Regime of improved confinement in neutral-beam<i>–</i>heated limiter discharges of a tokamak

Sengoku, S.; Funahashi, A.; Hasegawa, Mitsuru; Hoshino, K.; Kasai, S.; Kawakami, T.; Kawashima, H.; Matoba, T.; Matsuda, Toshiaki; Matsumoto, Hiroshi; Miura, Y.; Mori, Masahiro; Ogawa, Hideyuki; Ogawa, T.; Ohtsuka, Hokuto; Shoji, T.; Suzuki, Norio; Tamai, Hiroshi; Uesugi, Yoshihiko; Yamamoto, T.; Yamauchi, Toshihiko

doi:10.1103/physrevlett.59.450

Cited by 48 publications

(13 citation statements)

References 11 publications

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“…Note that a material limiter configuration is incompatible with the high edge temperature indicative of the H-mode since high edge temperature causes severe sputtering. This may be a possible reason why improvement in the energy confinement is modest and transient in JFT-2M limiter discharges which exhibit an H-modelike transition [18].…”

Section: B Dtmentioning

confidence: 99%

Possible applications of a resonant helical magnetic field in the tokamak boundary

Ohyabu¹,

deGrassie²

1987

Nucl. Fusion

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Section: B Dtmentioning

confidence: 99%

Possible applications of a resonant helical magnetic field in the tokamak boundary

Ohyabu¹,

deGrassie²

1987

Nucl. Fusion

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“…These feedback loops underpin the now familiar 'predator-prey' model structure [2]. Both GAMs and ZFs frequently have been detected in tokamak edge turbulence [3] and have been observed to respond to changes in plasma conditions and to proximity to the L-H transition [4][5][6], and those driving mechanisms has been theoretically and numerically studied [7][8][9][10][11][12][13].…”

Section: Introductionmentioning

confidence: 97%

Novel states of pre-transition edge turbulence emerging from shearing mode competition

Miki¹,

Diamond²

2011

Nucl. Fusion

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A novel model handling zonal flow, geodesic acoustic mode (GAM), and turbulence self-consistently as a predator-prey system with multiple frequency shearings is introduced. ZF with finite frequency has different shearing relation from that with zero frequency depending to their auto-correlation times. Splitting ZF broadband spectrum into the two modes of wave populations enables us to state different shearing weights to the turbulence contributions of the ZFs. We define states with no ZF and GAM states as L-mode-like state, with ZF and without GAM as ZF-only state, with GAM and without ZF as GAM-only state, and both with ZF and GAM as the coexisting state. Since the coexisting state does not appear in the minimal model, mode-competition effects are introduced. We introduce one which originates from higher order perturbation of wave actions. The model exhibits a sequence of transition between various roots as the driving flux increases. In some chosen parameters, bi-stability is evident, which suggests the origin of the hysteretic behavior in the turbulence intensity field during power ramp up/down studies. In the presence of noise due to ambient turbulence offers a novel and interesting mechanism to explain the bursts and pulsations observed in the turbulence field prior to the L-H transition.

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“…Modest drops in Dot light during the supershot to H-mode transition may be due to the inherently low recycling level of the inir2_l supershot plasma. This is different from divertor H-modes, however, such behavior ha:, _,een observed for limiter H-modes on other tokamaks [11,12]. Distinct broad edge ped¢,.....ls of ne and "le form following the supershot to H-mode transition, clearly reflecting a reduction in edge heat and particle transport.…”

Section: H-modes a General Resultsmentioning

confidence: 76%

Characteristics of the TFTR limiter H-mode: The transition, ELMs, transport and confinement

Bush¹,

Bretz²,

Nazikian³

et al. 1992

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H-Modes obtained through transitions from the supershot regime have been studied on TFTR. The characteristics of these H-modes are similar to those found on other tokamaks with one main exception, the density profiles can be highly peaked. In the best cases the enhanced confinement in the core of the initial supershot is retained in the H-mode phase, while the confinement in a broad edge region is enhanced. Thus in TFTR, ali of the important physics of H-modes such as transitions, enhanced edge confinement, ELMs and other phenomena are studied in a large circular limiter tokamak with the added feature of centrally peaked density profi!es and the advantage of an extensive set of diagnostics. The threshold power for the transition is found to be a linear function of plasma current. "Transitions and ELMs are affected by the mix of co-and counter-neutral beam injection (NBI) and by perturbations introduced by pellet injection, gas puffing, and current ramping before and during NBI. Fluctuations near both transition and ELM events have been • characterized. High frequency magnetic fluctuations in the range > 100-250 kHz usually decrease during the transition. Microwave scattering spectra of density fluctuations in the plasma edge show a feature at high frequency ( > 1.5 MHz at k.t.= 5.5 cm -1) during the Hmode, which is not observed in the plasma core and which is consistent with an edge poloidal rotation velocity, V0, of~104 m/s. The fluctuations begin at the transition, propagate in the direction of electron diamagnetic drift, and have modulation correlated with ELMs. Several TFqTRH-modes showed a modest improvement in confinement over that of the supershots from which they originated, and an understanding of these may eventually lead to a plasma with the combined advantages of both the supershot and the Hmode. The characteristics and physics of the _ H-modes are considered relative to other tokamaks and in light of various theoretical studi,ls.

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Regime of improved confinement in neutral-beam–heated limiter discharges of a tokamak

Cited by 48 publications

References 11 publications

Possible applications of a resonant helical magnetic field in the tokamak boundary

Possible applications of a resonant helical magnetic field in the tokamak boundary

Novel states of pre-transition edge turbulence emerging from shearing mode competition

Characteristics of the TFTR limiter H-mode: The transition, ELMs, transport and confinement

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