Reflection of Alfvén waves from boundaries with different conductivities

The reflection of Alfvén waves from the ionosphere plays a crucial role because the reflected wave can reduce or enhance the electric field pattern of the incident wave. The ionosphere is typically treated as a conducting surface, which has a height integrated Pederson conductivity. This approximation is appropriate in considering the reflection of Alfvén waves because the wavelengths along the magnetic field are large compared to the height of the ionosphere. Shear Alfvén wave reflection experiments have been performed in the large plasma device [W. Gekelman, H. Pfister, Z. Lucky, J. Bamber, D. Leneman, and J. Maggs, Rev. of Sci. Instrum. 62, 2875 (1991)] at the University of California, Los Angeles. A single frequency wave is launched from an antenna and reflects from a large plate inserted into the plasma column. By alternatively using a conducting and an insulating plate, the two extremes of conductivity relative to the Alfvén conductivity, 1∕(μovA) are tested. The data are compared with the expected theoretical behavior of the interference pattern of incident and reflected waves. Perhaps due to experimental effects, the conducting reflector is found to behave in much the same fashion as the insulator.