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Title: Turbulence and sheared flow structures behind the isotopic dependence of the L-H power threshold on DIII-D

Abstract

Measurements of long wavelength (k$$\perp$$p i < 1) density fluctuation characteristics in the edge of both Deuterium (D) and Hydrogen (H) plasmas across the L-H transition on DIII-D demonstrate the existence of single or double bands of low-wavenumber turbulence observed near the edge of H and D plasmas. These are strongly correlated with the L to H-mode transition power threshold (P LH) and can help explain the isotopic and density dependence of P LH, and how the P LH difference is reduced at higher density. Understanding and accurately predicting the L-H power threshold is critical to accessing to H-mode, and operating and achieving high confinement in burning plasmas such as ITER. Above about n e ~ 4 × 10 19 m -3, P LH is seen to converge for H and D, and increases for both with higher density. Surprisingly, the P LH increases significantly at low density in H but not in D plasmas. Two distinct frequency bands of density fluctuations are observed in the D plasmas at low density, n e ~ 1.2-1.5 × 10 19 m -3, but not in H plasmas with similar density, which appears to be correlated to the much lower power threshold in D at low density. Consistently, E × B shear in the region of r/a ~ 0.95-1.0 is larger in D plasmas than in H plasmas at low density; as the P LH increases with increasing density, the dual mode structure disappears while E × B shear becomes similar and small for both D and H plasmas at higher density, n e ~ 5 × 10 19 m -3, where P LH is similar for both D and H plasmas. Lastly, the increased edge fluctuations, increased flow shear, and the dualband nature of edge turbulence correlating with lower P LH may account for the strong isotope and density dependencies of PLH and support current L-H transition theories but suggest a complex behavior that can inform a more complete model of the L-H transition threshold.

Authors:
 [1];  [2];  [1];  [2];  [3];  [4];  [2]
  1. Univ. of Wisconsin, Madison, WI (United States)
  2. General Atomics, San Diego, CA (United States)
  3. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  4. Univ. of California, Los Angeles, CA (United States)
Publication Date:
Research Org.:
General Atomics, San Diego, CA (United States); Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Sponsoring Org.:
USDOE Office of Nuclear Energy (NE)
OSTI Identifier:
1392632
Alternate Identifier(s):
OSTI ID: 1398958
Grant/Contract Number:  
FC02-04ER54698; FG02-89ER53296; FG02-08ER54999; AC02-09CH11466; FG02-08ER54984
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 57; Journal Issue: 12; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; L-H transition; transition power threshold; turbulence dynamics; Reynolds stress

Citation Formats

Yan, Zheng, Gohil, Punit, McKee, George R., Eldon, David, Grierson, Brian, Rhodes, Terry, and Petty, Craig C. Turbulence and sheared flow structures behind the isotopic dependence of the L-H power threshold on DIII-D. United States: N. p., 2017. Web. doi:10.1088/1741-4326/aa82c9.
Yan, Zheng, Gohil, Punit, McKee, George R., Eldon, David, Grierson, Brian, Rhodes, Terry, & Petty, Craig C. Turbulence and sheared flow structures behind the isotopic dependence of the L-H power threshold on DIII-D. United States. doi:10.1088/1741-4326/aa82c9.
Yan, Zheng, Gohil, Punit, McKee, George R., Eldon, David, Grierson, Brian, Rhodes, Terry, and Petty, Craig C. Mon . "Turbulence and sheared flow structures behind the isotopic dependence of the L-H power threshold on DIII-D". United States. doi:10.1088/1741-4326/aa82c9. https://www.osti.gov/servlets/purl/1392632.
@article{osti_1392632,
title = {Turbulence and sheared flow structures behind the isotopic dependence of the L-H power threshold on DIII-D},
author = {Yan, Zheng and Gohil, Punit and McKee, George R. and Eldon, David and Grierson, Brian and Rhodes, Terry and Petty, Craig C.},
abstractNote = {Measurements of long wavelength (k$\perp$pi < 1) density fluctuation characteristics in the edge of both Deuterium (D) and Hydrogen (H) plasmas across the L-H transition on DIII-D demonstrate the existence of single or double bands of low-wavenumber turbulence observed near the edge of H and D plasmas. These are strongly correlated with the L to H-mode transition power threshold (PLH) and can help explain the isotopic and density dependence of PLH, and how the PLH difference is reduced at higher density. Understanding and accurately predicting the L-H power threshold is critical to accessing to H-mode, and operating and achieving high confinement in burning plasmas such as ITER. Above about ne ~ 4 × 1019 m-3, PLH is seen to converge for H and D, and increases for both with higher density. Surprisingly, the PLH increases significantly at low density in H but not in D plasmas. Two distinct frequency bands of density fluctuations are observed in the D plasmas at low density, ne ~ 1.2-1.5 × 1019 m-3, but not in H plasmas with similar density, which appears to be correlated to the much lower power threshold in D at low density. Consistently, E × B shear in the region of r/a ~ 0.95-1.0 is larger in D plasmas than in H plasmas at low density; as the PLH increases with increasing density, the dual mode structure disappears while E × B shear becomes similar and small for both D and H plasmas at higher density, ne ~ 5 × 1019 m-3, where PLH is similar for both D and H plasmas. Lastly, the increased edge fluctuations, increased flow shear, and the dualband nature of edge turbulence correlating with lower PLH may account for the strong isotope and density dependencies of PLH and support current L-H transition theories but suggest a complex behavior that can inform a more complete model of the L-H transition threshold.},
doi = {10.1088/1741-4326/aa82c9},
journal = {Nuclear Fusion},
number = 12,
volume = 57,
place = {United States},
year = {Mon Sep 18 00:00:00 EDT 2017},
month = {Mon Sep 18 00:00:00 EDT 2017}
}

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