Superdense core mode in the Large Helical Device with an internal diffusion barrier

Morisaki, T.; Ohyabu, N.; Masuzaki, S.; Kobayashi, M.; Sakamoto, R.; Miyazawa, J.; Funaba, H.; Ida, K.; Ikeda, K.; Kaneko, O.; Morita, S.; Mutoh, S.; Nagaoka, K.; Nagayama, Y.; Nakajima, N.; Narihara, K.; Oka, Y.; Osakabe, M.; Peterson, B.J.; Sakakibara, S.; Shoji, M.; Suzuki, Y.; Takeiri, Y.; Tamura, N.; Tanaka, K.; Tsumori, K.; Watanabe, K. Y.; Yamada, I.; Yamada, H.; Komori, A.; Motojima, O.

doi:10.1063/1.2718530

Cited by 31 publications

(16 citation statements)

References 29 publications

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“…Extremely peaked density profile is formed by the central fueling with ice-pellet injection [4][5][6]. The electron density at the center exceeds 10 21 m −3 .…”

Section: Introductionmentioning

confidence: 99%

Density Collapse Events Observed in the Large Helical Device

Ohdachi¹,

Sakamoto

Miyazawa

et al. 2010

Contrib. Plasma Phys.

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A core density collapse (CDC) phenomenon is a rapid collapse events observed in super dense core (SDC) plasma with internal diffusion barrier (IDB) in the Large Helical Device (LHD). By CDC, the central beta is decreased by up to 50%. The collapse starts from the edge region of the plasma. CDCs appear with plasma parameters where the high-n ballooning modes are unstable at ρ ∼ 0.8. With less collisional conditions, m = 1 type oscillations are observed with similar beta profile. The origin of the m=1 oscillations is not clarified.

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“…Extremely peaked density profile is formed by the central fueling with ice-pellet injection [4][5][6]. The electron density at the center exceeds 10 21 m −3 .…”

Section: Introductionmentioning

confidence: 99%

Density Collapse Events Observed in the Large Helical Device

Ohdachi¹,

Sakamoto

Miyazawa

et al. 2010

Contrib. Plasma Phys.

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“…beyond the accumulation window, indicating that the onset of purification is not exclusively determined by the core confinement: the injection experiments are sensitive to the core confinement whereas the global intrinsic impurity behaviour might be dominated by edge shielding processes as well, which is no contradiction. Likewise, the Super Dense Core (SDC) plasmas with internal diffusion barrier (n e (0)=5-6A10 20 m -3 , T e (0)=660-850 eV) obtained in LHD by frequent pellet injection in the presence of a helical divertor or the local island divertor (LID) plasmas presumably do not suffer severely from enhanced radiation [14,15], although impurity 9 accumulation and long impurity confinement are indicated [16]. In both cases, consequently, a very effective shielding of the impurity influx in LHD has to be suggested which can most likely be assigned to the same intrinsic edge screening mechanism discussed above, so that the observations at LHD and W7-AS seem to be consistently explained by the same screening mechanism.…”

Section: Impurity Influx Shielding In the Edge/sol Of Divertor Plasmasmentioning

confidence: 99%

On impurity handling in high performance stellarator/heliotron plasmas

Burhenn¹,

Feng²,

Ida³

et al. 2009

Nucl. Fusion

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Abstract. The Large Helical Device (LHD) and Wendelstein 7-X (W7-X, under construction) are experiments specially designed to demonstrate long pulse (quasi steady-state) operation, which is an intrinsic property of Stellarators and Heliotrons. Significant progress had been made in establishing high performance plasmas. A crucial point is the increasing impurity confinement at high density observed at several machines (TJ-II, W7-AS, LHD) which can lead to impurity accumulation and early pulse termination by radiation collapse. In addition, theoretical predictions for non-axisymmetric configurations predict the absence of impurity screening by ion temperature gradients in standard ion-root plasmas. Nevertheless, scenarios were found where impurity accumulation was successfully avoided in LHD and W7-AS due to the onset of friction forces in the (high density and low temperature) scrape-off-layer, the generation of magnetic islands at the plasma boundary and to a certain degree also by ELMs, flushing out impurities and reducing the net-impurity influx into the core. In both the W7-AS High Density H-mode (HDH) regime and in the case of application of sufficient ECRH heating power a reduction of impurity core confinement was observed. The exploration of such purification mechanisms is a demanding task for successful steady-state operation. Impurity transport at the plasma edge/SOL was identified to play a major role for the global impurity behaviour in addition to the core confinement.

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“…3) Without strong toroidal plasma currents, the Greenwald density limit is not observed and at a given fusion power, the alpha-particle pressure and the drive for fastion driven instabilities are reduced. As a consequence, densities far beyond an equivalent Greenwald limit have been observed [3], [4]. However, stellarator confinement also has several disadvantages.…”

Section: Introductionmentioning

confidence: 96%

Wendelstein 7-X Program—Demonstration of a Stellarator Option for Fusion Energy

Wolf

Beidler

Dinklage

et al. 2016

IEEE Trans. Plasma Sci.

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The superconducting stellarator Wendelstein 7-X is currently being commissioned. First plasmas are expected for the second half of 2015. W7-X is designed to overcome the main drawbacks of the stellarator concept and simultaneously demonstrate its intrinsic advantages relative to the tokamaki.e., steady-state operation without the requirement of current drive or stability control. An elaborate optimization procedure was used to avoid excessive neoclassical transport losses at high plasma temperature, while simultaneously achieving satisfactory equilibrium and stability properties at high β in combination with a viable divertor concept. In addition, fastion confinement must be consistent with the requirements of alpha-heating in a power plant. Plasma operation of Wendelstein 7-X follows a staged approach following the successive completion of the in-vessel components. The main objective of Wendelstein 7-X is the demonstration of steady-state plasma at fusion relevant plasma parameters. Wendelstein 7-X will address major questions for the extrapolation of the concept to a power plant. These include divertor operation at high densities, plasma fueling at high central temperatures, avoiding impurity accumulation, and an assessment of the effect of neoclassical optimization on turbulent transport and fast-ion confinement. A power plant concept based on an extrapolation from Wendelstein 7-X, the helical advanced stellarator, has been developed.Index Terms-Fusion power plant, steady-state magnetic confinement, stellarator.

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Superdense core mode in the Large Helical Device with an internal diffusion barrier

Cited by 31 publications

References 29 publications

Density Collapse Events Observed in the Large Helical Device

Density Collapse Events Observed in the Large Helical Device

On impurity handling in high performance stellarator/heliotron plasmas

Wendelstein 7-X Program—Demonstration of a Stellarator Option for Fusion Energy

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