A new model of the L–H transition and H-mode power threshold

Xingquan Wu*, Guosheng Xu, Baonian Wan, Jens Juul Rasmussen, Volker Naulin, Anders Henry Nielsen, Liang Chen, Chen Ran, Yan Ning, Shao Linming

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

In order to understand the mechanism of the confinement bifurcation and H-mode power threshold in magnetically confined plasma, a new dynamical model of the L–H transition based on edge instability phase transition (EIPT) has been developed. With the typical plasma parameters of the EAST tokamak, the self-consistent turbulence growth rate is analyzed using the simplest case of pressure-driven ballooning-type instability, which indicates that the L–H transition can be caused by the stabilization of the edge instability through EIPT. The weak E × B flow shear in L-mode is able to increase the ion inertia of the electrostatic motion by increasing the radial wave number of the tilted turbulence structures, which play an important role for accelerating the trigger process of EIPT rather than directly to suppress the turbulent transport. With the acceleration mechanism of E × B flow shear, fast L–H and H–L transitions are demonstrated under the control of the input heating power. Due to the simplified scrape-off-layer boundary condition applied, the ratio between the heating powers at the H–L and L–H transition respectively differs from the ratio by Nusselt number. The results of the modeling reveal a scaling of the power threshold of the L–H transition, PL−H ∝ n0.76B0.8 for deuterium plasma. It is found finite Larmor radius induces an isotope effect of the H-mode power threshold.
Original languageEnglish
Article number094003
JournalPlasma Science and Technology
Volume20
Issue number9
Number of pages12
ISSN1009-0630
DOIs
Publication statusPublished - 2018

Keywords

  • L-H transition
  • Power threshold
  • E x B flow shear
  • Turbulence suppression
  • Edge instability

Cite this

Wu, Xingquan ; Xu, Guosheng ; Wan, Baonian ; Rasmussen, Jens Juul ; Naulin, Volker ; Nielsen, Anders Henry ; Chen, Liang ; Ran, Chen ; Ning, Yan ; Linming, Shao. / A new model of the L–H transition and H-mode power threshold. In: Plasma Science and Technology. 2018 ; Vol. 20, No. 9.
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title = "A new model of the L–H transition and H-mode power threshold",
abstract = "In order to understand the mechanism of the confinement bifurcation and H-mode power threshold in magnetically confined plasma, a new dynamical model of the L–H transition based on edge instability phase transition (EIPT) has been developed. With the typical plasma parameters of the EAST tokamak, the self-consistent turbulence growth rate is analyzed using the simplest case of pressure-driven ballooning-type instability, which indicates that the L–H transition can be caused by the stabilization of the edge instability through EIPT. The weak E × B flow shear in L-mode is able to increase the ion inertia of the electrostatic motion by increasing the radial wave number of the tilted turbulence structures, which play an important role for accelerating the trigger process of EIPT rather than directly to suppress the turbulent transport. With the acceleration mechanism of E × B flow shear, fast L–H and H–L transitions are demonstrated under the control of the input heating power. Due to the simplified scrape-off-layer boundary condition applied, the ratio between the heating powers at the H–L and L–H transition respectively differs from the ratio by Nusselt number. The results of the modeling reveal a scaling of the power threshold of the L–H transition, PL−H ∝ n0.76B0.8 for deuterium plasma. It is found finite Larmor radius induces an isotope effect of the H-mode power threshold.",
keywords = "L-H transition, Power threshold, E x B flow shear, Turbulence suppression, Edge instability",
author = "Xingquan Wu and Guosheng Xu and Baonian Wan and Rasmussen, {Jens Juul} and Volker Naulin and Nielsen, {Anders Henry} and Liang Chen and Chen Ran and Yan Ning and Shao Linming",
year = "2018",
doi = "10.1088/2058-6272/aabb9e",
language = "English",
volume = "20",
journal = "Plasma Science and Technology",
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A new model of the L–H transition and H-mode power threshold. / Wu, Xingquan; Xu, Guosheng; Wan, Baonian; Rasmussen, Jens Juul; Naulin, Volker ; Nielsen, Anders Henry ; Chen, Liang; Ran, Chen; Ning, Yan; Linming, Shao.

In: Plasma Science and Technology, Vol. 20, No. 9, 094003, 2018.

Research output: Contribution to journalJournal articleResearchpeer-review

TY - JOUR

T1 - A new model of the L–H transition and H-mode power threshold

AU - Wu, Xingquan

AU - Xu, Guosheng

AU - Wan, Baonian

AU - Rasmussen, Jens Juul

AU - Naulin, Volker

AU - Nielsen, Anders Henry

AU - Chen, Liang

AU - Ran, Chen

AU - Ning, Yan

AU - Linming, Shao

PY - 2018

Y1 - 2018

N2 - In order to understand the mechanism of the confinement bifurcation and H-mode power threshold in magnetically confined plasma, a new dynamical model of the L–H transition based on edge instability phase transition (EIPT) has been developed. With the typical plasma parameters of the EAST tokamak, the self-consistent turbulence growth rate is analyzed using the simplest case of pressure-driven ballooning-type instability, which indicates that the L–H transition can be caused by the stabilization of the edge instability through EIPT. The weak E × B flow shear in L-mode is able to increase the ion inertia of the electrostatic motion by increasing the radial wave number of the tilted turbulence structures, which play an important role for accelerating the trigger process of EIPT rather than directly to suppress the turbulent transport. With the acceleration mechanism of E × B flow shear, fast L–H and H–L transitions are demonstrated under the control of the input heating power. Due to the simplified scrape-off-layer boundary condition applied, the ratio between the heating powers at the H–L and L–H transition respectively differs from the ratio by Nusselt number. The results of the modeling reveal a scaling of the power threshold of the L–H transition, PL−H ∝ n0.76B0.8 for deuterium plasma. It is found finite Larmor radius induces an isotope effect of the H-mode power threshold.

AB - In order to understand the mechanism of the confinement bifurcation and H-mode power threshold in magnetically confined plasma, a new dynamical model of the L–H transition based on edge instability phase transition (EIPT) has been developed. With the typical plasma parameters of the EAST tokamak, the self-consistent turbulence growth rate is analyzed using the simplest case of pressure-driven ballooning-type instability, which indicates that the L–H transition can be caused by the stabilization of the edge instability through EIPT. The weak E × B flow shear in L-mode is able to increase the ion inertia of the electrostatic motion by increasing the radial wave number of the tilted turbulence structures, which play an important role for accelerating the trigger process of EIPT rather than directly to suppress the turbulent transport. With the acceleration mechanism of E × B flow shear, fast L–H and H–L transitions are demonstrated under the control of the input heating power. Due to the simplified scrape-off-layer boundary condition applied, the ratio between the heating powers at the H–L and L–H transition respectively differs from the ratio by Nusselt number. The results of the modeling reveal a scaling of the power threshold of the L–H transition, PL−H ∝ n0.76B0.8 for deuterium plasma. It is found finite Larmor radius induces an isotope effect of the H-mode power threshold.

KW - L-H transition

KW - Power threshold

KW - E x B flow shear

KW - Turbulence suppression

KW - Edge instability

U2 - 10.1088/2058-6272/aabb9e

DO - 10.1088/2058-6272/aabb9e

M3 - Journal article

VL - 20

JO - Plasma Science and Technology

JF - Plasma Science and Technology

SN - 1009-0630

IS - 9

M1 - 094003

ER -