(note: Below is the start of our series on the history of barium usage in atmospheric science's research projects. Part 1 is an excerpt from page 179 of the book, "The Century of Space Science", Published 2001 by J. A. M. Bleeker, Johannes Geiss, M. Huber)
Barium cloud experiments in the upper atmosphere
Space techniques using sounding rockets, satellites and space probes made it possible to send instruments into space not only to measure the physical parameters of the surrounding atmosphere, but also to carry out experiments in order to learn about matter and fields in space.
When injecting barium clouds into space, both measurement and experimentation occurs. The barium can be used to trace the movement of atmospheric plasma and thus to measure the electric fields. This is only valid if the artificial plasma cloud does not disturb the surrounding atmosphere too much. (associated image is an example of program plasmacloud.java, from cs.princeton.edu)
By injecting a stronger cloud, it is possible to study the active interaction with the surrounding magnetic field. In this way, one might study interesting general phenomena of a plasma.
Experimentation occurs if the pressure of the artificial plasma is much stronger than the pressure of the magnetic field in space.
Experiments with artificial plasma clouds have provided new possibilities for studying the plasma under conditions that cannot be easily set up or may even be impossible to realise in a laboratory.