Details

Autor(en) / Beteiligte

• Filleul, F
• Caldarelli, A
• Takahashi, K
• Boswell, R W
• Charles, C
• Cater, J E
• Rattenbury, N

Titel

Helicon waves in a converging-diverging magnetoplasma

Ist Teil von

• Plasma sources science & technology, 2023-11, Vol.32 (11), p.115015

Ort / Verlag

IOP Publishing

Erscheinungsjahr

2023

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• Abstract 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, up to a five-fold increase in axial plasma density between the antenna and the magnetic mirror throat is observed together with an Ar II blue-mode. 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.