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

Abstract

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 [E.S. Marmar et al., Nucl. Fusion 55, (2015)] to study this phenomenon, allowing detailed observations of the plasma profiles and fluctuations. Langmuir probe (LP) measurements show a clear two decay length n e 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. We have carried out the flux-driven non-linear turbulence simulations of two C-Mod discharges which allows 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. Furthermore, 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 entiremore » SOL, indicating that the transport reduction in the near-SOL cannot result from a simple quench rule.« less

Authors:
 [1];  [2]; ORCiD logo [2]; ORCiD logo [3]
  1. General Atomics, San Diego, CA (United States); Ecole Polytechnique Federale Lausanne (Switzlerland). Swiss Plasma Center
  2. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
  3. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Publication Date:
Research Org.:
General Atomics, San Diego, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
OSTI Identifier:
1378095
Alternate Identifier(s):
OSTI ID: 1366571
Grant/Contract Number:  
FG02-95ER54309; AC02-09CH11466
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 24; Journal Issue: 7; Journal ID: ISSN 1070-664X
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY

Citation Formats

Halpern, Federico D., LaBombard, Brian, Terry, James L., and Zweben, Stewart J.. Outer midplane scrape-off layer profiles and turbulence in simulations of Alcator C-Mod inner-wall limited discharges. United States: N. p., 2017. Web. doi:10.1063/1.4989705.
Halpern, Federico D., LaBombard, Brian, Terry, James L., & Zweben, Stewart J.. Outer midplane scrape-off layer profiles and turbulence in simulations of Alcator C-Mod inner-wall limited discharges. United States. doi:10.1063/1.4989705.
Halpern, Federico D., LaBombard, Brian, Terry, James L., and Zweben, Stewart J.. Tue . "Outer midplane scrape-off layer profiles and turbulence in simulations of Alcator C-Mod inner-wall limited discharges". United States. doi:10.1063/1.4989705. https://www.osti.gov/servlets/purl/1378095.
@article{osti_1378095,
title = {Outer midplane scrape-off layer profiles and turbulence in simulations of Alcator C-Mod inner-wall limited discharges},
author = {Halpern, Federico D. and LaBombard, Brian and Terry, James L. and Zweben, Stewart J.},
abstractNote = {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 [E.S. Marmar et al., Nucl. Fusion 55, (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 Te 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. We have carried out the flux-driven non-linear turbulence simulations of two C-Mod discharges which allows 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. Furthermore, 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.},
doi = {10.1063/1.4989705},
journal = {Physics of Plasmas},
number = 7,
volume = 24,
place = {United States},
year = {Tue Jun 27 00:00:00 EDT 2017},
month = {Tue Jun 27 00:00:00 EDT 2017}
}

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