Critical velocity ionization in the environment of large spacecraft

The authors discuss some potential problems of critical velocity ionization in the environment of large spacecraft, such as the Space Station. Outgassing, exhaust, and reflection of ambient species may form a significant environment of a large spacecraft. As a result of beam plasma interactions, Alfven's critical ionization velocity (CIV) phenomenon may occur. CIV has been demonstrated to occur in the laboratory. CIV experiments in space have been inconclusive. Most CIV space experiments have used barium vapor beams injected into the space plasma. They point out that there exist restrictive conditions which may explain the low yields in the CIV space experiments. The finite width of the beam allows energetic electrons to escape along magnetic field lines easily without ionization, thus reducing the probability of ionization chain reaction. The finite longitudinal length of a beam pulse, or cloud, may not allow enough time for electron heating along magnetic field lines. The parallel component of the lower hybrid plasma wavelength may be too long that it does not fit into the beam. These conditions may become less restrictive for the environment of large spacecraft. If CIV ionization really occurs in the spacecraft environment, the vicinity of the Space Station may be a more likely place. As a consequence, the transport of ions and electrons may pose contamination and radiation problems on the instruments aboard