Stability of Solar Wind against Electromagnetic Streaming Instability

The stability of the solar wind in the presence of small concentrations of helium against highfrequency (w2 p2) electromagnetic streaming instability is explored. For relative abundances of helium to hydrogen up to 20 percent for the expected magnetic fields, densities, and temperatures of the solar wind, this instability can be triggered only if the relative streaming of protons with respect to a-particles exceeds the electron thermal velocity. The solar wind cannot satisfy this requirement and hence is stable against this instability. Subject headings: instabilities - plasmas - solar wind