Recent progress towards a physics-based understanding of the H-mode transition
Name
Recent progress.pdf
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2.18 MB
Format
Adobe PDF
Checksum (MD5)
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Author(s)
Tynan, G R
Cziegler, I
Diamond, P H
Malkov, M
Hubbard, Amanda E
Hughes Jr, Jerry
Terry, James L
Irby, James Henderson
Date Issued
January 2016
Journal
Plasma Physics and Controlled Fusion
Publisher
IOP Publishing
Citation
Tynan, G R et al. “Recent Progress Towards a Physics-Based Understanding of the H-Mode Transition.” Plasma Physics and Controlled Fusion 58, 4 (January 2016): 044003 © 2016 IOP Publishing Ltd
Version
Author's final manuscript
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 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.
MIT Department
Massachusetts Institute of Technology. Plasma Science and Fusion Center
Terms of Use
Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use.
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DOI of Published Version
https://doi.org/10.1088/0741-3335/58/4/044003
