Galileo Energetic Particles Detector measurements of hot ions in the neutral sheet region of Jupiter's magnetodisk

Hot ions discriminated by mass, look direction, and energy have been detect ed by the Energetic Particles Detector (EPD) on the Galileo spacecraft in t he Jovian magnetosphere. Using techniques adapted from analysis of Voyager ibn measurements, EPD data have been fitted to a three-species convected ka ppa distribution function using a nonlinear least squares technique. The io n species were assumed to be sulfur, oxygen, and protons of arbitrary charg e. The bulk flow speed of ions in the neutral sheet region of Jupiter's mag netodisk deduced from the model was found to increase slightly with increas ing radial distance from Jupiter within a 20-60 R-J region near local midni ght. The resulting flow speed of similar to 0.5 times the rigid corotation speed beyond 30 R-J is similar to that found from analysis of Voyager measu rements. The behavior of protons, sulfur, and oxygen is consistent with adi abatic cooling (T/B = constant) with increasing radial distance in the regi on analyzed. The distribution functions are similar to those derived from V oyager measurements, with sulfur contributing the largest component of the total hot ion pressure.