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Article Dans Une Revue Physics of Plasmas Année : 2013

Spatio-temporal evolution of the H -> L back transition

K. Miki
  • Fonction : Auteur
P.H. Diamond
  • Fonction : Auteur
L. Schmitz
  • Fonction : Auteur
D. C. Mcdonald
  • Fonction : Auteur
T. Estrada
  • Fonction : Auteur
Özgür D. Gürcan
G.R. Tynan
  • Fonction : Auteur

Résumé

Since ITER will operate close to threshold and with limited control, the H → L back transition is a topic important for machine operations as well as physics. Using a reduced mesoscale model [Miki et al., Phys. Plasmas 19, 092306 (2012)], we investigate ELM-free H → L back transition dynamics in order to isolate transport physics effects. Model studies indicate that turbulence spreading is the key process which triggers the back transition. The transition involves a feedback loop linking turbulence and profiles. The I-phase appears during the back transition following a slow power ramp down, while fast ramp-downs reveal a single burst of zonal flow during the back transition. The I-phase nucleates at the pedestal shoulder, as this is the site of the residual turbulence in H-mode. Hysteresis in the profile gradient scale length is characterized by the Nusselt number, where Nu = χi,turb/χi,neo. Relative hysteresis of temperature gradient vs density gradient is sensitive to the pedestal Prandtl number, where Prped = Dped/χi,neo. We expect the H-mode to be somewhat more resilient in density than in temperature.

Dates et versions

hal-01550974 , version 1 (29-06-2017)

Identifiants

Citer

K. Miki, P.H. Diamond, L. Schmitz, D. C. Mcdonald, T. Estrada, et al.. Spatio-temporal evolution of the H -> L back transition. Physics of Plasmas, 2013, 20 (6), pp.062304. ⟨10.1063/1.4812555⟩. ⟨hal-01550974⟩
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