Divertor Detachment with Multi-Species Impurity Seeding in LHD

Mukai, K.; Masuzaki, S.; Hayashi, Y.; Oishi, Tetsutarou; Suzuki, C.; Kobayashi, M.; Tanaka, Hirohiko

doi:10.1585/pfr.15.1402051

Cited by 8 publications

(4 citation statements)

References 7 publications

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“…Impurity gases (Ne and Kr) are puffed from the 5.5-L port. Total plasma radiation, P rad , and radiation brightness profiles are measured by resistive bolometer arrays [7]. Ne and Kr emission profiles are measured with EUV spectroscopy [8] and SOXMOS [9][10][11].…”

Section: Experimental Setup On Lhdmentioning

confidence: 99%

Steady-state sustainment of divertor detachment with multi-species impurity seeding in LHD

et al. 2021

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Multi-species impurity seeding is an advanced operation scenario to mitigate the divertor heat load for the realization of future fusion reactors. In the Large Helical Device (LHD), divertor detachment is successfully sustained using higher-Z (krypton, Kr) and lower-Z (neon, Ne) superimposed seeding. Emission from Kr impurities is drastically enhanced if it is followed by Ne seeding. Plasma radiation can be enhanced even at the upstream region in the edge plasma compared with Ne only seeded plasmas with suppression of impurity accumulation toward the central plasma. The characteristics of divertor heat load reduction and energy confinement are comparable between the Kr+Ne seeding and Ne only seeding under the same radiation fraction. However, while the detachment in Ne only seeding is transient, the detachment in Kr+Ne seeding is stable. It indicates that multi-species impurity seeding can be competitive for steady-state operation although further investigation is desired about the balance between divertor heat load reduction, impurity screening, and confinement degradation. The Kr emission enhancement is strongly affected by electron density and temperature at the last closed flux surface resulting in impurity penetration.

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Section: Experimental Setup On Lhdmentioning

confidence: 99%

Steady-state sustainment of divertor detachment with multi-species impurity seeding in LHD

et al. 2021

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“…Large tokamak and stellarator devices such as ITER, DEMO, LHD, Wendelstein 7-X, JET, ASDEX Upgrade, JT-60U, EAST, etc., are expected to have inert gases as the external impurities, which are injected into the machine as the coolant gases [5][6][7][8][9][10][11][12][13]. Many impurity seeding experiments have been conducted in the existing fusion plasma devices using Nitrogen (N 2 ), and inert gases such as Neon (Ne), Argon (Ar), and Krypton (Kr), to study the radiation enhancement and reduction in the particle heat load in the divertor region for divertor detachment [10,[13][14][15][16]. In earlier studies, the spectroscopic measurements of highly charged Kr 18+ , Kr 17+ , Kr 24+ , and Kr 25+ ions along with lower ionization states, viz.…”

Section: Introductionmentioning

confidence: 99%

Study of Electron Impact Excitation of Na-like Kr Ion for Impurity Seeding Experiment in Large Helical Device

Gupta,

Oishi,

Murakami

2023

Atoms

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In this work, a krypton gas impurity seeding experiment was conducted in a Large Helical Device. Emission lines from the Na-like Kr ion in the extreme ultraviolet wavelength region, such as 22.00 nm, 17.89 nm, 16.51 nm, 15.99 nm, and 14.08 nm, respective to 2p63p(2P1/2o)−2p63s(2S1/2), 2p63p(2P3/2o)−2p63s(2S1/2), 2p63d(2D3/2)−2p63p(2P3/2o), 2p63d(2D5/2)−2p63p(2P3/2o), and 2p63d(2D3/2)−2p63p(2P1/2o) transitions, are observed. In order to generate a theoretical synthetic spectrum, an extensive calculation concerning the excitation of the Kr25+ ion through electron impact was performed for the development of a suitable plasma model. For this, the relativistic multiconfiguration Dirac–Hartree–Fock method was employed along with its extension to the relativistic configuration interaction method to compute the relativistic bound-state wave functions and excitation energies of the fine structure levels using the General Relativistic Atomic Structure Package-2018. In addition, another set of calculations was carried out utilizing the relativistic many-body perturbation theory and relativistic configuration interaction methods integrated within the Flexible Atomic Code. To investigate the reliability of our findings, the results of excitation energies, transition probabilities, and weighted oscillator strengths of different dipole-allowed transitions obtained from these different methods are presented and compared with the available data. Further, the detailed electron impact excitation cross-sections and their respective rate coefficients are obtained for various fine structure resolved transitions using the fully relativistic distorted wave method. Rate coefficients, calculated using the Flexible Atomic Code for population and de-population kinetic processes, are integrated into the collisional-radiative plasma model to generate a theoretical spectrum. Further, the emission lines observed from the Kr25+ ion in the impurity seeding experiment were compared with the present plasma model spectrum, demonstrating a noteworthy overall agreement between the measurement and the theoretical synthetic spectrum.

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“…In the Large Helical Device (LHD), several operation scenarios have been proposed and applied to realize and maintain the divertor detachment. One of the methods to induce the divertor detachment is impurity seeding, where gas-puffing of nitrogen or noble gases are frequently used [3][4][5][6][7][8]. When impurities are introduced in the plasma, they are ionized and then some of them are distributed in the edge plasma with lower ionization states, while others are distributed in the core plasma with higher ionization states.…”

Section: Introductionmentioning

confidence: 99%

Spatial Profiles of NeVI-NeX Emission in ECR-Heated Discharges of the Large Helical Device with Divertor Detachment Induced by RMP Application and Ne Impurity Seeding

Oishi

Kobayashi

Takahashi

et al. 2022

Plasma and Fusion Research

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In the Large Helical Device, the divertor detachment has been attempted by application of resonant magnetic perturbation (RMP) field and Ne gas puffing in electron cyclotron resonance-heated discharges for compatibility of high central electron temperature and low divertor heat load. Two kinds of divertor detachment phases were observed. The first one appeared transiently just after the Ne gas puffing (1st detachment), and the second one appeared steadily in the latter half of the discharge (2nd detachment). Space-resolved extreme ultraviolet spectroscopy revealed that NeVI-NeVIII emissions increased slightly outside the last closed flux surface (LCFS), while NeIX and NeX emissions increased inside the LCFS in the 1st detachment phase. Although in the 1st detachment the divertor heat load was significantly reduced, the central electron temperature also decreased because the Ne ions were penetrated inside the LCFS as a radiation source. In the 2nd detachment phase, NeVI-NeVIII emissions increased outside the LCFS while NeIX and NeX emissions kept low intensity inside the LCFS. In this phase, low divertor heat load and high central electron temperature were obtained simultaneously because the Ne ions were localized outside the LCFS as a radiation source. The profile measurements of Ne emission show that the edge island structure created by the RMP application impacts on the impurity emission distribution, where the peak of the emission shifts radially stepwise as the detachment proceeds.

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Divertor Detachment with Multi-Species Impurity Seeding in LHD

Cited by 8 publications

References 7 publications

Steady-state sustainment of divertor detachment with multi-species impurity seeding in LHD

Steady-state sustainment of divertor detachment with multi-species impurity seeding in LHD

Study of Electron Impact Excitation of Na-like Kr Ion for Impurity Seeding Experiment in Large Helical Device

Spatial Profiles of NeVI-NeX Emission in ECR-Heated Discharges of the Large Helical Device with Divertor Detachment Induced by RMP Application and Ne Impurity Seeding

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