| 1. |
- Hollmann, E M, et al.
(författare)
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Estimate of pre-thermal quench non-thermal electron density profile during Ar pellet shutdowns of low-density target plasmas in DIII-D
- 2021
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 28:7
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Tidskriftsartikel (refereegranskat)abstract
- The radial density profile of pre-thermal quench (pre-TQ) early-time non-thermal (hot) electrons is estimated by combining electron cyclotron emission and soft x-ray data during the rapid shutdown of low-density (ne≲1019m−3) DIII-D target plasmas with cryogenic argon pellet injection. This technique is mostly limited in these experiments to the pre-TQ phase and quickly loses validity during the TQ. Two different cases are studied: a high (10 keV) temperature target and a low (4 keV) temperature target. The results indicate that early-time, low-energy (∼10 keV) hot electrons form ahead of the argon pellet as it enters the plasma, affecting the pellet ablation rate; it is hypothesized that this may be caused by rapid cross field transport of argon ions ahead of the pellet or by rapid cross field transport of hot electrons. Fokker-Planck modeling of the two shots suggests that the hot electron current is quite significant during the pre-TQ phase (up to 50% of the total current). Comparison between modeled pre-TQ hot electron current and post-TQ hot electron current inferred from avalanche theory suggests that hot electron current increases during the high-temperature target TQ but decreases during the low-temperature target TQ. The uncertainties in this estimate are large; however, if true, this suggests that TQ radial loss of hot electron current could be larger than previously estimated in DIII-D.
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| 2. |
- Svenningsson, Ida, 1996, et al.
(författare)
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Hot-Tail Runaway Seed Landscape during the Thermal Quench in Tokamaks
- 2021
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 127:3
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Tidskriftsartikel (refereegranskat)abstract
- Runaway electron populations seeded from the hot tail generated by the rapid cooling in plasma-terminating disruptions are a serious concern for next-step tokamak devices such as ITER. Here, we present a comprehensive treatment of the thermal quench, including the superthermal electron dynamics, heat and particle transport, atomic physics, and radial losses due to magnetic perturbations: processes that are strongly linked and essential for the evaluation of the runaway seed in disruptions mitigated by material injection. We identify limits on the injected impurity density and magnetic perturbation level for which the runaway seed current is acceptable without excessive thermal energy being lost to the wall via particle impact. The consistent modeling of generation and losses shows that runaway beams tend to form near the edge of the plasma, where they could be deconfined via external perturbations.
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| 3. |
- Teicher, S. M.L., et al.
(författare)
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Weyl nodes and magnetostructural instability in antiperovskite Mn3ZnC
- 2019
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Ingår i: APL Materials. - : AIP Publishing. - 2166-532X. ; 7:12
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Tidskriftsartikel (refereegranskat)abstract
- The room temperature ferromagnetic phase of the cubic antiperovskite Mn3ZnC is suggested from first-principles calculation to be a nodal line Weyl semimetal. Features in the electronic structure that are the hallmark of a nodal line Weyl state - a large density of linear band crossings near the Fermi level - can also be interpreted as signatures of a structural and/or magnetic instability. Indeed, it is known that Mn3ZnC undergoes transitions upon cooling from a paramagnetic to a cubic ferromagnetic state under ambient conditions and then further into a noncollinear ferrimagnetic tetragonal phase at a temperature between 250 K and 200 K. The existence of Weyl nodes and their destruction via structural and magnetic ordering are likely to be relevant to a range of magnetostructurally coupled materials. © 2019 Author(s).
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