Characteristics of suprathermal H+ and He++ in plasmoids in the distant magnetotail

We have obtained rest frame distribution functions of suprathermal (∼6 to ∼150 keV/amu) H + and He ++ ions during 20 particle intensity increases observed in the distant magnetotail (≳80 R E ) using data from the University of Maryland/Max‐Planck Institut ULECA sensor on ISEE‐3. All twenty increases were characterized by isotropic ∼100 keV electrons preceded by beaming electrons and velocity‐dispersed proton distributions, signatures typically associated with plasmoids. In each of these 20 plasmoids we find both H + and He ++ to be convected tailward with speeds ranging from 200 to 1000 km/s. The distribution functions of H + and He ++ in each event are well represented by an exponential dependence on particle speed. The sample averages of the proton number density, n, energy density, u, and effective temperature, kT eff = (2/3)(u/n), are respectively 0.018 cm −3 , 160 eV/cm³ and 6.1 keV, while the He ++ to H + number density and effective temperature sample average ratios are 0.03 and 3.25 respectively. We conclude that the acceleration mechanism is fairly efficient, depends on the particle velocity, and that the solar wind is a dominant plasma source. Furthermore, our observations indicate that the plasmoids are expanding at speeds of ∼100 km/s during their tailward propagation.