Density Regimes of Complete Detachment and Serpens Mode in LHD

Miyazawa, J.; Masuzaki, S.; Goto, M.; Tamura, N.; Sakamoto, R.; Peterson, B.J.; Yamada, I.; Narihara, K.; Tanaka, K.; Tokuzawa, T.; Shoji, M.; Funaba, H.; Sakakibara, S.; Kobayashi, M.; Osakabe, M.; Morita, S.; Arimoto, Hajime; Kondoh, Katsumi; Murakami, S.; Nishiura, M.; Ashikawa, N.; Morisaki, T.; Nishimura, K.; Yamada, H.; Ohyabu, N.; Komori, A.; Motojima, O.

doi:10.1585/pfr.1.026

Cited by 6 publications

(3 citation statements)

References 39 publications

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“…This has been evidenced by the strong reduction of the energy content. Then, the plasma reaches a quasi steady state termed 'Serpens mode' [17], with a rotating radiation belt inside the LCFS being detected [18]. Till now, a radiation layer outside the confinement region could not yet be stabilized experimentally.…”

Section: Detachment Transition and Marfe Formationmentioning

confidence: 98%

Fluid features of the stochastic layer transport in LHD

Feng¹,

Kobayashi²,

Morisaki³

et al. 2008

Nucl. Fusion

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Section: Detachment Transition and Marfe Formationmentioning

confidence: 98%

Fluid features of the stochastic layer transport in LHD

Feng¹,

Kobayashi²,

Morisaki³

et al. 2008

Nucl. Fusion

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“…it is assumed that radiating collapse takes place at a critical radiation loss fraction of P rad /P tot ∝ n 2 e /P tot , and therefore, the critical density is proportional to P 0.5 tot [14,15]. However, a large scatter in the radiation loss fraction that ranges from 30% to 100% [8,18] suggests that this scenario is not sufficient to explain the density limit in LHD. Nevertheless, the threshold edge density for complete detachment does increase with P 0.5 tot , as in equation ( 3) (see also figure 3).…”

Section: Derivation Of the Power Dependence From Experimental Observa...mentioning

confidence: 99%

Density limit study focusing on the edge plasma parameters in LHD

et al. 2008

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In the Large Helical Device (LHD) experiment, complete detachment takes place when the plasma column shrinks inside the last-closed-flux-surface (LCFS). The density at the LCFS that results in this shrinking corresponds to the maximum LCFS density achievable under the attached condition. The critical LCFS density increases with the square root of the heating power, as is predicted by the conventional density limit scaling for helical plasmas, called the Sudo scaling. High line-averaged electron densities reaching 3 × 1020 m−3, which correspond to ∼3 times as high as the Sudo scaling, have been achieved in the plasmas with strongly peaked density profiles generated by hydrogen ice pellet injection. Even in the pellet-fuelled plasmas, however, the LCFS densities are similar to those in gas-fuelled plasmas with flat density profiles and well reproduced by Sudo scaling with a factor 0.8. According to these observations, Sudo scaling has been reinterpreted as the ‘edge’ density limit scaling. The square root type power dependence in the Sudo scaling has been reconsidered. Instead of a simple power balance between the heating power and the radiation loss, it is deduced by combining the critical LCFS temperature for complete detachment and the electron temperature dependence on the heating power and the electron density. Higher edge density than in the attached plasmas can be sustained in the completely detached plasmas, where the plasma edge shrinks inside the LCFS. The edge density limit scaling is extended for completely detached plasmas by taking into account the shrinking plasma edge.

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“…This provides us possibilities to investigate geometrical effects on the detachment stability. In LHD, the analyses on radiation pattern during the radiative collapse phase [12] as well as on operational space of detachment realization [13] were performed.…”

Section: Introductionmentioning

confidence: 99%

Detachment stabilization with n/m=1/1 resonant magnetic perturbation field applied to the stochastic magnetic boundary of the Large Helical Device

et al. 2010

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It is found that the remnant island structure created by n/m=1/1 resonant magnetic perturbation field in the stochastic magnetic boundary of the Large Helical Device (LHD) [A. Komori et al., Nucl. Fusion 49, 104015 (2009).] has a stabilizing effect on formation of radiating plasma, realizing stably sustained divertor detachment operation with the core plasma being unaffected. The data from the several diagnostics, (profiles of electron temperature & density, radiation and temporal evolution of divertor particle flux) indicate selective cooling around X-point of the island and thus peaked radiation there, which is stabilized outside of the last closed flux surface throughout the detachment phase. The VUV spectroscopy measurements of high Z impurity (iron) emission shows significant decrease during the detachment, indicating core plasma decontamination. The results from the 3D edge transport code EMC3 (Edge Monte-Carlo 3D) [Y. Feng et al., Contributions to Plasma Physics, 44, 57 (2004).]-EIRENE [D. Reiter et al., Fusion Sci. Technol., 47 172 (2005).] show similar tendency in the radiation pattern. The island size and its radial location are varied to investigate the magnetic topology effects on the detachment control. The divertor particle flux and neutral pressure exhibit intermittent oscillation as well as modification of recycling pattern during the detachment, which are found to reflect the island structure.

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Density Regimes of Complete Detachment and Serpens Mode in LHD

Cited by 6 publications

References 39 publications

Fluid features of the stochastic layer transport in LHD

Fluid features of the stochastic layer transport in LHD

Density limit study focusing on the edge plasma parameters in LHD

Detachment stabilization with n/m=1/1 resonant magnetic perturbation field applied to the stochastic magnetic boundary of the Large Helical Device

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