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| Main Authors: | , , , , , , |
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| Format: | Preprint |
| Published: |
2023
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| Subjects: | |
| Online Access: | https://arxiv.org/abs/2307.06747 |
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| _version_ | 1866929216842366976 |
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| author | Filleul, Félicien Caldarelli, Antonella Takahashi, Kazunori Boswell, Rod Charles, Christine Cater, John Rattenbury, Nicholas |
| author_facet | Filleul, Félicien Caldarelli, Antonella Takahashi, Kazunori Boswell, Rod Charles, Christine Cater, John Rattenbury, Nicholas |
| contents | Waves propagating along a converging-diverging rf magnetoplasma having the characteristics of a bounded m=0 helicon mode are reported and characterised. The discharge features a 30 cm separation between the region of radiofrequency energy deposition by a single loop antenna and the region of maximum magnetic field applied by a pair of coils. With 200 W of rf input power, the resulting plasma exhibits a strong axial plasma density gradient peaking at the magnetic mirror throat where an Ar II blue-core is observed. Two dimensional B-dot probe measurements show that the rf magnetic fields are closely guided by the converging-diverging geometry. The wave is characterised as a m=0 mode satisfying the helicon dispersion relation on-axis with radial boundary conditions approximately matching the radii of the plasma column. Analysis of the wave phase velocity and wave axial damping failed to identify collisionless or collisional wave-plasma coupling mechanisms. Instead, the wave axial amplitude variations can be explained by local wave resonances and possible reflections from localised rapid changes of the refractive index. A Venturi-like effect owing to the funnel-shaped magnetoplasma and conservation of the wave energy may also explain some level of amplitude variations. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2307_06747 |
| institution | arXiv |
| publishDate | 2023 |
| record_format | arxiv |
| spellingShingle | Helicon waves in a converging-diverging magnetoplasma Filleul, Félicien Caldarelli, Antonella Takahashi, Kazunori Boswell, Rod Charles, Christine Cater, John Rattenbury, Nicholas Plasma Physics Waves propagating along a converging-diverging rf magnetoplasma having the characteristics of a bounded m=0 helicon mode are reported and characterised. The discharge features a 30 cm separation between the region of radiofrequency energy deposition by a single loop antenna and the region of maximum magnetic field applied by a pair of coils. With 200 W of rf input power, the resulting plasma exhibits a strong axial plasma density gradient peaking at the magnetic mirror throat where an Ar II blue-core is observed. Two dimensional B-dot probe measurements show that the rf magnetic fields are closely guided by the converging-diverging geometry. The wave is characterised as a m=0 mode satisfying the helicon dispersion relation on-axis with radial boundary conditions approximately matching the radii of the plasma column. Analysis of the wave phase velocity and wave axial damping failed to identify collisionless or collisional wave-plasma coupling mechanisms. Instead, the wave axial amplitude variations can be explained by local wave resonances and possible reflections from localised rapid changes of the refractive index. A Venturi-like effect owing to the funnel-shaped magnetoplasma and conservation of the wave energy may also explain some level of amplitude variations. |
| title | Helicon waves in a converging-diverging magnetoplasma |
| topic | Plasma Physics |
| url | https://arxiv.org/abs/2307.06747 |