Observation of Cross-Field Transport of Pellet Plasmoid in LHD

Sakamoto, R.; Yamada, H.

doi:10.1585/pfr.6.1402085

Cited by 7 publications

(9 citation statements)

References 18 publications

(19 reference statements)

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“…when no average effect has come into play yet. It is found that the direction given by the HPI2 code for plasmoids of small parallel length, agrees with the drift estimated from fast camera images (see Figure 12) and with the deposition profiles shifted towards the LFS plasma edge, an effect that has been reported for LFS injections in several tokamaks [5], [13,62] and in the LHD [66].…”

Section: Modelling Of Pellet Injections and Comparison With Tj-ii Expsupporting

confidence: 85%

Experimental studies and simulations of hydrogen pellet ablation in the stellarator TJ-II

Panadero¹,

McCarthy²,

Koechl

et al. 2018

Nucl. Fusion

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Plasma core fuelling is a key issue for the development of steady-state scenarios in large magnetically-confined fusion devices, in particular for helical-type machines. At present, cryogenic pellet injection is the most promising technique for efficient fuelling. Here, pellet ablation and fuelling efficiency experiments, using a compact pellet injector, are carried out in Electron Cyclotron Resonance and Neutral Beam Injection heated plasmas of the stellarator TJ-II. Ablation profiles are reconstructed from light emissions collected by silicon photodiodes and a fast-frame camera system, under the assumptions that such emissions are loosely related to the ablation rate and that pellet radial acceleration is negligible. In addition, pellet particle deposition and fuelling efficiency are determined using density profiles provided by a Thomson Scattering system. Furthermore, experimental results are compared with ablation and deposition profiles provided by the HPI2 pellet code, which is adapted here for the stellarators Wendelstein 7-X (W7-X) and TJ-II. Finally, the HPI2 code is used to simulate ablation and deposition profiles for pellets of different sizes and velocities injected into relevant W7-X plasma scenarios, while estimating the plasmoid drift and the fuelling efficiency of injections made from two W7-X ports.

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Section: Modelling Of Pellet Injections and Comparison With Tj-ii Expsupporting

confidence: 85%

Experimental studies and simulations of hydrogen pellet ablation in the stellarator TJ-II

Panadero¹,

McCarthy²,

Koechl

et al. 2018

Nucl. Fusion

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“…Such a strong acceleration inferred from equation (2) would characterize the drift during the ablation or the very early phase of homogenization, before the plasmoid expansion becomes significant. Experimentally, a breakaway plasmoid released from the ablation cloud was measured by a bifurcated fibrescope [21], and a velocity of up to 30 km s −1 was reported [31]. Although the time resolution of the experimental data, of about 5-10 µs, is insufficient to allow a comparison with theoretical predictions for the velocity on a timescale of the plasmoid detachment, the fast propagation of the deposited mass towards the direction down the magnetic field gradient is confirmed by the measurement.…”

Section: ∇B-induced Drift In the Lhdmentioning

confidence: 99%

“…Similarly to what is typically obtained in the case of LFS launched pellets in tokamaks, an outward shift of the deposited mass with respect to the ablation location was identified [20] by the Thomson scattering measurements. The propagation of the deposited mass across the magnetic field was observed spectroscopically using fast-imaging cameras [21], showing that ablatant cloudlets are expelled out of the most emissive part of the ablation cloud and then drift down the local magnetic field gradient.…”

Section: Introductionmentioning

confidence: 99%

Modelling of the pellet deposition profile and ∇B-induced drift displacement in non-axisymmetric configurations

Matsuyama¹,

Koechl²,

Pégouriè³

et al. 2012

Nucl. Fusion

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Drift displacement during density homogenization is modelled for hydrogen pellets injected into the Large Helical Device (LHD). The pellet ablation and deposition profiles are simulated for neutral-beam injection heated plasmas and are shown to reproduce well the main characteristics of the observed drift displacement for both low-field side and high-field side (HFS) injected pellets. The model describes the parallel expansion of ionized ablated pellet particle cloudlets (plasmoid) in non-axisymmetric magnetic configurations and the associated evolution of the plasmoid drift acceleration force exerted by the average magnetic field gradient over the plasmoid length. It is shown that, during the ablation and early homogenization phases, plasmoids are strongly accelerated towards the inverse direction of the local magnetic field gradient. In the case of the LHD, its direction and magnitude depend mainly on the pellet launching location with respect to the external helical coils. While such an initial drift—induced near the ablation region—is efficiently damped by plasmoid internal currents as soon as the plasmoid length becomes comparable to a toroidal connection length, a weak drift acceleration force is maintained over the whole homogenization time, whose direction depends on whether the confining magnetic field possesses a magnetic well or hill structure. Simulations show that, in a strong magnetic hill configuration like the LHD, this small but long-term drift becomes significant and results in a radially outward displacement of the mass deposition even for pellets injected from the HFS.

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“…It is considered that the profiles mainly changed within 1 ms from the previous results. After the pellet injection, a plasmoid component is formed 31 , 32 in the background plasma. The pellets are injected into a horizontally elongated cross-section of the plasma.…”

Section: Resultsmentioning

confidence: 99%

Electron temperature and density measurement by Thomson scattering with a high repetition rate laser of 20 kHz on LHD

Funaba

Yasuhara

Uehara

et al. 2022

Sci Rep

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Thomson scattering measurements with a high-repetition-rate laser have commenced in the Large Helical Device. As an example of the fast phenomena captured by this diagnostic system, measurements at a 20 kHz repetition-rate in hydrogen pellet-injected plasmas are presented. Signal processing methods for this measurement have been developed and electron temperature profiles with almost 70 spatial points were evaluated at time intervals of 50 $$\upmu$$ μ s. After Raman scattering calibration, electron density profiles were derived. Fast changes in the electron temperature and density profiles within 1 ms were observed.

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Observation of Cross-Field Transport of Pellet Plasmoid in LHD

Cited by 7 publications

References 18 publications

Experimental studies and simulations of hydrogen pellet ablation in the stellarator TJ-II

Experimental studies and simulations of hydrogen pellet ablation in the stellarator TJ-II

Modelling of the pellet deposition profile and ∇B-induced drift displacement in non-axisymmetric configurations

Electron temperature and density measurement by Thomson scattering with a high repetition rate laser of 20 kHz on LHD

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