CONCLUSIONS:


  1. Excellent statistics for He+ pickup ions (~50 counts / Estep / hour), although no reliable absolute efficiencies yet.
  2. Reasonable agreement of the pickup He+ spectra shapes with a pickup ion distribution based on Vasyliunas & Siscoe (1976) and a hot model for the neutral interstellar He in the heliosphere.
  3. When the IMF turns radial, the pickup flux density in the antisunward direction is systematically decreased close to the cut-off energy as a result of incomplete pitch angle scattering . The effect stows a clear trend with the IMF angle.
  4. The cut-off in the pickup He+ distribution is found to depend not only on the solar wind speed, but also on the neutral He inflow. Measuring the variation of the cut-off as a function of ecliptic longitude will provide a tool to study the neutral inflow velocity distribution.