Abundanes and spectra of suprathermal H+, He++ and heavy ions in a fast moving plasma structure (Plasmoid) in the distant geotail

Rest frame distribution functions have been deduced for 3 to 150 keV/amu H+, He++ and (Q> or =3) ions (Q is the charge state) during a 16 min particle intensity increase in the distant magnetotail (>200 R/sub E/) using data from the University of Maryland/Max-Planck-Institut ULECA sensor on the ISEE-3 Geotail Mission. This event was characterized by isotropic electron distributions and has been identified as a tailward moving plasmoid. We show that these suprathermal ions are convected nearly tailward at an average speed of 1000 +- 50 km/s. From the measured dependence of distribution functions on velocity v, f(v)proportional exp(-v/v0), we derive a number density ratio for n/sub H//sub e/++/n/sub H/+ of 0.033 +- 0.003 and for n/sub() Qless-than-or-equal3//n/sub H//sub e/++ of 0.057 +- 0.010, indicating that the solar wind is a dominant plasma source for these ions and that they are likely to be accelerated by a velocity dependent process. The energy density of these suprathermal ions is 150 eV/cm3, accounting for a large portion of the total pressure. Our observations combined with typical values for the thermal plasma in the near and far plasma sheet suggest that adiabatic cooling of the plasma has taken place as the plasmoid propagates tailward and expands, and indicates a crosstail expansion speed of approx.80 km/s