Multi-Species Measurements of the Firehose and Mirror Instability Thresholds

Recent investigations have examined how various temperature anisotropy and drift instabilities in different space environments constrain plasma parameters such as temperature anisotropy, beta, and differential flow. These investigations have tended to look at each species separately, and how the distribution of its parameters is separately constrained by the resonant kinetic instability arising from free energy in its own distribution. In reality, however, plasma stability depends on all species simultaneously. Here, we present an analysis which combines all major species (protons, alphas, electrons) together, and considers both anisotropies and drifts on an equal footing. A large data set from the 3DP and SWE instruments on the Wind spacecraft in the solar wind was used. We have found that when all species are combined, the long-wavelength firehose and mirror thresholds appear to well-constrain the distributions. The fractional contributions of each species to the thresholds were determined.