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H and HL transitionsMiki, Kazuhiro; Diamond, P. H.*; Fedorczak, N.*; G
rcan, 
. D.*; Malkov, M.*; Lee, C.*; Kosuga, Yusuke*; Tynan, G. R.*; Xu, G. S.*; Estrada, T.*; et al.
Nuclear Fusion, 53(7), p.073044_1 - 073044_10, 2013/07
Times Cited Count：24 Percentile：72.36(Physics, Fluids & Plasmas)Understanding the LH and HL transitions is crucial to successful ITER operation. In this paper we present novel theoretical and modelling study results on the spatio-temporal dynamics of the transition. We place a special emphasis on the role of zonal flows and the micromacro connection between dynamics and the power threshold dependences. The model studied evolves five coupled fields in time and one space dimension, in simplified geometry. The content of this paper is (a) the model fundamentals and the space-time evolution during the LIH transition, (b) the physics origin of the well-known 
B-drift asymmetry in power threshold, (c) the role of heat avalanches in the intrinsic variability of the LH transition, (d) the dynamics of the HL back transition and the physics of hysteresis.
L back transitionMiki, Kazuhiro; Diamond, P. H.*; Schmitz, L.*; McDonald, D. C.*; Estrada, T.*; Grcan, . D.*; Tynan, G. R.*
Physics of Plasmas, 20(6), p.062304_1 - 062304_9, 2013/06
Times Cited Count：19 Percentile：64.31(Physics, Fluids & Plasmas)Since ITER will operate close to threshold and with limited control, the HL back transition is a topic important for machine operations as well as physics. Using a reduced mesoscale model, we investigate ELM-free HL 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. Relative hysteresis of temperature gradient vs density gradient is sensitive to the pedestal Prandtl number.
Schaffer, M. J.*; Snipes, J. A.*; Gohil, P.*; de Vries, P.*; Evans, T. E.*; Fenstermacher, M. E.*; Gao, X.*; Garofalo, A. M.*; Gates, D. A.*; Greenfield, C. M.*; et al.
Nuclear Fusion, 51(10), p.103028_1 - 103028_11, 2011/10
Times Cited Count：35 Percentile：80.59(Physics, Fluids & Plasmas)Experiments at DIII-D investigated the effects of ferromagnetic error fields similar to those expected from proposed ITER Test Blanket Modules (TBMs). Studied were effects on: plasma rotation and locking; confinement; L-H transition; edge localized mode (ELM) suppression by resonant magnetic perturbations; ELMs and the H-mode pedestal; energetic particle losses; and more. The experiments used a 3-coil mock-up of 2 magnetized ITER TBMs in one ITER equatorial port. The experiments did not reveal any effect likely to preclude ITER operations with a TBM-like error field. The largest effect was slowed plasma toroidal rotation v across the entire radial profile by as much as 
via non-resonant braking. Changes to global 
, 
and 
were 
3 times smaller. These effects are stronger at higher 
and lower 
. Other effects were smaller.
Snipes, J. A.*; Schaffer, M. J.*; Gohil, P.*; de Vries, P.*; Fenstermacher, M. E.*; Evans, T. E.*; Gao, X. M.*; Garofalo, A.*; Gates, D. A.*; Greenfield, C. M.*; et al.
no journal, ,
A series of experiments was performed on DIII-D to mock-up the field that will be induced in a pair of ferromagnetic Test Blanket Modules (TBMs) in ITER to determine the effects of such error fields on plasma operation and performance. A set of coils producing both poloidal and toroidal fields was placed inside a re-entrant horizontal port close to the plasma. The coils produce a localized ripple due to the toroidal field (TF) + TBM up to 5.7%, which is more than four times that expected from a pair of representative 1.3 ton TBMs in ITER. The experiments show that the reduction in the toroidal rotation is sensitive to the ripple. On the other hand, the confinement is reduced by up to 15-18% for local ripple 
3% but is hardly affected at 1.7% local ripple.
Miki, Kazuhiro; Diamond, P. H.*; Schmitz, L.*; McDonald, D. C.*; Gurcan, O.*; Tynan, G. R.*
no journal, ,
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, we investigate ELM-free H-L back transition dynamics. 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-down 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 profile gradient is characterized by the Nusselt number. Relative hysteresis of temperature gradient vs density gradient is sensitive to the pedestal Prandtl number. We expect the H-mode to be somewhat more resilient in density than in temperature.
