Energy loss for grassy ELMs and effects of plasma rotation on the ELM characteristics in JT-60U

Oyama, N.; Sakamoto, Y.; Isayama, A.; Takechi, M.; Gohil, P.; Lao, L. L.; Snyder, P. B.; Fujita, T.; Ide, S.; Kamada, Y.; Miura, Y.; Oikawa, T.; Suzuki, Takahiro; Takenaga, H.; Toi, K.

doi:10.1088/0029-5515/45/8/014

Cited by 133 publications

(163 citation statements)

References 30 publications

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“…3, we have now achieved QH-mode operation with all coinjection in discharges exhibiting rapid co-rotation in the edge pedestal region. Previous experiments on JT-60U which produced QH-mode with net co-injection actually exhibited counter-rotation in the edge pedestal region, possibly due to edge ion loss caused by toroidal field ripple [6,7]. …”

Section: Ex/8-4mentioning

confidence: 91%

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Edge pedestal control in quiescent H-mode discharges in DIII-D using co-plus counter-neutral beam injection

et al. 2009

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Abstract. We have made two significant discoveries in our recent studies of quiescent H-mode (QH-mode) plasmas in DIII-D. First, we have found that we can control the edge pedestal density and pressure by altering the edge particle transport through changes in the edge toroidal rotation. This allows us to adjust the edge operating point to be close to, but below the ELM stability boundary, maintaining the ELM-free state while allowing up to a factor of two increase in edge pressure. The ELM boundary is significantly higher in more strongly shaped plasmas, which broadens the operating space available for QH-mode and leads to improved core performance. Second, for the first time on any tokamak, we have created QH-mode plasmas with strong edge co-rotation; previous QH-modes in all tokamaks had edge counter rotation. This result demonstrates that counter NBI and edge counter rotation are not essential conditions for QH-mode. Both these investigations benefited from the edge stability predictions based on peeling-ballooning mode theory. The broadening of the ELM-stable region with plasma shaping is predicted by that theory. The theory has also been extended to provide a model for the edge harmonic oscillation (EHO) that regulates edge transport in the QH-mode. Many of the features of that theory agree with the experimental results reported either previously or in the present paper. One notable example is the prediction that co-rotating QH-mode is possible provided sufficient shear in the edge rotation can be created.

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Section: Ex/8-4mentioning

confidence: 91%

“…All previous QH-mode plasmas have exhibited edge rotation in the counter direction [1][2][3][4][5][6][7][8]. As is shown in Fig.…”

Section: Qh-mode With Strong Edge Co-rotationmentioning

confidence: 99%

Edge pedestal control in quiescent H-mode discharges in DIII-D using co-plus counter-neutral beam injection

et al. 2009

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“…21͒ and ASDEX-U ͑Ref. 22͒ groups, various small ELM regimes at JT-60U, 23,24 ASDEX-U, 25 NSTX, 26,27 JET, 28 C-Mod, 29 JFT-2M, 30,31 Compass-D ͑Ref. 32͒ and DIII-D, 33 and ELM-free operation in the QH-mode.…”

Section: Introductionmentioning

confidence: 99%

Effect of island overlap on edge localized mode suppression by resonant magnetic perturbations in DIII-D

Fenstermacher¹,

Evans²,

Osborne³

et al. 2008

Physics of Plasmas

151

233

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Recent DIII-D [J. L. Luxon et al., Nucl. Fusion 43, 1813 (2003)] experiments show a correlation between the extent of overlap of magnetic islands induced in the edge plasma by perturbation coils and complete suppression of Type-I edge localized modes (ELMs) in plasmas with ITER-like electron pedestal collisionality νe*∼0.1, flux surface shape and low edge safety factor (q95≈3.6). With fixed amplitude n=3 resonant magnetic perturbation (RMP), ELM suppression is obtained only in a finite window in the edge safety factor (q95) consistent with maximizing the resonant component of the applied helical field. ELM suppression is obtained over an increasing range of q95 by either increasing the n=3 RMP strength, or by adding n=1 perturbations to “fill in” gaps between islands across the edge plasma. The suppression of Type-I ELMs correlates with a minimum width of the edge region having magnetic islands with Chirikov parameter >1.0, based on vacuum calculations of RMP mode components excluding the plasma response or rotational shielding. The fraction of vacuum magnetic field lines that are lost from the plasma, with connection length to the divertor targets comparable to an electron-ion collisional mean free path, increases throughout the island overlap region in the ELM suppressed case compared with the ELMing case.

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“…For this reason, research on confinement regimes which can reach high energy confinement levels without ELMs remains a priority for ITER. In this respect, the QH-mode regime, originally developed at the DIII-D tokamak [7,8] and investigated in other current devices [9][10][11], has been found to provide high energy confinement without transient energy fluxes to PFCs associated with ELMs. In DIII-D, this operational regime has recently been extended towards conditions suitable for ITER operation such as low torque input [12] and high normalized density operation [13] thus overcoming two important restrictions for its suitability for ITER.…”

Section: Introductionmentioning

confidence: 99%

Nonlinear MHD simulations of Quiescent H-mode plasmas in DIII-D

et al. 2015

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In the Quiescent H-mode (QH-mode) regime, the edge harmonic oscillation (EHO), thought to be a saturated kink-peeling mode (KPM) driven unstable by current and rotation, is found in experiment to provide sufficient stationary edge particle transport to avoid the periodic expulsion of particles and energy by edge localized modes (ELMs). In this paper, both linear and nonlinear MHD modelling of QH-mode plasmas from the DIII-D tokamak have been investigated to understand the mechanism leading to the appearance of the EHO in QH-mode plasmas. For the first time nonlinear MHD simulations with low-n modes both with ideal wall and resistive wall boundary conditions have been carried out with 3-D non-linear MHD code JOREK. The results show, in agreement with the original conjectures, that, in the nonlinear phase, kink peeling modes are the main unstable modes in QH-mode plasmas of DIII-D and that the kink-peeling modes saturate non-linearly leading to a 3-D stationary state. The characteristics of the kink-peeling modes, in terms of mode structure and associated decrease of the edge plasma density associated with them, are in good agreement with experimental measurements of the EHO in DIII-D. The effect of plasma resistivity, the role of plasma parallel rotation as well as the effect of the conductivity of the vacuum vessel wall on the destabilization and saturation of kink-peeling modes have been evaluated for experimental QH-mode plasma conditions in DIII-D.

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Energy loss for grassy ELMs and effects of plasma rotation on the ELM characteristics in JT-60U

Cited by 133 publications

References 30 publications

Edge pedestal control in quiescent H-mode discharges in DIII-D using co-plus counter-neutral beam injection

Edge pedestal control in quiescent H-mode discharges in DIII-D using co-plus counter-neutral beam injection

Effect of island overlap on edge localized mode suppression by resonant magnetic perturbations in DIII-D

Nonlinear MHD simulations of Quiescent H-mode plasmas in DIII-D

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