Barium cloud experiments in the upper atmosphere
by J. A. M. Bleeker, Johannes Geiss, M. Huber
[Plasma] experiments are comparable to methods of observing the velocity of a homogeneous fluid.
A typical method involves spreading some coloured particles or metallic dust into the fluid. Normally, one uses only very small amounts in order not to disturb the behaviour of the fluid. (image right of equilibrium of sugar molecules, from pitt.edu)
More than 90 percent of the cosmic objects are in a plasma state, but are also very dilute and therefore not visible except where concentrated in stars.
The cosmic plasma consists mainly of ionized hydrogen and helium molecules, which have an extremely small cross section for light-scattering and so, like the even smaller electrons, do not scatter enough light to make their presence visible.
Therefore, it would be interesting to inject into a cosmic plasma a suitable material that with has a cross section large enough for light-scattering to make the motion of cosmic plasma visible.
For a plasma with very high electrical conductivity, this is of particular interest, since every motion perpendicular to the magnetic field lines of force can be described as the motion of the magnetic lines force. (image left is of: waves of electromagnetic energy passing through a vacuum between two plates of silicon carbide, from Georgia Tech)