Recent Developments in Plasma Edge Theory

Stacey, Weston M.

doi:10.1002/ctpp.201610060

Cited by 5 publications

(5 citation statements)

References 22 publications

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“…Using experimental data to evaluate the theoretical expressions, we find in [12] and for additional shots in this paper (i) that the intrinsic co-current rotation (due to IOL) contribution to the carbon toroidal rotation in the plasma edge in L-mode decreases in H-mode, producing a transient decrease in the total co-current toroidal rotation of a magnitude similar to that measured; and (ii) that the theoretical particle pinch expression [10] evaluated with experimental data is small in L-mode but changes to strongly inward in H-mode, consistent with the measured increase in particle confinement from L-mode to H-mode.…”

Section: Discussionsupporting

confidence: 51%

“…[2][3][4][5]) notwithstanding, the cause of H-mode is not fully understood and remains a topic of intense research interest. Recent summaries of the physics of H-mode are given in [6][7][8] A particular interest in this paper is the utilization of particle and momentum balance in conjunction with energy conservation to determine the different effects for L-mode and H-mode of two non-diffusive transport mechanisms, ion orbit loss (IOL) and electromagnetic particle pinch, on particle transport in the edge [9][10][11]. The purpose of this paper is to determine if a decrease in the measured carbon toroidal rotation near the separatrix, and a significant decrease in the calculated pinch velocity, are characteristic of the L-H transition, and if they are correlated with a reduction in the calculated intrinsic rotation at the plasma edge.…”

Section: Introductionmentioning

confidence: 99%

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Change in ion orbit loss, intrinsic rotation and particle pinch across the L–H transition in DIII-D plasmas

Piper

Stacey

Groebner

2019

Plasma Phys. Control. Fusion

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Two interesting L-H transition phenomena are further investigated in DIII-D. Firstly, it has previously been observed in co-current rotating DIII-D discharge #118897 that at the L-H transition there is an immediate increase in the measured carbon toroidal co-rotation velocities for ρ0.94, as would be expected for improved confinement in H-mode, but for the edge pedestal (0.94<ρ<1.0) there is a decrease in the measured carbon toroidal co-rotation that persists for about 20 ms before also beginning to increase. Calculations indicate that ion orbit loss of predominantly counter-current rotating ions in the edge plasma, which produces an intrinsic co-rotation, is reduced in H-mode relative to L-mode, consistent with the observed reduction of the measured carbon co-rotation immediately after the L-H transition. Secondly, a theoretical expression for the radial particle pinch (predominantly electromagnetic) predicted a weak pinch when evaluated for the measured L-mode plasma conditions prior to the L-H transition, but predicted a strongly inward pinch velocity when evaluated for the measured H-mode plasma conditions immediately following the L-H transition. We have now refined the data fitting and repeated this investigation for the same and two additional L-H transitions in DIII-D, essentially confirming the generality of the previous results.

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Section: Discussionsupporting

confidence: 51%

Section: Introductionmentioning

confidence: 99%

Change in ion orbit loss, intrinsic rotation and particle pinch across the L–H transition in DIII-D plasmas

Piper

Stacey

Groebner

2019

Plasma Phys. Control. Fusion

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“…The subject of neoclassical direct ion orbit losses and their contribution to the edge flows and electric fields has been treated substantially, both computationally and theoretically [43][44][45][46][47][48][49][50][51][52] . Here, we offer a new argument to support our claim that the potential structure at the LFS is due to the excursions of trapped ions on their banana orbits.…”

Section: Banana Tip Distributionmentioning

confidence: 99%

Analysis of equilibrium and turbulent fluxes across the separatrix in a gyrokinetic simulation

et al. 2018

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The SOL width is a parameter of paramount importance in modern tokamaks as it controls the power density deposited at the divertor plates, critical for plasma-facing material survivability. An understanding of the parameters controlling it has consequently long been sought (Connor et al. 1999 NF 39 2). Prior to Chang et al. (2017 NF 57 11), studies of the tokamak edge have been mostly confined to reduced fluid models and simplified geometries, leaving out important pieces of physics. Here, we analyze the results of a DIII-D simulation performed with the full-f gyrokinetic code XGC1 which includes both turbulence and neoclassical effects in realistic divertor geometry. More specifically, we calculate the particle and heat E × B fluxes along the separatrix, discriminating between equilibrium and turbulent contributions. We find that the density SOL width is impacted almost exclusively by the turbulent electron flux. In this simulation, the level of edge turbulence is regulated by a mechanism we are only beginning to understand: ∇B-drifts and ion X-point losses at the top and bottom of the machine, along with ion banana orbits at the low field side (LFS), result in a complex poloidal potential structure at the separatrix which is the cause of the E × B drift pattern that we observe. Turbulence is being suppressed by the shear flows that this potential generates. At the same time, turbulence, along with increased edge collisionality and electron inertia, can influence the shape of the potential structure by making the electrons non-adiabatic. Moreover, being the only means through which the electrons can lose confinement, it needs to be in a balance with the original direct ion orbit losses to maintain charge neutrality.

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“…The total ion flow velocities in the plasma (i.e. the flow velocities that would be measured and that enter equation ( 1))) consist of flow velocities that are determined by the fluid forces acting within the plasma (discussed in the following section) plus 'intrinsic rotation' caused by the preferential ion orbit loss from the plasma of counter-current directed thermalized ions, leaving the remaining thermalized ions with a net co-current intrinsic rotation [13][14][15][16][17][18][19][20][21] due to these kinetic effects of ion orbit loss…”

Section: Edge Pressure Gradientsmentioning

confidence: 99%

“…Chang et al [7,8] subsequently predicted such ion orbit loss based on numerical particle-following calculations. deGrassie et al [9][10][11][12] have related intrinsic rotation resulting from ion orbit loss to experimental observations in DIII-D. Stacey et al [13][14][15][16][17][18][19][20][21][22] developed the Miyamoto theory [6] into a computational model for ion orbit loss of particles, energy and momentum and for intrinsic rotation, and applied it to interpret DIII-D experiments.…”

Section: Introductionmentioning

confidence: 99%

On the physics of the pressure and temperature gradients in the edge of tokamak plasmas

Stacey¹

2018

Nucl. Fusion

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An extended plasma fluid theory including atomic physics, radiation, electromagnetic and themodynamic forces, external sources of particles, momentum and energy, and kinetic ion orbit loss is employed to derive theoretical expressions that display the role of the various factors involved in the determination of the pressure and temperature gradients in the edge of tokamak plasmas. Calculations for current experiments are presented to illustrate the magnitudes of various effects including strong radiative and atomic physics edge cooling effects and strong reduction in ion particle and energy fluxes due to ion orbit loss in the plasma edge. An important new insight is the strong relation between rotation and the edge pressure gradient.

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Recent Developments in Plasma Edge Theory

Abstract: Recent developments in electromagnetic particle pinch, ion orbit loss, intrinsic rotation, rotation theory and radial electric field theory in the tokamak plasma edge are described.

Cited by 5 publications

References 22 publications

Change in ion orbit loss, intrinsic rotation and particle pinch across the L–H transition in DIII-D plasmas

Change in ion orbit loss, intrinsic rotation and particle pinch across the L–H transition in DIII-D plasmas

Analysis of equilibrium and turbulent fluxes across the separatrix in a gyrokinetic simulation

On the physics of the pressure and temperature gradients in the edge of tokamak plasmas

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