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Alfvén
waves are believed to be of fundamental importance in auroral
physics. If the source of an Alfvén wave is a low frequency
current channel with a radius on the order of the collisionless
skin depth, Early observations of Alfvén waves in the LAPD include verification of the shear Alfvén wave dispersion relation, the observation of wave reflections, and wave production from extended sources. Current work involving the study of Alfvén wave cones: Experimental Observations of Alfvén Wave Cones, W. Gekelman,D. Leneman, J. Maggs, S. Vincena, Phys. Plasmas,1, 3775-3783,(1994), and the companion theoretical paper, Structure of Alfvén Waves at the Skin-Depth Scale, G. Morales, R. Loritsch, J. Maggs, Phys. Plasmas,1,3765-3774 (1994) Waves from multiple sources can interfere constructively or destructively at large distances from the exciters. We use this to study the interference patterns from two sources driven in and out of phase. Press to view the dynamics of the interaction of two Alfvén wave cones. A thorough review of the properties of Alfvén wave cones in the context of space plasmas illustrating their three dimensional propagation and interference effects has been published and may be downloaded. W. Gekelman, S. Vincena, D. Leneman, J. Maggs, Laboratory Experiments on shear Alfvén waves and their relationship to space plasmas, Journal of Geophysical Research, 10T2, 7225-7236 (1997) The three dimensional current structure of Alfvén wave cones is presented in: W. Gekelman, S. Vincena, D. Leneman, Experimental Observations of Shear Alfvén waves generated by narrow current channels, Plasma Phys. and Control. Fusion, 39, A101-A112 (1977) A review paper on Alfvén wave experiments over the years: W. Gekelman, Review of laboratory experiments on Alfvén waves and their relationship to space observations, Jour. Geophys. Res., 104,14,14,417-14,435 (1999) Note the above documents are in pdf form, best viewed with Adobe Acrobat 3.0 or higher |
,
the shear waves are radiated in cones; the cone angle given
by
,
where 
is the Alfvén wavenumber. Wave energy is thus transported
across the background magnetic field. The parallel electric
field of the wave is self consistant with the electron current.
The LAPD offers a unique, highly reproducable plasma
(He, n = 4x10^12 cm^-3, B=1-2.5 KG, plasma length 10m, diameter
50 cm which is 3x10^4 Debye lengths and 50-100 ion cyclotron
radii )
