Investigation of Current-Density Modification during Magnetic Reconnection by Analysis of Hydrogen-Pellet Deflection

Waller, Vincent; Pégouriè, B.; Giruzzi, G.; Huysmans, G. T. A.; Garzotti, L.; Géraud, A.

doi:10.1103/physrevlett.91.205002

Cited by 7 publications

(9 citation statements)

References 16 publications

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“…In such conditions, the pellet fuelling efficiency is high: typically higher than 50% and up to 100%. In the case where the injected power is high, over-ablation is observed-often localized-that is due to the interaction of the pellet with the high-energy The same picture with the trajectory calculated by taking into account the Spitzer-Härm distorsion of the electron distribution superimposed (circles) [37]. electrons or ions.…”

Section: Ablation Rate and Pellet Penetrationmentioning

confidence: 84%

“…These features are interpreted as the signature of the rapid development of an m = n = 1 island whose evolution leads to a total reconnection in the plasma centre. Following this picture, the sharp deflection of the pellet trajectory at the crossing of the q = 1 surface would be due to the negative current singularity that develops at the island X-point and the absence of deflection in the plasma centre as the consequence of the loss of the most energetic electrons during the reconnection [37].…”

Section: Mhd Phenomenamentioning

confidence: 99%

“…In ohmic plasmas, the asymmetry is due to the distortion of the electron distribution function by the parallel electric field [35], figure 4. The observed deflection can then be used to characterize the electron distribution, as was done in RFX and Tore Supra [36,37] or to determine the current profile, as in T10 [38,39], see section 8.2. At low density, the origin of the unbalance of ablation can be the increase in the population of runaways consecutively to the injection of a previous pellet [40,41].…”

Section: Pellet Trajectorymentioning

confidence: 99%

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Review: Pellet injection experiments and modelling

Pégouriè

2007

Plasma Phys. Control. Fusion

125

158

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During the last decade, significant progress has been made in the field of pellet injection with (1) the identification of the drift of the deposited material in the inhomogeneous magnetic field that opened the possibility of fuelling efficiently the plasmas from the high-field side of the torus, (2) the technique to mitigate ELMS in H-mode discharges with shallow pellet injection at high frequency and (3) with the development of high density, high performance scenarios close to the ITER requirements. Both the experimental and theoretical aspects of this domain are reviewed in this paper.

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Section: Ablation Rate and Pellet Penetrationmentioning

confidence: 84%

Section: Mhd Phenomenamentioning

confidence: 99%

Section: Pellet Trajectorymentioning

confidence: 99%

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Review: Pellet injection experiments and modelling

Pégouriè

2007

Plasma Phys. Control. Fusion

125

158

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“…The ρ-dependence of the former leads to a peaking of the source with respect to the ablation profile, and negative values of sim S would be obtained even in the absence of ∇B-induced drift. It is a purely geometrical effect, with no link with the fact, noted elsewhere, that a nearly central pellet penetration (inside the q = 1 surface) could lead to the magnetic reconnection of the centre of the discharge [27][28][29].…”

Section: Comparison With Experiments (Lfs Launched Pellets)mentioning

confidence: 94%

Homogenization of the pellet ablated material in tokamaks taking into account the ∇B-induced drift

et al. 2006

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A model of the pellet deposition profile is presented, which describes in a self-consistent way the homogenization process and the simultaneous drift of the ablated material. Its main features are (i) that the drift is stopped by a parallel current that appears in the drifting flux tube and reduces the polarization of the expanding ablatant and (ii) that the pellet material does not move as a solid body but homogenizes in a radial interval of extent equal to its displacement. From the pellet and plasma pre-injection characteristics, the model yields the post-injection density and temperature profiles, allowing a quantitative comparison with measurements. The simulation results are compared with experimental data for both the homogenization phase and ∇B-induced displacement. In particular, (i) the calculated characteristics of the homogenization and drift (time constants and velocities) are in agreement with the measurements, (ii) for pellets launched from the low field side (LFS), the model reproduces the dependence of both the fuelling efficiency and the outward displacement on the pellet penetration and (iii) for pellets launched from the high field side (HFS), which are less documented, the calculated fuelling efficiency is always equal to 100%, larger than what is observed, suggesting a transient increase in the plasma (radial) transport. Practically, the main results are that the displacement is smaller for the HFS than for the LFS launched pellets and that, for deep fuelling, one must inject the pellet along the drift direction.

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“…This deviation in trajectory depends on the pellet ablation process, which inherently is determined by the distribution of energetic particles inside the plasma. Conversely, the pellet trajectory deflection has been used as a tool to estimate the distribution of energetic particles in the reverse field experiment (RFX) [6], and current distribution during magnetic reconnection in a tokamak [7]. In order to study the pellet ablation process in high-temperature plasmas, a clear understanding of the interaction between the pellet and the energetic particles is necessary.…”

Section: Introductionmentioning

confidence: 99%

Observation of three-dimensional motion of the pellet ablatant in the Large Helical Device

et al. 2011

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Application of two-point stereoscopic diagnostics using a fast camera and bundled fibre has enabled the observation of the three-dimensional nature of the pellet trajectory in the Large Helical Device. It has been observed that the pellet trajectory deviates from its injection direction, toroidally and vertically depending on the direction of the tangentially applied neutral beams. The magnitude of the toroidal deviation is similar in the clockwise as well as counter-clockwise neutral beam directions and is of 15–20 cm with a deflection speed of up to 400 m s−1. In contrast, an asymmetry in trajectory deflection has been observed in the vertical direction. Experimental results also indicate that the starting radius of the pellet trajectory bending in the counter-clockwise neutral beam case is more inward to that of the plasma. Collectively this leads to less penetration of the pellet inside the plasma and is prominent in the case of the clockwise neutral beam. Additionally, this fact supports evidence that the fast ion plays an important role in the pellet ablation process in the Large Helical Device. The pellet deflection is explained by the rocket effect due to unilateral ablation by the fast ions. The possible cause of the difference in the vertical deflection is explained by considering the geometrical aspects of the magnetic field structure.

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Investigation of Current-Density Modification during Magnetic Reconnection by Analysis of Hydrogen-Pellet Deflection

Cited by 7 publications

References 16 publications

Review: Pellet injection experiments and modelling

Review: Pellet injection experiments and modelling

Homogenization of the pellet ablated material in tokamaks taking into account the ∇B-induced drift

Observation of three-dimensional motion of the pellet ablatant in the Large Helical Device

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