Characteristics of Radiating Collapse at the Density Limit in the Large Helical Device

Peterson, B.J.; Miyazawa, J.; Nishimura, K.; Masuzaki, S.; Nagayama, Y.; Ohyabu, N.; Yamada, H.; Yamazaki, K.; Katō, Takako; Murakami, Izumi; Ashikawa, N.; Xu, Yuhong; Kostrioukov, A.; Liu, Yi; Sakamoto, R.; Goto, M.; Narihara, K.; Osakabe, M.; Tanaka, K.; Tokuzawa, T.; Shoji, M.; Funaba, H.; Morita, S.; Morisaki, T.; Kaneko, O.; Kawahata, K.; Komori, A.; Sudo, S.; Motojima, O.

doi:10.1585/pfr.1.045

Cited by 25 publications

(19 citation statements)

References 24 publications

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“…The achieved fraction with Ne seeding is 52% during relatively low density discharges (n e, bar ~ 1.3 × 10 19 m −3 just before the seeding), while the fraction before the seeding namely in pure hydrogen plasmas is constant around 15% over the range of n e, bar investigated. The fraction is limited up to around 30% in hydrogen plasmas without Ne seeding even for high density plasma (n e, bar > 1 × 10 20 m −3 ) just below the radiative collapse [13]. The radiative collapse is attributed to a radiative thermal instability of light impurities, mainly carbon, in the plasma edge region [13].…”

Section: Operation Region Of the Radiation Enhancement In Ne Seeded P...mentioning

confidence: 97%

Development of impurity seeding and radiation enhancement in the helical divertor of LHD

et al. 2015

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Impurity seeding to reduce the divertor heat load was conducted in the large helical device (LHD) using neon (Ne) and krypton (Kr) puffing. Radiation enhancement and reduction of the divertor heat load were observed. In the LHD, the ratio between the total radiated power and the heating power, f rad = P rad /P heating , is limited up to around 30% in hydrogen plasmas even for high density plasma just below the radiative collapse (n e, bar > 1 × 10 20 m −3 ), where n e, bar is the line averaged density. With Ne seeding, the ratio could be raised to 52% at n e, bar ~ 1.3 × 10 19 m −3 , albeit with a slight reduction in confinement. f rad ~ 30% could be sustained for 3.4 s using multi-pulse Ne seeding at n e, bar ~ 4 × 10 19 m −3 . The localized supplemental radiation was observed along the helical divertor X-points (HDXs) which is similar to the estimated structure by the EMC3-EIRENE code. Kr seeding was also conducted at n e, bar ~ 3.1 × 10 19 m −3 . f rad ~ 25% was obtained without a significant change in stored energy. The radiation enhancement had a slower time constant. The supplemental radiation area of the Kr seeded plasma moved from the HDXs to the core plasma. Highly charged states of Kr ions are considered to be the dominant radiators from the plasma core region.

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Section: Operation Region Of the Radiation Enhancement In Ne Seeded P...mentioning

confidence: 97%

Development of impurity seeding and radiation enhancement in the helical divertor of LHD

et al. 2015

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“…First, we describe the discharge conditions in this experiment since the observed spectral feature strongly depends on them. Since an achievable plasma density tends to be limited by the total heating power, a phenomenon called radiation collapse is often triggered by a rapid increase in density or a decrease in heating power [19]. Hence, some discharges are stably sustained after pellet injection, while others proceed to a radiation collapse.…”

Section: Discharge Conditionsmentioning

confidence: 99%

Analysis of EUV spectra of Sn XIX–XXII observed in low-density plasmas in the Large Helical Device

Suzuki

Katō

Sakaue

et al. 2010

J. Phys. B: At. Mol. Opt. Phys.

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We have measured extreme ultraviolet (EUV) spectra from highly charged tin ions in low-density and high-temperature plasmas produced in the Large Helical Device at the National Institute for Fusion Science. The EUV spectra emitted after injection of a tin pellet into a hydrogen plasma were monitored by a grazing incidence spectrometer whose wavelength resolution is about 0.01 nm. Two different types of spectral feature were measured in the 13-17 nm region depending on whether the discharge was stably sustained or underwent radiation collapse. The measured EUV spectra were analyzed by considering the difference in dominant charge states observed in the two types of spectra. Apart from the complex quasi-continuum structure around 13.5 nm, several strong lines occurring at wavelengths longer than 14 nm were found to originate from the transitions between excited states of Sn XXI and Sn XXII by comparison with the other experimental data including the charge exchange collisions experiments. Most of the strong spectral lines which were not identified as Sn XXI or Sn XXII were assigned to the resonance transitions of Sn XIX and Sn XX from comparison with the results of theoretical calculations.

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“…However, it has been found that the radiation power is less than 30% of heating power even in high density operation usually [27]. Therefore, the maximum heat flux in the long pulse discharge is estimated to be 1-1.5 MW/m 2 .…”

Section: Plasma Facing Componentsmentioning

confidence: 99%

Design and installation of the closed helical divertor in LHD

Masuzaki

Shoji

Tokitani

et al. 2010

Fusion Engineering and Design

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Characteristics of Radiating Collapse at the Density Limit in the Large Helical Device

Cited by 25 publications

References 24 publications

Development of impurity seeding and radiation enhancement in the helical divertor of LHD

Development of impurity seeding and radiation enhancement in the helical divertor of LHD

Analysis of EUV spectra of Sn XIX–XXII observed in low-density plasmas in the Large Helical Device

Design and installation of the closed helical divertor in LHD

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