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Title: Recent progress towards a physics-based understanding of the H-mode transition

Abstract

Results from recent experiment and numerical simulation point towards a picture of the L-H transition in which edge shear flows interacting with edge turbulence create the conditions needed to produce a non-zero turbulent Reynolds stress at and just inside the LCFS during L-mode discharges. This stress acts to reinforce the shear flow at this location and the flow drive gets stronger as heating is increased. The L-H transition ensues when the rate of work done by this stress is strong enough to drive the shear flow to large values, which then grows at the expense of the turbulence intensity. The drop in turbulence intensity momentarily reduces the heat flux across the magnetic flux surface, which then allows the edge plasma pressure gradient to build. A sufficiently strong ion pressure gradient then locks in the H-mode state. The results are in general agreement with previously published reduced 0D and 1D predator prey models. An extended predator–prey model including separate ion and electron heat channels yields a non-monotonic power threshold dependence on plasma density provided that the fraction of heat deposited on the ions increases with plasma density. Possible mechanisms to explain other macroscopic transition threshold criteria are identified. A number ofmore » open questions and unexplained observations are identified, and must be addressed and resolved in order to build a physics-based model that can yield predictions of the macroscopic conditions needed for accessing H-mode.« less

Authors:
 [1];  [1];  [2];  [3];  [4];  [4];  [4];  [4]
  1. Univ. of California, San Diego, CA (United States). Center for Momentum Transport & Flow Organization (CMTFO)
  2. Univ. of California, San Diego, CA (United States). Center for Momentum Transport & Flow Organization (CMTFO) and Center for Astrophysics & Space Science
  3. Univ. of California, San Diego, CA (United States). Center for Astrophysics & Space Science
  4. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Plasma Science and Fusion Center (PSFC)
Publication Date:
Research Org.:
Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States); Univ. of California, San Diego, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1235490
Alternate Identifier(s):
OSTI ID: 1235967; OSTI ID: 1438464
Grant/Contract Number:  
FC02-99ER54512; SC0008689; SC0008378; SC0001961
Resource Type:
Published Article
Journal Name:
Plasma Physics and Controlled Fusion
Additional Journal Information:
Journal Name: Plasma Physics and Controlled Fusion Journal Volume: 58 Journal Issue: 4; Journal ID: ISSN 0741-3335
Publisher:
IOP Science
Country of Publication:
United Kingdom
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; turbulence; h-mode; L-H transition; predator–prey; Reynolds stress

Citation Formats

Tynan, G. R., Cziegler, I., Diamond, P. H., Malkov, M., Hubbard, A., Hughes, J. W., Terry, J. L., and Irby, J. H. Recent progress towards a physics-based understanding of the H-mode transition. United Kingdom: N. p., 2016. Web. doi:10.1088/0741-3335/58/4/044003.
Tynan, G. R., Cziegler, I., Diamond, P. H., Malkov, M., Hubbard, A., Hughes, J. W., Terry, J. L., & Irby, J. H. Recent progress towards a physics-based understanding of the H-mode transition. United Kingdom. doi:10.1088/0741-3335/58/4/044003.
Tynan, G. R., Cziegler, I., Diamond, P. H., Malkov, M., Hubbard, A., Hughes, J. W., Terry, J. L., and Irby, J. H. Fri . "Recent progress towards a physics-based understanding of the H-mode transition". United Kingdom. doi:10.1088/0741-3335/58/4/044003.
@article{osti_1235490,
title = {Recent progress towards a physics-based understanding of the H-mode transition},
author = {Tynan, G. R. and Cziegler, I. and Diamond, P. H. and Malkov, M. and Hubbard, A. and Hughes, J. W. and Terry, J. L. and Irby, J. H.},
abstractNote = {Results from recent experiment and numerical simulation point towards a picture of the L-H transition in which edge shear flows interacting with edge turbulence create the conditions needed to produce a non-zero turbulent Reynolds stress at and just inside the LCFS during L-mode discharges. This stress acts to reinforce the shear flow at this location and the flow drive gets stronger as heating is increased. The L-H transition ensues when the rate of work done by this stress is strong enough to drive the shear flow to large values, which then grows at the expense of the turbulence intensity. The drop in turbulence intensity momentarily reduces the heat flux across the magnetic flux surface, which then allows the edge plasma pressure gradient to build. A sufficiently strong ion pressure gradient then locks in the H-mode state. The results are in general agreement with previously published reduced 0D and 1D predator prey models. An extended predator–prey model including separate ion and electron heat channels yields a non-monotonic power threshold dependence on plasma density provided that the fraction of heat deposited on the ions increases with plasma density. Possible mechanisms to explain other macroscopic transition threshold criteria are identified. A number of open questions and unexplained observations are identified, and must be addressed and resolved in order to build a physics-based model that can yield predictions of the macroscopic conditions needed for accessing H-mode.},
doi = {10.1088/0741-3335/58/4/044003},
journal = {Plasma Physics and Controlled Fusion},
number = 4,
volume = 58,
place = {United Kingdom},
year = {2016},
month = {1}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record
DOI: 10.1088/0741-3335/58/4/044003

Citation Metrics:
Cited by: 15 works
Citation information provided by
Web of Science

Figures / Tables:

Figure 1 Figure 1: (a) Reynolds force arising from the gradient of the turbulent Reynolds stress, (b) time-averaged radial profile of poloidal flow, (c) nonlinear turbulent flow production, P. data from HL-2A ECH heated discharges. Results from the HL-2A device. Figure taken from [22].

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    Works referencing / citing this record:

    Parallel electron force balance and the L-H transition
    journal, May 2016


      Figures/Tables have been extracted from DOE-funded journal article accepted manuscripts.