Study of carbon pellet ablation in ECR-heated W7-AS plasmas

Ledl, L.; Burhenn, R.; Lengyel, L.L.; Wagner, F.; Team, W As; Sergeev, V. Yu.; Timokhin, V. M.; Kuteev, B. V.; Skokov, V. G.; Egorov, S.M.

doi:10.1088/0029-5515/44/5/004

Cited by 15 publications

(14 citation statements)

References 17 publications

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“…the passing pellet cools the local plasma instantaneously. It is found here that no inward precooling wave, as reported elsewhere [33], is observed by the ECE diagnostic, albeit in TJ-II such a wave is sometimes observed during TESPEL injections (V TESPEL = ~200 m s −1 ) [34]. In figure 3(b), it can be seen that for NBI-heated plasma the central T e recovers to pre-injection values within a few milliseconds, while the central ion temperature, T i , measured by NPA recovers more slowly.…”

Section: Pellet Ablation and Plasma Responsesupporting

confidence: 92%

Plasma fuelling with cryogenic pellets in the stellarator TJ-II

McCarthy¹,

Panadero²,

Velasco³

et al. 2017

Nucl. Fusion

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Cryogenic pellet injection is a widely used technique for delivering fuel to the core of magnetically confined plasmas. Indeed, such systems are currently functioning on many tokamak, reversed field pinch and stellarator devices. A pipe-gun-type pellet injector is now operated on the TJ-II, a low-magnetic shear stellarator of the heliac type. Cryogenic hydrogen pellets, containing between 3 × 10 18 and 4 × 10 19 atoms, are injected at velocities between 800 and 1200 m s −1 from its low-field side into plasmas created and/or maintained in this device by electron cyclotron resonance and/or neutral beam injection heating. In this paper, the first systematic study of pellet ablation, particle deposition and fuelling efficiency is presented for TJ-II. From this, light-emission profiles from ablating pellets are found to be in reasonable agreement with simulated pellet ablation profiles (created using a neutral gas shielding-based code) for both heating scenarios. In addition, radial offsets between recorded light-emission profiles and particle deposition profiles provide evidence for rapid outward drifting of ablated material that leads to pellet particle loss from the plasma. Finally, fuelling efficiencies are documented for a range of target plasma densities (~4 × 10 18 -~2 × 10 19 m −3 ). These range from ~20%-~85% and are determined to be sensitive to pellet penetration depth. Additional observations, such as enhanced core ablation, are discussed and planned future work is outlined.

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Section: Pellet Ablation and Plasma Responsesupporting

confidence: 92%

Plasma fuelling with cryogenic pellets in the stellarator TJ-II

McCarthy¹,

Panadero²,

Velasco³

et al. 2017

Nucl. Fusion

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“…With an assumption that intensity of line emissions from the ablation cloud is proportional to the ablation rate, trajectory of the pellet or shape of the clouds is deduced from the temporal variation of the emission intensity [4][5][6][7][8]. Detailed information about atomic processes taking place in the ablation cloud is necessary for more quantitative understanding of the ablation mechanism.…”

Section: Introductionmentioning

confidence: 99%

Plasma Spectroscopy on an Aluminum-Pellet Ablation Cloud in an LHD Plasma with an Echelle Spectrometer

Fujii

Shikama

Morita

et al. 2020

Atoms

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We developed an echelle spectrometer for the simultaneous observation of the whole visible range with a high instrumental resolution, for example, 0.055 nm (full width at the half maximum) at 400 nm and 0.10 nm at 750 nm. With the spectrometer, the emission from an ablation cloud of an aluminum pellet injected into a high-temperature plasma generated in the Large Helical Device (LHD) was measured. We separated the emission lines into Al I, II, III and IV groups, and estimated the electron temperature and density of the ablation cloud from the line intensity distribution and Stark broadening respectively, of each of the Al I, II and III groups. We also determined the Stark broadening coefficients of many Al II and III lines from the respective Stark widths with the estimated electron temperature and density.

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“…Conventionally, the temporal variation of intensity of an emission line from the ablation cloud is regarded as a measure of the spatial profile of particle deposition, where it is assumed that the line intensity is proportional to the ablation rate [10]. Actually, in [11] the assumption of proportionality between the change of chord-resolved electron density and the temporal behaviour of the intensity of a CII line is experimentally verified. Although this result is useful for practical purposes, the ablation mechanism is not yet well clarified.…”

Section: Introductionmentioning

confidence: 99%

“…With regard to the experimental study of pellet ablation, most measurements have focused on taking pictures of ablation clouds through an interference filter at the wavelength of a certain emission line. Pellet trajectories and cloud shapes have been derived from such pictures [1,2,7,11,14]. With this kind of measurement, however, it is difficult to investigate the detailed atomic processes in the ablation cloud.…”

Section: Introductionmentioning

confidence: 99%

Spectroscopic study of a carbon pellet ablation cloud

Goto¹,

Morita²,

Koubiti³

2010

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

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Carbon pellets were injected into high-temperature plasmas produced in the Large Helical Device (LHD), a heliotron-type fusion experimental device. Radiation from a high-density plasma formed around the pellet core, the so-called ablation cloud, was observed and its spectrum in the UV-visible wavelength range was obtained. The observed spectrum is found to be dominated by emission lines of CII and CIII ions, and their level populations are determined from the measured line intensities. The result suggests that LTE (local thermodynamic equilibrium) is established over the measured excited levels for both ions, and the electron temperature is determined to be 2.5 eV and 3.0 eV for the CII and CIII ions, respectively, on the assumption that level populations follow a Boltzmann distribution. For the plasma dominated by the CII lines, the electron density, n e = 6.5 × 10 22 m −3 , and plasma volume, V = 5.3 × 10 −6 m 3 , are simultaneously derived from a fit of the CII λ 723 nm ([1s 2 2s 2 ]3p 2 P o -3d 2 D) line profile which is subject to various broadening effects such as Stark broadening. For the plasma dominated by CIII lines, V = 4.5 × 10 −2 m 3 is derived from an analysis of the reabsorption effect appearing in fine structure lines of the CIII λ 117 nm ([1s 2 ]2s2p 3 P o -2p 2 3 P) transition. The assumption of electric charge neutrality in the ablation cloud yields n e = 4.7 × 10 20 m −3 . These results suggest such a structure in the ablation cloud that a dense plasma dominated by the CII lines is surrounded by a larger and lower density plasma which is responsible for the CIII lines. The assumption of complete LTE for CIII levels, which is used in the analysis, is shown to be approximately true with the help of collisional-radiative model calculations, for which the reabsorption effect is taken into account. Thus, in this study various plasma parameters in the ablation cloud are determined and information about the cloud structure is obtained.

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Study of carbon pellet ablation in ECR-heated W7-AS plasmas

Cited by 15 publications

References 17 publications

Plasma fuelling with cryogenic pellets in the stellarator TJ-II

Plasma fuelling with cryogenic pellets in the stellarator TJ-II

Plasma Spectroscopy on an Aluminum-Pellet Ablation Cloud in an LHD Plasma with an Echelle Spectrometer

Spectroscopic study of a carbon pellet ablation cloud

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