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  4. Outer midplane scrape-off layer profiles and turbulence in simulations of Alcator C-Mod inner-wall limited discharges
 
research article

Outer midplane scrape-off layer profiles and turbulence in simulations of Alcator C-Mod inner-wall limited discharges

Halpern, Federico D.
•
Labombard, Brian
•
Terry, James L.
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2017
Physics Of Plasmas

A region of steep plasma gradients, the so-called "narrow-feature," has been found in the near scrape-off layer (SOL) of inner-wall limited (IWL) discharges. Dedicated IWL discharges were carried out in Alcator C-Mod [Marmar et al., Nucl. Fusion 55, 104020 (2015)] to study this phenomenon, allowing detailed observations of the plasma profiles and fluctuations. Langmuir probe (LP) measurements show a clear two-decay length ne and T-e profile structure at the outer midplane. The Gas-Puff Imaging (GPI) diagnostic shows large turbulent fluctuations across the last closed flux-surface, hence supporting the hypothesis that turbulent phenomena play a role in setting the profile steepness. Flux-driven non-linear turbulence simulations of two C-Mod discharges have been carried out, allowing a three-way comparison between LP, GPI, and simulation data. Observations and simulations correlate the steep gradient region characterizing the narrow feature with sheared poloidal flows and a deviation of the plasma potential from its floating value. The E x B shear rate exceeds the linear ballooning growth rate, indicating that the narrow feature could result from the effects of sheared flows, although causality could not be established. The fluctuation level in the narrow feature remains of order unity across the entire SOL, indicating that the transport reduction in the near-SOL cannot result from a simple quench rule. Published by AIP Publishing.

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Type
research article
DOI
10.1063/1.4989705
Web of Science ID

WOS:000406767900031

Author(s)
Halpern, Federico D.
Labombard, Brian
Terry, James L.
Zweben, Stewart J.
Date Issued

2017

Publisher

Amer Inst Physics

Published in
Physics Of Plasmas
Volume

24

Issue

7

Article Number

072502

Editorial or Peer reviewed

REVIEWED

Written at

EPFL

EPFL units
SPC  
Available on Infoscience
September 5, 2017
Use this identifier to reference this record
https://infoscience.epfl.ch/handle/20.500.14299/140254
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