Experimental observations of the dynamics of pellet ablation on the Texas Experimental Tokamak (TEXT)

Durst, R.; Rowan, W. L.; Austin, M. E.; Collins, R. A.; Gandy, R. F.; Phillips, P. E.; Richards, B.

doi:10.1088/0029-5515/30/1/001

Cited by 49 publications

(56 citation statements)

References 14 publications

(33 reference statements)

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“…The shift is likely associated with the position of the pellet relative to the plasmoid boundaries in the moment of triggering the CCD camera. Analogous conclusion can be arrived at on the basis of the photographic images of Durst et al [29] in which bulging of the plasmoid boundary in the direction of pellet motion is visible and is possibly caused by the approaching pellet. The time resolution used by Durst (exposure times under 1 μs) is finer than the one used for Fig.…”

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confidence: 63%

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Pellet – Plasma Interaction: an Analysis of Pellet Injection Experiments by Means of a Multi‐Dimensional MHD Pellet Code

Lengyel

Schneider

Kardaun

et al. 2008

Contrib. Plasma Phys.

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This work is aimed at the analysis of pellet injection experiments by means of a magnetohydrodynamic code that computes the processes of pellet ablation, expansion, ionization, and magnetic confinement of the ablated substance. In particular, experimental pellet injection scenarios stemming from the tokamak ASDEX-Upgrade (D2 pellets) and the stellarator W7-AS (carbon pellets) are analyzed by means of this time-dependent quasithree-dimensional MHD pellet code. Pellet penetration depths measured in ASDEX-Upgrade at LFS (lowfield-side) and HFS (high-field-side) pellet injection, are compared with computational results.It was found that the penetration depths of deuterium pellets observed in about twenty randomly selected LFS and HFS injection scenarios could accurately be reproduced by a single code in which drift effects were intentionally ignored. This may be understood as an indication of the negligible effect drift exerts on the ablation process. At the same time, the distribution of the ablated and partially ionized substance may very well be affected by the drift of the ionized particles in the direction of the decreasing magnetic field.With the help of the Dα radiation patterns observed, the magnitudes of the heat fluxes affecting the pellet and the ablation cloud were estimated. The calculations show that the thermal heat fluxes (electron and ion) acting along the magnetic field lines are not sufficient to explain the size of the radiating filaments observed.The effect of extra-thermal electrons on the ablation history of pellets injected in W7-AS is demonstrated: the particle end energy fluxes causing measured pellet ablation profiles are determined.Based on a statistically well-designed computational data set, an empirical scaling of the penetration depths in terms of the background plasma parameters was attempted. It is shown that the form of the temperature profile of the background plasma cannot be ignored while deriving scaling laws; the specification of the central or the bulk temperature alone is insufficient.Quantitative data are provided for the magnitudes of various additional processes such as the anomalous thermal conduction across the field lines or the grad(B)-induced drift of the shielding cloud surrounding the pellet.The modelling of supersonic gas jets, a fuelling method that appears to be an alternative to pellet injection, is also considered. Since the massive stream of a cold gas represents a disturbance for the recipient plasma similar to that of a pellet, its dynamics can be described by the same means as the evolution of pellet clouds.

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confidence: 63%

“…Here D 2 pellets were injected into deuterium plasmas. (Analogous pictures were presented already by Durst et al [29] and others; see Section 2.1 of the review paper by Milora et al [30]). …”

mentioning

confidence: 84%

Pellet – Plasma Interaction: an Analysis of Pellet Injection Experiments by Means of a Multi‐Dimensional MHD Pellet Code

Lengyel

Schneider

Kardaun

et al. 2008

Contrib. Plasma Phys.

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“…In order to extrapolate a fueling scenario into a future fusion reactor, therefore, it is important to understand the dynamics of a high density plasmoid which is composed of pellet ablated material. The initial stage of the plasmoid movement has been observed using a two-dimensional framing camera in TEXT [10], while the author did not refer to the possibility of ∇B induced drift because there had been no such notion at that time. The dynamics of the plasmoid have been observed directly by use of a one-dimensional fiber optics array in RTP and ASDEX-upgrade [11,12], and the rapid transport of the pellet plasmoid toward magnetically low field side has been confirmed.…”

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confidence: 99%

Observation of Cross-Field Transport of Pellet Plasmoid in LHD

Sakamoto

Yamada

2011

Plasma and Fusion Research

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A three-dimensional observation of the solid hydrogen pellet ablation has been performed by using a fast stereo imaging camera to investigate the pellet ablation dynamics. The initial velocity component of the injected pellet is maintained during ablation in a hot plasma, and the pellet penetrates to the core plasma. On the other hand, it has been observed that part of high density pellet plasmoid, which is formed around the pellet substance by ablating hydrogen pellet, intermittently breaks away from the pellet ablating position and the breakaway plasmoid is transported across a confinement field. The breakaway plasmoid recurrently develops at the rate of about 100 times per millisecond and it is non-diffusively transported approximately 0.1 m during its several 10 µs lifetime in the opposite direction to the pellet motion, namely, toward the low magnetic field side. This observation gives a reasonable explanation for the difference between the pellet ablation position and the effective particle deposition profile.

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“…Already the early experiments [17,18] showed that the pellet is surrounded by a cigar shaped cloud which is elongated along the field lines, thus L.L. Lengyel and his co-workers [19,20] were focusing on understanding this observation.…”

Section: Introductionmentioning

confidence: 99%

Role of shielding in modelling cryogenic deuterium pellet ablation

et al. 2008

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Abstract. For the better characterization of pellet ablation, the numerical LLP code has been enhanced by combining two relevant shielding mechanism: that of the spherically expanding neutral cloud surrounding the pellet and of the field elongated ionized material forming a channel flow. In contrast to our expectations the presence of the channel flow can increase the ablation rate although it reduces the heat flux traveling through it. The contribution of the different shielding effects in the ablation process is analyzed for several pellet and plasma parameters and an ablation rate scaling is presented based on simple regression in the ASDEX Upgrade pellet and plasma parameter range. Finally the simulated results are compared to experimental data from typical ASDEX Upgrade discharges.

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Experimental observations of the dynamics of pellet ablation on the Texas Experimental Tokamak (TEXT)

Cited by 49 publications

References 14 publications

Pellet – Plasma Interaction: an Analysis of Pellet Injection Experiments by Means of a Multi‐Dimensional MHD Pellet Code

Pellet – Plasma Interaction: an Analysis of Pellet Injection Experiments by Means of a Multi‐Dimensional MHD Pellet Code

Observation of Cross-Field Transport of Pellet Plasmoid in LHD

Role of shielding in modelling cryogenic deuterium pellet ablation

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