Observation of Impurity Accumulation After Hydrogen Multi-Pellet Injection in Large Helical Device

Dong, Chuanfei; Sakamoto, R.

doi:10.1088/1009-0630/15/3/08

Cited by 4 publications

(4 citation statements)

References 20 publications

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“…Since the impurity accumulation itself is not the main subject of this paper, we do not describe the details here. The details of the impurity accumulation can be found in [55].…”

Section: Nb-heated Discharges With Iron Impurity Buildupmentioning

confidence: 99%

Effective screening of iron impurities in the ergodic layer of the Large Helical Device with a metallic first wall

et al. 2013

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In the Large Helical Device (LHD) operated with a metallic (stainless steel) first wall, it is found that the iron density, nFe, at the plasma core is fairly low (nFe ⩽ 108 cm−3) in general neutral beam (NB)-heated discharges, while the iron quickly increases with the appearance of impurity accumulation when a multi-hydrogen ice pellet is injected or the NB input power is largely reduced. Although the highest iron density (nFe ⩽ 1010 cm−3) at the plasma centre in the LHD is observed from such discharges, it suggests a still low iron concentration (nFe/ne < 10−3). Therefore, the edge iron transport in the ergodic layer, which determines the iron influx to the core plasma, is studied to clarify why the iron density in the core plasma is low. A line ratio of Fe XV located in the vicinity of the last closed flux surface to Fe VIII (or Fe IX) located in the ergodic layer decreases with density. The two-dimensional (2D) edge iron emission of Fe XVI and Fe IX is enhanced in the vicinity of the X-point with a larger number of magnetic field lines directly connected to divertor plates, which suggests that iron ions from the first wall move downstream. The density of edge Fe15+ ions giving the iron influx to the core plasma is analysed with the 2D distribution. The analysis also shows that the iron influx to the core plasma decreases with density. These results clearly indicate that the screening effect developed in the ergodic layer works well for iron ions coming from the first wall. A three-dimensional edge transport simulation with EMC3-EIRENE can also predict an effective impurity screening for heavy impurities compared to light impurities.

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“…Since the impurity accumulation itself is not the main subject of this paper, we do not describe the details here. The details of the impurity accumulation can be found in [55].…”

Section: Nb-heated Discharges With Iron Impurity Buildupmentioning

confidence: 99%

Effective screening of iron impurities in the ergodic layer of the Large Helical Device with a metallic first wall

et al. 2013

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“…5) However, the iron emission from lower ionization stages obviously increases after hydrogen multi-pellet injection because the emission location moves from the plasma edge to the plasma core owing to a sudden temperature decrease. 26,27) To examine the temporal resolution of the upgraded EUV spectrometer system, the temporal behavior of FeXV (284.147 Å) vertical profiles is observed in n-NBI discharges with p-NBI modulation and hydrogen multi-pellet injection. The sampling time of the CCD is set to 50 ms.…”

Section: Temporal Evolution Of Impurity Vertical Profilesmentioning

confidence: 99%

Performance improvement of two-dimensional EUV spectroscopy based on high-frame-rate CCD and signal normalization method in Large Helical Device

Zhang

Morita

Oishi

et al. 2015

Jpn. J. Appl. Phys.

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In the Large Helical Device (LHD), two-dimensional (2D) distribution of edge impurity line emissions from the ergodic layer with a three-dimensional (3D) magnetic field structure has been observed in the wavelength range of 30–650 Å by horizontally scanning a space-resolved extreme ultraviolet (EUV) spectrometer during a steady phase in electron cyclotron heating (ECH) and ion cyclotron range of heating (ICRF) discharges with long pulse duration (τd ≥ 10 s). The 2D distribution of impurity line emissions can be measured at the upper or lower half in the full vertical range of LHD plasmas by a single horizontal scan. The performance of 2D EUV spectroscopy, however, was not sufficient for discussing the impurity transport in the ergodic layer from the viewpoints of the quality of 2D images and the requirement of long pulse discharges. The 2D EUV spectrometer is therefore modified by installing a high-frame-rate charge-coupled detector (CCD) and increasing its horizontal scanning speed. As a result, the quality of 2D images is significantly improved with increased horizontal spatial resolution, and then the 2D measurement is also possible for neutral beam injection (NBI) discharges with short pulse duration (τd ∼ 3 s). In addition, temporal and shot-by-shot intensity variations in the edge EUV emission are significantly reduced by applying a signal normalization method using another EUV spectrometer with high time resolution. A 0.5 µm poly(ethylene terephthalate) (PET) filter is also installed in front of an entrance slit of the space-resolved EUV spectrometer. The spike noise originating from high-energy neutral particles, which are enhanced in low-density NBI discharges, has been successfully reduced. Typical examples of the 2D distribution of impurity line emissions with improved quality are presented for several impurity species.

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“…[12] Experimental impurity transport investigations have been performed in many magnetic confinement devices and most of the impurity transport studies have been carried out using the spatial profiles of absolute intensities of spectral emissions from spectroscopic measurement and comparison with an impurity transport code to determine the transport coefficients. [13][14][15][16][17][18] A future reactor will use high-Z plasma facing components (PFCs) such as tungsten in order to provide low erosion, sputtering yield and tritium retention. Since 2012, the first wall material of EAST has been mostly changed into molybdenum, which makes molybdenum as the most commonly seen metal impurity.…”

Section: Introductionmentioning

confidence: 99%

Measurement of molybdenum ion density for L-mode and H-mode plasma discharges in the EAST tokamak*

Shen¹,

Zhang²,

Lyu³

et al. 2020

Chinese Phys. B

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We report the measurement of total molybdenum ion density for L-mode and H-mode plasmas on EAST using spectral lines observation and calculation based on an impurity transport code. A flat-filed extreme ultraviolet spectrometer with some spatial resolution is used to obtain the radial profiles of molybdenum spectral line emissions. The absolute calibration for the extreme ultraviolet spectrometer is finished by comparing the calculated bremsstrahlung intensity with the readings of CCD detector. Molybdenum ion transport study is performed using the radial ion density profiles and one-dimensional impurity transport code STRAHL. The total molybdenum density profiles are determined from the transport analysis. The molybdenum density during L-mode and H-mode phases are obtained, which are about 3 and 4 orders of magnitude smaller than the electron density, respectively. An inward pinch is found during the H-mode phase that leads to the peaked profile of molybdenum density.

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Observation of Impurity Accumulation After Hydrogen Multi-Pellet Injection in Large Helical Device

Cited by 4 publications

References 20 publications

Effective screening of iron impurities in the ergodic layer of the Large Helical Device with a metallic first wall

Effective screening of iron impurities in the ergodic layer of the Large Helical Device with a metallic first wall

Performance improvement of two-dimensional EUV spectroscopy based on high-frame-rate CCD and signal normalization method in Large Helical Device

Measurement of molybdenum ion density for L-mode and H-mode plasma discharges in the EAST tokamak*

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