Kinetic Instabilities that Limit beta in the Edge of a Tokamak Plasma: A Picture of an H-Mode Pedestal

D. Dickinson; C. M. Roach; S. Saarelma; R. Scannell; A. Kirk; H. R. Wilson

doi:10.1103/PhysRevLett.108.135002

Kinetic Instabilities that Limit beta in the Edge of a Tokamak Plasma: A Picture of an H-Mode Pedestal

D. Dickinson, C. M. Roach, S. Saarelma, R. Scannell, A. Kirk, H. R. Wilson

Physics

Research output: Contribution to journal › Article › peer-review

Abstract

Plasma equilibria reconstructed from the Mega-Amp Spherical Tokamak have sufficient resolution to capture plasma evolution during the short period between edge-localized modes (ELMs). Immediately after the ELM, steep gradients in pressure, P, and density, n(e), form pedestals close to the separatrix, and they then expand into the core. Local gyrokinetic analysis over the ELM cycle reveals the dominant microinstabilities at perpendicular wavelengths of the order of the ion Larmor radius. These are kinetic ballooning modes in the pedestal and microtearing modes in the core close to the pedestal top. The evolving growth rate spectra, supported by gyrokinetic analysis using artificial local equilibrium scans, suggest a new physical picture for the formation and arrest of this pedestal.

Original language	English
Article number	135002
Pages (from-to)	1-5
Number of pages	5
Journal	Physical Review Letters
Volume	108
Issue number	13
DOIs	https://doi.org/10.1103/PhysRevLett.108.135002
Publication status	Published - 26 Mar 2012

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10.1103/PhysRevLett.108.135002

http://prl.aps.org/abstract/PRL/v108/i13/e135002

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title = "Kinetic Instabilities that Limit beta in the Edge of a Tokamak Plasma: A Picture of an H-Mode Pedestal",

abstract = "Plasma equilibria reconstructed from the Mega-Amp Spherical Tokamak have sufficient resolution to capture plasma evolution during the short period between edge-localized modes (ELMs). Immediately after the ELM, steep gradients in pressure, P, and density, n(e), form pedestals close to the separatrix, and they then expand into the core. Local gyrokinetic analysis over the ELM cycle reveals the dominant microinstabilities at perpendicular wavelengths of the order of the ion Larmor radius. These are kinetic ballooning modes in the pedestal and microtearing modes in the core close to the pedestal top. The evolving growth rate spectra, supported by gyrokinetic analysis using artificial local equilibrium scans, suggest a new physical picture for the formation and arrest of this pedestal.",

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AU - Scannell, R.

AU - Kirk, A.

AU - Wilson, H. R.

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N2 - Plasma equilibria reconstructed from the Mega-Amp Spherical Tokamak have sufficient resolution to capture plasma evolution during the short period between edge-localized modes (ELMs). Immediately after the ELM, steep gradients in pressure, P, and density, n(e), form pedestals close to the separatrix, and they then expand into the core. Local gyrokinetic analysis over the ELM cycle reveals the dominant microinstabilities at perpendicular wavelengths of the order of the ion Larmor radius. These are kinetic ballooning modes in the pedestal and microtearing modes in the core close to the pedestal top. The evolving growth rate spectra, supported by gyrokinetic analysis using artificial local equilibrium scans, suggest a new physical picture for the formation and arrest of this pedestal.

AB - Plasma equilibria reconstructed from the Mega-Amp Spherical Tokamak have sufficient resolution to capture plasma evolution during the short period between edge-localized modes (ELMs). Immediately after the ELM, steep gradients in pressure, P, and density, n(e), form pedestals close to the separatrix, and they then expand into the core. Local gyrokinetic analysis over the ELM cycle reveals the dominant microinstabilities at perpendicular wavelengths of the order of the ion Larmor radius. These are kinetic ballooning modes in the pedestal and microtearing modes in the core close to the pedestal top. The evolving growth rate spectra, supported by gyrokinetic analysis using artificial local equilibrium scans, suggest a new physical picture for the formation and arrest of this pedestal.

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Kinetic Instabilities that Limit beta in the Edge of a Tokamak Plasma: A Picture of an H-Mode Pedestal

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