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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. These 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:
; ; ; ; ; ; ;
Publication Date:
DOE Contract Number:  
FC02-99ER54512; SC0008689; SC0008378; SC0001961
Research Org.:
Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Plasma Science and Fusion Center; Univ. of California, San Diego, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES)
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY
OSTI Identifier:
1880640
DOI:
https://doi.org/10.7910/DVN/5MQ6UY

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 States: N. p., 2019. Web. doi:10.7910/DVN/5MQ6UY.
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 States. doi:https://doi.org/10.7910/DVN/5MQ6UY
Tynan, G. R., Cziegler, I., Diamond, P. H., Malkov, M., Hubbard, A., Hughes, J. W., Terry, J. L., and Irby, J. H. 2019. "Recent progress towards a physics-­based understanding of the H-­mode transition". United States. doi:https://doi.org/10.7910/DVN/5MQ6UY. https://www.osti.gov/servlets/purl/1880640. Pub date:Thu Jan 10 00:00:00 EST 2019
@article{osti_1880640,
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. These 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 = {10.7910/DVN/5MQ6UY},
journal = {},
number = ,
volume = ,
place = {United States},
year = {2019},
month = {1}
}

Works referencing / citing this record:

Recent progress towards a physics-based understanding of the H-mode transition
journal, January 2016