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241 results on '"filaments"'

1. A study of turbulent filaments in the edge plasma of the Wendelstein 7-X stellarator

Author

A. Buzás, G. Kocsis, C. Biedermann, G. Cseh, T. Szepesi, M. Szűcs, and the W7-X Team

Subjects
plasma, fusion, w7x, stellarator, turbulence, filaments, Nuclear and particle physics. Atomic energy. Radioactivity, QC770-798
Abstract

Filaments are studied by examining fast camera images on the Wendelstein 7-X stellarator. Fast cameras offer a unique perspective, revealing the complex 3D structure of filaments in the entire poloidal cross-section of the plasma. By correlating individual pixels, their location, shape, and movement are analyzed in standard and high- ι configurations. The presence of filaments is not uniform poloidally around. The number of active areas matches the number of magnetic islands in both configurations. Filaments are found to extend to multiple toroidal turns in standard configuration. No time delay is observed between the different toroidal sections. Such behavior is not seen in high- ι configuration. Filaments are observed within and without the edge shear layer, indicated by the direction of their poloidal rotation. Inside the shear layer, their velocity scatters around 1.25 km s ^−1 , accompanied by a lifetime between 80 and 120 µ s. Outside, their velocity shows greater absolute values and variance, but still in a few km s ^−1 range. The similarities and differences between the two configurations are discussed and compared to previous results.

Published
2024
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2. Cumulative Effects in 100 kHz Repetition‐Rate Laser‐Induced Plasma Filaments in Air

Author

Tie-Jun Wang, Mehdi H. Ebrahim, Ivi Afxenti, Dionysis Adamou, Adetunmise C. Dada, Ruxin Li, Yuxin Leng, Jean-Claude Diels, Daniele Faccio, Arnaud Couairon, Carles Milián, and Matteo Clerici

Subjects
filaments, fluorescence, high-repetition-rate, hydrodynamic models, light–matter interaction, plasma, Applied optics. Photonics, TA1501-1820, Optics. Light, QC350-467
Abstract

Cumulative effects are crucial for applications of laser filaments, such as for the remote transfer of energy and the control of electric discharges. Up to now, studies of cumulative effects in the air of high‐repetition‐rate pulse trains have been performed at lower rates than 10 kHz. Herein, the nonlinear effects associated with short plasma filaments produced by pulses of moderate energy (0.4 mJ per pulse) and repetition rates up to 100 kHz are experimentally characterized. With increasing repetition rate, a decrease in absorption, fluorescence emission, and breakdown voltage and concurrently an increase in peak intensity and third‐harmonic‐generation efficiency are observed. Hydrodynamic simulations of the heated gas show that the observed decreases are directly related to a quasi‐stationary state of reduced gas density in the filament. However, further investigations are required to fully understand the physics underpinning the observed sharp reduction of the breakdown voltage at 100 kHz repetition rates. The results may prove relevant for energy and information delivery applications by laser‐induced air waveguide or electric discharge and lightning control.

Published
2023
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6. The Effect of Low-Frequency Magnetohydrodynamic Modes on the Development of Filaments in the Globus-M Tokamak.

Author

Bulanin, V. V., Gusev, V. K., Kurskiev, G. S., Minaev, V. B., Patrov, M. I., Petrov, A. V., Petrov, Yu. V., Prisyazhnyuk, D. V., Sakharov, N. V., Solokha, V. V., Tolstyakov, S. Yu., Khromov, N. A., and Yashin, A. Yu.

Subjects
*FIBERS, *FUSION reactors, *BACKSCATTERING
Abstract

Experimental data are presented that indicate the effect of the magnetohydrodynamic tearing mode in the Globus-M spherical tokamak on the occurrence of filamentary structures (filaments). The filaments are recorded by the Doppler backscattering method. The groups of filaments localized in the toroidal direction are discovered, the appearance of which is synchronized with the propagation of the tearing mode. Possible causes of the effect of low-frequency magnetohydrodynamic oscillations on the occurrence of filament groups are considered. [ABSTRACT FROM AUTHOR]

Published
2019
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