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Comparison of BES measurements of ion-scale turbulence with direct gyro-kinetic simulations of MAST L-mode plasmas
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Field, A. R., Dunai, D., Ghim, Y.-c., Hill, P. (Peter), McMillan, Ben F., Roach, C. M., Saarelma, S., Schekochihin, A. A. and Zoletnik, S. (2014) Comparison of BES measurements of ion-scale turbulence with direct gyro-kinetic simulations of MAST L-mode plasmas. Plasma Physics and Controlled Fusion, Volume 56 (Number 2). Article number 025012. doi:10.1088/0741-3335/56/2/025012 ISSN 0741-3335.
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Official URL: http://dx.doi.org/10.1088/0741-3335/56/2/025012
Abstract
Observations of ion-scale (kyρi ≤ 1) density turbulence of relative amplitude gsim0.2% are available on the Mega Amp Spherical Tokamak (MAST) using a 2D (8 radial × 4 poloidal channel) imaging beam emission spectroscopy diagnostic. Spatial and temporal characteristics of this turbulence, i.e., amplitudes, correlation times, radial and perpendicular correlation lengths and apparent phase velocities of the density contours, are determined by means of correlation analysis. For a low-density, L-mode discharge with strong equilibrium flow shear exhibiting an internal transport barrier in the ion channel, the observed turbulence characteristics are compared with synthetic density turbulence data generated from global, non-linear, gyro-kinetic simulations using the particle-in-cell code NEMORB. This validation exercise highlights the need to include increasingly sophisticated physics, e.g., kinetic treatment of trapped electrons, equilibrium flow shear and collisions, to reproduce most of the characteristics of the observed turbulence. Even so, significant discrepancies remain: an underprediction by the simulations of the turbulence amplitude and heat flux at plasma periphery and the finding that the correlation times of the numerically simulated turbulence are typically two orders of magnitude longer than those measured in MAST. Comparison of these correlation times with various linear timescales suggests that, while the measured turbulence is strong and may be 'critically balanced', the simulated turbulence is weak.
Item Type: | Journal Article | ||||||||
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Divisions: | Faculty of Science, Engineering and Medicine > Science > Physics | ||||||||
Journal or Publication Title: | Plasma Physics and Controlled Fusion | ||||||||
Publisher: | Institute of Physics Publishing Ltd. | ||||||||
ISSN: | 0741-3335 | ||||||||
Official Date: | February 2014 | ||||||||
Dates: |
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Volume: | Volume 56 | ||||||||
Number: | Number 2 | ||||||||
Article Number: | Article number 025012 | ||||||||
DOI: | 10.1088/0741-3335/56/2/025012 | ||||||||
Status: | Peer Reviewed | ||||||||
Publication Status: | Published | ||||||||
Access rights to Published version: | Restricted or Subscription Access |
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