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Title: Tokamak parameter regimes with low toroidal momentum diffusivity

Abstract

The strong, sharp flow structures that are seen frequently in tokamak cores, and large amplitude spontaneous global toroidal rotation are both surprising in light of current theories where toroidal flow evolution is dominantly diffusive. Mechanisms for spontaneously generating strong poloidal shear flows have been extensively investigated, but these processes were thought not to apply to toroidal flows. We confirm, however, that there is a regime with near-zero toroidal momentum diffusivity, where toroidal flow structures are spontaneously generated, as shown in earlier global gyrokinetic simulations. This allows strong rotation with negligible applied external torque, and the regime where this occurs is also favourable for strong turbulence stabilisation by rotation. In conclusion, the transition to low momentum diffusivity occurs for tight aspect ratio, low safety factor and at low levels of heat flux, in agreement with a simple zero-dimensional model for the flow–turbulence interaction.

Authors:
ORCiD logo [1]; ORCiD logo [2]
  1. Univ. of Warwick, Coventry (United Kingdom)
  2. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Publication Date:
Research Org.:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Sponsoring Org.:
USDOE
Contributing Org.:
Partially supported by EPSRC grants EP/N035178/1 and EP/R034737/1
OSTI Identifier:
1558751
Grant/Contract Number:  
AC02-09CH11466
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Plasma Physics
Additional Journal Information:
Journal Volume: 85; Journal Issue: 3; Journal ID: ISSN 0022-3778
Publisher:
Cambridge University Press
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; fusion plasma; plasma confinement; plasma flows

Citation Formats

McMillan, B. F., and Dominski, J. Tokamak parameter regimes with low toroidal momentum diffusivity. United States: N. p., 2019. Web. doi:10.1017/S0022377819000333.
McMillan, B. F., & Dominski, J. Tokamak parameter regimes with low toroidal momentum diffusivity. United States. doi:10.1017/S0022377819000333.
McMillan, B. F., and Dominski, J. Mon . "Tokamak parameter regimes with low toroidal momentum diffusivity". United States. doi:10.1017/S0022377819000333.
@article{osti_1558751,
title = {Tokamak parameter regimes with low toroidal momentum diffusivity},
author = {McMillan, B. F. and Dominski, J.},
abstractNote = {The strong, sharp flow structures that are seen frequently in tokamak cores, and large amplitude spontaneous global toroidal rotation are both surprising in light of current theories where toroidal flow evolution is dominantly diffusive. Mechanisms for spontaneously generating strong poloidal shear flows have been extensively investigated, but these processes were thought not to apply to toroidal flows. We confirm, however, that there is a regime with near-zero toroidal momentum diffusivity, where toroidal flow structures are spontaneously generated, as shown in earlier global gyrokinetic simulations. This allows strong rotation with negligible applied external torque, and the regime where this occurs is also favourable for strong turbulence stabilisation by rotation. In conclusion, the transition to low momentum diffusivity occurs for tight aspect ratio, low safety factor and at low levels of heat flux, in agreement with a simple zero-dimensional model for the flow–turbulence interaction.},
doi = {10.1017/S0022377819000333},
journal = {Journal of Plasma Physics},
number = 3,
volume = 85,
place = {United States},
year = {2019},
month = {5}
}

Journal Article:
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