Impact of the α parameter on the microstability of internal transport barriers

C. Bourdelle, G.T. Hoang, X. Litaudon, C.M. Roach, Tuomas Tala

Research output: Contribution to journalArticleScientificpeer-review

44 Citations (Scopus)

Abstract

In plasmas exhibiting an internal transport barrier (ITB), locally very high pressure gradient (∇P) is obtained. It induces high values of the magnetohydrodynamic α parameter (α = −q 2 βRP/P, with R the major radius, q the safety factor, P the pressure, ∇ the radial gradient and β the ratio between kinetic and magnetic pressure). Similarly to low or negative magnetic shear (s), high α reduces the curvature and ∇ B drifts driving curvature-type microinstabilities. Therefore, high values of α can stabilize part of the microturbulence, which leads to higher pressure gradient and to even higher α. This possibility for entering a positive feedback loop is very attractive to sustain ITBs in high performance plasmas. Indeed, α scales favourably with higher pressure and does not require any external momentum input. In this paper, after having discussed the α stabilization mechanism in detail, we report the experimental microstability analyses of ITBs from an international multi-machine database—the International Tokamak Physics Activity database, accessible on the webb. We show that α is indeed a relevant parameter of ITB physics that should be taken into account in interpretative and predictive one-dimensional transport codes.
Original languageEnglish
Pages (from-to)110 - 130
Number of pages21
JournalNuclear Fusion
Volume45
Issue number2
DOIs
Publication statusPublished - 2005
MoE publication typeA1 Journal article-refereed

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pressure gradients
curvature
safety factors
positive feedback
physics
magnetohydrodynamics
stabilization
shear
momentum
gradients
radii
kinetics

Keywords

  • JET
  • plasma
  • fusion energy
  • fusion reactors
  • internal transport barriers

Cite this

Bourdelle, C. ; Hoang, G.T. ; Litaudon, X. ; Roach, C.M. ; Tala, Tuomas. / Impact of the α parameter on the microstability of internal transport barriers. In: Nuclear Fusion. 2005 ; Vol. 45, No. 2. pp. 110 - 130.
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Impact of the α parameter on the microstability of internal transport barriers. / Bourdelle, C.; Hoang, G.T.; Litaudon, X.; Roach, C.M.; Tala, Tuomas.

In: Nuclear Fusion, Vol. 45, No. 2, 2005, p. 110 - 130.

Research output: Contribution to journalArticleScientificpeer-review

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T1 - Impact of the α parameter on the microstability of internal transport barriers

AU - Bourdelle, C.

AU - Hoang, G.T.

AU - Litaudon, X.

AU - Roach, C.M.

AU - Tala, Tuomas

PY - 2005

Y1 - 2005

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AB - In plasmas exhibiting an internal transport barrier (ITB), locally very high pressure gradient (∇P) is obtained. It induces high values of the magnetohydrodynamic α parameter (α = −q 2 βR∇P/P, with R the major radius, q the safety factor, P the pressure, ∇ the radial gradient and β the ratio between kinetic and magnetic pressure). Similarly to low or negative magnetic shear (s), high α reduces the curvature and ∇ B drifts driving curvature-type microinstabilities. Therefore, high values of α can stabilize part of the microturbulence, which leads to higher pressure gradient and to even higher α. This possibility for entering a positive feedback loop is very attractive to sustain ITBs in high performance plasmas. Indeed, α scales favourably with higher pressure and does not require any external momentum input. In this paper, after having discussed the α stabilization mechanism in detail, we report the experimental microstability analyses of ITBs from an international multi-machine database—the International Tokamak Physics Activity database, accessible on the webb. We show that α is indeed a relevant parameter of ITB physics that should be taken into account in interpretative and predictive one-dimensional transport codes.

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