression by RMPs indicate it can provide a "diffusivity hill" at the pedestal top that can impede pedestal growth and thereby stabilize P-B modes and suppress ELMs. Finally, transport equations for plasma density, electron and ion pressures and, most importantly, the plasma toroidal rotation frequency (and hence, via radial force balance, the radial electric field) in the presence of plasma transport due to collisional, paleoclassical, microturbulence-induced and 3D field effects are presented. . These instabilities cause roughly periodic edge-localized-modes (ELMs) that abruptly relax the large edge plasma gradients and deposit undesirable bursts of plasma heat and particles on divertor plates. Pedestals evolve in various stages after an ELM [3]. Within a few to 10 ms after an ELM crash the pedestal quasi-equilibrium is re-established. But then it continues to grow slowly (for 10s of ms or longer) until a P-B instability precipitates an ELM. Externally imposed three-dimensional (3D) resonant magnetic perturbations (RMPs) have been used in DIII-D [4] to limit this progression and mitigate [5][6][7] or suppress [8] ELMs in tokamaks. The present challenge for edge plasma modeling is to develop and experimentally validate predictive transport models for the profiles and evolution of the pedestal density, temperature, flow and radial electric field profiles with and without 3D fields. This paper mainly reviews recent research results [9]-[16] on key paleoclassical and 3D transport processes involved in determining the structure of plasma profiles in low collisionality H-mode pedestals without [9] and with [8] RMPs in ITER-similar-shape DIII-D plasmas. The emphasis is on a validation process comparing theoretical models to relevant experimental data.This paper is organized as follows. The next section provides a characteriz...

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“…Integrating this result for electrons from a reference radius ρ ref to ρ yields [10] (for regions II and III in Fig. 1)…”

Section: Motivation and Introductionmentioning

confidence: 96%

“…Neglecting again the typically negligibleṄ contribution (here < ∼ 3 % for the DIII-D pedestal in Fig. 1 [9]) yields the predictions [10,23] (for regions II and III in Fig. 1):…”

Section: Motivation and Introductionmentioning

confidence: 98%

Section: Motivation and Introductionmentioning

confidence: 98%

Section: Motivation and Introductionmentioning

confidence: 99%

“…1. Thus, a pedestal structure model [10] based on paleoclassical transport has been developed recently and validation studies undertaken [10]- [12].…”

Section: Motivation and Introductionmentioning

confidence: 99%

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Pedestal Structure without and with 3D Fields

Callen

2014

Contrib. Plasma Phys.

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Random field effects on the phase diagrams of spin-1/2 Ising model on a honeycomb lattice

Yüksel

Akıncı

Polat

2012

Physica A: Statistical Mechanics and its Applications

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Ising model with quenched random magnetic fields is examined for single Gaussian, bimodal and double Gaussian random field distributions by introducing an effective field approximation that takes into account the correlations between different spins that emerge when expanding the identities. Random field distribution shape dependence of the phase diagrams, magnetization and internal energy is investigated for a honeycomb lattice with a coordination number q = 3. The conditions for the occurrence of reentrant behavior and tricritical points on the system are also discussed in detail.

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Validation of transport models using additive flux minimization technique

et al. 2013

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A new additive flux minimization technique is proposed for carrying out the verification and validation (V&V) of anomalous transport models. In this approach, the plasma profiles are computed in time dependent predictive simulations in which an additional effective diffusivity is varied. The goal is to obtain an optimal match between the computed and experimental profile. This new technique has several advantages over traditional V&V methods for transport models in tokamaks and takes advantage of uncertainty quantification methods developed by the applied math community. As a demonstration of its efficiency, the technique is applied to the hypothesis that the paleoclassical density transport dominates in the plasma edge region in DIII-D tokamak discharges. A simplified version of the paleoclassical model that utilizes the Spitzer resistivity for the parallel neoclassical resistivity and neglects the trapped particle effects is tested in this paper. It is shown that a contribution to density transport, in addition to the paleoclassical density transport, is needed in order to describe the experimental profiles. It is found that more additional diffusivity is needed at the top of the H-mode pedestal, and almost no additional diffusivity is needed at the pedestal bottom. The implementation of this V&V technique uses the FACETS::Core transport solver and the DAKOTA toolkit for design optimization and uncertainty quantification. The FACETS::Core solver is used for advancing the plasma density profiles. The DAKOTA toolkit is used for the optimization of plasma profiles and the computation of the additional diffusivity that is required for the predicted density profile to match the experimental profile.

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Pedestal Structure Model

Cited by 12 publications

References 24 publications

Pedestal Structure without and with 3D Fields

Pedestal Structure without and with 3D Fields

Random field effects on the phase diagrams of spin-1/2 Ising model on a honeycomb lattice

Validation of transport models using additive flux minimization technique

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