Time‐dependent plasma transport simulation for the study of edge impurity radiation dynamics with magnetic island in large helical device

Kobayashi, M.; Tokar, M. Z.

doi:10.1002/ctpp.201900138

Cited by 6 publications

(4 citation statements)

References 13 publications

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“…The 1D model elaborated in the present paper is not appropriate to reproduce important features of the RMP influence. A 2D modeling approach proposed and numerically realized in [21] allows us to demonstrate in calculations many characteristics experimentally observed in the LHD configuration with the RMP. In particular, it is possible to reconstruct in 2D computations the concentration of impurity radiation losses in the vicinity of the magnetic island X-point, where finally a thermal collapse is initiated.…”

Section: Discussionmentioning

confidence: 99%

Modeling of the resonant magnetic perturbation effect on detachment in the Large Helical Device

Tokar¹,

Kobayashi²

2020

Plasma Phys. Control. Fusion

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An approach to describe the plasma parameter variation with the effective minor radius across the edge region in the heliotron Large Helical Device (LHD) in configurations without and with a resonant magnetic perturbation (RMP) is elaborated, by averaging fluid equations for transport of particles, momentum and heat over the flux surfaces. Numerical solutions of one-dimensional, time-dependent equations derived and analytical estimates performed allow to interpret the LHD experiments on the density limit. Calculations reproduce qualitatively the principal difference between situations without and in the presence of RMP: in the former case a thermal collapse of the discharge occurs immediately after the plasma detachment from the divertor target plates at a radiation level of 0.4-0.5; in the latter one the radiating layer is localized at the plasma edge even if the power radiated exceeds 90% of the input one. The prominent role for such a behavior of plasma particle flows along magnetic field lines perturbed by RMP, leading to a positive radial gradient of the plasma density inside the magnetic island, is demonstrated.

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Section: Discussionmentioning

confidence: 99%

Modeling of the resonant magnetic perturbation effect on detachment in the Large Helical Device

Tokar¹,

Kobayashi²

2020

Plasma Phys. Control. Fusion

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“…Although the mechanism of the ETB formation at the detachment onset is not yet clear, the shear flow of the parallel flow is one possible candidate. In the numerical simulation on detachment with an edge magnetic island [19], parallel flow along the separatrix is observed at the detachment transition. This flow is developed in order to supply particles to the X-point of the island, where density condensation occurs due to the X-point cooling by a thermal instability.…”

Section: Core and Divertor Plasmas With And Without An Rmp Fieldmentioning

confidence: 96%

Confinement improvement during detached phase with RMP application in deuterium plasmas of LHD

et al. 2022

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In order to explore compatibility of good core plasma performance with divertor heat load mitigation, interaction between cold edge plasma and core plasma transport including edge transport barrier (ETB) has been analysed in the divertor detachment discharges of deuterium plasmas in LHD with RMP (resonant magnetic perturbation) field application. The RMP application introduces widened edge stochastic layer and sharp boundary in the magnetic field structure between the confinement region and the edge stochastic layer. The widened edge stochastic layer enhances impurity radiation and provides stable detachment operation as compared with the case without RMP. It is found that ETB is formed at the confinement boundary at the onset of detachment transition. However, as the detachment deepens resistive pressure gradient driven MHD mode is excited, which degrade the ETB. At the same time, however, the core transport decreases to keep global plasma stored energy (Wp) unchanged, showing clearly core-edge coupling. After gradual increase of density fluctuation during the MHD activity, spontaneous increase of Wp and recovery of ETB are observed while the detachment is maintained. Then the coherent MHD mode ceases and ELM like bursts appear. In the improved mode, the impurity decontamination occurs, and the divertor heat load increase slightly. Key controlling physics in the interplay between core and cold edge plasma is discussed. Comparison between deuterium and hydrogen plasmas show that the hydrogen plasmas exhibit similar features as the deuterium ones in terms of density and magnetic fluctuations, impurity decontamination toward higher confinement etc. But most of the features are modest in the hydrogen plasmas and thus no clear confinement mode transition with clear ETB formation is defined. Better global confinement is obtained in the deuterium plasmas than the hydrogen ones at higher radiation level.

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“…The triggering mechanism for the RMP induced H-mode is not clear and its investigation is ongoing. One hypothesis of the mechanism is that the parallel flow enhancement along the separatrix of the n/m = 1/1 island and its associated shear flow generation might trigger the RMP induced H-mode, where the enhanced parallel flow is induced by the radiative cooling at the x-point during the divertor detachment [16,52]. As can be seen is this figure, a current density of 342 A m −2 , which is far above the specification of the ITER-NBI, was achieved by the ionsource.…”

Section: Realization Of Divertor Detachment and Confinement Improvementmentioning

confidence: 99%

Recent results from deuterium experiments on the large helical device and their contribution to fusion reactor development

et al. 2022

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In recent deuterium experiments on the Large Helical Device (LHD), we succeeded in expanding the temperature domain to higher regions for both electron and ion temperatures. Suppression of the Energetic particle driven resistive InterChange mode (EIC) by a moderate electron temperature increase is a key technique to extend the high temperature domain of LHD plasmas. We found a clear isotope effect in the formation of the Internal Transport Barrier (ITB) in high temperature plasmas. A new technique to measure the hydrogen isotope fraction was developed in the LHD in order to investigate the behavior of the isotope mixing state. The technique revealed that the non-mixing and the mixing states of hydrogen isotopes can be realized in plasmas. In deuterium plasmas, we also succeeded simultaneously realizing the formation of the Edge Transport Barrier (ETB) and the divertor detachment. It is found that Resonant Magnetic Perturbation (RMP) plays an important role in the simultaneous formation of the ETB and the detachment. Contributions to fusion reactor development from the engineering point of view, i.e. Negative-ion based Neutral Beam Injector (N-NBI) research and the mass balance study of tritium, are also discussed

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Time‐dependent plasma transport simulation for the study of edge impurity radiation dynamics with magnetic island in large helical device

Cited by 6 publications

References 13 publications

Modeling of the resonant magnetic perturbation effect on detachment in the Large Helical Device

Modeling of the resonant magnetic perturbation effect on detachment in the Large Helical Device

Confinement improvement during detached phase with RMP application in deuterium plasmas of LHD

Recent results from deuterium experiments on the large helical device and their contribution to fusion reactor development

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