Neoclassical ion heat flux and poloidal flow in a tokamak pedestal

Kagan, Grigory; Catto, Peter J.

doi:10.1088/0741-3335/52/5/055004

Cited by 28 publications

(103 citation statements)

References 18 publications

(46 reference statements)

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“…The altered poloidal ion flow can lead to an increase in the bootstrap current in the pedestal where the radial profile variation is strong because of the enhanced coefficient of the ion temperature gradient term near the electric field minimum. Unlike the banana regime [11], orbit squeezing does not affect the plateau regime results.…”

Section: Introductionmentioning

confidence: 74%

Neoclassical plateau regime transport in a tokamak pedestal

Pusztai

Catto

2010

Plasma Phys. Control. Fusion

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In subsonic tokamak pedestals the radial scale of plasma profiles can be comparable to the ion poloidal Larmor radius, thereby making the radial electrostatic field so strong that the E × B drift has to be retained in the ion kinetic equation in the same order as the parallel streaming. The modifications of neoclassical plateau regime transport -such as the ion heat flux, and the poloidal ion and impurity flowsare evaluated in the presence of a strong radial electric field. The altered poloidal ion flow can lead to a significant increase in the bootstrap current in the pedestal where the spatial profile variation is strong because of the enhanced coefficient of the ion temperature gradient term near the electric field minimum. Unlike the banana regime, orbit squeezing does not affect the plateau regime results.

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Section: Introductionmentioning

confidence: 74%

Neoclassical plateau regime transport in a tokamak pedestal

Pusztai

Catto

2010

Plasma Phys. Control. Fusion

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“…However, recent results differ from the results in the original theory 5,6 in both the S and the RU 2 p;m Þ dependences. 13,14 Especially, the new results show that the effects of orbit squeezing enhance the ion energy losses even though the width of the orbits is reduced. The discrepancy is attributed in Refs.…”

Section: Introductionmentioning

confidence: 82%

“…II, the width of squeezed orbits is derived. From the expression for the orbit width, the key difference between the original theory 5,6 and the new results 13,14 is addressed. It shows that the discrepancy is a result of the incorrect expression for the width of the orbit.…”

Section: Introductionmentioning

confidence: 99%

Neoclassical theory inside transport barriers in tokamaks

Shaing

Hsu

2012

Physics of Plasmas

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Inside the transport barriers in tokamaks, ion energy losses sometimes are smaller than the value predicted by the standard neoclassical theory. This improvement can be understood in terms of the orbit squeezing theory in addition to the sonic poloidal E Â B Mach number U p;m that pushes the tips of the trapped particles to the higher energy. In general, U p;m also includes the poloidal component of the parallel mass flow speed. These physics mechanisms are the corner stones for the transition theory of the low confinement mode (L-mode) to the high confinement mode (H-mode) in tokamaks. Here, detailed transport fluxes in the banana regime are presented using the parallel viscous forces calculated earlier. It is found, as expected, that effects of orbit squeezing and the sonic U p;m reduce the ion heat conductivity. The former reduces it by a factor of jSj 3=2 and the later by a factor of RðU 2 p;m Þ expðÀU 2 p;m Þ with RðU 2 p;m Þ, a rational function. Here, S is the orbit squeezing factor.

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“…Already important simulation and theoretical work are forthcoming, focused on including the non-local transport effects caused by large gradients in the density and temperature 17,23,[44][45][46] .…”

Section: Discussionmentioning

confidence: 99%

Poloidal asymmetries in edge transport barriers

et al. 2015

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Measurements of impurities in Alcator C-Mod indicate that in the pedestal region, significant poloidal asymmetries can exist in the impurity density, ion temperature, and main ion density. In light of the observation that ion temperature and electrostatic potential are not constant on a flux surface [Theiler et al., Nucl. Fusion 54, 083017 (2014)], a technique based on total pressure conservation to align profiles measured at separate poloidal locations is presented and applied. Gyrokinetic neoclassical simulations with XGCa support the observed large poloidal variations in ion temperature and density, and that the total pressure is approximately constant on a flux surface. With the updated alignment technique, the observed in-out asymmetry in impurity density is reduced from previous publishing [Churchill et al., Nucl. Fusion 53, 122002 (2013)], but remains substantial (nz,H/nz,L∼6). Candidate asymmetry drivers are explored, showing that neither non-uniform impurity sources nor localized fluctuation-driven transport are able to explain satisfactorily the impurity density asymmetry. Since impurity density asymmetries are only present in plasmas with strong electron density gradients, and radial transport timescales become comparable to parallel transport timescales in the pedestal region, it is suggested that global transport effects relating to the strong electron density gradients in the pedestal are the main driver for the pedestal in-out impurity density asymmetry.

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Neoclassical ion heat flux and poloidal flow in a tokamak pedestal

Cited by 28 publications

References 18 publications

Neoclassical plateau regime transport in a tokamak pedestal

Neoclassical plateau regime transport in a tokamak pedestal

Neoclassical theory inside transport barriers in tokamaks

Poloidal asymmetries in edge transport barriers

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